Polycord Slippage

[wireties]

We are doing much the same thing but the rollers (usually) turn. Look at the rollers first. How difficult is it to rotate the rollers (with polycord-induced tension but w/o motors attached)? If you can't easily turn them with your hands (but they need not spin freely), the polycord will slip. Try grease, better alignment, change polycord from 10% to 5% - something will work because ours work just fine.

Good luck!

[MrForbes]

3% stretch is working ok for us. We are using 1-1/2" ABS (about 2" outside diameter) rollers that are about a foot long. We're using ball bearings in end caps to support the rollers. We don't have any grooves in them, instead we have a simply plywood "comb" above the lower roller to keep the cords in place.

Pictures of your robot would help us help you figure out what's wrong...

[Bruceb]

How about a picture of the "comb" Does it help rerail derailed cords?
Thanks
Bruce

[MrForbes]

Here's our comb. It doesn't allow the cords to derail, they're pretty well contained. But you have to experiment to figure out if it will work for you, it will not prevent the cords getting tangled up if for example the balls are trying real hard to push the cords sideways.

[Phyrxes]

Here is sample of ours from a past robot.

The rectangles with the diagonals are cut out to create gaps for the cords to move through. This particular one was designed to keep two bunches of cords together, not space individual cords. The final version that was use was significantly less material but this was the first iteration.

Circles are rivets to attach this to the bottom (or top) of piece spanning the run.

We usually make the comb out of hdpe or nylon.

[Chris Fultz]

In the past, we have used PVC pipe (1-1/4 size, which is 1-5/8 OD) and then used the couplings as cord spacers. With 3/16 cord, we had about 5/16+ spacing.

Using bearings in the ends of the rollers helps considerably. There is a lot of tension on the tubes from the belts, and having a solid rolling surface for the bolts / axles is important.

We have used a 90% belt size in the past with no issues. They are tight, but stay tight through the season.

[AdamHeard]

It's also possible the belts are too loose and aren't getting enough normal force to get enough traction.

A more likely issue is a sheave that is not stiff enough causing friction through deflection.

[de_]

add an adjustable belt tensioner