chain transmission without tensioning

[apples000]

We do this every year with 25, and it works really well. We machine the robot sides to the exact center to center distance for the sprocket, and it works well. If you chain does stretch, just throw an idler sprocket in there.

[Rosiebotboss]

Is it a cantilevered drive system? If not, you can add an aluminum stand off with a piece of pvc/teflon/nylon/delrin around it. You want the ID of the plastic to be slightly larger than the OD of the stand off so it spins freely. Off set teh stand off and route the chain up and around it. Slot the holes if you need to.

[Andy Brockway]

In 2004 we ran #35 chain. Center distance between the wheels was 1/8" longer than nominal. We have a chain puller so we used that to pull the chain tight enough to put in the master link. Never touched it again. The chain stretched enough in the first few hours to take the strain off the bearings and by the end of the season there was a notably sag.

[ajlapp]

We run #25 chain on theoretical center distance without tensioners all the time. Alignment is key. The chain wants to jump when the sprockets aren't axially aligned properly.

Placing these holes can be done with a manual mill. No particularly high tolerance process is required. +-0.005" will work all day long.

Example Chassis with untensioned #25 chain runs.

FRC118 ran this setup for 2013 with zero maintenance issues or chain failures.

[yash101]

Can't you spring-load a sprocket to do automatic tensioning? (or am I missing the point here?)

[EricH]

Originally Posted by yash101

Can't you spring-load a sprocket to do automatic tensioning? (or am I missing the point here?)

You're missing it--the point is that they don't want to use ANY tensioning if at all possible.


That said, I've seen folks just put a loose sprocket into their chain runs that need tensioning--best one I saw was a rubber one in the drive chain; ran back and forth as needed to get a good tension. Though I do second the Delrin recommendation. If you happen to be running the chain over structural members, stretch the chain over a block of Delrin on one of them, and let the chain dig in a bit until it finds its happy zone.