[Thad House]

Originally Posted by ollien

Hate to ask such a stupid question (my team has never used chain. Only belts and even then only for the DT), but here goes.

A) What do you mean by the "weighted" wheel? Do you mean the dropped wheels?

B) What do you mean by preloading chain? How would this help? You said something about moving the robot forward and then back, but I don't understand how this would help.

Thanks so much!

The weighted wheel would be the wheel with the most weight on it that is not the dropped wheel. For the setup being discussed, you couldn't easily put an encoder on the center dropped shaft. So the encoder would be mounted to one of the outer wheels. It the encoder is mounted to the wheel that is on the heavier side of the robot, that wheel will usually be in contact with the ground, and therefore the encoder is directly driven instead of through chain or belt. Its not a big difference, but sometimes the little differences help.

As for preloading, if your chains are not preloaded, as you start to drive the motors, there will be a split second where the motors will accelerate, but the wheels will stay stationary. This is because there is some slop in the gears and the chain or belt. This will then jolt the wheels when everything in the geartrain gets loaded, which can cause control issues if you want to be precise. If you preload the geartrain, which you do by moving the robot manually in the opposite direction you want to move, this jolt goes away, which allows much more controlled starts and more controlled acceleration.