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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 18 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
  • Double Sided Belt Added, First Full Throttle Test

    18 days ago • 3 comments

    It's officially been a year now since I started putting together Goliath (2/14/15) and I got to start this year out well by doing more testing.

    Since the last tests I've ordered and installed the new 30 mm wide double sided belt and installed the new pulleys for it. I've also relocated and redesigned the tensioner for the double sided belt (pulley and tensioner layout). This was to put it in the proper location to take up the slack that develops in the belt.

    Relocating this was what took the longest amount of time. I was trying to mirror what I did on the single belt side, but due to the structural layout there isn't as much room and ran into packaging issues. ( I know it's a 10' quadcopter, I really shouldn't have those, but I did)

    Here's a top view of the single sided tensioner. The center beams angle away from the tensioner.

    Here's the top view of the double sided tensioner. The center beams angle towards the tensioner. The made it hard to find a good location at the right angle to mount the springs too. Additionally, I didn't have room for the larger springs so I initially downsized the springs.

    Once that was in place I finally got to testing. Since the single sided belt testing went well I went straight to testing with the flight props. Here's the video with Tests 17, 18 & 19.

    Test 17 went well, but the double sided belts were still seeing a bit of oscillation. I figured this was due to the smaller springs being used. Below is a picture of the different springs I've been using, and the smallest one is the one I used for Test 17. They were shorter and didn't have enough travel to take up all of the slack developing. So for Test 18 I re-arranged the pulleys to get the medium sized springs in the tensioner.

    Test 18 definitely showed an improvement to the belts, but I still thought it could be better. I then spent the better part of the day re-arranging pulleys and adding another pulley to allow the tensioner to fit the largest spring. These are the same ones I use on the single sided belt.

    So that finally did the trick. For Test 19, Goliath started up and at quarter throttle ran smoothly. After a few seconds to verify that everything was running smoothly, I gave it full throttle.....and Goliath didn't hover....

    The great news is that it didn't fly apart. The belts oscillated a bit as it came up to speed, but damped back out at full throttle. The propellers held together as well.

    So why didn't it hover?

    Short answer, I need more data. Weight is a likely culprit, more hardware was added than anticipated to get the drive system working. Power is another possibility, it could be that the engine isn't providing the required power.

    Next step is to get a good weight measurement and add tachometers to determine what RPM the system is achieving. Looking closely at the video there does seem to be some settling as I set it back to 1/4 throttle, so I think I'm getting close.

  • Test #15 and #16 Complete

    2 months ago • 2 comments

    Finally got everything together to start testing again. I'll talk about the last couple of details needed to get Goliath ready after the video. The tests had some hiccups, (nothing was damaged) but it looks like the wider belts are working out better.

    One of the last things needed was new belt guards for the new frame dimensions. I cut a new set, making them 2 inches wide instead of 3 inches. This was because the rotors needed to be placed one notch closer to the engine, leaving a little less room for the belt guard. The second change was to add an extra fold to increase the stiffness.

    The new belt guard is on the left and the old one is one the right. Below you can see the tab made with the extra fold to add stiffness.

    Next, the throttle servo had to be redone. Previously when the servo was mounted, I had to reverse the servo direction on the RC transmitter. This time I mounted the servo with the linkage on the opposite side of the servo so the controls didn't have to be reversed.With that done it was time to get back to testing.

    So the first test was the one with the hiccups. Since I was using the test props, I figured I wouldn't really need the guy lines to keep Goliath from twisting. The starter obviously provides a lot of torque and caused the vehicle to twist and rock back and forth. The second issue was that part way though the test was that the throttle servo got disconnected. When this happened the engine went to full throttle. Fortunately I was able to shut it off quickly. The culprit turned out to be a missing screw on the servo, (which was obviously missing in the above photo) and the control horn fell off during the test ( below).

    I quickly screwed the control horn back on and added the guy lines and did the next test (#16). This time things went well. The exhaust is rattling around and I need to tighten some more screws, but the tensioner is doing what its supposed to be doing now. Since I now the wider belts help, I'm going to place the order for the second belt.

    In the meantime I'll be checking things over, coming up with better mounts for the exhaust and likely the throttle servo as well. I'll also need to think about addressing a throttle linkage failure leading to the engine being stuck at full throttle. Seems like a spring or something else is needed to ensure that's not the case.

  • Firmware and Flight Stacks

    2 months ago • 0 comments

    With the days shorter and the weather colder, I've had some time inside to dedicate towards figuring out the firmware. Early in the project I'd settled on the pixhawk (PX4) controller running the Ardupilot software. My goal was to modify the Ardupilot software to handle Goliath's unique control system. This seemed like a possible path since it had been done previously for the single and co-axial copter.

    Now that I've had some time to learn the details of the hardware and related software I have a better understanding of the system and my options. To start with, there is the PX4 hardware. The hardware runs a Real Time Operating System (RTOS) called NuttX. The autopilot software, called a Flight Stack, which actually controls the vehicle, is run by the operating system. What I didn't know before is that in addition to the Ardupilot Flight Stack, the Pixhawk has it's own Flight Stack that the user can choose.

    Ardupilot is open source and there is a large development community out there, the documentation for developers is somewhat lacking. Also as @J Groff pointed out, "it's quite a software thicket". It's doable (as demonstrated by the single and co-axial copters), but it'd be a significant amount of work to get the Ardupilot software modified for Goliath. The PX4 Flight Stack however has documentation on getting started as a developer and tutorials for developers to write their own Flight Stack. This seems like a better option, because I can get some simple code working to test Goliath out, and build up the code as Goliath matures. Once I get things nailed down, then I can work on integrating it with the rest of the PX4 Flight Stack.

    I've created a fork to the PX4 Firmware and I've started with some basic code based off the tutorials. For now it resides as seprate module, so the code I'm writing lives under /src/modules/goliath_simple. So far I just have some basic logic to start the controller in a startup state (MAIN_STATE_INIT), initialize some variables and look for a valid RC signal. When a RC signal is received then the controller will be switched to another mode. (for now MAIN_STATE_MANUAL). My next steps will be add some basic logic to deal with the ignition and starter relays and to shut off the relays if the RC signal is lost. (This code is primarily meant for the test stand for now, so I want to make sure thing shutdown if I can't communicate with it.)

    Things are still coming together on the actual hardware, hopefully just a few more items and it'll be back to the test stand to test out the changes.

View all 38 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 2 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 3 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 3 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 4 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 4 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 4 months ago point
I dont know if this will work, however it might...

Like this?

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Rebelj12a wrote 4 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 4 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 4 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 4 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 5 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 5 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 5 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 5 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 5 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 5 months ago point
Thanks Mike!

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CHOPPERGIRL wrote 6 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 6 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 6 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 6 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 6 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 6 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 6 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 6 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 6 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 6 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 6 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 6 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 6 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 6 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 6 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 6 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 6 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 6 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 6 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 6 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 6 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 6 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 6 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 6 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 6 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 6 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 6 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 7 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 7 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 7 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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