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Goliath - A Gas Powered Quadcopter

A BIG Gas Powered Quadcopter

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

Overview

Goliath is a prototype vehicle for developing large scale quadcopters. The current design is based on a single central gas engine with a belt drive providing power to the four propellers. Control of the vehicle is provided by control vanes placed under the propellers. Each propeller will be 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 are used.

The Mk I vehicle was focused on developing the drive train. The Mk II vehicle was built with lighter weight aluminum frame. Even when completed Goliath is intended as a starting point for future vehicles.

Flight control will be performed using the Pixhawk controller running the PX4 flight stack.

Related Projects

#Inexpensive Composite Propellers/Rotors

#Drone Test Stand

#Measuring Engine RPM with the Pixhawk

#EVPR: Electric Variable Pitch Rotor

Current Status: HOVERING!

The Mk II vehicle has been assembled and hovered for the first time in September 2016.


Details

Structure

The initial Mk I frame was 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. This allowed for multiple iterations of the drive system to be tested with a minimum of time and cost.


The Mk II frame is built using aluminum tube and assembled using aluminum gussets and and stainless steel rivets. This leads to a lightweight, vibration resistent design that can be assembled easily.

Engine

An electric powered design would have been the most straightforward approach. Electric motors are more efficient than gas motors, but the energy density of gasoline is much greater than today's batteries. So until battery technology improves, for large scale vehicles, gas power seemed the way to go.

Goliath currently uses a single 30 Hp vertical shaft engine and a belt system to transfer power to the four propellers. The setup was chosen because at this scale, four smaller gas engines have a smaller power to weight ratio than a single larger engine. The specific engine, an 810cc Briggs and Stratton Commercial engine was chosen primarily because of its relative low cost per power ratio.

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.

Propellers

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.

Control

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.

Exhaust

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...

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  • 1 × 30 HP vertical shaft gas engine Should equipped with a starter and alternator
  • 1 × Pixhawk Open Source Flight Controller
  • 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)
  • 1 × Main Pulley Bushing QD Bushing with 1 1/8" Bore

View all 22 components

  • Control Hardware Starting to Take Shape

    Peter McCloud03/27/2017 at 02:42 0 comments

    Up till now the work on Goliath has concentrated the drive train and the structure. The controls were put on the back burner until the other design problems were addressed. The other items aren't done, but the project has progressed to the point that having a control system would be helpful.

    When Goliath was originally conceived three years ago, the default control scheme was to use vanes underneath the rotors to direct the airflow for control. This was chosen because it was the simplest hardware setup to implement and it's been demonstrated to work for hovercraft. Back in October I started doing some basic calculations to size the control vanes and determine the required servo sizes. Turns out assuming that if it works for a hovercraft, it'll work for Goliath was a bad assumption.

    The issue with using vanes is the rotor downwash velocity. Goliath has a similar amount of horsepower as a hovercraft, but instead of 1 fan, there are 4 rotors, so the power per area is reduced by a factor of 4. Additionally the equation for the force generated by a vane is:


    So if the downwash is reduced by a factor of 2, the force created by the vane is decreased by a factor of four. The end result is that at full thrust, a single vane would have generated only two pounds of force. Which would be grossly inadequate. More force can be generated using multiple vanes in parallel, but the forces would still be low.

    I was discussing this issue with @Benchoff at the OSHW summit, and he suggested using grid fins instead. Doing some back of the envelope calculations show that grid fins should generate enough force. The downside is that the the grid fins have much higher drag, which would reduce the payload or flight time.

    Ignoring their complexity, variable pitch rotors would be the ideal control scheme. Variable pitch rotors would be able to generate larger moment torques than either vanes or grid fins. However, the increased complexity and the fact that Goliath is already a complex project, convinced me not to pursue this.

    However, it's been three years and I really want to see Goliath fly, so I've decided to start building both grid fins and a variable pitch rotor. If I pick one scheme and it doesn't work, then it'll be that much longer before it can fly. So I'll incrementally develop both and see which one works out better.

    Grid Fins

    The grid fins I'll document as part of Goliath as they are relatively straight forward. I have sourced some material to create the fins. The fins will be made from aluminum louvers for florescent lighting. It was difficult finding sheets big enough to make a 36" disc from, but I finally found some 4'x4' sheets (shown below).

    The next step will be cutting out a test disc and placing it under a rotor to determine the control forces generated.

    Variable Pitch Rotors

    The variable pitch rotors are a different story. I had decided not to pursue this until I came across some research that made me realize that it may be possible to create an electrically actuated variable pitch rotor with the servos contained inside the rotor hub.

    I've created a separate project, #EVPR: Electric Variable Pitch Rotor, and I'll be documenting the progress there. I'll be populating more of the design details there, be sure to follow the project if you're interested and want to get updates. Additionally, I think that the project can be useful for other multi-rotors and even conventional aircraft, so I'm entering #EVPR: Electric Variable Pitch Rotor in the 2017 Hackaday Prize. If you think it's worthwhile, but sure to give it a like.

  • Evaluating Aerodynamics

    Peter McCloud03/12/2017 at 00:26 0 comments

    Goliath hovered for the first time in September of 2016. The hover performance was less than desirable since it required a higher throttle setting than hoped and the vehicle did not rise evenly. It tended to favor the port side or the aft. Even more puzzling, was that it tended to lift off first on the side that had the most weight. Ballast could fix the issue, but understanding why is also important. Testing has continued to evaluate the aerodynamics of the setup. Below is a video compilation of some of those tests.

    Test 12 was a simple flow visualization of the rotor downwash. Tufts of yarn were added to the frame to show the flow direction along the radius of the rotor and into the frame. The tufts behaved as expected, with the tufts under the rotor mostly steady. Inside the frame, the tufts indicated the flow reversed and flowed upward due to ground effects. While the tufts wiggled, there did not appear to be anything that suggested any unsteady flow phenomena.

    Tests were also conducted outside to see if the shop walls and ceiling were effecting the aerodynamics. Occasionally in the past, loose debris had been ingested into the rotors and the debris recirculated inside the wake as the flow got turned around by the walls and got re-ingested. Testing outside reduced the re-circulation.

    Test 16 nearly ended up with the vehicle getting damaged. There were four hold-downs, intended to allow the vehicle to move slightly upward, yet remain captive. They weren't made long enough and the hold-downs failed on the aft end of the vehicle. Fortunately, the throttle was reduced in time and the vehicle settled back on the stand (albeit precariously).

    The hold-downs were fixed and the testing continued. During Test 17, the vehicle again lifted up, favoring the port side, but at a reduced throttle setting. However, the test stand didn't allow enough movement for a full hover to be achieved. The test showed that the asymmetries were present, regardless.

    In theory, the rotors themselves should have been out of ground effect as they were at least one diameter above the ground. However, for quadcopters, it may be that the ground effect is dependent on the length scale of the four rotors together and not the length scale of a single rotor. If that is true, then perhaps the port rotors are experiencing higher thrust since they are slightly closer to the ground. It's difficult to tell exactly. This may be why the Mallory Hoverbike has the offset rotors catty-corner from each other.

  • Mitigating the vibrations

    Peter McCloud12/12/2016 at 05:04 0 comments

    I'd hoped to be well into working on the controls on Goliath by now, but the shorter days and colder weather mean less time in the shop. I'm still nailing down some lingering issues with the drive train. The new pulleys are weeping grease because the bearings are getting too hot. I suspect it's because I'm using all thread axles and nuts to keep the bearings in place. I'm working on building the proper axles and axles mounts to go with the new pulleys.

    Meanwhile I wanted to document the progress made on mitigating the vibrations that the avionics experience. This was accomplished by better isolating the engine from the frame and the avionics tray from the frame. The new engine mounts are made primarily of rubber, but are built such that if the rubber fails, the bolts are still captive. Stainless steel bolts are used to attach the mounts.

    The avionics tray was switched from aluminum to steel. This was to add mass to help reduce the displacement of the avionics tray. Below is the new tray with some of the avionics populated.

    The tray is mounted to the frame using four Expansion Nuts. I forgot to take a picture of them before I installed them, so here is a link. Below is a shot showing the flange on the expansion nut between the tray and the frame.

    So how much did all the changes help? Data from the Pixhawk shows a huge reduction in the pitch rates down by a factor of 5 to 10. This means that the Pixhawk should be able to control Goliath once the rest of the hardware is complete.

    Hopefully the next log update in the not too distant future will be about fixing the bearing issues.

  • Quick Status Update

    Peter McCloud11/21/2016 at 05:25 0 comments

    It's been a little over two months since Goliath hovered for the first time. Here are some of things that have gone on since then.

    First was a trip to the Portland Maker Faire, September 11 and 12th at OMSI. It was a lot of fun showing off the vehicle, especially now that it hovers. Thanks to everyone who came out and checked out the project. I had a lot of great conversations that weekend.

    After getting back to the shop and making sure everything was in working order, it was time to get back to work. The first order of business was to finalize some of the hardware. While Goliath hovered, the center of gravity didn't seem to be in the most ideal location. In order to remedy this, all of the hardware needs to be finalized with the flight weight components, particularly the remaining steel pulleys.

    This was the same process as before, but since these are idlers and tensioners, no holes are needed for bolts. The last of of these components are complete, with each saving around a pound of weight. There is now only one one steel pulley left on the vehicle, the main engine pulley.

    There was also a hiccup with the battery and solenoid. The battery died, likely because it was undersized and was being deeply discharged. A new bigger battery was added with 18Ah, 80% more capacity than the previous battery, but with only 4 more lbs. Some thought was given to switching from the lead AGM type to a Lithium based battery, which would save about 10 lbs. However, the AGM has been demonstrated to work with the high vibration environments.

    The solenoid failed again, the second on that's failed on Goliath. It's obvious that the stock lawnmower ones aren't built for the vibrations that Goliath creates. It was replaced with another stock solenoid as a temporary fix, but a heavy duty one needs to be sourced for the future.

    Lastly, the temporary Avionics Tray was replaced with a permanent one. This time it was made from 16 gauge steel. It weighs a little more than a pound. The idea is that the added mass will help to dampen the vibrations. The tray is isolated from the frame. using rubber expansion nuts.

    I'll have more details in a future log post, but the great news is that between the new engine mounts and the avionics tray have reduced the vibrations that the Pixhawk experiences low enough for it to work now.

    Stay tuned for more details.

  • Goliath Mk. II Hovers!

    Peter McCloud09/08/2016 at 05:21 8 comments

    Over Labor Day weekend the assembly of the Mk. II vehicle was completed. The new vehicle was weighed and the current weight is 170 lbs, 50 lbs lighter than the previous vehicle. The first couple of tests were conducted and Goliath has hovered for the first time!

    There is obviously a lot more to be done, but hovering is a big step in the right direction.

    Also, if you're in the Portland area this weekend, come see Goliath at the Maker Faire!


  • Assembly Nearly Complete, 1 Week to the Portland Maker Faire

    Peter McCloud09/03/2016 at 20:44 0 comments

    Work has continued on the Mk II vehicle and it's nearly complete. The latest work has been attaching the idler pulleys, tensioners and the battery.

    The ilder pulleys were mounted to same 1/8" plate used for the engine mounting plate. Aluminum angle was riveted around the edges and the plates were bolted to the frame.

    Below, the two idler pulleys for the single sided belt are attached.

    The center idler for the double sided belt required a different approach. The upper attachment was already part of the engine mounting plate. The lower attachment was made from a smaller piece of plate and riveted to two cross members that were added to the frame. Below is a shot looking at the underside of the frame where the cross members were added.

    The other idler for the double sided belt was attached using two different methods. On the lower side, the aluminum plate with angle was used and bolted to the frame. For the upper side just a plate was used was bolted to the engine mounting plate, using the same bolts for the engine mount.

    With the idler pulleys all attached and the tensioner attachment method decided upon, some additional gussets were added to reinforce the aft end of the vehicle.


    With the aft gussets attached, the exhaust pipes could mounted.

    Not shown are the flexible mounts scavenged from the original frame.

    Next a tray for the battery was created from angle pieces.

    A rubber liner was added to the bottom of the tray.

    To keep the battery in place an additional piece of angle was bolted in place on top of the battery.
    Now all that remains to complete the Mk. II vehicle is to add to the electronics and the fuel tank. With some luck, the vehicle could be complete and running by Labor Day.

    Stay tuned...

  • Come see Goliath Mk. II at the Portland Mini Maker Faire (Sept 10th and 11th)

    Peter McCloud08/25/2016 at 23:23 0 comments

    Goliath Mk. II will be at the Portland Mini Maker Faire on Saturday and Sunday, September 10th and 11th at OMSI. This will be the first time the Mk. II vehicle will be shown in public. I'm working on completing the vehicle and having its first test before the Maker Faire. The vehicle will not be run at the Faire. Look for it at the McCloud Aero Corp booth.

    More details can be found at:

    https://www.facebook.com/makerfairepdx/

  • Lower Frame Completed, Upper and Lower Halves Joined

    Peter McCloud08/15/2016 at 04:26 0 comments

    This last weekend was productive and the major portions of the frame are now complete.

    After attaching the engine mounting plate to the frame, the next step was assembling the lower frame. The lower frame is similar to the lower ring of the upper frame, so it was possible to reuse the jig for the upper frame with some minor modifications. This was simply making new wood rotor shaft mounts for the lower frame and swapping them out in place of the old ones. Then all of the lower frame elements were cut and placed in the jig.

    With all of the elements in place, the same process for riveting the gussets was followed.

    Next the lower rotor shaft mounts were machined out of metal. There was a couple of hiccups due to the double sided tape not holding and bit breaking.

    Once the mounts were completed, the shaft mounts were attached with bolts to the lower frame in the same manner of the upper frame.
    In the future the gussets would be attached to the top side of the lower frame. However, at this stage the method of attaching the idler pulleys and tensioners hadn't been finalized. Therefore the upper gussets were left off at this point.

    With the two halves completed, it was time to start attaching them together. Both halves of the frame were attached to the rotor axles to hold the two halves relative to each other. It was easiest to work with the frame flipped over since most of the riveting was on the bottom.

    Four lengths of tubing were initially cut and attached on the sides of the frame along with the gussets for the lower frame. Clecos were used to hold the parts together prior to riveting.

    Next the lower cross members were added to the lower frame

    With all of the new elements attached, it was time to riveting the parts and finalized the attachment between the frames. At that point the frame was flipped back over to see the progress.

    At this point about 80% of the frame is complete. the frame members at the front of back need to be added and some smaller cross members need to be added to stiffen the frame. However, before completing the frame elements, the attachment hardware needs to be completed to make sure there aren't any issues with the remaining structure. Once the attachment hardware has been finalized, then the frame can be finalized.

  • Attaching the Engine Mounting Plate to the Upper Frame

    Peter McCloud08/02/2016 at 19:32 0 comments

    Progress on the Mk. II vehicle is moving along and the engine mounting plate is now attached to the upper frame.

    The first step was to start measuring and cutting the tubing that attach the engine mounting plate to the upper frame. This was starting by making a simple jig to hold the pieces at the right elevation to each other.

    This worked for doing some preliminary alignment, but to make sure everything fit well, it was decided to redo the jig so that the engine could be placed on the vehicle while it was in the jig. This was done by further elevate all the pieces, with 2x4 blocks holding up the engine mounting plate.

    When all of the tubing was cut, the holes were drilled on the ends attached to the mounting plate and the parts were held together with Clecos.

    The plate with the tubes attached was put back in the jig and aligned with the upper frame. Then the gussets for the remaining joints were made and attached with more Clecos.

    The gussets are wrapped around the tubing and will also serve as the attachment points between the upper and lower halves of the frame. This required bending the gussets with a larger 3/4" radius. To get a good radius bend, the press brake was used with a 3/4" diameter steel bar placed along side the sheet metal to provide the right shape for bending.

    Once all the gussets were in place, the engine was mounted to double check that there was adequate clearance, before permanently attaching the plate to the frame.

    All of the clearances checked out and with no glaring design issues present, the rest of the rivets were pulled on the frame side of the tubes. Since there wasn't enough clearance to pull the rivets under the engine mounting plate, the frame was flipped over and the last of the rivets in the plate were installed.

    A quick note on the rivets for the engine plate. Rivets are designed to join a specific thickness of material. The 1/8" thick plate is thicker than the gussets, so slightly longer rivets had to be used. So care has to be taken to make sure the right rivets are used in the different locations.

    At this point, the frame is about 50% complete. The frame was weighed in it's current configuration (without the engine) and weighs 14 lbs, 2 oz. This means that the final structure weight is sill on track to weigh around 30 lbs.

    Next up for the Mk. II vehicle is to build the lower half of the frame and machine the lower rotor shaft mounts. Once that work is complete, the two halves of the frames can be joined together.

  • Engine Mounting Plate Complete

    Peter McCloud07/26/2016 at 14:34 0 comments

    The engine mounting plate has been completed and the middle portion of the Mk. II frame is now complete.

    Designing the engine mounting plate required working though a few iterations before the coming to current design. The plate is made from 1/8" thick 6061-T6 Al plate from Aircraft Spruce. It wasn't cheap, so making sure the design was good before cutting the material was important.

    The first step was setting up the initial layout, using cardboard to layout the engine mounts and make sure that the plate wouldn't be in the way of the exhaust. The engine mounts are made of rubber and steel and should help with dampening some of the vibration from the engine.

    After doing the cardboard layout, and comparing it to the Mk. I design, it became apparent that it would make sense to go ahead and incorporate the mount one of the idler pulleys as part of the design.

    Next, the part was designed using CAD and another prototype was machined using foam board. One other feature incorporated. at this point was multiple tabs on the sides of the plate for attaching to both the lower and upper frames. The tabs would be bent +/- 15 degrees depending on which half of the frame it would be attached to.

    However, after holding the part inside the new frame a very big design flaw become apparent. The middle tabs were meant to be bent downwards, but that would place them in the way of the idler pulley, which will be placed below the engine plate. Second, I could go to both the lower and upper frame from the engine plate directly, otherwise the structure would have to pass through the belts. If that was done I'd have to assemble and re-assemble the frame every time the belts were added or removed.

    It was decided to just attached the engine plate to the upper frame, similar to how the Mk I frame is laid out. The plate was redesigned. one last time, this time adding engine mounts to the front and back and also adding a mounting area for the motor servos at the aft end of the plate.

    After a test fit, the design was complete and the part was ready to be machined using the aluminum plate. Since the CNC router needs to go slow to cut the aluminum plate, it took about an hour to cut the part. In the images, the edges of the plate look somewhat rough. This is actually the protective film that is on both sides of the plate. The actual edges come out very clean.

    After cutting, the tabs were bent to the correct angles using the press brake. The protective film has been left on to prevent marring the material.

    After getting all of the bends to the right angle, the mounts were placed on the plate and the engine was test fit to make sure all of the clearances looked good.

    With the engine plate complete, it was time to start attaching it to the upper frame. I'll have those details in the next log.

View all 72 project logs

  • 1

    THINK BEFORE YOU START

    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 COMPOSITES

    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

    BUILDING THE UPPER FRAME

    Tools - Miter Saw, Jig Saw or Tin Snips, File, Drill with #30 drill bit,Rivet Puller

    A) Build the Jig for the Upper Frame

    To properly build the frame, jigs are required to hold all of the frame elements in place. The jig is constructed from particle board. Below the completed jig is shown with the upper frame elements in place.


    B) Cut the Upper Frame Elements

    Using a miter saw, cut all of the frame elements and place them in the jig to ensure a proper fit.

    C) Cut the Common Gussets

    Cut the common gussets (4 A & 4 B), layout and drill the holes with the #30 drill bit.



    D) Assemble the Upper Deck Elements

    1) Remove the frame elements for the upper ring, leaving just the pieces for the upper deck


    2) Clamp the common gussets in place and drill half of the holes into the frame. Use Clecos to fill in the holes as you go.

    3) With half of the holes filled with Clecos, drill the remaining holes and fill them with rivets.


    4) Remove the Clecos and fill in the remaining holes with rivets.

    5) Remove the upper deck from the jig, flip it over and place it back in the Jig

    E) Cut the Corner Gussets

    F) Assemble the Upper Ring

    1) Place the remaining frame elements back in the Jig

    2) Attach the corner gussets




    G) Join the Upper Ring to the Upper Deck

    1) Cut the Angle Gussets



    2) Attach each of the angle gussets




    The Upper Frame is now complete and can be removed from the Jig


View all 11 instructions

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Discussions

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?

  Are you sure? yes | no

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.

  Are you sure? yes | no

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.

  Are you sure? yes | no

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

  Are you sure? yes | no

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.

  Are you sure? yes | no

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

  Are you sure? yes | no

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...

CG

  Are you sure? yes | no

zakqwy wrote 09/17/2014 at 02:34 point
You should post your design to HaD.io! 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.

  Are you sure? yes | no

Peter McCloud wrote 09/17/2014 at 21:33 point
I agree with Zakqwy, you should post your project to HaD.io. 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 (http://hackaday.io/project/996-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.

  Are you sure? yes | no

PointyOintment wrote 09/18/2014 at 02:15 point
66
Placing your heavy motor on the top makes it inherently unstable.
99

This is not true: https://en.wikipedia.org/wiki/Pendulum_rocket_fallacy

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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 (http://copter.ardupilot.com/wiki/singlecopter-and-coaxcopter/)
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.

John

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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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John Burchim wrote 09/04/2014 at 23:24 point
Peter,

Had a thought, for the purpose of testing only, your details show the support under the main body of the unit. If you shift your support to under the propellers, you would have a better view of the stress caused when it is try to lift using them.

If your struts do not support the motor how can it lift it under load?

John

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Peter McCloud wrote 09/05/2014 at 23:04 point
Goliath is capable of supporting itself at the propellers. The saw horse are under the center to take up less room in the garage and allow the shop crane in and out.

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John Burchim wrote 09/04/2014 at 16:53 point
Peter,
using the Metal framing for your structure, do you have the ability to put an extra bend into one face of it for a second angle. It should make the overall structure much more rigid, without adding weight?

John

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Peter McCloud wrote 09/05/2014 at 22:53 point
I have a sheet metal brake, that's in pieces. I could use it to add the bends. The current frame is intended for prototyping.

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mr.nathan.richter wrote 09/04/2014 at 01:26 point
wow, this is incredible. why did you choose to go with a belt drive over shaft drive?

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Peter McCloud wrote 09/04/2014 at 11:01 point
Thanks! After researching belt, chains and drive shafts, I chose a belt system because it was light, could handle the RPM/torque I was targeting and able to handle shock loads well. If I use drive shafts I'd have to have a gear box at each propeller to change direction as well as a a larger gearbox at the engine to attach multiple shafts.

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John Burchim wrote 09/04/2014 at 00:58 point
Peter,
I like the idea, but not the approach. You should consider slightly different approach. At least research drive system stress details, Torque details, and give some planning for rotation speeds required to gain lift.
How do you plan to change altitude?
Could you use some sort of flywheel to aid in rotation control?
Consider using a less direct drive to change the stress points to a better location, while increasing rotation speeds.
There are multiple thoughts that could be helpful depending on some of the requirements you are looking for.
Bicycle or motor cycle drive systems or indirect drive systems would be a good place to start.

John

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Peter McCloud wrote 09/04/2014 at 11:05 point
Thanks for the feedback John. I did start this project looking at motor cycle, bike and aircraft drive systems. I have sized the components to the loads, as well as done the calculations for lift, I just have documented the details. I'll have to get those added at some point.

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John Burchim wrote 09/03/2014 at 22:18 point
Peter,
I noticed your framing flexed and that is with no load, you might need to add either tubing or reverse angle framing to reinforce your struts. have you considered using chains instead of belts as they tend to flex less. Also was wondering about your shaft sizes, your shafts should all be close to the same size for the torque they are receiving which should be similar.
I don't know if any of this is helpful but hope it works out for you either way.

John

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Peter McCloud wrote 09/04/2014 at 10:54 point
I do need to fix some of the flex. I'm still debating on the best method that won't add too much more weight. The shafts for all the props are 3/4" all thread.

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Hacker404 wrote 09/03/2014 at 21:41 point
Hi Peter,
What are the props made of? I look at this and see a 810cc motor that must be 30+ Kg and then I look at the pitch and surface area of the props and wonder how they don't tear apart from centripetal force at the prop RPM you will need to lift 30+ Kg.

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Peter McCloud wrote 09/04/2014 at 10:51 point
The props are made from a foam core with wood stiffeners and then covered with 3 layers of 9 oz fiberglass. I have a few project logs detailing the progress, the last is: http://hackaday.io/project/1230/log/6507-not-so-rapid-prototyping

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bruceb75 wrote 09/03/2014 at 21:10 point
You might want to take a look at how other belt powered propeller jigs have worked.... https://www.youtube.com/watch?v=rG9clKE6268 shows a universal hovercraft UH-14P.... There is added weight, but these belts really whip around.... constraining them like shown is a good way to keep them out of the prop

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Adam Fabio wrote 09/01/2014 at 06:28 point
Hey Peter, Sorry you're having trouble starting the engine. I'm no small engine expert, but I've fought with a few of them in my day.
You know the old saying - gas engines need air, fuel, and spark. You know you're getting fuel to the carb, but is it letting that fuel in to the intake. (closed needle valve?)

Spark - the easiest way to do this one is to place the spark plug wire somewhere near the engine, and look for a spark while cranking. (You want to disconnect your props for this)
You could also disconnect the entire spark plug, touch the threaded portion of the plug to the block, and check for spark. If you're not getting spark, check your ignition system - sometimes these engines have a low oil cutout, which could be causing you problems. (You did put oil in it, right?)

Finally air - check for a clogged air filter, (could be packed in a plastic bag from the factory).

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Peter McCloud wrote 09/01/2014 at 14:56 point
Thanks Adam. I did put oil in it, but perhaps it needs more now that it's been circulated around a bit. The air cleaner wasn't wrapped, but I did remove it to get at the carburetor and left it off for the last few tests. I had been leaving testing the spark until last since the gas setup is sketchy, but if the oil doesn't work I'll try those spark tests.

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Jasmine Brackett wrote 08/15/2014 at 19:30 point
Hello Peter, you need to add a few more bits of documentation on Hackaday Projects to give your project the best chance of going through to the next round of The Hackaday Prize.

By August 20th you must have the following:
- A video. It should be less than 2 minutes long describing your project. Put it on YouTube (or Youku), and add a link to it on your project page. This is done by editing your project (edit link is at the top of your project page) and adding it as an "External Link"
- At least 4 Project Logs (you have this covered)
- A system design document (I can't see one. You should highlight it in the Details)
- Links to code repositories, and remember to mention any licenses or permissions needed for your project. For example, if you are using software libraries you need to document that information.

You should also try to highlight how your project is 'Connected' and 'Open' in the details and video.

There are a couple of tutorial video's with more info here: http://hackaday.com/2014/07/26/4-minutes-to-entry/

Good luck!

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Zorro wrote 08/09/2014 at 06:58 point
Wow... This reminds me of Terminator 4...

Forgive me if I am stating something obvious or dumb, cuz I'm a complete newbie to this area , but have you considered making this as a tri-copter? You wouldn't need custom blades since all the blades are the same spin direction, the yaw control and flight stability is better, plus three blades instead of four would mean lighter design?

If nothing else, it'd be nice to understand the reasons why you chose a quad-copter over other designs.

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Peter McCloud wrote 08/09/2014 at 14:33 point
I wanted to do a quad-copter because by having two clockwise and two counter clockwise propellers, the torque from the propellers will cancel out. To be honest I hadn't considered a tri-copter. Tri-copters tilt the rear rotor to offset the torque like a helicopter tail-rotor. The belt system doesn't allow the blades to tilt. I guess Goliath could be built as a Tri, but the the control surfaces would have to be bigger to compensate for the torque.

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Steve Shaffer wrote 08/09/2014 at 00:32 point
I just discovered this electric clutch and figured it might interest you, at least you must agree it is interesting: http://www.ebay.com/itm/Electric-PTO-Clutch-for-Scag-61-72-Hydraulic-Drive-3-Wheel-Riding-Lawn-Mowers-/121060668200?pt=LH_DefaultDomain_0&hash=item1c2fc73328

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Peter McCloud wrote 08/09/2014 at 14:36 point
This is interesting. WillyMacD had suggested electric clutches, but I didn't find these when I was looking around. I'll have to look into these.

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Steve Shaffer wrote 08/07/2014 at 18:34 point
Invent a pulley that can expand and contract by turning something. This will give you prop speed control, and thus allow simple control by all the normal RC control baords.

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Peter McCloud wrote 08/08/2014 at 14:36 point
That would certainly make things easier. CVTs use a conical pulley to adjust the radius to do what you're talking about, but I don't think it'll work with a toothed belt. An expanding and contracting pulley would have to allow the teeth to slip in some manner. Perhaps a Derailleur setup might work, but I don't think it'd be responsive enough.

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Steve Shaffer wrote 08/08/2014 at 14:54 point
I agree it's hard. The more I read the others comments the more it really sounds like you should spring for 1/5th scale helicopter assemblies and blades, then simple servos can adjust pitch and therefore thrust just like an electric quadcopter. I just created a guided rocket powered by the 4hp edf from Dr. Mad Thrust, with vectored thrust by flaps, flaps suck, couldn't get stabilization good enough with the multiwii controller. Just a heads up. I've given up with flaps for good thrust vectoring and am changing the design of the craft and giving it swivel nozzle styled vectored thrust.

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zakqwy wrote 08/09/2014 at 01:42 point
Steve, I'd like to see your project if you do a gimbaled thruster. In my experience, it's not easy.

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Stephane wrote 07/07/2014 at 19:52 point
For the propellors; when I built my composite uav wings I used the scraps from the hotwire cutting as a support for vacuum bagging. Since you mill your cores you may want to mill shells that fit around the props when bagging? Also some UD carbon on both sides of the prop will increase the bending strength :)

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Peter McCloud wrote 07/08/2014 at 00:20 point
Thanks! Milling support shells sounds like a good idea. I do plan on eventually switching to carbon to increase the strength, but I'd rather get all the kinks worked out with cheaper fiberglass.

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PK wrote 07/03/2014 at 21:35 point
Awesome project! Would love to see it fly.

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Peter McCloud wrote 07/05/2014 at 03:09 point
Thanks! I'm looking forward to seeing it fly too!

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