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Thread: Building a small transmission

  1. #11
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    Jul 2005
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    Thanks guys -

    Like i said earlier though i've got the material and gears sitting around and i'd like to build a transmission just for the heck of it. At this point, i'm not building this because i want a mini-bike. I've built plenty of go-karts w/ torque converters or just chain drive and they work pretty well, in fact one will hit 45mph on a straight shot. I've built small transmissions for go-karts but they were from small gears used in a self-propelled walk behind mower. They were never designed to take the stress that driving a go-kart at 20+mph put on them. If i wasn't breaking a part i made then i was breaking gears. Now i have some heavy duty ones from an old heavy riding mower. I'd like to do something with those-build a more sophisticated transmission just for fun. I though a mini-bike would be an interesting medium for the new trans since i've never made one before. I really appreciate all of the advice though. I guess i should have made it clear that the main purpose of this mini-bike was to have something that used a new, "sophisticated" homemade transmission. I'll keep thinking and playing around until i settle on something. Hopefully i can post some pictures. It should be a fun project.

  2. #12
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    May 2006
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    Sorry we got off track but what an undertaking if your talking a real syncromesh transmission, unbelievable amount of design work with tapered gear hubs and syncro rings and engagement recesses --- your talking boocoo time and lots of work for a mini bike! If i had to id do what Topct said, go with shifting dogs like in a motorcycle trans, lot less work and if you build it tough enough you can shift it without a clutch of any kind, expect a little hash in the oil after awhile, still tons of work for a mini bike, do something cool like a diesel powered pogo stick, or put a little YZ 80 engine and trans on one of those 6.2 volt rascal scooters for the handicapped, thats what i want to do.... ooops - thing i got off track again.

  3. #13
    Join Date
    Aug 2001
    Location
    Illinois
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    696

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    A.K. Boomer:
    Sorry no brake or extra parts are required to make this work. All that is needed is what you see. Well maybe some bearings and a case to mount all the parts in. But the only thing needed to cause a speed change, is to change the "ratio of the variable pulleys".

    Lets see if this helps?
    To achieve an overall one to one ratio, forward rotation, set the variable pulleys to a one to one ratio.

    To achieve a neutral, set the variable pulleys to a two to one ratio. At this point everything will be spinning around joyfully EXCEPT the output shaft.

    To achieve an overall one to one ratio, reverse rotation, set the variable pulleys to a three to one ratio.

    Yep this can be a real mind bender, however when you are dealing with differential or planetary gearing it is typical to have your brain flip over a few times and go bouncing across the floor.

    As far as its maximum power handling ability it is like any belt driven device and is limited to how much torque the belt can transmit before it starts to slip.

  4. #14
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    I've built plenty of go-karts w/ torque converters or just chain drive and they work pretty well, in fact one will hit 45mph on a straight shot.
    Those were the good ole days. I had one that was "tagged" at 116mph at Mid-Ohio Race Track (Summer of 1989). ... On a slightly more than stock Briggs 5hp. And I didn't win. Some of the upper class karts were hitting 130+. The ground moves by mighty fast when your rear-end is only 1" off the pavement.

  5. #15
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    Wow! What did you use as your drive train? The only ones i've ridden that would hit near 100mph was a shifter kart. I'm not sure what a well designed one would hit with a torque converter. The kart that had a torque converter on it was a heavy beast - good for towing the others but that was about it. I don't think i ever broke tripple digits the course was too small for me to feel comfortable to push it very hard. Besides it wasn't my kart - i'd feel pretty bad if i busted it up because the guy who owned the track was letting me and some other kids drive for free! :O

  6. #16
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    May 2006
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    Ahhhhhh so thats whats missing!!! sorry i took for granted it was a typical torqe converter with centifugal expander on one pulley and spring loader on the other, this explains everything, --------------- everything except the manual mechanism that operates the tork converter that is


    Quote Originally Posted by Mad Scientist
    A.K. Boomer:
    Sorry no brake or extra parts are required to make this work. All that is needed is what you see. Well maybe some bearings and a case to mount all the parts in. But the only thing needed to cause a speed change, is to change the "ratio of the variable pulleys".

    Lets see if this helps?
    To achieve an overall one to one ratio, forward rotation, set the variable pulleys to a one to one ratio.

    To achieve a neutral, set the variable pulleys to a two to one ratio. At this point everything will be spinning around joyfully EXCEPT the output shaft.

    To achieve an overall one to one ratio, reverse rotation, set the variable pulleys to a three to one ratio.

    Yep this can be a real mind bender, however when you are dealing with differential or planetary gearing it is typical to have your brain flip over a few times and go bouncing across the floor.

    As far as its maximum power handling ability it is like any belt driven device and is limited to how much torque the belt can transmit before it starts to slip.

  7. #17
    Join Date
    Aug 2001
    Location
    Illinois
    Posts
    696

    Thumbs up

    A.K. Boomer:
    Right no slippy torque converters here just a slippy belt and a lever to manually select the speed. However if one did not care about reverse a centrifugal expander could be used make it an automatic.

    Fasttrack:
    This Saturday there is going to be a car show in your area, if you want a break from all that homework stop by and say hi.

  8. #18
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    Jan 2003
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    Deep in the Heart of Texas!
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    I used a Centrifugal clutch and chain drive. Track setups were done with different sprokets. These weren't the cheap Comet style clutches though. The clutches were tunable with weights and shoes. The rate as well as the engagement speed was adjustable. The engines burned 100% Methanol through a bigger carb and short intake. The exhaust was tuned with different lengths of straight pipe. A solid rod with pressure oil feed via a "cup" took care of keeping the piston and rod inside the engine. A few other "secret" mods inched out a couple of extra horsepower and rpm. On the fly mixture control along with monitoring a head temp gauge made good horsepower and torque at nearly 6,000 rpm. 4-wheel hydraulic disk brakes were a must. Not exactly your average lawnmower engine.

    The "open" class machines really got bizarre.

  9. #19
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    Jul 2005
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    Bloomington, IN
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    "Not exactly your average lawnmower engine. "

    No doubt about that! I've rebuilt all of my engines to squeeze as much power and speed out of them as i can w/o actually buying anything - like a larger carb. (All of the stock carbs laying around have fixed jets) A milled head, no breather valve, advance timing and homemade forced air and a few other slight tweeks have made a big difference for top speed and power though. That was trouble at first with those cheap comet clutches - i was building my power at higher rpm and my clutch was engaging at about 2000rpm. Had to play with that to get it to engage later. Man those racing set ups are expensive! I've looked pretty seriously at it before and for a decent clutch nowadays your looking at $300!! Engines are super expensive!

    Mad Scientist - thank you so much for reminding me! I almost forgot; its at calvary church right? I'll try my hardest to make it out there - i've got some freinds who would also be very interested to go. thanks again for the reminder, i would have forgotten otherwise!

  10. #20
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    Aug 2005
    Location
    Greenfield, Indiana
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    29

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    I like the idea of a diesel powered pogo stick.
    KMFDM
    Better Than The Best
    Megalomaniacal
    And Harder Than The Rest

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