Correct chain tensioners

My team is having trouble figuring out how to tension the chain of our drivetrain. Our problem is that our chain is mounted in between our wheel and versaframe and one chain is 1/4 away from the versaframe and the other is 3/4 of an inch, making it hard to mount a majority of the McMaster chain tensioners. Does anyone have a recommendation on a chain tensioner to use?

(This picture was taking on bag day, not today)

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One trick I’ve seen and used is to insert a larger idle plate sprocket inside the chain run about halfway between the two functional sprockets. This sprocket should engage both sides of the chain, and will simply turn as the chain is run; it won’t tend to move one direction or the other.


We did this last year and never had an issue. I believe we had 15t #35 sprockets spresd roughly 11" apart, and we stuck a 26t sprocket in. The only issue was sometimes we would get into a pushing match or hard impact and knock the sprocket out of our chain. We did end up crushing the sprocket during the off season while in the chain, causing it to get stuck in our chain, pop it off, and also destroy our encoder, so just sometime to look out for.

Here’s a sprocket idler we used temporarily this build season while we waited for the belt replacement to arrive. This was a bit larger than it should be, because our chain break broke and we had to work with an oversized chain, but it worked fine.
A smaller idler sprocket is more secure, but you can add thin side plates to capture it better if necessary.

It may be too late for you now, but if you’re using a VersaFrame-based drive, VersaBlocks are built to enable chain tensioning. Simply drill a larger hole than your axle and pull the block until the chain is tense. Secure the clamping bolts. Preferably use a cam tensioner to maintain the distance, but I’ve seen instances where chains retained tension without the cams.

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A quick solution is to run the chain over a plastic guide that maintains tension. There usually don’t need to be replaced more than once per competition.

Yeah there’s a bunch of different solutions you can have. Personally I think the vex bearing blocks+cam is the best solution but it may not work with how your drivetrain is set up. We have used a delrin tensioner a while back and those seem to work well. Personally my least favorite solution is a floating sprocket but that’s probably the quickest way.

Would you be able to do a cantilevered chain tensioner? Basically you would pass a bolt through the versa-stock and then put an idler gear on that bolt. If you get a 1-3/4" bolt it will be long enough to reach through the stock (1"), clear the gap between the chassis and chain (1/4"), and then fit the nut on the end to retain.

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