pic: Gerrish Gearbox MK-III

[P.J. Baker]

This looks like a pretty cool idea. Thanks for sharing. Here are my thoughts:

Without doing too much analysis, I think that this works as follows: The two motors adjust their speed until both are exerting the same amount of force on the two gears on the output section of the differential. The driven speed of the output will be the average of the two input shaft speeds. Essentially, it forces the motors to output the same torque, rather than the same speed – which is what happens with the more traditional dual motor designs. I don’t see any reason why it wouldn’t work in a robot.

However, it will suffer from the same problem as a car differential if one motor loses power – almost no torque will be transmitted through the drive train even if though there is still one good motor. The dead input shaft (unless it is somehow locked up) will be backdriven by the good input shaft, and the output of the differential into the treads or wheels of the robot will barely move.

I wouldn’t consider this to be a fatal flaw in the design, just one to be aware of. If one motor burns up or some how becomes mechanically or electrically disconnected from the transmission, the other will be just as useless.

Also, rather than matching free speeds between the two motors, I might suggest matching the stall torques. The differential design appears to have problems when motor A is supplying a lot more torque than motor B. Therefore, I would suggest gearing the motors to have similar torque performance rather than similar speed performance.

Good Luck,

P.J.