Floating tension sprockets are perfectly legal. Might want to support the end of that shaft by the way.
What could be illegal about that sprocket?
Looks like they’ve got the holes to mount the bearing block…
And teams have used floating idlers for years, they work great.
For anyone who is interested in getting sprocket center distances just right, I’ve had fair luck using the numbers from this calculator http://www.team-moon.com/index.php/calculators/chain/, at least for #35.
The sprocket might be fine, but in this particular photo I would have some very real safety concerns about things (such as human hands) getting caught in the chain.
I’m sure that a guard for the chain and/or a robot exterior that inhibits access have been removed for clarity, but just a friendly reminder that just because a part is legal, the application of that part will not neccesarily pass tech if it is deemed to be unsafe.
Jason
I’d be more worried about that P60’s internals.
I would, too.
From the Banebots site: “We recommend maximum torque not exceed 35 ft-lb for all P60 Series Gearboxes. It is possible to mount motors that will exceed this in higher gear reductions. Higher reduction gearboxes should be utilized primarily for speed reduction. Designs utilizing a P60 gearbox / motor combination that will exceed 35 ft-lb should include a method of limiting torque to prevent damage to the gearbox.”
I can’t see the whole arm in this picture. If it swings past the top, shock load through a tight chain just might cause the hole in the P60’s output carrier plate to deform from its nice double D shape into an ugly bow tie.
You should be able to run these gearboxes like this ok, just scoot the gearbox over and run that sprocket right next to the face. That way, almost all of the load is torsional with a little bit of shear and hardly any bending. Four more holes and you’re running like a champ!
Thanks for all the replys, they have all been great. I took this picture right after we put the sprocket in and now it does have a 2nd point of contact. Our arm is a 4 bar linkage with a 30in “finger” on the end of it and it weighs about 35lb, so I think our gear box should be fine. Our main mentor loved the idea of putting a guard on the chain, that will come out sometime tomorrow.
a 35 lbs arm that is longer than a foot to its center of mass will be a problem for that bane bots. i would recommend some more reduction. ex, our wrist is similar, but weighs 15 lbs and the torque of the the gear setup powering it is well over 130 ft lbs.
I would be careful on relying on the p60 gear box for that application. You said your arm is 35 pounds, well if that is true any time the center mass of the arm is greater than 1 foot away from your pivot point. The gear box is at a significant risk of stripping its inner gears.
Torque= Force X Distance
35 ft-lb=35lb X 1ft
Ok, quick update we kept the whole arm as our 30lbs with holding allowance, and it only weighed 22lbs!! Including the supports. So the p-60’s were only lifting about 20lbs.
I wonder if the banebot people monitor this forum or is it too much for them to endure.
Please let us know here how that gearbox held up in competition, we’re interested.
The gearbox took competition like a boss!(after adding a new reduction stage and a 30t sprocket on top) We had no problems at all! It was a great year!
I don’t understand!!! Is that dynamic tensioning, or does it just keep one level of tension?
With that sprocket, one level of tension. The sprocket will stay in one place as the chain moves, since it’s moving the same distance on both sides of the sprocket. To adjust tension, you’d move the sprocket a few links one way or another or swap in a larger sprocket. You could make it dynamically tension by buying or machining an actual floating tensioner. It looks about the same as that, but with a huge hole in the middle that leaves it with rather thin walls. That lets it flex and deform into an egg-shape to make a more dynamic tensioner.
The primary downsides of the floating tensioner are the space required in the chain path and the fact that it’s going to reduce the contact angle on both your sprockets. The latter won’t matter too much unless you’re running a really small (9-12 tooth) sprocket under lots of load, which you really shouldn’t be doing anyways.
We’ve done that. It worked since the load wasn’t that bad, until the robot accidentally tried to lift itself using its arm. When that happened, the (steel) sprocket broke into three pieces. To fix it problem a 1/4 in. polycarbonate plate was zip-tied onto the arm so that it would slide off of the pegs rather than catching on them (the added benefit was faster scoring since it was easier to release tubes and turn back for more).