Help Needed Badly - Gasoline Engine Quad (Variable Pitch) - Discussions

Hey!

This is my first post ever over here. I'll be honest I'm not a lot into making quads or anything of this sort but my professor asked me if I could do it and I said yes, as I need this project to graduate.

So now I'm stuck with poor knowledge about quads.

The task that I'm stuck on is that there are four engines that my professor ordered. They're JC120 EVO, 12.5hp gas engines. I want make/order a variable pitch propeller for it. Can you help me find exact dimensions and where should I order it from?

The JC120 EVO detailed specifications can be seen here. http://www.hobbyking.com/hobbyking/store/__33546__jc120_evo_gas_engine_version_2_w_cd_ignition_120cc_12_5hp_8_000rpm.html

Also the quad is being designed to carry a load of at least a 100lb. Does the assembly of the variable pitch and the propellers have to do anything with the weight? Do they have to be stronger than the usual? He asked me to machine it. But honestly I think doing it in 2 weeks will be not be easy for me.

Any help will be greatly appreciated!! I can not graduate until I complete this task =(.

Sorry if I sound negative, but I'd say you have little chance to get this to work.

You need two props to spin the opposite way than the others for a start, so those two would need additional gearing.

As multi-rotors are so unstable, they need very quick speed changes to each prop as demanded from the flight controller to fly.

The thrust from the prop is one factor, but the torque is also needed for yaw, and stay straight. Variable pitch (with constant speed) only addresses one of these requirements, so you'd need custom firmware to control each throttle individually also for yaw, and compensating the pitch as it does. Or, if you forget variable pitch and try to use the conventional motor/ESC control to each engine, the throttle response is simply not fast enough.

Another factor is safety. Quads and Hex's have no redundancy - any failure of a motor / prop / flight controller etc and they fall uncontrollably from the sky, usually in an unpredictable way at great speed. I've just re-built my hex following a crash caused by a compass issue (I think), and the horizontal impact speed was 45mph according to the logs. The weight of that (a few kg) is enough to cause serious damage, a quad with 4 engines, gearboxes, frame etc etc out of control would easily kill someone.

Personally I can't see how this will work, and if it does, ever be safe.

A better bet might be to use one engine to drive a (small) alternator, to re-charge a small battery pack, to power conventional ESCs / motors. I'd suggest an Octo, for lift and redundancy, and design in a big enough battery to keep it flying for a few minutes if the engine stops so you can land in a controller manner. That way you can get extended flight times (just add fuel) and lifting capacity, with a safety margin.

Or... forget trying to re-invent the wheel and build a traditional RC helicopter!

Replies

- Alan D July 16, 2014 at 2:20am
  
  That appears to be a hybrid, as I suggested?
iskess July 15, 2014 at 4:53pm

This could be done as a tricopter. A Tri uses a servo on the tail for yaw rather than motor torque. This doesn't address the safety issue which is a huge concern. These copters fall out of the sky all the time.
Alan D July 15, 2014 at 3:12pm

Sorry if I sound negative, but I'd say you have little chance to get this to work.

You need two props to spin the opposite way than the others for a start, so those two would need additional gearing.

As multi-rotors are so unstable, they need very quick speed changes to each prop as demanded from the flight controller to fly.

The thrust from the prop is one factor, but the torque is also needed for yaw, and stay straight. Variable pitch (with constant speed) only addresses one of these requirements, so you'd need custom firmware to control each throttle individually also for yaw, and compensating the pitch as it does. Or, if you forget variable pitch and try to use the conventional motor/ESC control to each engine, the throttle response is simply not fast enough.

Another factor is safety. Quads and Hex's have no redundancy - any failure of a motor / prop / flight controller etc and they fall uncontrollably from the sky, usually in an unpredictable way at great speed. I've just re-built my hex following a crash caused by a compass issue (I think), and the horizontal impact speed was 45mph according to the logs. The weight of that (a few kg) is enough to cause serious damage, a quad with 4 engines, gearboxes, frame etc etc out of control would easily kill someone.

Personally I can't see how this will work, and if it does, ever be safe.

A better bet might be to use one engine to drive a (small) alternator, to re-charge a small battery pack, to power conventional ESCs / motors. I'd suggest an Octo, for lift and redundancy, and design in a big enough battery to keep it flying for a few minutes if the engine stops so you can land in a controller manner. That way you can get extended flight times (just add fuel) and lifting capacity, with a safety margin.

Or... forget trying to re-invent the wheel and build a traditional RC helicopter!
iskess July 15, 2014 at 2:31pm

I gotta see this! Keep us posted.

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