Interesting belt problem

[SteveO]

Hey there everyone, I have an interesting little problem maybe someone has encountered before.

First, as a reference photo so that maybe everyone will know what I am talking about check this:


or perhaps you were lucky enough to see the gearbox in person in Phoenix

Anyway, here is the problem:
As you can see from the photo our setup uses the stock gearbox and CIMs leading to our "shifter transmission" which has three speeds, and for this we are using a trapezoidal tooth conveyor belt (makes it easy to push with a pneumatic cylinder). During testing, we put two Goodyear belts, I'm not sure of the size but I am fairly sure they were 3/8" belts made of rubber with Kevlar. These belts lasted us for almost two weeks of testing on various surfaces, concrete and carpet etc. without breaking or wearing the teeth off. These belts we ordered from MSC I believe.
Finally, a few days before ship date (of course), the belts snapped, so we replaced them with what we thought were the same belts from the catalog. They came from a different order because we wanted to make sure this thing worked before we made a final decision. These belts wore down within a day. We ordered them from the same catalog and whatnot, I think the only difference we could see on the belts was the different lot number. We snapped all of these before ship date so we tried some different belts made of neoprene and polyester I believe, from McMaster. We've had moderate success with these but they still don't last as long as the original belts. We've noticed some shredded teeth and needed to change them out a few times after several matches.
Because it is a reliability issue (the belts take about 5-10 minutes to replace, time you don't have in the semis or finals), and we honestly haven't shifted that much except to get back behind the line at the end of a match or two, we have discussed taking off the shifter box and just using stock gearbox perhaps with some different sized sprockets. This would give us the weight for better lexan, and a few cool features we have had to omit
My questions are: What do you think about those belts? Was it a bad lot? Nothing changed between the replacement of the original belts. We have felt for sharp edges and whatnot. I have looked for some easily replaceable alternative, like belt we could crimp on, instead of having to take apart the transmissions to slide the belt loop on, but haven't found anything affordable that I think would work. Does anyone know if such a thing exists?
The team has pretty much decided that on Thursday in Vegas they will try going stock and see how it performs. If there are no major drawbacks that is fine, plus it leaves weight for cameras and claws and lights and other goodies I guess another question I have is how often people are shifting that have the ability to.

Anyway, any help/comments/chit-chat is appreciated as always And if anyone has any questions about anything I described you can post them or PM me.


Oh, and I apologize for my apparent lack of knowledge on the specific parts we ordered and whatnot, I didn't really help much with this design/implementation but I will be contacting someone from the team who knows a little more about it than me this weekend.

Thanks
-Steve

[sanddrag]

I'm not sure exactly how your shifting takes place. Are you actually moving the belt to shift.? Anyhow, I have had only one experience with belts on a FIRST robot and based on that experience I would never use them again. I don't belive there is any mechanical job to do on any (robust) FIRST robot that is best done by belts. I wish someone could prove me wrong but I just do not have good feelings toward belts. They are a nice lightweight solution but as you have pointed out, durability and reliability can be a major problem. Especially over such a small distance, it won't cost you much weight to go with sprockets and chain or gears instead.

In your shifter-box, is it possible to replace the pulleys with gears? Or with (small) sprockets and chain?

[KenWittlief]

what are the specs on the belts you ordered?

and what is the stall torque (force) being applied to them?

[SteveO]

Originally Posted by sanddrag

In your shifter-box, is it possible to replace the pulleys with gears? Or with (small) sprockets and chain?

Yes, it would be, but probably not worth the time and effort involved for the rest of this season I think you guys shift, right sanddrag? How often do you guys shift? Reliability is more of a side-issue, these belts have actually proven fairly reliable, especially the first set we had. The team just sees there is more pro then con to taking them off (it removes a complexity, weight, and in Phoenix we only used it 2-3 times in the many matches we played). It just kinda bothers me that it was working so well and then all of a sudden it becomes a pain

Ken, I'm not exactly sure on the specs yet as the team member who ordered the belts is probably sleeping I'll see if I can dig something up tonight.

Thanks for you guys' input.

-Steve