Originally Posted by Andy Baker

One of the best chain rack and pinion designs I have seen in FIRST was on the ChiefDelphi 2000 robot. Its purpose was to entend and retract their boom-like arm. Here is a picture.

I wish I could find a picture of the back face of the robot. This view would show that 2 van door motors drove a chain up and down. The chain was attached to two aluminum tubes and was wrapped, serpentine-like, between sprockets on the 2 motors.

Can anyone from CheifDelphi give us a better picture of this?

This machine was and still is a thing of beauty. It is my favorite robot in all of FIRST, for all time. This design feature was just one of its strong points.

Andy B.

Originally Posted by Al Skierkiewicz

Green,
There are several good suggestions, I like Chris's chain in a "U" extrusion as a simple and effective approach. But a simple and lighter alternative is to wrap the chain around a sprocket (180 degree wrap) and terminate in a spring. The spring holds tension on the chain as the cylinder moves the sprocket. There is no need to have a bearing surface under the rack and no reason to hold the chain in alignment since that is automatic. This is similar to the loop approach discussed but doesn't add the weight of the second sprocket, bearing, and extra chain.