We were planning on using a polyurethane rubber roller (70OO durometer, 1/8" thick; McMaster #8514K61) for our intake (on 2" blocks and 2.7" whiffle balls) when we noticed this wear, as shown in the pictures attached, on the roller. The wear comes in two types, one which is more like surface wear (a kind of fraying?) and the other which is the polyurethane peeling off. We attached the rubber to a TETRIX aluminum tube using superglue (I believe it was gorilla super glue), which has seemed to hold well until recently. Although we have used it a fair amount in testing, we haven’t actually used this roller in competition yet, so we are worried that we’re doing something wrong with regards to attachment or usage that is causing the said problems. Hopefully this is a clear enough statement of the issue we are facing; please let me know if more information is needed. I couldn’t find any other past information here or elsewhere that suggested similar problems, hence a new thread. I’m also posting this here since it is technically a question from FTC, but let me know if there is a better thread to post this in.
My personal guesses as to what could have possibly gone wrong are as follows:
Normal or excessive wear. Seems rather odd that this would happen, especially since we haven’t used it all that much and, as far as I know, a fair number of FRC teams use this as well for intaking.
Superglue. I haven’t found a clear answer on this, but at least some sources (e.g. this source) suggest that cyanoacrylate (which is a major chemical in superglue) doesn’t work well with rubber, while other people say superglue can bond rubber to metal. Could this be the cause, and if so, are there other suggested methods of bonding the rubber to the metal?
Poor installation. It is possible that we just installed the rubber on this roller somewhat poorly, which might explain the rubber peeling off the tube.
An accident. Nothing is wrong with the setup, but we may have dripped or rubbed something else on the roller that caused it to react in the way it is.
Friction with other components of the robot. The only thing it really rubs against is our hopper (storage component for game elements). I don’t think it could have been the cause of all of the wear, since it only contacts the rubber in a couple places, but it’s possible, I suppose, that the edge of the thin polycarbonate we use could have dug into the rubber.
Anyone have any thoughts on what might be causing the issue? Thanks in advance!
(Also, I think I attached the two images properly, but if not just let me know and I’ll find another way to include them)
That’s a tough one, soft and compressible as well as abrasion resistant. You might try neoprene foam sheet (wetsuits). It may be more wear resistant.
It looks like a materials problem to me. Wrong material for the use.
As far as bonding rubber, get the recommended adhesive from manufacturer’s literature and follow to the letter. Wrong glue/bad method can yield a worthless bond.
When you see polyurethane used for intakes in FRC, it’s much more often in this form (McMaster #9697K138 or similar). Yours is a bit softer than the softest tubing, which also likely has something to do with it (in general, softer polyurethane/rubber/tread material wears faster). If you go down the polyurethane tubing route, I’d probably suggest the 1/2" ID tubing for Tetrix tubing, but it will be tight. Best of luck!
A design we’ve had success with for a “harvester” is to use “fingers”:
drill hole along shaft normal to axis
press fit or glue flexible extension springs into the holes
push soft latex tubing over springs
You can adjust the length and stiffness of the spring, and length of rubber “fingers” to achieve varying performance. We used this to collect the wiffle balls last year. It’s like what a lot of team do with zip ties, but the rubber grabs much better.
We haven’t really had the funds to test a bunch of different materials or hardnesses (and our tournament is this weekend, so time doesn’t present us with a lot of options), so more out of curiosity…do you think that the hardness of the polyurethane would affect the intaking ability significantly, specifically for the debris in this year’s game? I assumed that increased compression of the roller would be beneficial, and so picking a durometer would be a balance between this and the rate of wear, but I haven’t really had the resources to test this theory. Also, in order to better understand how we can improve this if we continue down this route, do you think buying it in tube form makes a significant difference, or is hardness more likely the culprit, and a full tube would just help it to hold together better? Also, would you recommend attaching it to the tube using something like rivets or an adhesive, or does it usually rotate with the tube just by friction?
We have considered a surgical tubing intake as well. From what I’ve seen and tested, I personally like the roller because of the “control” aspect—at least in theory, once the intake makes contact with the game element, it immediately pulls it in—whereas a surgical tubing intake may have to spin several times to actually collect debris and is pushing the debris more than grabbing it (plus some other quirks about the two). That said, it may come down more to implementation and driving than the fine differences, and both can be executed well.
