Twin Engine Rack Mount

Discussion in 'Motorized Bicycle General Discussion' started by mombo390, Feb 19, 2013.

  1. mombo390

    mombo390 New Member

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    Hello all, im new to the forums and did a search and could not come up with anything regarding my build so here goes. Im building a rack mount dual engine bicycle build for my high school senior project so far i have stripped the bike (im not keeping the bicycle aspect of the bike and am replacing the cranks with a welded aluminum pipe to use as foot pegs. The engine I am using is a homelight 26cc weedeater engine and i am planning to use two engines because the rack has enough room to accomodate two motors.

    My first question is that the crankshaft of the weedeater engine is 3/8 inch diameter and all the go kart clutches (maxtorque clutches) which have sprockets attached to them are 5/8 inch diameter. How would i adapt the 5/8 clutch to work on a 3/8 shaft?

    My second question is that how would I sync both engines together? would both engines need to have clutches? or can I run a belt from one shaft to another and only have one clutch?

    Alternatively if I cannot sync both engines together can I mount the engines facing opposite sides of the rack mount and run two clutches with two chains down to 2 sprockets on either side of the rear wheel?


    Thank you very much all input is greatly appreciated
     
  2. Dan

    Dan Staff
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    To increase the size of a drive shaft, you could use a bushing.

    Pure conjecture on my part but for the very few gains of 2 weed whackers, might not be worth it. Will only go ever so slightly faster then the lesser performing engine for double the fuel consumption. The only advantage I can see is a power increase which would be more easily optained by using one larger engine. To sync em, only way I could think of is to use one throtle cable to both and use a small engine tachometer to adjust so the rpm get close with the uni-throttle.

    Another option would be to mount one on the front wheel and use a RT & Left thumb throttle. Just a thought. But would keep it simple and only use one engine.

    I highly suggest keeping the pedals. Run out of gas or have engine failure and you can bike home or to the gas station. LOL, every one reading this who has had to push a bike home is nodding their head right now.

    But they are just some thoughts and I would really enjoy seeing you do this. Would be a one of a kind, for sure.

    Post lots of pics!

    cvlt1
     
  3. 2door

    2door Moderator
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    Twin engine gokarts were common years ago. You just had to get them running close to the same RPM at any given throttle setting. We used two cables to one gas pedal.
    If the engines are identical getting them to sync isn't that difficult.

    The problem I see is mounting. One engine will need to be mounted way off center to get chain/sprocket alignment. On a gokart it was not hard. One engine drove a wheel the other the live axle. On a bike you don't have the width to play with resulting in problems with sprocket alignment. Some guys modified the engine to run in reverse to drive both rear wheels.


    Removing the pedals in most states will make your bike a motorcycle in the eyes of the law. You might want to explore that before you get too far into your project.

    Tom
     
  4. WightBoy

    WightBoy New Member

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  5. mombo390

    mombo390 New Member

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    Thanks guys, the reason im going with a twin engine setup is because i have the engines already pulled them off my uncles weedeaters and they are identical models. I also fabbed the mount to have 9 inches of rack width to play with. so im assuming if i mount one engine further back and get that to drive the live axle of the engine which has the clutch that would work? I dont think sproket alignment would be much of an issue. Also are there any brands of clutches you all would suggest that has a built in sproket?

    I forgot to mention that the crank shaft of the engines is threaded where the original clutch was so how would i get the bushing to fit?

    Appreciate all the help im 17 and this is my first project so input from all you experienced folks is greatly appreciated
     
  6. 2door

    2door Moderator
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    You aren't planning on connecting the crankshafts of the engines, are you? I'm not clear on your design.

    "I also fabbed the mount to have 9 inches of rack width to play with. so im assuming if i mount one engine further back and get that to drive the live axle of the engine which has the clutch that would work?"

    Could you explain this better?

    Tom
     
  7. mombo390

    mombo390 New Member

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    I am thinking about mounting the clutch on one of the engines and running a belt or chain from one crank to the other.

    The rack i made using aluminum tubing for the frame and it has a piece of sheetmetal on top. the mounting surface is 9 inches wide and 19.5 inches long
     
  8. mombo390

    mombo390 New Member

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    I will post pictures tommorrow when i get to work on it tommorrow in engineering class
     
  9. bigbutterbean

    bigbutterbean New Member

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    It sounds to me like he wants twin engines on a single drivetrain.
     
  10. 2door

    2door Moderator
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    I see trouble with that concept. Linking the two engines by their crankshafts isn't the best way to go. They should each have their own seperate drive to the driven sprocket/pully.

    No matter how hard you try, getting the two engines synchronized precisely is going to be difficult. Linking them by their cranks can produce an imbalance that can give you all kinds of problems. Vibration will be just one. Premature wear/failure of the connecting components will be another issue you'll face.

    I'm not optimistic about your idea but I don't want to be a wet blanket either. I'd just hate to see you invest a lot of time and work on something that has questionable results and the potential for failure.

    I've seen two engine joined by their cranks but the builder went to extreme measures to get crankshaft rotation/piston position correct to eliminate the possibility of one engine firing when the other was approaching a power stroke. You would need to calculate the power strokes of each engine and join them at 180 degrees apart and that will require your link to be a 1:1 ratio. Lots of tricky stuff going on that I'm not sure you're aware of. It's just not as simple as connecting the engines by a chain and sprockets.

    Tom
     
  11. Nehmo

    Nehmo Member

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    No.
    Two 2-stroke engines, conceavably, could be arranged to drive one wheel or could be arranged to each drive its own wheel, but either arrangement would present difficulities. Since your experience is limited, start with a simpler one-engine arrangement.
    Simply because you have some particular material doesn't mean it's possible to use that material.
    Make a one-engin m-bike, and keep the remaining engine as a spare.

    (However, if you insist on using both engines, put caged propellers on them and make a duel-prop air-propelled bike.)
     
  12. mombo390

    mombo390 New Member

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    If linking them together will not work then can i just mount them opposite each other and run two chains to 2 different sprokets on either side of the rear wheel?
     
  13. mombo390

    mombo390 New Member

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    LMAO thanks for the tip nehmo!
     
  14. Mr. OrangeConeRacing

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    I want to eventualy do a side by side dual 66cc set up. That will be simple to do and I will just have both motors joined through the use of a jackshaft that will drive a multi speed internaly geared hub.
     

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