counter rotating driveshafts

[Dezertdirt]

I'm not sure where to put this. Anyway, recently I've seen several transmissions saying that the driveshafts will be rotating in different directions (counter rotating). So, Why would these transmissions do this? Will it help torque twist? Can it cause problems?

 

[bbrigg]

Having the driveshafts rotate in opposite directions will help with torque twist. Some crawlers, like the GMade BOM, come with their transmission set up that way for that specific reason. The Traxxas TRX-4 solved much of the torque twist problem by having the driveshafts rotate faster and dropping the ratio in the portals and the Losi Night Crawler did it with very high ratio worm drive differentials. The Axial SCX-10 II used a higher ratio and high pinion which also helps a lot. The only way to properly eliminate torque twist is MOA.

There are some after-market transmissions for vehicles like the Axial Wraith with the AR60 differentials which can have the differential ring gear flipped to put the gear teeth on the opposite side so that they can work in either direction. The only problem I would see is the build quality of the transmission internals don't appear to be available separately but the transmissions are available quite cheaply. They may also use non-standard bearing sizes so you would have to source bearings separately instead of the ease of just buying a kit. I'm thinking of buying a Wraith just to try this out.

 

[Itali83]

It does help with torque twist in theory and a perfect world. I have 3 ascenders, known for bad torque twist out of the box. The latest one I built with no sway bar but with a counter rotationg transfer case to try the theory. I am running the front axle overdriven 10% and have a motor forward setup. So, that being said, I notice that on flat level ground, the truck has torque twist to one side, but when doing steep climbing it twists the other way. Bottom line is that the ascender axles have such high gears, 1.85:1, that this truck twists to whichever axle has the most weight on it and traction. So the counter rotating transfer case may work in a perfect world, but bottom line, the rear end ratio of each truck decides how much torque twist the truck is will have.

Ben