Hi Everyone,
Heres a "little" project I started a little less then a year ago. It all begin with design requirements of a quadcopter with a 10 pound payload for a one hour flight time and ended up with a gasoline/variable pitch build. At the time and since then I've come across many blogs, discussions, pictures, and videos of people who have tried this kind of build and only one or two videos of anything remotely proof of concept ( a nitro and an electric single engine/motor variable pitch build that simply made it off the ground). Since as of 10 months ago I did not even know that diydrones.com existed I decided to wait until I could show up with my proof of concept. To the best of my knowledge this is the first successful gasoline powered quadcopter. I am a mechanical engineer and am working with a computer scientist and computer engineer who have their own equally ambitious plans. I have plans on selling these to farmers and other researchers some day but in the mean time I want to to lend my experience to anyone attempting a similar build and would like to see all those people who have started these builds to be able to finish.
This picture was taken on 4/17/2014 and was my first full system test. It was more then happy to to fly at the end of it's leash (which I made too short for it to hang itself) for 20 minutes before I landed because I smelt something burning. The burning turned out to be the clutch pads, which were entirely gone. Must have been too high pitch for not enough throttle.
My second test was less impressive. Lets just say that there are dozens of bolts that individually keep bad things from happening and it only takes one missing Loctite to vibrate out and let the bad things happen. I'm at least proud to say that after test two I am only waiting on two pairs of rotors in the mail.
At the moment This is what I have:
Control system- Arduino Uno and potentiometer with a spool of speaker wire in between (remember, mechanical engineer)
Engine- Zenoah G290RC
Gear Reduction- 17:57 (calculations based off having equal rotor tip speed as RC helicopters with the same engine)
Rotors- 325mm symmetric carbon/glass fiber main blades for the T-Rex450 (as cheep as I can find)
Rotor grips- Tail pitch assembly from Align 700/800 series
Servos- Protek 100SS (both for pitch and throttle)
Power Distribution- miter gears and torque tubes
Gas Storage- Two Danhakl Design tanks 32 oz each
One way bearings in each arm
Plans and ambitions:
3DR Pixhawk control hardware (my friends are scrapping the firmware) -or- RoboVero and a Gumstix (we have both hardware but are probably a month out from having a respectable control system).
Fully autonomous system
Self learning algerithiums
A foldable design that fits in a 2'x2'x4' box with 5 minutes in or out
Multiple test flights around an hour long
Auto-rotation
The ten pound payload
Individual rotor RPM sensors with Hall Effect switches
Sonar distance to ground sensor
50 miles per hour
Thoughts, comments or questions?
Comments
Hi Michael, We still don't have a solid solution to the control but what I did in the picture is just use an Arduino Uno and a potentiometer. If you see the brown wire in the bottom right hand corner of the picture that is all I used for control. I just ran a dumb script to increase pitch on all the rotters equally. This will give you mechanical proof of concept. Just make sure to have it tethered on at least three arms and probably all six. Enjoy.
Hi Silas,
Very interested in what you have accomplished so far. I am also part of a group building a gas powered drone however we have elected to go with 6 rotors and a power distribution system similar to a drone which is currently being sold by Curtis Youngblood (Stingray 500). Our unit is about 6 ft. diameter. We built our own variable pitch prop modules connected to a 12 HP 2 cycle aircraft engine. We are currently developing the flight control software but would like to take a shortcut and use software that has already been developed. Would you be able to help me in that regard? My calculations for this Hex copter indicate that it should be able to carry about 40 pounds for an hour but until we can get airborne, we won't know. The hardware is finished and assembled and we just need a controller. You can reach me at michael.marr@doublemdesign.ca if you are interested in helping out.
Hello Silas, we are working on similar project, about same size, ours is a bit more weighly, but probably fighting the same problems.
We get more than 3 hours flight time.
http://diydrones.com/profiles/blogs/successful-flight-test-of-gas-e...
Things are slow on this project but we did make it past the vibration issues. We have a pretty serious isolation system now. This breaks the rigid connection between the sensors and the frame so I have some mixed feelings about that. The main problem was the Gumstix/RoboVero vibrating apart and power cycling. Now we are using a Pixhawk so vibrations may be less of an issue; we'll see how this all turns out.
Silas,
Any updates on this gas powered quad? Last I heard you were having some vibration issues. Did you get those resolved?
Ambitious, but a controls engineer might be able to pull it off. On my end we've been stuck with stability issues for months. I've got a short clip of the first tethered flight I'll try to post in a somewhat timely manner, but everything after that just has the air frame bouncing around not even trying to be stable. 4m rotors is going to be monstrous and to milk out every bit of efficiency you're going to have to have some separation between the rotor tips. I am having a hard time comprehending the frame you will need on this. Some extreme trestle system with thin walled tubes of some form? Quick question, where will you be storing this? With 4m diameter rotors you have a wingspan of 8+ meters which is bigger then a 2 car garage. It sounds like you are using 4 engines? That's good in you won't have to transfer power from a central location out to the arms, but it is going to be a control nightmare with 4 throttles and 4 rotor pitches. I am fairly cretin you will need both throttle and pitch adjustment to gain the most efficiency and control. You may not even be able to do a low stable hover without both. The clutches in each engine will disengage below a set RPM so you won't have to worry about one way bearings. On you're gearing you have a very aggressive ratio. So aggressive that you'll have to check your shaft torques. I would recommend prototyping using 1.6m diam rotors or similar. This will let you use standard rotor and gear components of the 700-800 class T-Rex RC helicopter and build your proof of concept with the 4 engines. Any other large frame helicopter base would work fine. There will still be a high degree of efficiency with this setup and once you have that working you can step into the nightmare of 4m rotors.
Silas, Very nice project. Would like to see some video of the quad flying. I recently read the biography of the Wright Brothers and it sparked some creativity in me. I am a controls engineer, so I often need to study the relationships between two or more parameters in a system to determine the "sensitivity" of the system, or to optimize it. I've always been intrigued with helicopters and their freedom to fly in any direction. After looking at some momentum and kinetic equations, I learned that the power required for a helicopter is inversely related to it's rotor diameter. That started me down a path of looking into a "low power", "heavy" lift helo. My goal is to create a gas powered, full scale quadcopter. The advanced controls available today for multi-rotor craft make this a very enticing idea. Of course, the idea gets very complex, very quickly, but the basic parameters I'm working with are a set of 4 - 4m diam rotors, driven by 4-6 HP (4.5 kw) engines. My issue is designing a light, efficient, durable, inexpensive gearbox with a 25:1 gear ratio. It lends toward a 2 stage gearing, but I'm trying to keep it simple. Any thoughts? How is your gearing setup? 2 stage? What did you use for your one-way bearings in the arms? I just joined this site, but will start posting my project progress. It's in its infancy right now.
Typical headspeeds for '500' size blades is 2600-2800 rpm. Sorry, can't suggest anything about the gearing or if you should slow down, you're in uncharted territory! :) But for reference, a typical 450 heli weighs about 800g. So your disk loading is 2.3 kg/rotor so... that's quite a lot. I'm not sure it would fly at 2500 rpm. You can try though.
I think your machine might benefit from the asymmetric blades, if they were available in both rotations. They have much wider chord, and would offer much more potential thrust in a given disk size (solidity ratio). A 4 blade head would help too, as it also increases the solidity ratio. But just going to a larger disk is always going to be more efficient.
That's a really neat idea to use RC Car gears. Good job. You've done some really good work with minimal tools. I'm really impressed.
That's a really interesting paper, thanks! It fairly well ties into my theory. The FPVS system has slight better control with small input changes, but VPFS has more potential for power and response to large changes. Though, the testing is slightly flawed, because I think they used the same VP rotor system for both tests. This unecessarily hinders the FP test because a FP quad would typically use lighter rotors, which would respond better.
Another aspect of helicopters, is that most of us are using hobby machines, and these are optimized for acrobatics, not stability. There are things you can do to make them more mechanically stable, such as delta-3 hinged head.
Looks pretty neat! Is the thing on the bottom side (that's connected to the helical pinion) a clutch? Sorry I don't know anything about that since I've only flown electric.
About not trusting gears, what about the torque tube gears you're using, I guess those are not stock Align parts either, right?
And yes servo control is faster. What Rob says about stability makes sense. Since you have servo control, your quad should be more stable than a similar setup with fixed pitch control.
Check any 500 size helicopter manual for recommended headspeeds, and go from there.
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