PVC Rollers?
 

I've asked this before on the forum last build season, and absolutely no one replied :(

So I've come to ask it again.

Can anyone link me or show me where to get PVC rollers for conveyor systems utilizing polycord?

Last year we were so misguided we ended up buying those foam rollers (the ones used for exercise).

Thanks in advance.

Re: PVC Rollers?
 

I'm not sure what foam rollers you speak of, but a lot of teams just purchase PVC from Home Depot or a similar store for their rollers. It is just pvc tubing that teams can machine grooves into or put rings around the PVC pipe to capture the polycord in place, but it is nothing special.

Other teams use other materials for their tubing: aluminum, acetal, polycarbonate, etc.

Re: PVC Rollers?
 

I don't have a picture on me, but for some of the bots I saw, the grooves were HUGE and DEEP.

Like, anywhere from 1/4" to 1/2" deep. I haven't seen PVC with a wall that thick, unless they were using a bunch of small segments of PVC connected by some sort of fittings to simulate grooves.

Re: PVC Rollers?
 

I've seen more ABS rollers than PVC. ABS plastic is more appropriate for this type of application (less shatter-y, rougher surface finish), and generally comes in thicker walls, which can be machined. However, it can be much easier to add grooves onto the surface of a roller than cut them into it. The solution can be as simple as a couple of donuts cut from plate stock and epoxied to the surface of the roller.

Re: PVC Rollers?
 

McMaster catalog page

There are a variety of sizes and material options. Take a look around McMaster or Grainger searching for 'Conveyor rollers' and you'll turn up some more.

For what it's worth, 95 used some rollers from McMaster last season and they worked out alright. We ran actual conveyor belting around them. Our early tests using polycord was suggesting it was going to be more trouble keeping them on track then it was worth in weight savings.

Re: PVC Rollers?
 

On 330 we just cut thin sections of PVC pipe and then make a slit in the resulting ring. The sections are then glued to the main roller on either side of the spot where you want the belt to be using PVC cement. Simple, effective, and cheap

Re: PVC Rollers?
 

We prototype using PVC with wood plugs in the ends and 1/4 20 bolts sticking out long enough to put electric hand-drills on for proto-power...

On production, we use hollow aluminum tube with Nylon plugs in the ends and we press aluminum shafts in, spinning on lubricant-infused bushings.. I think going forward we'll skip the bushings and use sealed-bearings if weight/cost isn't an issue.

As for keeping Polycords in-place... we abide by the 148 Robowranglers credo... "IF gum-rubber isn't the answer, THEN you're asking the wrong question..."

LOL

SERIOUSLY, the black gum-rubber works _great_ creating channels and looks _awesome_!! < some scrolling pictures www.broncbotz.com > You need to apply at least TWO layers and super-glue each layer...

From McMaster:

4568T18 Architectural Anodized Aluminum (alloy 6063), Tube, .065" Wall Thk, 1-1/2" Od, 1.370" Id, 6' L
93625K58 Natural Gum Foam, Adhesive-backed, 1/8" Thick, 1-1/2" Width, 50' L
8541K56 3 Ft. Wear-resistant Black Nylon Rod, 1-3/8" Diameter

Re: PVC Rollers?
 

We machined them from 2" delrin round stock. Very simple to do.

Re: PVC Rollers?
 

We did the same.. expect out of 1.25 billet 6061.

Re: PVC Rollers?
 

This is exactly what we did as well, but with Polycarb tubing. It requires no machining time other than a bandsaw and provides the same function.

Re: PVC Rollers?
 

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.

Re: PVC Rollers?
 

'Tis just standard PVC and end caps (obviously drilled into them for the axle) purchased at the local home depot. The rings around the PVC that keep the polycord in place are just strips of another pipe of a slightly wider diameter (It may even be a end cap that we chopped up and slid on, I don't remember exactly).

Re: PVC Rollers?
 

It's great to mention and bring up in this topic regarding what materials you should use for your rollers. Everyone knows a combination of ABS, Delrin, Aluminum, PVC, ect. Another one to throw in there is wood and 1114 used it effectively this year on their intake. It's just a great thing to remember that some of the most "effective" components of a system may just be in a scrap pile in your high schools woodshop. :)

Re: PVC Rollers?
 

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.

Re: PVC Rollers?
 

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

Hope this is helpful...

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!!!

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.