Re: PVC Rollers?
 

This year 447 used schedule 40 PVC pipe has the roller and rather than machining grooves into the roller we used the corresponding PVC coupler. We only used the ends of the coupler as dividers. You can glue them into place, but I do not believe we did and they held up just fine all season. This works well for teams with limited machining capabilities since all you really need is a saw to cut the pipe and couplers.

Re: PVC Rollers?
 

It's also worth noting that with some research you can match up sched 80 ID's to sched 40 OD's to create nice and tall rings for your urethane belting "grooves".

We've done this on a couple robots starting in 2009. Our 2009 robot had something like (11) 22" wide rollers where the cost of ABS or Acetal was becoming an issue. The PVC on PVC rollers are super cheap, really light and easily reconfigured.

-Brando

Re: PVC Rollers?
 

No but we did end up adding the gum rubber which Michael Blake provided the part number for.

Our end caps were just UHMW disks with a hex in them.

Re: PVC Rollers?
 

In 2011 we cut PVC couplers to act as guides for our Polly cord with no groves at all. We wanted its to act as a slip clutch for our rollers on our claw that year. All in all it did the job. It had enough friction to pick up the tubes but not enough to stall out the motors once the tube was all the way in.



Last year we cut grooves directly into schedule 80 PVC and it worked pretty well as long as the cord was tight. Once the cord stretched a little it started to walk out of the groves but to fix it all you had to do was cut it and tighten it(probably like once a competition). The grooves where just shy of half of covering half of the cord which isn't ideal but worked all season long on both team 1592s and team 801 twin robots.



Looking back on this season I would Probably go with some ABS just so I could get a deeper grove but if is all you have access to its pretty cheap and its everywhere so go for it especially on a prototype. The Nice thing about first robotics is that there is more than one "right way" to solve a problem.

Re: PVC Rollers?
 

We used 1/16 thick clear polycarb rollers this year on our front convayor. It worked very well, no problems. Polycarb is very durable and springs back unlike thinwall aluminum tubing. We used thinwall aluminum for rollers inside the robot to reduce weight.

Instead of larger diameter rings I would suggest a belt comb. This year, we began with no belt combs and ended with a belt comb on all of our polyurthane belt runs. It's not that PVC rings don't work but a comb ensures that the belt can't walk down the roller. Even if you pull the belt off of its "spot" on the roller it'll walk back. If we use polyurthane belts in the future, which I'm sure we will, you can be sure that we will also use a belt comb.

Regards, Bryan

Re: PVC Rollers?
 

Do you have any pictures of this belt comb? I think I know what you're describing, but I'd like to see it to be sure.

The few times we've used beating, we always had it ride between larger pvc pipe sections that were covered in wheel tread to overcome the slippery nature of the plastic.

Re: PVC Rollers?
 

What is a belt comb? I can't find it on McMaster-Carr. Is there a different name they are called?

Re: PVC Rollers?
 

I looked for a good belt comb pic.

Here's a cropped picture of a belt comb on our practice robot. It's thin polycarbonate rolled around the roller and riveted, we neglected to take the film off of the polycarb so it's white.

Our belt combs inside the robot (where both rollers need to contact the ball) usually cover only the top (non-contacting) side of the belt and don't go around the roller.

These belts were under a lot of side load, so we needed a lot of combing to keep the belts on track. We actually didn't rivet the spacers on the other side so the belts can walk as they please under load and move back into shape when the ball has passed.

Re: PVC Rollers?
 

Basically what Andrew said.. The belt comb in his picture is pretty unconventional as it goes all the way around the roller.

More commonly one would use something like my attachment..

We usually use thin polycarb for ours but I have seen them made out of lots of different things.

The reason that we call them belt combs is because the applied piece we make looks like a comb before it is bolted on.

Regards, Bryan

Edit, In the second above picture by sportzkrazzy towards the top there is a clear piece that doesn't go all the way around the belt but still looks like its serving the same function.

Re: PVC Rollers?
 

This past year FRC2168 used some aluminum tube with threaded inserts and pop riveted tread to make our rollers. You can read more about it here: Lift & Hopper

Part numbers included: McMaster 60945K16, 1968T576, 5994K711

Re: PVC Rollers?
 

Here is the best picture that I have of the belt comb that my team used. It is just a piece of plastic with notches that the belt runs in.
(sorry, unzipped is too large of a file)

Re: PVC Rollers?
 

We never really had a name for it but yeah that's pretty much the function that is served. We just used a piece of Lexan that we bent in order for it to keep its shape and maintain strength rather than going all the way around the cord. Two rivets a small piece of lexan and 30 sec on the brake and your done. Simple and lightweight whats not to love.

Re: PVC Rollers?
 

We used simple PVC tubing from the store, and added a couple of "combs" to keep the belts straight. The combs were just pieces of polycarb with notches cut in them for the tubing. We placed them relatively close to the rollers, and didn't have a single issue with our belts all year (2 regionals, 2 off season competitions, a competition at the State Fair, and a few demo's that saw the robot running almost continuously for an entire day).

We had a similar conveyor system for Lunacy, but back then we used some solid ABS rollers (really heavy) and machined some grooves in them. I don't know what we did wrong with the grooves, but we had to go in after every match and reset the belts, as they kept jumping out of the grooves and wandering. Making the combs this year proved both easier and more reliable.

Re: PVC Rollers?
 

If you're just looking to drive the rollers rather than using the belts to react against a game piece, I'd recommend simply using lengths of PVC and round Nylon or Acetal Resin (DuPont's is Delrin - it's what most of the belted pulleys I designed were made of) to "plug" the ends of the rollers, into which you can machine grooves (assuming you can turn the material on a lathe). This gives you a solid piece of stock into which you can sink deep grooves to help minimize belt walk. As an added bonus, your belts can then be flush (or even recessed) in relation to the surface of the roller.

Of course, this is a very purpose-specific application. It doesn't work quite as well if your belts are meant for moving a game piece rather than simply driving a roller. The advantage is that it allows for a very light, strong roller with a uniform surface while still providing a solid mounting point and great freedom in the depth of grooves. It also means that you can machine the plugs to either accommodate or fit through a bushing or bearing.

Re: PVC Rollers?
 

I would recommend checking out our website. We have CAD drawings up for rollers that we made to suit pneumatic tubing bands. If you have any trouble please ask, we are happy to share.

http://igknighters.com/Robotics/Resources.shtml

The links are near the bottom of the page.

Good luck!!!