Re: Chain Tensioning
 

This is very true. But I will probably be making a list of everything that is said in this thread. Just so that it will be easily accessible from here on out. ;)

Thank you everybody for all of your help. I never thought of looking through the patents... I'll definitely have to do that from now on.

Are there any other ways that you guys know of to tension chains?

-Rion

Re: Chain Tensioning
 

http://www.andymark.biz/am-0286.html

I've also seen teams with leadscrews attached to their drive bearings (which are attached to their frame in a slotted fashion). They tighten the screw to pull the bearing towards the end of the frame and tension the chain.

I've seen a number of teams use a hard-mounted idler sprocket (as mentioned a couple times in this thread), but also attach a shaft encoder to that sprocket (instead of to the gearbox or drive wheels).

Re: Chain Tensioning
 

Whenever I could get away with it, I slapped the gearboxes and the motor on the frame, put some chain in there and got everything snug. Then I would drill the mounting holes and throw a little shim in somewhere if the chain wasn't strung tight enough to almost sing. That was with decent #35 chain, so wear wasn't a problem. On a real long chain run then perhaps you have to have a bit of a tensioner.

There are really a couple of different issues. You don't want a lot of slack in a bidirectional drive mechanism. If the drive is in one direction, then you can make a chain guide to prevent excess slop so you don't throw a chain, but "tension" is not so much of a concern.

Re: Chain Tensioning
 

Did you get away with having wheels in the bumper zone on the 08 robot?

Re: Chain Tensioning
 

spring and an idle wheel, enough said

Re: Chain Tensioning
 

Only the very smallest wheels could avoid being in the bumper zone, since it began five inches from the floor.

Re: Chain Tensioning
 

2/3 perimeter is covered + min 6" segments = good bumpers. '08 was the first year bumpers were required but the rules were not as detailed. Abstract concepts like the BUMPER/FRAME PERIMETER (set of exterior vertices) and rule prohibiting extending past it that perimeter came the next year. Plenty of mechanisms had to reached far past their robot perimeter was to acquire/hurdle giant trackballs, so wheels are the least of your concern.

Re: Chain Tensioning
 

No, not enough said. Please re-read this thread, where you'll find the information on why this system is not adequate for a FIRST application.

Re: Chain Tensioning
 

The inverse of stiffness is compliance! :)

Re: Chain Tensioning
 

Thank you for getting to that before me. :)

Re: Chain Tensioning
 

For applications that don't require a continuous rotation (like an arm perhaps), we've used a turnbuckle to tension chain. Now obviously, the turnbuckle cannot pass over the sprocket.

Re: Chain Tensioning
 

Actually, Craig, an idle wheel and a spring would work. If you had the spring pulling up on the wheel. This would only apply force in an "upward" direction. This is in a completely different plane than the chain. Thus, no matter which way the chain was moving, it would still work. At least, I'm pretty sure.

-Rion

Re: Chain Tensioning
 

A third idler (What I assumed he was referring to) was addressed earlier. To reiterate, it will only tension in a single direction. If you switch directions, you will be directly pushing against the idler spring. Unless you're using a hefty spring, this will not be an adequate tensioning method, and you will have chain skipping and hopping in one direction.

We ran into this exact issue with a belt one year, which led us to develop the bolt pulled tensioner (You can search my CD Media submissions to find it). Once we implemented that, we had zero chain failures, and never needed to change tension to the system for entire regionals.

Re: Chain Tensioning
 

Team 975 once used an old skateboard wheel for a tensioner/idler. A groove was turned in the tire to prevent lateral movement.

Re: Chain Tensioning
 

Our team just slotted our wheels and then on each side of the wheel's axle we put small cams and then just turned them till the chain was tight, then we tighted down countersunk screws into them to keep them in place