Shaft Drive?

The kiwi drive has got me thinking about different drive systems.
I’ve seen
Direct Drive - each wheel has a motor directly driving it
Chain drive - chain is used to transfer power. Could either be one direct driven wheel and chain transferring power to the other wheel on the same side or the motor located between both wheels and chain transferring power to both
Gear Drive - like a chain drive, but gears are used to transfer power

Has anyone used or seen a drive shaft system on an IQ robot? This would be one motor turning a long shaft and using either worms or bevel gears to transfer the power perpendicularly to the wheels. I’m envisioning a standard gear mounted in the middle of a long shaft. The motor is mounted adjacent with a gear driving that first gear. At each end of the shaft is a worm gear in turn driving a gear on the wheel axle.

I don’t think there is any advantage, but for 8th grade IQ students, it would be a learning experience for transferring power perpendicularly.


There isn’t much of a reason to make one because you would be working with multiple motors and you’d also then have to make a steering mechanism, which isn’t as effective as just powering each side of the robot individually.

EDIT: I assume you are talking about differentials as they are used in cars. Sure, you could stick a bevel or worm in your drivetrain, but that’s just adding more mechanisms for no apparent reason other than more friction and boasting of a more complex structure.

The HexBug kits often use this sort of drive, I think a good example is the Offroad Truck:

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As I said, my reason would be to offer a learning opportunity for the students who have already experimented with direct drive, chain drive and gear drive. Exposing them to the concept in this way may spark other applications.

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The truck drive is cool. I was thinking of something like this…


You can’t drive a worm gear with a spur gear…it only works the other way.

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Worm gears have pretty high mechanical losses compared to spur and bevel gears, and are sometimes (frequently) impossible to backdrive depending on the pitch of the gears.

(@kmmohn Only sometimes are they impossible to backdrive. I think these are some of the ones where it’s impossible, though, so you’re probably right for the case of the VEX IQ ones.)

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Actually the VEX Offroad Truck uses a differential connected to the drive motors with normal spur gears. There is no drive shaft running front-to-back.

There is, however, front and rear suspension, rack and pinion steering, and a new control system.



I know that in practice what I illustrated would probably not work (though I have seen worm gears get backdriven), but given these plastic parts I’d like to experiment to see if it would work.

If it doesn’t work, then this might work


Actually, if you flipped the motor into the space between the tires, , or above the shaft, you’d get a much narrower drive train, which might be helpful given the 11" x 19" rule

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Actually, if the worms can’t be backdriven, it might open some opportunities when normally you are applying power to keep an arm raised.

Or the EDR guys might have been interested in it for shoving to get the platform in Turning Point

Indeed, some worm gears can be back-driven, just not the VEX ones. This is a better plan. You’ll want to boost the gear ratio to so that drive shaft is spinning pretty fast, or your bot will be a bit on the slow side.

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