Physics Behind Different Drive Builds

So for example

  • if you have a 6 motor drivetrain and on each side all motors are connected to eachother by gears to wheels

  • or if each motor is geared to its own wheel

Which is a better build? For less friction? More torque?

Currently I have a drive train that seems to be pused easier on the side that has (2) motors geared together and (1) alone rather than the other side with all (3) motors geared together.

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as far as friction goes, typically fewer moving parts = lower friction. So fewer gears would mean lower friction. if, by separating the gearing, you reduce the gear count, you will have lowered friction.

However, there is a very good reason to gear together the whole drive. If you have a separate motor for 3 wheels, and one or more wheels lose perfect contact with the ground, say while being pushed, or just due to an imperfect center of mass, or say a middle wheel which is either slightly bigger or smaller than the outer two, then the loss in traction in one wheel will result in a loss in power through the whole drive. But if all wheels had been linked together, if one wheel loses traction, power isn’t lost, but just distributed to the other two wheels.
It also forces all the wheels to run in sync with each other, so the whole drive is working together at the exact same speed and torque per wheel. This just means the robot will be performing with consistency and reliability under varying and unpredictable conditions, and is well worth the slight added friction.


Okay thank you! I will do tests for each side of my drive and post them here once I finish for others to see.

Side with all motors connected:

avg. rpm’s: 65
avg. torque(Nm): .13

Side with 2 motors geared ogether and 1 not:

avg. rpm’s 66-67
avg. torque(Nm): .08

It’s possible that the friction could be different between both sides, but I believe they are very similiar.
These are 200rpm motors geared 7:3 so output of 466.7 if at %100 power.

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if you’re just doing an experiment and this bot isn’t for competition use, then the answer would be that there’s more friction on the side that’s geared together because there’s simply more contact area for all the rotating parts. the torque of the drivetrain will be basically the same (the friction from more gears should be negligible if assembled correctly) assuming you’re using the same drive ratio on each

if this is for a competition robot, ironically I wrote something about this recently. Do you know why teams gear together tank drivetrains even though it adds more friction? Because it guarantees even distribution of power between your powertrain, ensures that all wheels are rotating at the same speed regardless of differences in traction, and (as a consequence of the other things) makes autonomous programming much more consistent. There’s a large net benefit from doing so despite adding potential sources for more friction to your drivetrain.

if you’re noticing a significant difference in friction for each side, you’re probably doing a poor job of assembling the drivetrain. Make sure you’re using bearing flats, that your gears are meshed properly, that your spacing isn’t excessive, etc.


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