Round Belting - Solid vs. Hollow, Polycord vs. McMaster

Technical Technical Discussion
#1

I was admiring some of the robots in the 2006 “Behind the Design” book, and noticed that round belting was commonly used in some of the nicer ball handling mechanisms. Team 121 specifically referred to using Polycord belting material.

Searching back through CD (yes… I do search before I post!) I found this thread as the best reference but it was a bit out of date and didn’t quite answer the questions I had, so:

  1. McMaster Lists both solid core (you join it by welding the ends) and hollow core (you use a barbed insert) round belting material. The hollow costs a little more, but should be easier to join. There is a welding kit for the solid stuff, but it is expensive, and it should be possible to rig something similar at home. Does anyone have sufficient experience with both the solid and hollow core belt to recommend one over the other? Is it as easy to rig up a welding set up for the solid core stuff as it looks like it should be?

  2. The McMaster belt material runs about $1.00/ft (more for hollow, less for solid) in the 1/4" size. Smallparts.com lists similar sized Polycord for $4.20/ft (when buying 10 foot lengths). Has anyone experimented with this enough to compare it to McMaster’s offerings?

Thanks,

Jason

Incidentally, if you’re stuck for ideas on how to play this year’s game, you could do worse than read the Behind the Design book. There are some great ball-handling ideas in there.

#2

Don’t waste $500 on the McMaster “welding kit”; the solid core polycord can be welded with just a lighter. Just cut the cord 10% shorter than the actual distance necessary, melt the ends with the lighter, stick them together (use the inside of aluminum angle to keep them lined up), and wait five minutes. Now use a razor and trim off all the globs of melted cord around the joint so it is smooth and wait another half hour to let it cure and achieve full strength.

I’ve used the McMaster round belting as well as name-brand Polycord from Small Parts. They are pretty much the same, except McMaster ships a lot faster. Just watch out: the endless belts offered by McMaster are nice in the fact that they already come preset to the length you want, however they are a lot more expensive per foot to buy (0.25" continuous belt is about 4x more expensive per foot than plain belting).

// Also, for anyone else who may be reading this thread: if you want to purchase polycord material from McMaster, don’t search for polycord, as this will only bring up one result. Search for round belting to get the whole list of hollow and solid core belting in the various colors (green, orange, clear).

#3

What is the advantage of polycord over urethane round belt?

#4

I have bought poly cord in the past but we didn’t put it on a ‘production’ robot.

During AimHigh a girl on a team from Florida showed me how to weld it. She used a lighter and heated the ends and pressed the ends together and clamped it. I cannot remember the setup hold times but if you setup a jig it should go easy.

Also the cord is designed to have a certain amount of tension so you need to figure out how long you really want it then make the cables and then mount them. Think of them as tough rubber bands.

If you know someone that has a nice sheet fed Heidleberg press you can probably some some of this stuff in action.

I’m gonna run on a little more while I’m here.

FYI - we may make a conveyer out of timing belt, probably the XL size, and use plastic pulleys scattered across a drive shaft will filler between the pulleys. the filler will be turned down the the inner pitch diameter of the pulley. plastic pulleys are cheap and you can get them with single, double, and no flange.

timing belt is made in large tubes then is sliced like a giant salami.

you can go buy any width timing belt you want if you order it from www.econobelt.com or www.sdp-si.com , for example 2 foot wide if you like. There are whole families of standard length.

and the belts don’t need to be as wide as a moon rock, only wide enough to touch the crown.

and similiar to the timing belt, you can get flat belt (un-timing belt).

right after we shipped aim high robot I went to a Harley Davidson bike ralley and saw some custom bikes with 4 inch wide belts driving between the engine and wheel. It was totally cool looking and had graphics imprinted onto the belt.

does anyone know how to do the printing ?

#5

In 2006 in fact, our robot actually used the belting for our ball gatherer system. This is what I found:

We initially had some of the solid core stuff laying around, so we used it… it was actually pretty difficult to melt though. We used a heat gun to melt the edges and pushed them together and waited for them to dry. The resulting seem was strong, but it was difficult to make, and it required testing to find out how much the joint would shrink/grow from the original cut of the material. We later used the hollow core belts with the barbs. To me this seemed a lot easier. The barbs are simple enough to use, and they allow your loop to be the exact size as the length you cut. We never had a barb pull out in competition, and they were just as strong if not stronger as our weld joints (of course this might have been due to shoddy welding). unless the belting is making particularly tight turns, the barbs should not necessarily be a problem.

Hint for using either type: make your loop first, THEN try looping it around where you need it… I made the mistake of trying to stretch it into place and assemble it my first time… Dont make fun of me, I was a freshman!!

#6

I would agree with Arthur, don’t waste your time with the hollow core. I think i did all the polycord for 610’s 06 bot in like an hour by melting the ends with a one of those small table top heaters (melting the material on a piece of AL placed on top of the heater as to not ruin the heater) and then stuck them together and trimmed the excess with a exacto-knife. Polycord make belting systems really easy to put together, not tight enough just cut a bit off and reattach.

#7

Thanks to everyone for the helpful replies. For 1/4" belting the solid core at McMaster is $.90/ft and the hollow is $1.22/ft. It sounds like we can’t go wrong by getting either of them, and it is pretty apparent that the custom welding set up won’t be needed.

As for the brand-name polycord at smallparts… well… it doesn’t sound like the 400% increase in price ($4.20 in 10’ lengths) is worth it.

And the tips on the wide belting from econobelt are good too.

Thanks to all,

Jason

#8

But when cutting the polycord, make sure you cut at a 45 degree angle. Creates a MUCH stronger bond when melting the ends together.

Good luck!

#9

Polycord is a brand name of Habasit for their urethane round belt product. They are the same material.

#10

We used the namebrand polycord in our 2006 bot. Just melt the ends and stick and you have a solid connection. We did not break one belt through the entire season. However, from what I’ve heard you dont need the name brand stuff. Its cheap enough that you can buy a few different types from mcmaster to see whats best for you.

#11

I am not sure if this Dayton Urethane Round Belt is the same quality as mcmaster. But this company has more specifications about the different types of belts (its roughly the same price).

http://www.drillspot.com/products/424954/Dayton_1DYV9_Round_Belt

What do most people suggest in terms of texture of the belt ?

Orange = Smooth (hardness = Shore A 90)
Green = Rough
Clear = Smooth (hardness = Shore A 80)

What’s the difference between clear & orange, mainly hardness ?

How does hardness affect ball collecting ability?

#12

I would say hardness affects how grippy it is. Shore A is still decently grippy, a colson wheel is 65 A for reference. I imagine if it was too soft, and in the 30-65 range like banebots/colson wheels (just as a reference), it would wear too quick and be too weak.

#13

To put things in perspective, the average longboard wheel is between 70a and 81a. An average skateboard wheel is between 90a and 98a, depending on the brand.

#14

We have some of that green polycord stuff lying around…

We’ve never used it, it doesn’t look like it could apply sufficient grip to lift the balls.

Has anyone tested it out on the balls?

We’ve always used neoprene o-rings from mcmaster. They’ll only last the season before falling apart, but they have tremendous grip and are very strong.

#15

So I’ve been searching for these on McMaster, and I’ve narrowed it down to 3 colors. One of these colors (green) has a larger minimum pulley diameter than the other two. Aside from obviously needing to use a larger pulley, what does this mean about the belt itself? Someone mentioned that the green was more rough than the other colors, it also happens to be the one that needs a larger pulley. Is this because it is more rough?

I also just noticed that the green stuff is $5.40 per foot as opposed to the other ones that are $.99 per foot.

#16

How is the polycord with the grip on the balls? Is it similar to surgical tubing?

#17

Is the grip with the polycord similar to surgical tubing?

#18

Having handled both lately, the polycord feels a bit grippier. I can’t offer you any better insight with regard to hard figures, but there’s a difference.

I’ve had bum experiences with hot plastics in the past, which makes me leery of using any custom heating rigs. That said, I also wouldn’t want to use some bum setup with hollow-core belts. Has anyone had bad experiences with them in an FRC setting?

#19

Falconmaster–
NO, Polycord or the less expensive versions are very different than surgical tubing. Round belt urethane belts are MUCH less elastic than surgucal tubing. The are also, however, less “sticky”, but far more than enough to move the 2009 game balls. Surgical tubing stretches too much and is a bit more difficult to attach to itself (Although a volunteer at Hartford Ct regional [can’t remeber his name] told me the perfect way. Roll the surgical tubing back on itself and put 1/2 of a one inch section of pneumatic air hose from the KoP up to the edge. Coat the edge of the tube with Crazy Glue then roll the tubing onto the hose. Repeat the process with the other end of the surgical tube and the other half of the hose and you’ll have a closed loop which will NEVER break at that point.)
We prototyped the round urethane belt conveyance for this year and it moved it beautifully. The key is deciding if you are going to have one set of belts roll against a stationary wall or have two belts rolling the ball between them. Both worked for us, obviously one is twice as fast as the other.

One mistake many people may have when first trying to adhere two ends together is to heat with a simple flame and hold them together. Using a short (6" or so) length of aluminum angle to maintain allignment, heat to a liquid melt then touch together and pull apart about 1/16 to 1/8" . This is crucial. Failure to do so may give a false sense of adhesion. The separation prevents the hot urethane from being squeezed out by the non-melted belting.

Don’t be intimidated by the product. We’ve used it in '06 and could gather the small balls going 12fps, as fast as we could drive over them.

I hope this helps you. Any questions… message me and I’ll help out as best I can.

#20

Thanks!