# Plantery Gearbox Efficiency

I have been trying to design a drive train using the 12:1 plantery gearbox for the small CIMs, that way I can just adjust the speed a bit more with only one stage of chain/gear, which makes things really simple. I have a few concerns regarding the plantery gearbox, however.

1. What is the efficiency of the gearbox?
2. If efficiency is a problem, does lost efficiency come in the form of lost speed or torque?
3. And lastly, if it is lost torque, will I lose a pushing match against a robot geared to similar ratios, using same motors and wheels. Or, will I tie that pushing match (since my motor is at stall, no part of the transmission is moving, and itâ€™s just solid contacts everywhere:) )

Help please, and thanks in advance.

I believe the estimate is about 80-90% efficiency for those planetaries. Efficiency is typically considered as lost torque due to frictional losses in the gears meshing. As far as losing a pushing matchâ€¦ Thatâ€™s dependent on FAR too many variables. If youâ€™re assuming the robots are exactly identical save for one having a more efficient gearboxâ€¦ then yes, the less efficient one will lose. But thereâ€™s so many other variables as to make that meaningless.

Based on the efficiency of similar planetary gearboxes, I would guess the Banebots planetary to be around 90% efficient.

I donâ€™t think the difference in efficiency between the planetary and any other gearbox will be large enough to affect the outcome of your pushing matches. You really should be gearing your robot to slip the wheels rather than stall the drive motors anyway, in which case the efficiency of your transmissions will not matter.

Thanks guys. I guess 80~90% isnâ€™t bad at all. That dispels all my worries.

I may be way off hereâ€¦ but I think iâ€™m quoting Dr. Joe Johnson hereâ€¦

A planetary stage is about 85% efficient, so .85^2~ 72.

90% overall seems kind of fishy to me since that is the efficieny of a single spur gear reduction.

I would agree but spur gears are 90%~95% efficient if designed correctly. and with 2 stages in this transmission that puts the efficiency at 81-90%. This is using the standard method of multiplying the number of stages by the efficiency . But in a planetary since there are much points of contact per stage it is not entirely accurate.

now knowing the history of these transmissions and how poorly they are crafted and not taking into account the multiple contact points per stage I would suspect it would be at the bottom of that range close to 80%.

what we really need is for someone to take a cim motor and create a testing torque curve. Then mount that same cim motor in the tranny and test it again. We can then find out the true looses in the system.

Anyone got a torque cell lying around?