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Goliath - A Gas Powered Quadcopter

A BIG Gas Powered Quadcopter

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This project was created on 05/25/2014 and last updated 7 days ago.

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)

See all components

Project logs
  • We Interrupt our Regularly Scheduled Broadcast...

    7 days ago • 1 comment

    Well, I said I'd be able to fix the vehicle quickly and go back to testing right away. The weather did not cooperate. There was about 4 inches of standing water underneath Goliath on Saturday and it's still drying out. Unfortunately I'm out of time to do anymore testing for a while.

    Next week I'll be moving to Longview, Washington about an hour outside of Portland, Oregon. This is the reason has slowed down on Goliath recently. It'll likely be several weeks before I get set back up at the new place, so I won't be posting again until then.

    The good news is I'm getting an upgrade in shop space. The new house comes with a 24'x60' shop (below, and no it didn't come with the mill. I did ask though), so I'll have lots more room and I should be able to test Goliath rain or shine (after routing the exhaust outside of course).

    The new house sits on 2 acres, so I'll also have enough room to test once Goliath is able to fly.

    So if all goes well, in a few weeks, I'll have Goliath reassembled in the new shop and get back to testing on a regular basis!

  • Progress on the Test Stand and Broken Bolts

    11 days ago • 0 comments

    The last few weeks have seen some progress on instrumenting the #Drone Test Stand. You can check out that project for more details, but so far I've made a prototype of electronics to measure the thrust while Goliath is being tested and put together the hardware to incorporate the load cells into the test stand.

    Previously the support lines were directly attached from Goliath to the test stand. The new setup has Goliath attached to two support bars, one for the front and one for the back. Each support stand rests on (2) load cells, one under each end. The load cells are mounted on 2x4 blocks that have a recess to keep the load cells in place. To ensure that the load cells receive a purely axial load, two brackets that swivel on a piece of all-thread hold the support bar in place. The all thread also helps to keep the 2x10s spread apart at the correct distance to keep the support bar in place on the load cells.

    I attached one of support bars to the test stand and decided that it'd be good to run a test with just the one support bar to make sure the setup works before adding the second support.

    The plan for the test was to start up with the choke on, make sure the support bar was okay, and then keep running the engine on idle to warm up the engine. After that I would shut it off and turn off the choke (there's no servo setup for it yet) and then try another run at full power. Here's the video for the test:

    As you can see from the video one of the propellers broke free after idling for a while. The propeller broke free after all three of the bolts that hold it onto the pulley failed. Replaying the video after test it was clear that there was a increase in oscillations before it failed. It's likely that one bolt failed and then the others failed under the increase in load. Fortunately having the shaft supported at both ends keeps the prop captive instead of the prop sailing off in the sky. There was no damage to the vehicle other than the three bolts. Here's a closeup of where the bolts broke.

    The bolts were just generic zinc 1/4" cap screws 3 1/2" long. The bolt passes through the pulley and are threaded into the QD bushings and hold the two parts together. The bushings come with shorter 1" long bolts for this purpose, but I swapped them out with the longer bolts so that they also served the purpose of the prop bolts. The prop then goes over the bolts and nylon lock nuts go on above the prop to hold it in place. The bolts broke where the prop and bushing interface.

    The easiest fix for this is to get higher strength bolts (grade 5 or grade 8). Unfortunately it looks like I'll have to special order them as I need the full length threaded and all the local hardware stores only carry partially threaded. I did find some stainless one today that I can use in the meantime, but stainless is a little weaker than a Grade 5 bolt so I'll just use those temporarily until I receive the others. It should be relatively quick to swap them out at all the propellers, add the second support bar and do the next test.

  • Checking the Numbers

    24 days ago • 0 comments

    During the last test, Goliath was run at full throttle and failed to hover. One thing I did find after going over the vehicle the next day was that the choke was set to 25%. This would prevent the engine from producing full power. I haven't had the opportunity to go back and retest yet. I'd also like to instrument the test stand to measure the thrust before doing any testing. Along those lines I've started a separate hackday project, Drone Test Stand to document those details, so if you're interested in that check it out!

    However, before getting into modifying the test stand, the first thing I did was to go back and check the calculations to make sure the engine can produce enough lift. There's been a couple of comments around the interwebs stating that 30 Hp isn't enough to the lift Goliath. I've double checked the numbers before, so I guess it's triple-checked, but it just made since to re-check before investing more time and effort into the test stand. I also haven't documented how I had calculated the power required, so it seemed like a good time to do so.

    So I've put together a spreadsheet to calculate the power required and I've placed it on github as part of the documentation. The equations are from "Helicopter Performance" by Donald Layton. Inputs are in red and the output is in blue. Essentially you tell it how much lift you need, the rotor rpm, the air density and the airfoil properties, and it spits out how much power & torque is needed. Here's a screenshot of the results for Goliath.

    For a fully loaded vehicle at 255 lbs, using 36" diameter propellers at 3080 RPM, 25 Hp is required to hover (assuming standard air density at sea level). This would leave a 5 Hp or 20% margin for climb or maneuvering. This isn't much compared to other quad copters, but Goliath isn't intended to be nimble. Eventually ducting will be added that should help to improve these numbers.

    One note on the Propeller Figure of Merit (FM) shown in the spreadsheet. This is somewhat equivalent to efficiency. For a vehicle hovering off the ground the efficiency is essentially 0% since you are expending X amount of power to no realized work. Figure of Merit (FM) is calculated by comparing the rotor to an idealized or perfect rotor. For this case Goliath would require a rotor that is 80.9% efficient. A less efficient rotor would require additional power. 80.9% is on the higher side, but it is a doable number.

    The last element that needs to be considered is how the power required matches the power produced by the engine. Here is a plot of the power required vs. the engine power.

    The required power curve was created by plugging different RPM values into the spreadsheet. Keep in mind that there is a 1:1.1 pulley ratio between the engine and the rotors so that the rotors spin 10% faster than the engine. Thus for a 2800 RPM engine speed, the rotors spin at 3080 RPM. The two curves cross at 2800 RPM, so for a fully loaded vehicle at 255 lbs the engine should run at that speed.

    So can Goliath hover? The laws of physics say it's certainly possible. In reality it's more complicated than that and more data is needed to figure out where things are going wrong. These calculations don't account for belt losses (should be low, but it isn't zero) and bearing losses, but there is 20% margin available. If anyone's interested and feels like checking the numbers or calculations in the spreadsheet, let me know if you find anything. Also if you have suggestions on improvements to the spreadsheet let me know.

    In the meantime I'll be moving forward on adding thrust measurements to the test stand!

View all 41 project logs

Build instructions
  • 1


    Before you start this project, take some time to REALLY think about what your 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 handle putting 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 quadcopter be mindful of your safety and the safety of others.

  • 2


    Building the composites pieces takes the longest amount of time. It's recommended to start these pieces first, and the rest of the components can be likely be built while waiting for 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

See all instructions


Adam Fabio wrote 3 months ago 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 2 months ago 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 4 months ago 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 4 months ago 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 5 months ago 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 5 months ago 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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PointyOintment wrote 5 months ago point
I dont know if this will work, however it might...

Like this?

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Rebelj12a wrote 5 months ago 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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Rebelj12a wrote 5 months ago 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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Peter McCloud wrote 5 months ago 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 5 months ago 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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gnoejuan wrote 6 months ago 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 6 months ago 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 6 months ago 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 6 months ago point
I am interested in designing/ building a recovery system for this monster! I have emailed you.

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Peter McCloud wrote 5 months ago point
I look forward to hearing about your ideas. I'll contact you soon!

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Mike Berti wrote 6 months ago point
This is by far one of the most compelling quadcopters I've seen to date.

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Peter McCloud wrote 6 months ago point
Thanks Mike!

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CHOPPERGIRL wrote 7 months ago 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 7 months ago 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 7 months ago 1 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 7 months ago point
Placing your heavy motor on the top makes it inherently unstable.

This is not true:

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J Groff wrote 7 months ago 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 7 months ago 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 7 months ago 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 7 months ago 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 7 months ago 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 7 months ago 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 7 months ago 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 7 months ago 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 7 months ago point

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?


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Peter McCloud wrote 7 months ago 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 7 months ago point
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?


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Peter McCloud wrote 7 months ago 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 7 months ago 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 7 months ago 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 7 months ago point
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.


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Peter McCloud wrote 7 months ago 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 7 months ago point
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.


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Peter McCloud wrote 7 months ago 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 7 months ago 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 7 months ago 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:

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bruceb75 wrote 7 months ago point
You might want to take a look at how other belt powered propeller jigs have worked.... 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 7 months ago 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 7 months ago 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 wrote 8 months ago 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:

Good luck!

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Zorro wrote 8 months ago 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 8 months ago 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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