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Old 04-26-2012, 09:34 AM   #1
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Default gearing for "kit bashed TC"

Question for you RC design folks. Why do TC's have a multiplier built into the drive train?Pan cars don't-is it really necessary in a TC? Thanks, Don
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Old 04-26-2012, 10:13 AM   #2
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Pan cars are two wheel direct drive, so the motor pinion meshes with the spur that is directly attached to the rear axle, so you just need to worry about the gear ratio and the size of your rear tires to give you the rollout

TCs are 4wd so the pinion meshes with a spur that is attached to the center layshaft. From there you have layshaft pulleys which connect to the differential pulleys, usually by belts. So you need to factor in the ratio of the differential pulleys divided by the layshaft pulleys to give you the internal ratio. You take the gear ratio (spur divided by pinion) and multiply it by the internal ratio to give you the Final Drive Ratio.
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Old 04-26-2012, 10:15 AM   #3
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Don,

The additional weight of the TC and the need for torque to move the 4wd and weight make gear reduction a necessity.
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Old 04-26-2012, 10:36 AM   #4
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Thank you!! I had a funny feeling it was along those lines. Don
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Old 04-28-2012, 09:34 AM   #5
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The main problem is gearing, with just one pair of gears you can't get the gear ratio you needed for a touring car.

The Corally Assassin had a direct drive option, with a single belt drive from rear to front diff, for those running in stock classes where you could use a lower gear ratio, as well as a standard twin belt option for modified. The Assassin had the rear arms swept forwards to move the inboard suspension mounts as far back as possible, and you also have the motor pushed right into the rear corner of the car. It did have to lift the diffs quite high in the car as you need a big spur gear on the rear diff to move the motor far enough forward to clear the rear suspension arms, something that's not a problem on pan cars.
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