PVC Rollers?

[ajlapp]

If you're specifically interested to machine a roller from PVC then you might try schedule 80. It's thicker than Schedule 40 and usually dark grey.

McMaster sells it.

We have used it in the past with polycord. It worked well.

[Michael Blake]

I ADDED to my above post the materials we use purchased from McMaster.com

Hope this is helpful...

[J_Miles]

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.

[Lil' Lavery]

Originally Posted by Joe G.

Do you do anything to fill the gap that spreading the ring makes? We did this method one year, and it worked, but looks left more than a bit to be desired.

We've used shelf-liner to both fill that gap and help increase friction between the polycord and the roller.

http://www.chiefdelphi.com/media/photos/32753 (maroon in that photo, the outer PVC portions are wrapped in black tape)

[nnfuller]

I wonder whether people have had different results with different guiding sytems when using polycord vs. urethane belting. Can anyone who has used both present an argument for one or the other, or list pros and cons. I know that one thing that the urethane belting has as an advantage is that it has a smaller pulley minimum diameter. Besides this though, what is the difference?

[kramarczyk]

How do we make grooves to retain our polycord?

We don't. We use flat belting.

We use McMaster-Carr p/n: 6075K19 flat belting on a simple PVC pipe. To control the belt tracking we put 3-4 wraps of hockey tape on the center of where we want the belt to be. If the belt gets pushed, it tracks back on to the tape auto-magically. The belting is a bit expensive, at $4/foot for the 2" wide stuff we use, but it requires fewer lineal feet than round belting needs to cover the same span. Additionally the flat belt typically has a smaller minimum roller diameter than round belt which can help packaging. Because we do not need to cut grooves in the roller, the wall thickness can be thinner thus saving weight and cost in the rollers. The big advantage is time saved by simply not needing to make parts.

Here is an example from our 2012 conveyor.

[Tom Line]

We've used pvc rollers for several years now. You can buy plastic tubing from mcmaster to cut and put over the pvc to act as guides that are pretty much a perfect fit. Superglue in place.

The biggest difference I noticed this year for teams that used round belting was tension. If you put a LOT of tension on the round pvc belts, they don't deflect nearly as much and will track very straight. Of course, you'll want bearings and not bushings on your rollers to minimize friction if you're going this route.

Our shafts are all mounted in a slot and terminate in small block of aluminum, and we use a bolt to push on the block of aluminum to tension them. (Call it a jack screw if you'd like). That allows us to account for any variability in our manufacturing, because we don't have CNC ability and everything is fabbed by hand, so nothing ever comes out perfectly straight.

[Lil' Lavery]

Originally Posted by Tom Line

Our shafts are all mounted in a slot and terminate in small block of aluminum, and we use a bolt to push on the block of aluminum to tension them. (Call it a jack screw if you'd like). That allows us to account for any variability in our manufacturing, because we don't have CNC ability and everything is fabbed by hand, so nothing ever comes out perfectly straight.

I believe I understand what you are saying, but anyway we can see a picture of this set up? Just curious to see the relationship you have between your mounting blocks and your frame members in order to faciltate this "jack screw."

[Tom Line]

Originally Posted by Lil' Lavery

I believe I understand what you are saying, but anyway we can see a picture of this set up? Just curious to see the relationship you have between your mounting blocks and your frame members in order to faciltate this "jack screw."

Absolutely. Here is our 2009 setup. The bolt is in front of the wheel. The small block that the bolt runs through is welded to the frame was tapped. It is backed all the way out in the picture so it is not pushing the shaft end.

CD won't let me embed a photo from flickr, so here is the link:
http://www.flickr.com/photos/69166132@N06/6329918057

Here, you can see it on the left side and you can also see a bit of the slot that the shaft rides in:
http://www.flickr.com/photos/6916613...n/photostream/

We improved upon that this year. Instead of welding to the frame, we used 1/8" thick aluminum angle and rivited to the frame, then used a couple jam nuts on the bolt. That got rid of the welding and the tapping. We also put a small aluminum square on the shaft and drilled a hole for the bolt end to rest in, so it didn't try to walk off the shaft under high load.

[Gregor]

Originally Posted by kramarczyk

We don't. We use flat belting.

We use McMaster-Carr p/n: 6075K19 flat belting on a simple PVC pipe. To control the belt tracking we put 3-4 wraps of hockey tape on the center of where we want the belt to be. If the belt gets pushed, it tracks back on to the tape auto-magically. The belting is a bit expensive, at $4/foot for the 2" wide stuff we use, but it requires fewer lineal feet than round belting needs to cover the same span. Additionally the flat belt typically has a smaller minimum roller diameter than round belt which can help packaging. Because we do not need to cut grooves in the roller, the wall thickness can be thinner thus saving weight and cost in the rollers. The big advantage is time saved by simply not needing to make parts.[/IMG]

How did you customize the belts to the correct length? Did you weld them? Also why does it require fewer lineal feet than round belting needs to cover the same span.

[kramarczyk]

Originally Posted by Gregor

How did you customize the belts to the correct length? Did you weld them? Also why does it require fewer lineal feet than round belting needs to cover the same span.

We buy the belt in bulk so we mount the rollers and wrap the large piece of belting in place and mark it with a sharpie. We pull it snug, but do not attempt to tension the belt at this point. Then we pull the belt off and measure the length we marked out above. We subtract 1% off the length for tension then cut the belt at the new mark and weld it up. I think only once have we had to increase the belt tension, but I think we only had 2% cut off even then. We try to keep the tensions down to minimize frictional losses in the system.

In the past we have welded these belts with just a heat gun and some blocks of wood which is is not a great experience. This year we sprung for the heating tool, McMaster-Carr p/n: 62065K11 which greatly simplifies the welding process.

The span I am referring to is the width of the conveyor. Poor word choice on my end. As can be seen in the photo above we only used two flat belts to manage the 8" ball width. Using 1/4" round belt would have taken 2-3x as many belt runs to keep the ball from pushing past the belts. This cuts the cost premium for flat belts at least in half.

[cmrnpizzo14]

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!!!

[scott]

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.

[Brandon Holley]

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

[sportzkrazzy]

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.