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Goliath - A Gas Powered Quadcopter

A BIG Gas Powered Quadcopter

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Goliath is a open source prototype vehicle for developing gas powered quadcopters.


Goliath is a prototype vehicle for developing large scale quadcopters. The design is based on a single central gas engine with a belt drive providing power to the four propellers. Control is done using control vanes placed under the propellers. Each propeller is enclosed within a duct that protects the rotors and contributes to the lift. Goliath itself will be open source with the creative commons license, and whenever possible open source components were used. It's currently a work in progress, and even when completed it's intended as a starting point for future vehicles.

THP Semi-Finalist Video

Flight control will be performed using the Pixhawk controller running a modified version of the Ardupilot flight software. Modifications to the Ardupilot software are needed to work with Goliath's unique control system. Both the Pixhawk and Ardupilot are open source. The modifications made will be open source as well. A USB radio receiver will be attached to the flight controller and setup to receive ADS-B signals. These signals will allow the operator to be aware of other aircraft operating in the area.Additionally Goliath will have a WiFi interface allowing the public to interact and connect with Goliath. Data and Video Feeds will be available and observers can notify the operator of potential issues.


An electric powered design would have been the most straightforward approach. Electric motors are more efficient than gas, but the power density of gasoline is much greater than today's batteries. So until battery technology improves, gas power seemed the way to go. Goliath uses a single 30 Hp engine and a belt system to transfer power to the four propellers. The setup was chosen because at this scale, four smaller engines have a smaller power to weight ratio than a single larger engine.

Drive System

The drive system uses High Torque Drive (HTD) belts. These belts are made of neoprene rubber with continuous fiberglass cords. HTD belts are able to transfer more power per weight than roller chain and can also run at higher RPMs that Goliath requires.

To eliminate aerodynamic torque, the drive system rotates two propellers clockwise (CW) and two counter-clockwise (CCW). This is done by using two belts, one sided sided and the second double sided. The direction of rotation is changed by placing the outside of the double sided belt against the driving pulley.


The propellers are fixed pitch propellers 36 inches in diameter. They are custom made, starting from a foam blank with birch stiffeners. The blanks are machined using a CNC router and then fiberglass and epoxy are laid up over the machined core. This process produces a propeller that can carry over 60 lbs while only weighing one and a quarter pounds.


An electric quadcopter would traditionally maneuver by varying the speed of each propeller to control thrust. Since Goliath uses fixed pitch propellers and all the propellers turn at the same speed due to the belt drive, maneuvering will be done by control vanes similar to those used to steer hovercraft.


The frame is constructed using slotted galvanized angle, also known as Dexion, bolted together. While this is heavier than a steel tube or composite frame, the dexion is quickly assembled and can easily be reconfigured. At a later stage when the configuration is finalized the dexion could be swapped out for a lighter weight frame.


Each of the two exhaust pipes are built from Go-Kart hardware, which are easy to procure and inexpensive. The U-Build It Kits are easily assembled using a minimum of welding and highly customizable.

Electrical System

The electrical system is powered primarily from the alternator with the battery as a backup. The battery is 12V and designed for off-road vehicles, so it'll handle high vibration loads. The micro-controllers and servos are powered using a battery elimination circuit that provides 5V @ 10 amps. Solid State Relays are used to control the engine using the Pixhawk.

  • 1 × 30 HP vertical shaft gas engine Should equipped with a starter and alternator
  • 1 × Pixhawk Open Source Flight Controller
  • 1 × Raspberry Pi WiFi Interface
  • 2 × Clockwise Propellers (36" Diameter) See Detailed Build Instructions for Raw Materials (Forthcoming)
  • 2 × Counter Clockwise Propellers (36" Diameter) See Detailed Build Instructions for Raw Materials (Forthcoming)
  • 4 × Duct (37" Inner Diameter) See Detailed Build Instructions for Raw Materials (Forthcoming)
  • 8 × Control Vane (37" Wide) See Detailed Build Instructions for Raw Materials (Forthcoming)
  • 8 × Control Servo
  • 1 × Throttle Servo
  • 1 × Main Pulley (50 mm wide) HTD Pulley 50 mm wide,34 teeth, with QD Bore (Type SH)

View all 37 components

  • Goliath Mark II

    Peter McCloud14 hours ago 0 comments

    With the bugs worked out of the drive train and the belt and pulley configuration nailed down, it was time to take the project to the next phase. Work has already begun on a Mark II version of Goliath. The primary changes for the Mk II vehicle is a new lighter frame and ducts to enclose the rotors. Over the next couple weeks, there will be more project logs to document the new vehicle in more detail, but for now here's some of the progress that's been made.


    After considering several options, it was decided to go forward with an aluminum truss frame. The primary reason was cost and ease of manufacture. A composite structure would be lighter, but the cost would be significantly higher. A preliminary design has been completed and the structural analysis has been completed. Below is an image of the structure layout and the predicted deflections under load. More details will be provided in a later project log.

    The materials have been ordered and arrived this last week. Below is some of the tubing (3/4" and 1/2" diameter).

    However before the structure can be built, a jig is needed to assemble the parts. Work has begun on the jig for the upper portion of the vehicle.


    The other big change for the Mk II vehicle is the addition of ducts. The duct serves a couple of purposes, the foremost of which is safety. The duct will prevent the rotors from hitting people or objects and to potentially contain debris if the rotor itself fails. Secondly, the duct will improve the total thrust of the vehicle, if designed correctly.

    Each duct will be built in two halves to make building and assembling the ducts easier. A prototype duct piece has already been built to test out the manufacturing process. Eventually this duct will be tested on the new vehicle.

    The black material is the surface of the mold that stuck the duct because the directions for the mold release were misread.

    Stay tuned for more updates in the near future.

  • Vehicle back together and running smoothly

    Peter McCloud04/04/2016 at 22:11 1 comment

    A few tests back (Test 41), one of the rotor axles snapped, resulting in one of the rotors being damaged. The fix to this issue was to increase the shaft diameter to 3/4" from 5/8" and switch from using E-clips to retaining rings (project log with more details). Below is the new shaft with retaining rings holding the pulley in place.

    A new rotor was built to replace the one that was damaged when the axle snapped. Both counter-clockwise propellers got a new paint job to make the tips more visible. Eventually the other set of propellers will get the same set of markings.

    With all of the hardware fixed, it was time to test Goliath again. After a couple tests to make sure all of the hardware was secure and working properly, Goliath was run up to full throttle again.

    The bad news is that Goliath still isn't flying. The good news is that it's REALLY close. The vehicle is bouncing around on the tethers indicating that the lift is nearly equal to the weight. The other good news is that the vehicle is running smoother than it ever has in the past. This is because the two cylinders are now firing correctly and improvements were made both to the pulley layout and to the tensioner.

    Since Goliath wasn't flying, the next step was to figure out why. A friend let me borrow his optical tachometer. To avoid getting a signal from the overhead lights, the tachometer was mounted above one of the propellers and pointed downward.

    The vehicle was then run at different throttle settings and the RPM was recorded.

    Test 50
    Throttle (%) RPM
    Starter 510
    0 1740
    25 2190
    50 2850
    75 3210
    100 3240

    It appears that above 75% throttle, there is very little increase in RPM. This is likely due to the rotors requiring too much torque to accelerate above 3200 RPM. Since the rotor pulley ratio is 1.1:1, this means the engine is running at 2945 RPM, short of the 3200 to 3400 RPM that had been targeted.

    There are a couple of options available. One is to resize the pulleys closer to a 1:1 ratio. The pulleys were sized based on the power transfer capability. The main pulley is probably a little small since there still seems to be the occasional tooth skip at startup, so making it smaller to match the rotors isn't an option. All of the rotor pulleys would have to be bigger to make that work.

    Another option is to make wider diameter rotors. The required power decreases as the rotor diameter is increased. The downside is that it will increase the vehicle footprint. It's already difficult to transport as it is, so it's more of a last resort option.

    The option I'm currently leaning toward is to go ahead and build the ducts for the rotors. The ducts will decrease the power required by the props increasing the RPM speed. At the same time, if built correctly, the duct itself will act as a lifting surface. Literature suggests that the cumulative increase can be as much as 25%. That'd be about 55 lbs, based on the latest testing.

    Pixhawk Logs

    The last news of interest is that with the Pixhawk on-board, there is now quite a bit of data available. There is an interesting site for PX4 users where logs can be uploaded and the data is automatically plotted. The data for tests 48 and 49 are available at:

    Test 48 - Log Muncher

    Test 49 - Log Muncher

    The bad news is that the accelerations are high (kind of expected that). Based on feedback ( from the developers, the vibrations definitely need to be mitigated. This will have to be looked at in more detail down the road.

  • Pixhawk On-board

    Peter McCloud03/14/2016 at 05:11 0 comments

    The flight controller chosen for Goliath is the Pixhawk, running the PX4 flight stack. Up until now, integrating the flight controller hasn't been a priority. The design of the drive train is on-going, and there was the risk that the controller could be damaged or destroyed during testing.

    With 40 tests now complete and the risk of losing the controller reduced, it was time to put the controller on-board Goliath for future testing. The controller won't actually be doing anything initially. The idea is to just make sure the controller can reliably operate while Goliath is running. Once it's proven it can operate, the next step will be to control the throttle and choke servos and eventually the ignition and starter relays.

    The first step to get the Pixhawk on-board was to add the power module. On an electric quad copter, the power module goes in-between the battery and the ESC. The module is the primary source of power for the controller and also has a current sensing capability. Below is a picture of the power module from the Ardupilot documentation.

    On Goliath, the power module was placed between the alternator and the battery to measure the current being supplied by the alternator. The frame on Goliath acts as the ground path, so the XT60 connectors were cut off and the module was connected using the existing bullet connectors. Here's a photo of the power module mounted on Goliath (not yet grounded).

    The next step was placing the Pixhawk with the Delta 8 receiver and the safety switch on to the vehicle. The Pixhawk powers up when the master switch is turned on. The safety switch then has to be be triggered before the Pixhawk can be armed. Below is all of the hardware in place, but unsecured.

    The Pixhawk was successfully armed today and is properly logging the data and providing pre and post-flight summaries. The next step for the controller is to secure the hardware to get it ready for the next test.

    Additionally, work on the custom mixers and config file for Goliath has been started. The files can be found in the github repository at:

    As for the next test, it shouldn't be too far off. All of the new axles and pulleys are complete and are just waiting on the new mounts to be finished before they can be placed on the vehicle. The new rotor has been epoxied and came out the vacuum bag in good shape. It'll be ready after a few rounds of sanding and primer.

  • Engine Issues Resolved

    Peter McCloud03/05/2016 at 05:02 3 comments

    During the most recent tests, Goliath exhibited more vibration than was seen in earlier tests. After closer examination, it became apparent that the starboard cylinder was not firing. Test 41, when the axle broke, was an attempt to see if the engine had been fixed. Due to the vibration present during Test 41, the starboard cylinder was still not firing.

    The usual suspects to check for with a small engine is compression (air), fuel, and spark. There was obviously fuel getting to the cylinder since it's coming out the exhaust pipe. Spark was testing by removing the plugs, resting the ground side against the engine and running the starter. Both cylinders showed good spark. The last test was a compression test. Briggs and Stratton doesn't state minimum compression values, just that both cylinders should be tested and that they should come out the same.

    So with all those items checked out, it was quite puzzling as to what the real issue was. I took a trip to a local small engine shop to get some help. It was the right place to go because the guy there gave me great help. He suggested two possibilities. The first was to check the value clearances, that perhaps the hardware holding the values in place had come loose. The second possibility was that there was a bad diode connected to one of the ignition coil.

    The valves checked out ok, so the diode was the next thing to check out. What's makes this particularly difficult, is that there is no documentation provided by Briggs and Stratton on these diodes expect for the repair manuals, which are difficult to come by. After removing the wire harness it was very obvious that the starboard diode was failed.

    The failure modes are pretty interesting. The ignition switch works by grounding the ignition coils. The diodes act as a bridge to isolate the two coils from each other. When one of the diodes fail closed, the coil it's connected is no longer isolated from the other coil. When the other coil fires, it grounds the coil connected to the failed diode, preventing it from firing. This was precisely what happened on Goliath.

    With the cause identified, the next step was to repair the wire harness with the diodes. The diodes are potted in a clear plastic, so the failed diode was visible through the coating. It was difficult to get a good shot up close to show the charring.

    Typically the wire harness is replaced as a whole, is specific to the engine make and model and has to be special ordered. Instead the harness was torn down and the diodes part numbers were identified (IN4007). This is was simply a matter of getting the diodes from Radioshack and soldering the harness back together.

    The new hardware to repair Goliath with is in the process of being built, so the engine was tested with just a single belt and one pair of rotors to ensure that the engine was indeed fixed.

    The test was a success. Both cylinders are firing and the engine now runs much smoother. The increase in power is also clearly visible, with Goliath lifting up the one side with the two rotors. Looking at the video in slow motion, it's clear that one of the tethers reached it's full extension.

    After the new hardware is complete, Goliath can be fully reassembled and further testing can be conducted.

  • Broken Rotor Axle

    Peter McCloud02/17/2016 at 16:28 0 comments

    Test 41 was to determine if the starboard engine was working correctly again. After idling the engine for a while, the rear starboard rotor axle broke.

    Looking at the slow motion video, it's clear that the axle breaks, and then the belt tension pulls the pulley inwards. This caused the rotor to hit support arms and sheared off a piece of the rotor. The double sided belt then falls off all the pulleys since the tension has been lost. Here are some pictures of the damage.

    The rotor is the biggest issue, since a new one will have to be manufactured. The rotor pulley flange was dislocated as the belt came off, but it should be a simple fix to press it back on.

    As hindsight is 20/20, it's fairly obvious that adding the grooves for the E-clips made it so the remaining material was insufficient to handle the loads. A 0.07" groove depth didn't seem like much, but the remaining material was only 0.485" in diameter, significantly less than the 0.625" shaft diameter.

    The plan is to switch to 0.75" axles and bearings for the rotors. The new bearings are the same external size, so the pulleys won't have to be modified. The E-Clips will also be replaced with retaining rings. The rings won't be as easy to install or remove, but they only require a groove depth of 0.023", leaving 0.704" of material.

    The new hardware has been ordered and the process of building the new rotor has been started. Meanwhile, the engine still appears to be running rough, so that will hopefully be addressed by the time all of the new hardware is ready in a couple of weeks.

  • New Rotor Pulleys Working, New Engine Issues

    Peter McCloud02/15/2016 at 06:17 0 comments


    All of the new rotor pulleys have been installed and have been tested for a cumulative run time of 20 mins. (The video has yet to be edited together).) The great news is that there have been no occurrences of rotor bolts breaking and the new hardware is significantly lighter. For the last full power test (#21) the vehicle weighed 238 lbs. For the latest tests, the vehicle is now down to 213.8 lbs.

    This was mostly due to switching to the aluminum rotor pulleys, but some additional weight reduction came from trimming off the excess material for the arms supporting the rotors. Here's a shot of the vehicle in its current configuration.

    The excess length had been left on in case the rotor pulleys needed to be shifted outboard. Now that the design has had time to mature, the likelihood of moving the arms outboard seems low. There is still sufficient clearance to increase the prop diameter easily up to 40 inches if needed.

    Tension Issues

    The tension on the single sided belt is just right. The teeth haven't skipped and the tensioner hasn't had to be readjusted for the last 10 minutes of testing. This is due to improvements made to the tensioners. Prior to the changes, the all thread that holds the springs in place would sometimes bind up where it passes through the structure supporting it. The fix was to hold the spring captive with end caps fashioned from copper pipe caps. Below is the latest iteration of the double sided belt tensioner. This design also helps by allowing for a small degree of misalignment, allowing the tensioner assembly to rotate freely.

    Getting the tension correct on the double sided belt has been more problematic. The teeth occasionally skip on the double sided belt, particularly when the engine decelerates and more slack builds up. Several different tensioner configurations have been tried and none of them have completely solved the problem yet. The latest configuration appears to be promising, but fixing the tensioner has been put on hold since some engine issues have developed.

    Engine Issues

    In the twenty minutes of testing after all of the the new rotor pulleys were installed, the engine runs reasonably at idle. However, when the throttle is increased, the engine appears to bog down and the RPM does not increase. Part of the problem could be the tension issues with the double sided belt. However, the tensioners haven't been completely right in the past and the vehicle was able to get up to higher RPMs. The first sign that something else was wrong showed on the exhaust pipes. In the picture below there is a visible difference between the two exhaust pipes, with liquid present on the starboard exhaust pipe.

    At first glance it looked like oil, but upon closer inspection it appears to be mostly gas and soot. The spark plug on the starboard side was examined and it, too, was covered in a gas/soot mixture, which likely means the cylinder isn't firing. Below is a picture of the spark plug from the suspect cylinder.

    For comparison, here's a picture of the spark plug from the port cylinder that appears to be running fine

    It's not clear yet why the cylinder isn't firing. The next step is to do some additional troubleshooting. Once the cylinder is firing again, the tensioner issue can be addressed. It could be that the engine running rough on one cylinder could be the cause for the double sided belt skipping teeth. Either way, once both of those issues are resolved, then the next full throttle test can be performed.

  • Bearings and Axles

    Peter McCloud01/29/2016 at 00:20 0 comments

    In the previous project log, the first of the new rotor pulleys with the new axles had been tested. The new hardware was considered to be good because nothing broke (yes, not breaking is a low bar to set). The next step was supposed to be assembling the rest of the rotor pulleys and axles and doing a more complete test.

    Two things happened after that. The first as that there was a question regarding the fit of the axles. It wasn't required to press fit the axles into the rotor pulleys, which shouldn't have been the case. The second was an unidentified noise during the testing. The first hint of an answer to the second question came to me from YouTube user +visnevskiscom, who commented that during the latest video at 2:30 there was a vertical oscillation that appeared to correspond to the noise. After investigating this further, the source of the noise was found to be the rotor hitting the belt occasionally. It turns out that there was slight amount of play between the axle and the bearing to allow the rotor to wobble just slightly and just clip the belt.

    This led back to the suspicion that something wasn't right about the interference fit. The axles had just been ordered from McMaster Carr and the drawing states that the axle was 0.625" +0.000/-0.001". The bearings were pulled out of a set of idlers almost two years ago, and I knew less about. Below is the product page that hasn't changed from when the bearings were ordered. (link to site)

    So the inside diameter is stated to be 5/8" (0.625"). There is no tolerance set, so in theory the ID could be just slightly greater than 0.625" and the shaft could be a thousandth less and it wouldn't need an interference fit. Since there wasn't any more information from Circular Motion, I looked up the bearing part numbers and did some internet searching. It appears that the bearing is a specialty bearing and was hard to get the specs for, but after a while I did find a drawing. (link to site)

    The typical applications is stated to be a 5/8" sprocket idler bearing. However the drawing states that the ID is 0.635" , 0.01" larger than what Circular Motion states the ID to be. I don't know enough about sprocket idler design to know why the bearing is 0.01" larger that the nominal ID or if doing so is a standard practice. What is clear is that the current bearings wouldn't work with standard axle shafts (and that I'll never order another bearing without seeing a drawing sheet)

    After a short period of despair, thinking about the amount of time and money that went into a set of rotor pulleys that had useless bearings, a reasonable solution was found to the problem. It turns out that a bearing was available from McMaster-Carr that not only would fit the shafts correctly (0.625 +0.0000/-0.0005), the rotor pulleys just needed to be bored out just slightly larger to accommodate the new bearings AND they're cheaper.

    So after ordering a new set of bearings, boring the bearing pockets to be larger, and installing the new bearings, the hardware was reassembled. This time the bearings and the axles required a press to fit them together:

    Test 29 was mostly a repeat of Test 28. This time around, two of the new rotor pulleys were tested, both mated to the new axles. The latest revision of the flight rotors were also used.The test went well and there were no unidentified noises. The rotor bolts continue to hold up. The next step is now to complete the other rotor assemblies.

  • Testing New Rotor Pulleys and Axles

    Peter McCloud01/02/2016 at 17:51 0 comments

    The new rotor pulleys and axles are starting to be tested. At the end of November, the first rotor pulley as completed and before moving on to the other 3 pulleys, the first pulley was tested to ensure that the design was acceptable. To do this, Goliath was set up with just the single sided belt, with the new pulley with the original flight rotors and one old pulley with a dummy rotor. The original flight rotors were used so that if something breaks, I won't run the risk of having to make more update rotors. This test was number 27. The video for tests 27 and 28 is below:

    The first test went well. The rotor was run at idle for a while and the new pulley showed no issues and all of the bolts held. The one thing that is obvious in the video is that the nut underneath the pulley comes loose. The nuts above and below the pulley are held in place with external toothed lock washers. The don't always hold though, probably because it's difficult to tighten the nuts correctly when the rotor is attached to the pulley. After gaining some experience with machining the rotor pulleys, it was time to start making custom axles.

    The axles are just 5/8" drive shafts, 12" long (5947K14 from McMaster-Carr). The drive shaft and rotor are held in place using bowed E-clips (98398A140 from McMaster-Carr). I was a little hesitant to use E-clips to hold the thrust from the rotors considering they are only grabbing onto a small groove in the shaft. A look a the specs though show that the E-Clip is rated to about a 1000 lbs. The rotors will be putting out 70 lbs at max thrust, so there's a Factor of Safety of about 14.

    The machining went ok. I don't have the right grooving tools for this, but those are more expensive. If I end up doing this more, I'd get more appropriate tooling. Here's a shot of one of the grooves.

    Below is the E-clip compared to the bearings that are used. (Note this was just a test fit with the bearings in the old bushings)

    The overall axle has six grooves. Where the axles attach to the frame, I've left room for large washers to act as shims. This way I can adjust the height +/- the width of one of the washers. Once assembled the axles simply slides onto the frame with the frame between two of the washers.

    The entire assembly with the axle, E-clips, shims, rotor, rotor pulley and rotor bolts weighs 4.9 lbs.

    For test 28, Goliath was configured again with just the single sided belt. One of the rotors has the new pulley and the new axle. The other rotor has a new pulley, but with the old axle setup. Both rotors have the original flight rotors.

    The pulleys are still holding up and the axle also didn't have any issues. There is some unidentified nose in the test, that needs to be figured out. Either the belts are getting clipped by the rotors or the tensioner isn't configured correctly. That issue needs to be figured out and then additional testing can be done with more hardware.

  • Rotor Pulley Machining Complete

    Peter McCloud12/25/2015 at 19:41 0 comments

    The remaining three rotor pulleys are nearly complete. The most time consuming part, the machining, is now complete. Everything went smoothly making the parts, which I was not expecting since this is my first time making these types of parts. Here is a shot of the pulleys together:

    After adding the bearings and the flanges to the pulleys, it'll be time again to start re-assembling the vehicle and begin testing again, hopefully before the new year. For the next round of testing, the original set of rotors will be used initially in case something doesn't go right. Once the new pulleys have been tested and shown to work, then the latest rotors will be put on the vehicle.

    One other upgrade which may also be done by the next test is adding solid axles with bowed E-clips to hold the rotors in place. The current all-thread axles aren't well suited to their task and the nuts holding the rotors in place continue to come loose in spite of using the star type lock washers. I'm confident the rotors won't need to be adjusted height wise anymore, so it seems to be time to make the upgrade.

  • First Custom Pulley Finished

    Peter McCloud11/23/2015 at 05:25 1 comment

    The first of the custom pulleys was completed today. The custom pulleys are aluminum instead of steel and allow for six fitted mounting bolts instead of three fully threaded bolts. Here's an image of the new custom pulley connected to one of the previously used rotors.

    The custom pulleys are started from a 10" length of pulley stoc. Below is the stock mounted in the lathe.

    I won't go through all of the steps here. The manufacturing steps were outlined in the previous log and updated to reflect the as-built process. All of the photos showing each of the steps are in a Flickr album. Here's a shot showing the part after the machining was complete:

    Next, the flanges were put in place and a punch was used to roll over the edge in six spots to hold the flange in place. The bearings were press fit in place.

    Here's a shot with the six bolts holding the rotor in place. I'm confident this will solve the issue with the bolts breaking.

    The next step is to mount the new pulley onto Goliath and run a test to ensure that it doesn't have any issues. If that test is successful, then the other rotor pulleys can be manufactured.

View all 59 project logs

  • 1


    Before you start this project, take some time to REALLY think about what you're about to build. Seriously, this is a flying machine that weighs more than most people and runs on gasoline, a chemical that the states of Oregon and New Jersey have deemed too dangerous for the average citizen to pump into their own car.

    While Goliath is a big and powerful, it's only as dangerous as the user. As you build, test and fly your giant quad copter be mindful of your safety and the safety of others.

  • 2


    Building the composite pieces requires the longest amount of lead time. It's recommended to start these pieces first, and the rest of the components likely be built while waiting for the composite pieces. Components made from composites are:

    • Propellers
    • Ducts
    • Control Surfaces
  • 3


    Tools - Chop Saw or Reciprocating Saw, File, 5/16" Sockets and Wrenches

    A) Cut the Frame Pieces

    Start by cutting the all of the galvanized slotted angle pieces to the correct lengths using the cutting guide. A chop saw or a reciprocating saw are the best choices. All of the cuts are intended to be across the center of the nearest hole and the exact lengths won't matter as long as the correct holes are used.

    Afterwards be sure to file all the edges and corners.

    The pieces after being cut are:

    • 4× Center Beams ( 2 1/2" x 1 1/2" x 39 3/4")
    • 4× Side Beams ( 2 1/2" x 1 1/2" x 29 1/4" )
    • 4× Cross Beams ( 2 1/2" x 1 1/2" x 30" )
    • 4× End Beams ( 2 1/2" x 1 1/2" x 18" )
    • 8× Outer Prop Supports ( 1 1/2" x 1 1/2" x 30 3/4" )
    • 4× Inner Prop Supports - Fore ( 1 1/2" x 1 1/2" x 28 1/4" )
    • 4× Inner Prop Supports - Aft ( 1 1/2" x 1 1/2" x 32 1/4" )
    • 8× Shaft Mounts - ( 2 1/2" x 1 1/2" x 6")
    • 4× End Cross Bars ( 1 1/2" x 1/16" x 18" )
    • 4× Side Cross Bars ( 1 1/2" x 1/16" x 30" )
    • 1× Battery Plate ( 2 3/4" x 1/16" x 11 1/4" )

    B) Assemble the Top and Bottom Decks

    Follow steps B1 and B2 for each deck

    Note: The frame assembly uses only 5/16" bolts. All of the bolts, lock washers and hex nuts referenced will all be 5/16"

    1) Bolt the (2) Center Beams and the (2) End Beams together using (4) bolts, (4) lock washers, (4) hex nuts.

    2) Bolt the (2) Cross Beams to the (2) Center Beams using (4) bolts, (4) lock washers, (4) hex nuts.

    C) Join the Top and Bottom Decks

View all 11 instructions

Enjoy this project?



Jotham B wrote 13 hours ago point

I guess its easier to just test with new pulleys at this stage, but I was just wondering if you have considered using a 2 or 4 stroke motorcross bike engine? Light weight, high power, somewhat pricey, but not impossible to purchase. The engine units are generally well separated so the transmission part of the engine can be milled off the engine. Either way its a lot of work to do an engine swap. I can see a lot of work has gone into this project!

  Are you sure? yes | no

Peter McCloud wrote 11 hours ago point

Eventually a different engine would be ideal. I had not looked at motocross engines, I'll have to add that to the list. One reason I've stayed with the current engine is that it's inexpensive and if the vehicle crashes I'd rather lose this engine.

  Are you sure? yes | no

Poppy Ann wrote 01/20/2016 at 08:44 point

did you consider using a set up similar to :- 

which uses only one motor and then uses constant speed propeller blades that use the same system that helicopters use to alter the pitch  to adjust the lift of each corner?

I have been thinking of building a similar design of one power system but using one of the Honda silent generators for power then either still using separate motors at each blade or a single motor and belt drive like the Hobbyking Assault Reaper quad.

Regards Poppy Ann.

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Peter McCloud wrote 01/21/2016 at 00:10 point

That's been talked about a couple times in the comments. Essentially, it's a whole other project in itself to build adjustable pitch propellers. Once Goliath is flying I may investigate it then.

Thanks for pointing out the typo. I fixed the error in the instructions.

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Poppy Ann wrote 01/20/2016 at 08:36 point

Hi who did the editing of this page? I am dyslexic and noticed one obvious mistake as soon as I read it ie:- "Oregon and New Jersey have deemed too dangerous for the average citizen to handle putting their own car."

where is the average citizen trying to put their car that is so dangerous ? or did you mean :- "Oregon and New Jersey have deemed too dangerous for the average citizen to handle putting in their own car."

Regards Poppy Ann.

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ken wrote 12/01/2015 at 16:21 point

Increase the diameter of the pulley on the motor and add a centrifugal
clutch to allow the engine to start and addle be for engage the propellers this
will allow higher rpm to the propellers. Do this till the motor can’t increase
to the max rpm than back off a little this will tell you if the motor is too
small. I don’t think it is you just need to get the rpm’s up on the propellers.

And put a cage around it when you test it. I don’t think
your propellers will withstand the rpms needed for lift off. If one breaks very
bad news for ever who is around.

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Peter McCloud wrote 12/15/2015 at 14:40 point

Any recommendations on specific clutches? I looked around for one that would work my Goliath about a year ago and I didn't find any.

Thanks for the concern about safety. When Goliath is being tested, there is a safety net that is put up, and everyone is behind a big steel tool cabinet. There are some pictures of the safety net in the project logs.

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goldenshuttle wrote 11/04/2015 at 07:05 point

Great project. Have you taken a run on each part to reduce total weight ?

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thesunman84 wrote 09/05/2015 at 15:16 point

From my experience in the structural world, might I suggest adding a washer under the bolt head to distribute force evenly?  Right now, it looks like most of your bolt heads are only gripping a very small amount of the galvanized steel.  You are best off using a flanged nut with a washer under the bolt head.  I know you're trying to cut weight and washers won't help that but neither will a bolt head pulling through steel :)

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Peter McCloud wrote 09/11/2015 at 14:40 point

Thanks for the link and the suggestions.  I'll have to keep that in mind as I continue to develop the vehicle

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Aaron Cooper wrote 08/26/2015 at 21:04 point

Have you looked into lightening the engine itself? some features like the fuel shutoff solenoid are potentially un-needed as those were added to prevent a bad needle valve from flooding the engine during storage.  The various covers are potentially replaceable with lighter weight parts.  I was briefly interested in using a weed eater engine to power a RC plane, there is a community dedicated to modifying small engines for RC use. I believe some of them modified or replaced the flywheel to make it lighter.

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Peter McCloud wrote 08/27/2015 at 14:24 point

All good thoughts. I haven't concentrated on that area yet. I would like to leave the solenoid in to be able to shut off the fuel source in case there is an engine fire. It's a common practice for aircraft, though it's probably pretty unlikely that I'll have an engine fire and still be able to command the fuel to shut off.  The fuel solenoid is pretty small, so it'd not too big of a weight penalty.

The plastic covers would be fairly easier to replace. I could make molds off the existing ones and replace them with fiberglass.

I'd love to get a lightweight flywheel for the engine, that's probably be the most beneficial and it's relatively easy to swap out. I haven't found any out there for my particular engine model.

If you could share any links to the specific RC groups you mentioned that'd be great.

Thanks for the inputs!

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Aaron Cooper wrote 08/27/2015 at 19:14 point

Below is one site that has a bunch of info, they focus on the smaller engines but a lot of it should apply. Also a site that has parts that may be compatible or at least copy-able design wise for your engine.

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michael.rodenbarger wrote 07/21/2015 at 14:21 point

Very interesting! Great job thus far :).
Have you thought of using 2 stroke motors at all? You can generally get more power out of a lighter 2 stroker vs a 4 of the same size. How about using crankshafts instead of a belt driven system? Weight can be reduced with creative use of materials (carbon fiber or fiberglass shafts).

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Peter McCloud wrote 07/21/2015 at 21:19 point

Hirth makes an experimental aircraft engine that weighs the same as engine currently being used, but has more than 3x the HP. The issue is that it costs 10x the current engine.

The real issue with drive shafts isn't the shafts themselves, but the gears required to make them work.  I haven't found gearboxes that can support the Hp and are light enough.

Thanks for the interest in the project!

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surubarescu wrote 05/25/2015 at 08:49 point

I have some suggestions: for the belt pulleys you can use some with slightly barrel shape that will self center the belt (like on band saw), yet giving the power transmitted, the pulleys should have shoulders to keep the belt flying. Or you can use a transmission box like two mikey mouses heads connected at the neck: two big gears, one connected to the engine, the other used to reverse the rotation, and for each one 2 smaller gears to send the power to the propellers using shafts (either  via 2 sets of conic gears if the engine and propellers are level, or if the engine is very low shafts with universal joints). 

Almost forgot: this thing will have a gatling gun turret under it?

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Peter McCloud wrote 05/26/2015 at 19:49 point

Maybe I can add a paintball Gatling underneath and put it up against this guy:

As far the the barrel shaped pulleys belts go, I'm using those for the flat sided idlers.  All the toothed pulleys are flat faced, but they all do have shoulders.  You can't have the barrel shape and still maintain the right tooth profile.

I did look into gearboxes as well, but they are too heavy for what I need.

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surubarescu wrote 05/27/2015 at 07:55 point

Nice mech, but the driver is protected by chicken wire. You won't get a clear head shot, but you'll spray it well with paint. 

Let me draw you a little picture of how i see this "gearbox" (better said a collection of gears) [you'll need to view it using fixed font - paste it in notepad]

propeller                       |               propeller
----+-----            _____   __|__             ----+-----
    |                |  |  | |  |  |                |     
   _|_               |__|__| |__|__|               _|_    
   \|//|           |\\  |  / \  |  //|           |\\|/
      --------------- -----   ----- ---------------
      \|           |/               \|           |/

|  |  | this is a combination of cylindrical and conical gear
|__|__| the cylindrical part engages the other identical gear
\  |  / the conical engages the shaft conical gear
 -----  for each of these gears there are two shafts for two propellers
The only issue is that you'll have adjacent propellers rotating in the same direction (but you already choosed this configuration). You can also use sliding shafts to counter the bends in the propellers trusses.

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Rollyn01 wrote 05/25/2015 at 01:41 point

You ever thought of expanding this to build an actual factual flying car?

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Peter McCloud wrote 05/25/2015 at 03:21 point

Yes. I originally wanted to build a quadcopter large enough to carry a single person. However getting a more powerful engine and the hardware to go with it would have been expensive. I chose to make a smaller (relatively) prototype to test out the technology needed  before  going bigger. 

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Adam Fabio wrote 01/15/2015 at 05:57 point

Awesome work Peter! The wider belts do seem to be working out pretty well. I've made the same mistake leaving the screw out of a servo. I bet you needed a change of shorts after the unexpected jump to full throttle!

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Peter McCloud wrote 01/17/2015 at 03:00 point

When it happened, it seemed to be at full throttle for a while before I killed it, but after watching the video, it seemed much shorter. That's what adrenaline does I guess.

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dwardio wrote 12/03/2014 at 16:42 point
Very interesting project! Like many others, I'm curious as to how controlling thrust direction will replace variable prop pitch or speed.

Also, what is the estimated full-up weight at take-off? Current AMA guidelines are that any model weighing in at more than 50 pounds should be registered as an experimental aircraft. Needless to say, this bad boy is going to be potentially lethal, making sure you're within the rules is a good investment.

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Peter McCloud wrote 12/04/2014 at 22:31 point
Thanks for the interest! I'm hoping to have a gross takeoff weight of 240 lbs, with 40 lbs of payload capacity. Your right, Goliath can be hazardous and this is not something you simply take to the park and fly around.

Your right, knowing what the rules are is a good investment. I'm curious if you happen to have a link to the guidelines you're referring to. I did some looking and found AMA document 520A ( It simply states that AMA Large Model Aircraft 1 (LMA1) can be from 50 to 77.2 lbs and LMA2 can be from 77.3 to 150 lbs.
I did find a reference to the IMAA guidelines that states:
"IMAA qualification also requires the RC model be a maximum weight of 55 pounds, with fuel – ready to fly. Models over this weight up to 100 pounds, with fuel – ready to fly (known as Experimental Radio Controlled Aircraft) may also qualify as IMAA giant scale provided they have a Permit To Fly signed by an AMA certified “Experimental Inspector”"

My understanding is that drones are currently certificated by the FAA, and the guidelines that they are working on will be valid for 55 lbs and below. So this leaves Goliath in a questionable area. I'm not sure where I'll be able to fly it once it is flying. For now I'll just have to worry about it once I get Goliath flying.

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Rebelj12a wrote 11/10/2014 at 21:31 point
Odd thought, are you still having stability issues...

I wanted to make a gas powered one for more sustained flight anyways. Current electric quadrocopters dont have alot of flight time especially for heavier things.

I dont know if this will work, however it might...

One, place a direct porpeller on the motor itself. Primary lift comes from the center of the craft.

Recess the center motor further down, i.e. angle the quad rotors upwards by maybe... 20 Degrees 30 degrees?

Add brushless propeller motors on the ends of the quadrocopter.

Heres the "if" and I dont now if it will work... See if you can find an alternator and a flight controller. There are lots of electric ones, although it may need to be retooled but this will allow you to balance the quad with the brushless motors. The motors would be powered by the gas engine turning the alternator, well besides the initial first charge.

At the most maybe, it would need to be tuned to stay afloat, however instead of the rotors providing primary lift the engine would therefore making it more powerful and using the rotors for stabilization and guidance using the flight controller. That may need to be tuned im sure the physics are different. Although with the *hanging* design of having the motor propeller and camera/gimbal lower it should make stabilization a bit easier.

A thought I had bouncing around. In any case thought i'd throw it your way, never know.

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Peter McCloud wrote 11/11/2014 at 18:19 point
Thanks for the inputs. This is what I feel is all about, so please keep the inputs coming. The issues I've been having are oscillations with the belts themselves, I hope I have it fixed, but I haven't tested out the latest config.
A hybrid design would be nice, it certainly would solve the issues of having belts. I haven't done the math as to how much power I would need to maneuver using electrical power. The engine is already equipped with an alternator, so it'd just be extra weight of the control motors. Something to think about if the current fixes don't work out. Thanks!

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Rebelj12a wrote 11/12/2014 at 10:32 point
Possibly add an adjustable belt tensioner? Similar to this.

Also for fairly decent cheap parts this place is the place to look. Couldnt believe the prices so i'd question the build quality long term however for a working concept and for ideas on what to look for. This place has got the parts.

Also the idea to lower the engine and main rotor a bit came from here.

Look at the very bottom, theres the degrees of inclination. The lower center of gravity at the center as well makes it more stabile. Also.....

If you were to go with a single gas propellery and smaller control engines on the outside. I would use a propeller with a center connect and outside connection ring. Fix the propeller inside a round shell. That way it would have the stability if you wanted, to even attach the 4 control engines above the main main blade itself. It might offer a bit more stability as well, keeping the propeller blade from oscillating, attached to the motor.

Also for safety reasons too XD

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Peter McCloud wrote 11/13/2014 at 01:31 point
I have added spring loaded adjustable tensioners, that I built from scratch. They can be seen in the video link here.
Hopefully the remaining issue was having the pulley flanges setup right. Hopefully I'll find out it's all right with the next test.

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Rebelj12a wrote 11/13/2014 at 03:08 point
Oooh oh I dont know about springs. Makes it bouncy thats not good. I would have use screw adjustible ones you can lock into place. Especially because depending on temperature and wear the belts will loosen and tighten (dont know about you but its getting cold here XD)

If all else fails. I highly suggest looking at a chain based solution. Grab a couple old bikes for the gears and chains from thrift or garage sales.

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Rebelj12a wrote 11/12/2014 at 21:16 point
Also, of note on the page I linked is the motors they use and the kg of force they exert for flight.

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PointyOintment wrote 11/11/2014 at 22:47 point
I dont know if this will work, however it might...

Like this?

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gnoejuan wrote 10/17/2014 at 22:18 point
What i see here is a flying lawnmower. And that's exactly how I'd use it.

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Dave Hermeyer wrote 09/30/2014 at 11:11 point
I'm glad that you put a disclaimer "Think before you start" at the beginning of your instructions, but you go on to say "it's only as dangerous as the user". That's exactly the problem! There's plenty of fools out there, and I'd hate to imagine one of these machines in their hands. And what happens when you have engine problems in mid-flight, or a belt breaks?

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Peter McCloud wrote 09/30/2014 at 20:09 point
Yes there are people out there who could do bad things with Goliath, but there are many other things that they can get there hands on as well that'd be dangerous.
Once I start flying more than a few feet off the ground I intend to install a ballistic recovery chute. In an emergency the parachute is shot out using compressed gas or a rocket. There are some sized for ultralight aircraft. So that would be ideal. It'd be nice to have redundant belts, but I don't think there's enough weight margin for that.

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michaeldlewandowski wrote 10/17/2014 at 17:41 point
I am interested in designing/ building a recovery system for this monster! I have emailed you.

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Peter McCloud wrote 10/19/2014 at 02:07 point
I look forward to hearing about your ideas. I'll contact you soon!

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Mike Berti wrote 09/30/2014 at 02:35 point
This is by far one of the most compelling quadcopters I've seen to date.

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Peter McCloud wrote 09/30/2014 at 20:04 point
Thanks Mike!

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CHOPPERGIRL wrote 09/17/2014 at 01:59 point
Im designing my own heavy copter drone. Several points just looking cursorarily at your build out:

1. Placing your heavy motor on the top makes it inherently unstable. Far superior would be placing it underneath the center of gravity, not above it. The difference in stability is between either balancing a basketball on your finger tip (your design) or suspending a basketball from your finger on a string (like a helicopter with the aircraft body below the main rotor).

2. Hexa would be more failsafe than quad. On a hexa if two (or even 3) props go out, assuming the software can detect and compensate for the loss, the thing can remain stable and keep flying (long enough to return to a safe landing).

3. Your frame and engine look too heavy. You may be over building a lot of it, and galvanized steel and a heavy cast iron engine block may kill your efforts to get airborne. Look into ultalight aircraft engines or even mor advanced stuff. Yours looks like a generator or lawnmower engine which is designed for an application where engine weight is irrelevant. But for you, engine weight is VERY relevant.

4. You need a way to individually control rotation to each prop. Consider a fluidics type transmission. Basically, your engine is attached to a pump and creates continuous water pressure. If no torque is needed to any props, the water (or oil) recirculatesgoes around in a continous loop. If a prop needs torque, a valve shunts water into it in varying degrees to a reverse pump that drives the prop. In this way you could control all props variably instantly... and the motor would run at its optimal constant speed.

5. I myself want to buildone large enough to be controlled by and carry a pilot underneath. So I'm thinking even larger than your design...


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zakqwy wrote 09/17/2014 at 02:34 point
You should post your design to! Definitely interested to see your project.

I'd counter point (4); pumps are heavy. Hydraulic motors are heavy. Control valves are heavy. I could see using this for control surfaces (like an airplane), but the flow rates and pressure requirements needed for the propellers would make such a system difficult to integrate into a flying platform.

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Peter McCloud wrote 09/17/2014 at 21:33 point
I agree with Zakqwy, you should post your project to I'd like to go bigger as well, but this is step 1. In regards to your comments:
1. Yes it does make it unstable, but I haven't found a light weight way to do sling the engine underneath. The electronics will at least address the stability. Goliath should at least be slightly more stable than Gimbalbot ( :p
2. Going to hexa is an intriguing idea, but since Goliath theoretically has a extra thrust margin of about 10%, even going to hexa wouldn't help much. It still just fall fast.
3. Yes mass is the number one issue in making sure Goliath works. I've traded heavier mass for reduced cost and effort for Goliath, because I know there is going to be a learning curve and I'd rather wreck a this design and learn a few lessons than a higher performance and higher cost vehicle.
4. I actually did research doing a hydraulic design and as Zakqwy pointed out, it does get heavy. The pressures involved lead to very heavy motors and at least at the scales I looked at, it didn't work out. I also looked at the same concept using pneumatic design which was also interesting, but there's a lot of energy losses with the expanding air and there would need to be some sort of thermal recovery system.
5. I'd love to see your design! I've gotten great feedback from the community here at Hackaday Projects.

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PointyOintment wrote 09/18/2014 at 02:15 point
Placing your heavy motor on the top makes it inherently unstable.

This is not true:

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J Groff wrote 09/06/2014 at 20:19 point
That is quite a software thicket there sir. Have you considered abandoning the 'Arduino Way' and going for Atmel studio with JTAG/ISP through an inexpensive programmer like JTAG/ICE. Source level debugging and more available memory (no bootloader) and you get to use the USB port on the board. As you may have discovered the core of the Arduino platform is thin and they do stupid things like hogging timers for beeps and unnecessary delay functions. Unless you really want the IDE backward compatibility, but then it seems you had to fork that as well. I ended up doing it this way so I can speak to the benefits. Good luck.

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Peter McCloud wrote 09/06/2014 at 21:46 point
I do some programming, but haven't done any on a microcontroller yet, so almost all that went over my head in the first read. After googling most of what you wrote, that sounds pretty intimidating. (This coming from the guy who's testing a giant gas powered quadcopter in his driveway).
Now that I've done a bit of research, I agree with you that it would certainly make sense to go the Atmel studio route, especially for follow on versions of Goliath, and have an optimized bit of software. I do like the ideas behind the Ardupilot software and would like to contribute to their community. Also the singlecopter (
has demonstrated the control system route that I'd like to do, so I can possibly leverage the Ardupilot software already written for that.

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J Groff wrote 09/08/2014 at 22:08 point
Sorry. I guess a distilled version of that would be: you have so much code there that you might consider doing it the way the professional embedded systems developers do it with single step debug and viewing memory/registers etc instead of the way hobbyists do it Arduino style with printf and such ;] You can still use all the Arduino libraries this way, which is the bulk of what 'Wiring' really is. I think their platform is great for little one-offs but at a certain point you need real tools.

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Smerfj wrote 09/05/2014 at 17:49 point
Highly inefficient, but for simple control (until you can design something better) you can place a flat baffle under each prop that slides on the frame from the center outward. It could not only reduce the effective lift of a prop, but also shift the CG toward that prop, inducing roll in that direction. You probably don't even have to cover more than 1/4 of a prop to effectively reduce lift. Also, your actuator only has to overcome sliding friction since the aerodynamic force is perpendicular to the actuation direction.

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Peter McCloud wrote 09/05/2014 at 23:08 point
It's a good idea. My only concern is reducing the prop thrust. I don't have a lot of excess thrust currently so I might not be able to implement it. My hope with the vanes is that since airfoils provide more lift to drag, they'll able to produce a large amount of side force with a minimum of thrust reduction.

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zakqwy wrote 09/06/2014 at 14:25 point
I say baby steps first; get your thrust:weight ratio over 1 and sustain a constrained hover. I posted a link to the Project Morpheus video archive which has a lot of good test setups. Definitely worth a look!

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John Burchim wrote 09/05/2014 at 00:22 point
Can't get this project out of my thinking. Now I believe the reason to be your rotors. Your rotors are not opposite of each other, that is going to throw your torque off.

Should it not be front left and right rear same rotation? Opposite corners rotate the same?
not parallel.


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Peter McCloud wrote 09/05/2014 at 23:02 point
Electric quadcopters have the same rotation on opposite corners to do yaw control. They speed up the propellers that spin one direction and slow down the propellers that spin the other direction. This allows a torque difference that spins the vehicle, but the total thrust is balanced across the corners. Having them parallel still cancels out the torque, but if you tried to do yaw control, one side would drop.
Goliath has the props spinning parallel to allow the the belts to wrap around the drive pulley more and increase the torque transfered to the belt. Since I won't be using differential thrust, I can get away with doing parallel.

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