Limiting top speed.

Discussion in 'General Questions' started by Iovak, Jul 10, 2016.

  1. Iovak

    Iovak New Member

    I need to limit my 2 stroke,49cc motor to go around 15-20mph to meet local laws.How should i do it?
     

  2. Frankfort MB's

    Frankfort MB's Well-Known Member

    You don't have to limit it. Just don't go full throttle.

    I've never had problems with meeting laws, most cops around me don't care
     
  3. bakaneko

    bakaneko Active Member

    I mean check your speed as Frankfort suggest but if the police or DMV are really pressing you I would show them the engine specs and then show them the corresponding sprocket that would limit you to below 20 mph. This will probably be a 56T sprocket.

    http://www.diygokarts.com/speed-calculator.html

    Wheel diameter = 26"
    Engine Max RPM = 6000
    Teeth on Axle = 56T
    Teeth on Cluth = 10T
    Speed = 83 MPH!!!

    But, there is an internal 4:1 gear reduction for 2-stroke China engines I think... so speed is 20.75 MPH. And, this is no load so with load I'm sure it is below 20 mph.
     
  4. jaguar

    jaguar Well-Known Member

    without having some kind of electronic limiter in the CDI that cuts spark above a certain RPM it is not possible to do.
    Limiting the intake or exhaust volume limits engine power, not speed. With a limiter of volume you could still go fast downhill.
     
    HeadSmess likes this.
  5. bakaneko

    bakaneko Active Member

    Also, the reading on most motorized bicycle laws goes something like "cannot propel a X lb rider (180 in WI) faster than X mph (30 in WI) on a flat road with no wind." I am not sure if your local ordinance and laws reads similar but of course even with a 56T sprocket going downhill or with the wind you can go faster than 20 mph but on a flat road with no wind and if your 2-stroke engine max rpm is 6000 a 56T should not propel you faster than 20 mph. right?
     
    Frankfort MB's likes this.
  6. DanTheDIYGuy

    DanTheDIYGuy Member

    Sad that the government micromanages us like that eh?
     
    Last edited: Jul 11, 2016
  7. HeadSmess

    HeadSmess Well-Known Member


    now that i agree with... hmmm... thinking how this could be implemented...

    trigger voltage is charging a CR circuit, that is shunted with suitable zener, so once voltage across CR reaches certain level, thyristor is never triggered? im sure theres several ways to do it...
     
  8. Steve Best

    Steve Best Active Member

    A much longer intake or exhaust (like the PooPoo pipe) has this effect, but also increases power on hills below the max speed.
    A restriction on the intake or exhaust such as an intake gasket with a smaller hole will have this effect too.
    Combining a
    1) long exhaust
    2) a long intake
    3) low gearing (56T sprocket)
    4) an intake gasket with a hole sized to exactly limit speed
    will give tractor like power on the hills and trails while not going over your speed limit.

    Steve
     
    Iovak and Frankfort MB's like this.
  9. Frankenstein

    Frankenstein Active Member

    Why don't you help me with my battery problem thread, you know the powers you mess with.
     
  10. butre

    butre Well-Known Member

    QUOTE="HeadSmess, post: 415041, member: 11023"]now that i agree with... hmmm... thinking how this could be implemented...

    trigger voltage is charging a CR circuit, that is shunted with suitable zener, so once voltage across CR reaches certain level, thyristor is never triggered? im sure theres several ways to do it...[/QUOTE]
    I'm no electrical engineer, but wouldn't something that limits the frequency do the job? I would think a low pass filter set at for example 160 Hz to limit at 9600 rpm would do the job.

    alternatively, but a bit of a rube goldberg, does anyone make a tach with a shift light that will work on a single cylinder 2 stroke? hook the shift light output to a relay that cuts the spark and you've got an instant rev limiter.

    first option is a soft cut, nice and easy on the motor. second is a hard cut, way more fun than a soft cut.
     
    Last edited: Jul 13, 2016
  11. gary55

    gary55 Active Member

    Buy a speedometer a 56 tooth rear sprocket, and use your brakes going downhill.
     
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