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 =(.

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  • Great post Shenhyar and enjoyed reading all the comments.

    So it looks like you are in the right place collecting specialist knowledge in a short time-frame from helpfully people ready to support you.  

    The good news – you didn’t order the four engines and just maybe your professor might be a mad genius with a hidden motive/agenda and believes in your abilities to smash difficult problems.

    I’m no expert but the follow approach might help:

    - gain as much knowledge from this forum as you are doing right now!

    - gather up the BIG stuff
    leave the negativity out of it e.g. if it doesn't work/blocker list reasons why and demonstrate the knowledge you have learnt

    -  Drill the professor with questions and define the scope/limitations/objectives of your project so your efforts are measurable

    - Stay ice (keep cool and enjoy)

    Nice work so far – a good start!

  • It could work. You would just need accurate governors on each motor to ensure they maintain a constant RPM and do not differ from eachother...

    One single central engine would eliminate the need and complexity of keeping them all at the same rpm.

    As mentioned, there is no problem at all control a quad via collective pitch props. In fact, many times plugging up the pitch servo with where an ESC'S would normally connect on a FC works just fine (tuning required of course). Rarely do y out actually need any specific code. Unless of course you have extreme vibrations etc...

    Vibrations and harmonics are another problem with 4 multiple gas engines. They will wreak havoc with the harmonics at certain rpm.
  • Shenhyar,

    I think this is possible to get flying but I don't think direct drive props are the way to go. I just don't know where you will find 26-28 inch variable pitch props. I would look at using 4-800mm size flybarless helicopter heads. Use symmetrical 800 mm blade because 2 will be cw and 2 will be ccw. I would look at a 5:1 reduction of head speed from the engine. a good head speed is probably 1600 to 1750 rpm. Make sure everything is balanced. You will want all the engines to be running at the same rpm so I would look at using an electronic governor for each one.  I think any flight controller for a quad should work. Instead of increasing RPM you increase pitch and it should have the same effect as thrust and rotation. 

    However, I also agree with Rob Lefebvre regarding safety. A young man was recently killed in New York flying his helicopter with a smaller blade size than what I recommend.

    • +1! This is a much better response than mine. I tried to explain on the first page, but wasn't nearly as comprehensive as yours.
  • Shehryar, I'll be totally frank... this is hopeless.  Moreover, it's dangerous.

    I have been heavily involved in the Arducopter project for 3 years.  I'm quite knowledgeable about both multirotors and helicopters.  I am a degreed mechanical engineer who likes to get his hands dirty, I have a small machine shop and can TIG weld.  And I would love to take on a project like this.

    But my timeline for something like this would be on the order of a year.  It's a significant undertaking.

    If your professor persists in this endeavour with this kind of cheap and fast approach, he's going to get somebody killed and/or the project will fail and be a colossal waste of time and money.

  • I believe it was him and his dad who designed the flight controller also for his electric system. Im not sure about his gas system...hes also a very skilled pilot.   

  • I've done some thinking about this subject myself and concluded that the best and simplest way to try this would be with belt drive tails from helis! you could go 700 sized tails if you like but if i was going to give it ago i'd try 500 belt drive tails.

    mainly because it very simple to get two counter rotating blades by simply twisting the belt the other way :)

    to mount them all somehow " i have drawings somewhere if you'd like" basically each boom mount is @ 90deg's and you use the mainshaft/gear,anti rotation bracket/gear and two bearing blocks and have the motor pinion @ 45 deg's

    then you'd have to find your gear ratio and edit the code for CP instead of motor drive as you'd run a flat 100% curve for the motor there's not much todo there all the control is in the collective pitch and that has been done many times before , idk i think there is a chance you could get something working.

  • 3701785150?profile=originalHello  Shehryar Niazi

    Please tell your professor that his demand is pure Science Fiction...

    O yes it can be done, but if you can achieve that I suggest you go directly to DARPA..



    4 years  and still not finished, maybe your professor can help them...

  • OK, I'll say it.....if it looks like a duck and quacks like a duck....and it's yellow and it has webbed feet and it floats on water and it swims...and it's name is Donald..But let's assume for a second this is legit..

    Counter rotation - you may actually be able to change the timing so that the engine can run in the opposite direction - or, you may be able to mount two of the motors upside down (does that work?) or - servos for yaw.

    Problem 2 - What risk assessment would let you start the last motor with the spinning propellers of death right next to you - electric starter? wires, entanglement?  Nah.

    Vibration - hard to know how you would even approach isolating the IMU from frequencies and amplitudes associated with these engines - mount it on 5kgs of vibration damped steel?

    Constant speed - IF you could have two of the motors in counter rotation, and IF you could come up with a variable pitch prop, you could achieve yaw. However, this would rely on fine, fast response control of RPM. not sure how you do that on a petrol engine.

    The other option would be to have a single engine driving four variable pitch props with two geared for counter rotation. OR, you could have one big engine driving one big prop with individual variable pitch blades (for pitch and roll) with a smaller variable pitch prop controlling yaw. 

  • You selected one of the worst engine choices possible, likely to obtain the least expensive product.  I am an SME with regards to two stroke gas engines and I can only wish you all the luck you can hope for with your project,  Whatever else you do, the engine will let you down.

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