Re: PVC Rollers?
 

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)

Re: PVC Rollers?
 

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?

Re: PVC Rollers?
 

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.

Re: PVC Rollers?
 

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.

Re: PVC Rollers?
 

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.

Re: PVC Rollers?
 

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.

Re: PVC Rollers?
 

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."

Re: PVC Rollers?
 

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.

Re: PVC Rollers?
 

We used regular PVC pipe cut to length. We machined end caps that fit to the inside diameter of the pipe. We hex broached the end caps and ran a 1/2" hexed aluminum rod through the pipe with the end cap screwed into the pipe. We used .125" thick rectangular aluminum tube to create a frame. Then we ran timing belt inside the tubing to spin the rollers. We wanted to run the intake real fast so we used timing belt instead of poly cord. We can run our rollers at 20' per second to load the balls into the tower. Timing belt is superior in strength.

We had one of the best ball intakes last season. Poly cord is kaput to us.

https://picasaweb.google.com/1045493...19527586003058

Re: PVC Rollers?
 

Did you run center to center on the timing belt pulley distances or did you build in a tensioner?

In the picture it looks like the PVC was uncovered. That provided enough "grab" to move the balls with any covering?

- T

Re: PVC Rollers?
 

Center to center. We added tape over the the pvc to provide a rougher surface. The speed we ran the roller tended to slip on the surface of the ball. On the ends of the main roller we added thread to help grab the ball.