problems with drive-train

Before we bagged the robot, we noticed the robot was turning to the right significantly when we wanted to go straight. The drive-train we used is a standard tank drive powered by two WCP DS gearbox (2 stage gearbox) with two CIMs and the other wheels are powered by a chain(#25) and sprocket system. We took offer the chain to see if the chain was stressing out the axles, and that was not the problem. We are wondering if it is the transmission or a motor. If it is the transmission what would be the problem?

Some things to check, in no particular order:

• All your motors are running in the right direction (not fighting each other)
• Chains are stretched evenly
• No rubbing, scratching, points of obvious friction
• Power wires are same length, diameter
• Well greased on both sides

Really, the only way to ensure that your robot is driving straight is to “close the loop”. To do that though, you need feedback from a sensor (e.g. gyro, encoders). Assuming you don’t have this available right now, this should help you get started finding where your problem is.

The most common problem we’ve had that caused something like this is having a gear installed backwards (TB-mini gearbox). Even when it’s not that, it’s usually something rubbing where it ought not to rub. Check bearings, where gears are supposed to mesh, and where gears are not supposed to mesh but might if something’s out of line.
Turn the output shaft by hand (or with a wrench) and see if it’s sticking in a specific part of the rotation (likely a bad tooth somewhere or a chunk of grit) or if it’s even around the cycle (more likely a bearing/shaft or bearing/gear interaction).

The WCP gearboxes used to have peanut shaped mounting hole for the CIM motors to allow different Pinion sizes to be used. We had a problem with them in the past where the CIM’s slipped into the wrong hole during operation causing binding similar to what your describing

I will be at your event in Orlando, come buy 179’s pits and I can come over and help you out when you un-bag the robot on Thursday morning.

Also good to ensure that both gearboxes are in the same gear. If one is in high and one is in low, it will cause them to go different speeds, causing significant turn.