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
If you can build it big enough you can do localized crop spraying, almost down to the square yard application of pesticide and fertilizer, based on your drone survey.
Actually Jack, Curtis has managed to get a gas one to work.
I saw his video of it (manta ray actually flying 5 or 6 weeks ago.
On a blog here: http://diydrones.com/xn/detail/705844%3ABlogPost%3A1535247
I think it might have used bevel gears, pinions and drive shafts.
He is apparently thinking of actually developing it for sale for UAS use.
Best Regards,
Gary
Curtis Youngblood is still the only one to succeed in flying a variable pitch quad. He used belts. Making it stable enough to fly without tethers holding down all 4 corners is a big deal. Not sure why no-one has gotten gas engines to work.
The future of quad drones. Simply awesome.
Good luck.
There's no simple way to say if a 4 blade head would be more or less efficient than a 2-blade. The answer to every rotary aero question is "it depends".
Hi Silas, nice work! I really like the trestle design of the frame. Should end up being much lighter weight than what would be required if you used solid booms as most quads use. So what kind of numbers have you gotten? AUW? flight time per unit fuel? Just curious to see what you've accomplished.
I estimate your rotor speed at about... 3200 rpm, assuming 11,000 rpm on the engine. Is that about right? You can probably increase efficiency by slowing that down. It really depends on the weight you have. But you're not likely to even approach the peak efficiency point until the blade pitch is 5 degrees at least. Actually, the peak efficiency point of the blades is pretty close to the stall point. But there's only so far you want to push that before you actually have one stall.
I'd disagree with the comment about helicopter stability in the wind. What is that based on? A helicopter with no stabilization controller? I assure you, they are extremely stable.
This is awesome stuff! When I saw your post I vaguely remembered seeing a similar post. I did a little searching and found the post. I hope it helps you to gain a little traction in your design. Good luck!
http://diydrones.com/xn/detail/705844%3ABlogPost%3A1535247
Pedals2Paddles- A engine-generator-motor was my second design theory approach as the traditional battery-motor builds only run 40 minutes optimally and 20 for the payload requirement. After much research and calculations I concluded that generator approach was feasible, but only 50% of the engine's power would be seen by the props (Loosely simplified to 70% times 70% for average generator times motor efficiency). To further push me towards gas was the fact that I really should have variable pitch props anyway for an airframe of my size. Big props have exponentially bigger rotational inertia which much be overcome to facilitate control. The result is that the really big quadcopters can't do split second maneuvers like their comparably sized helicopters. The choice to go fully mechanical was painful though. I really did not want to deal with the nightmare of complicated and low tolerance mechanical power distribution, and I did spend months wrapping my head around the geometry. In the end I think I am running 90%+ efficiency with not too much of a weight trade off for more mechanical requirements.
Nick- More will be posted on my blog about what I've done but I probably wont cover every system. Feel free to ask any specific question and I will be able to answer at least all the mechanical ones. if you are serious about your own build start a spreadsheet to keep track of weight and price. Small gas engines aren't that small so the numberrs get big fast. A nitro system could be made smaller but has plenty of it's own issues including the price of fuel and the fact that the fuel is much less energy dens.
John- The easy and meaningless answer is that quadcopters are the current hip and trendy item in the drone world today. More practical answers include the fact that after applying stabilization software quadcopters are more stable then traditional helicopters, especially in wind. Smaller rotors tend to break fingers instead of cut them off and are cheaper to replace when they hit things harder then fingers. At the far end of complexity there are actually software algorithms to save a quadcopter in the event of one or more rotor failures (https://www.ethz.ch/en/news-and-events/eth-news/news/2013/12/new-al...). That coupled with autonomous auto-rotation and someone could shoot this thing with a rifle and provided they miss the central electronics the computer could manage a low velocity landing. Does this sound overly ambitious? Absolutely! But thats what we aim for.
Impressive build. But I have to ask. What are the advantages over a single rotor helicopter?
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