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

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 I found this thread as the best reference but it was a bit out of date and didn't quite answer the questions I had, so: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.

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

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).

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

What is the advantage of polycord over urethane round belt?

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

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 ?

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

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!!

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

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.

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

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

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

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!

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

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

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

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.

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

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/42...YV9_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?

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

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.

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

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.

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

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.

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

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.

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

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

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

Is the grip with the polycord similar to surgical tubing?

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

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?

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

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.

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

Thanks!

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

I have to coment on the post by Tom I. He is a friend of mine and he and i have had a change of heart with the bonding of the belting... though i would still not recomend it for a belt it works great bonded to a flat piece of the same material. we used this to make the fingers for our collector this year...

just my two cents...

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

some of the cord is reinforced, some is food grade, some is smooth surface, some is rough surface.

the material that is $5.40 / foot is reinforced.

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

datasheets are here, food grade and non-food grade

http://www.habasit.com/1976.html

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

I have a question about what rollers people are using with the polycord. Specifically for the drive roller and then the idlers. I had thought pvc pipe, but I presume there are other more elegant solutions available. Thanks.

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

custom heating rigs like the one you saw me successfully using friday?

if anyone wants to try this with the solid core go ahead and save yourself some money and buy "Weller®/Portasol® Super-pro Self-igniting Butane Soldering Iron Kit"....it has a chiseled tip and work like a dream, plus its like $60 as opposed to $500

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

Custom heating rigs like a fresh-cut 2007 kit wheel that burned the heck out of a couple of my fingers. I'm not saying it can't be done--safely, even--but I've just got my biases about the matter. Call me paranoid.

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

I believe I have found a vendor that is cheaper than Mcmaster and trust worthy. I'll post after checking thier stocks tommorrow.

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

Dcollins
We've milled ours out of delrin rod (lucky enough to have a sponsor who gives us just about all we want). For those less fortunate, you could use schedule 40 plastic pipe with grooves cut, that's a common method. You could also use 1/2" shaft with plywood pulleys. It's simple enough to turn on a lathe or milling machine. There's lots of options.

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

No, it needs a larger pulley diameter because it is stiffer. The fact that it is rougher is separate and not really related.

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

Back at the Atlanta Championships in 2006 I got a sample of some yellow polycord for a team (sorry I don't remember which team) that is very rough almost like sand paper. It is 1/4" in diameter. I am not seeing something like it at McMaster but it is hard to tell. Does anyone know the exact stuff I am talking about and where to get it? Maybe a part number? McMaster says the metric stuff is "rough" but how rough? It doesn't say about the texture of the inch stuff. What polycord products have teams used successfully in the past? We can't afford to buy a bunch of this stuff to try out so need to limit the selection.

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

We have a couple of igus rods from previous years (3/4" diameter iirc), so we'll add that to this year's rod and use those for our rollers. If you can mill a keyway in the rod, it mates perfectly with the black plastic hubs that attach directly to the window motors. If not, then perhaps you may get away with drilling & bolting through the hub and rod.

This simplicity is our only reason for using these rollers.

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

I just wanted to say "thanks!!!" to everyone posting on this thread for all the useful ideas. You saved us a lot of time. Will try some of the polycord and see how it compares to surgical tubing for our intended design in a quick mock-up.

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

Grainger has good prices on 50' roll of 1/4" round belting, If teams haven't already ordered.

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

Slightly different topic, but has anyone compared V Belt to the Polycord? Has anyone USED V Belt on a robot before? We found tons of examples of teams that used polycord, and have even used it ourselves, but have been experimenting with V Belt in our initial prototypes. It seems to work well and slip out less, but one of our mechanical engineers was thinking that as its used it has more potential to come out of the pulley...

Any thoughts?

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

We found out on Saturday that 10% is pretty tight, and you can safely get away with much less. We had round belting on 3" diameter PVC rollers with grooves laid in for the belting to follow. These rollers were mounted on 1/2 steel shafts in plywood "bearings." The plywood supports were about 25" apart. Four urethane belts at 10% did a number of the shafts. We could clearly see the shafts bowing, and our 18V Dewalts had a hard time turning the assembly. To alleviate some tension, we moved the rollers closer together. The distance around the rollers was originally measured at 55 inches (so we cut the belts to be 49.5" long. We moved the rollers a good 2" closer, and found the belts were still taut, and had no problems with belts slipping, even when we jammed in seven balls and put a board across the top opening.

In short, we found cutting the cord at 10% shorter to be pretty aggressive. At 3% shorter (instead of 10%) the balls moved just as well, and the whole assembly ran much smoother.

Art, is there any reason for the half hour cure time? After five minutes or so ours were cool to the touch, and we haven't had any fail that were joined using your welding method.

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

10% is a total flat out lie on McMaster's part.

In 06 we used 5/16" clear urethane belting (solid core) and ordered the recommended 10% short. It was near impossible to get them onto our rollers. The process we had to go through to do it was so jerry-rigged and dangerous that I won't even describe it here. Not to mention the fact that once it was on, the efficiency of the entire system was horrid.

I'd recommend more like 3-5% stretch for anyone else who hasn't joined their belts yet.

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

The 10% value comes from the manufacturer spec sheets. Normally, these belts are designed for conveyor-type installations, so having increased tension allows them to transfer more force through it. In our robots, we may not need the same level of tension depending on the application and polycord thickness. If you use something like 1/8" polycord, sticking to 8-10% reduction is a good idea.

As for the half hour cure time, again that's from the manufacturer recommendations. According to them, you can use the polycord after five minutes, but full strength in the joint isn't achieved until thirty minutes later.

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

Remember, if you make belts 3% stretched, they can always be a made shorter... you can't lengthen belts.

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

Dont see why you couldnt lengthen them. Just cut them and add in a piece just like you did to make the loop.
Bruce

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

BTW.. I just got done making 10 belts from 1/4 round solid urethane(orange) belting 10 percent short. They are tight but running on half inch steel shafts 10 inches long and in bearings they seem fine.
Bruce

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

We have used synchronous belts - they work well, but you need to design around a standard size and alsignment is critical or they will walk aout of the pulleys. V belts would be more tolerant, as they are continually being 'forced' into the v-groove. However, v-belts 'seem' to stretch more, because as they wear they get seated deeper into the pulley.


Regarding poly-cord like belting - the recommendation we received is 8%, and that is working. The belts are stretched to install but are holding up well (so far).

Also, both McMaster Carr and Durabelt provide minimum pulley diameters for each belt size. For 1/4" cord, MMC recommends a minimum of 2", Durabelt recommends 1-1/2 - 2", depending on the load being carried.

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

Any Durabelt distributors that you can point me to? I struck out- ours in Rochester moved.

What's the cost per foot (100 ft min is what I'm told).

Now to find cheap pulleys...

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

As advice to any teams looking to save money by purchasing round belting from Grainger right now: avoid it. 228 purchased 100 feet of 3/16" orange round belting from them almost a week ago, and despite being listed as "in stock" on their website we just received an email that it won't be shipped out until the first week of February.

Since this will be too late to really help us (except for replacement/stockpile parts), last night we ordered another 150 feet of it from McMaster and it'll probably be in sometime today or tomorrow.

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

I believe the problem is the 3/16 as to 1/4". They have plenty instock of the 1/4". It comes out of Chicago. I had no problem getting 1/4" . Used will call at our local Grainger to avoid shipping.

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

For clarification purposes, the 'round belting" we are talking about as actually called what?

In the McMaster online catalog I found this, EPDM Rubber Cord and Polyurethane Cord. Is this the 'right stuff'?

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

Mcmaster P/N# : 59725K704.... this is the same kind of 'stuff' your looking for.

This particular variety is 1/4" dia., orange in color (which is slightly softer durometer and matches rosie's colors ;)), and a 2" min. pulley diameter.

You can pick whatever variety you actually need.

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

Yeah, that's the stuff. I must have had a brain cramp. I couldn't find it. Thanks, Brando.

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

no problem!

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

Our team is trying out round belting, but we are having some trouble carrying the ball. The belts keep splitting and not grabbing the ball. Any suggestions?

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

Use more belts, closer together, with pulleys? Use less distance between axles ? Use less compression of the ball? Place the axles so that they form triangles between three, instead of having each one directly across from each other?

I'm not sure what you meant by splitting.

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

You need to make sure you put grooves in whatever pulleys you are using....otherwise, there is nothing keeping the belts from separating (i'm assuming thats what you meant by splitting).

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

Unless he means that the cords themselves are splitting when formed into a loop??
If that's the case, then your tension is way too high on your belting.
If you just heat up the ends & melt them together & let the completed loop cure for a while, they should suffice for a while.
Also, if you can, try using very thin wall shrink tubing to assist in holding the joint together as an added protection from the splitting.
Don't forget to put that on before you join the two ends though... or you may have a bit of an issue. :p


Another trick I heard of was to "tin" the ends?? I heard that terminology thrown around the shop before, but I'm not sure what it means exactly.
Maybe throwing some solder on the ends of the plastic helps the adhesion process a bit??
I'll have to find out, & report back here with my findings. Maybe it was just team slang for the heating process we used in the past? Not sure.

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

if you want the Green belting, the 6mm stuff is the same but in Green. Part #8112K33

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

The belts are separating while carrying the ball, and the ball is getting stuck.

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

Maybe increase the tension in the belts?

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

Try increasing the tension in the belts.

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

are there grooves in the pulleys?? if no, then add them....if yes, increase tension

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

Depending on the length of your belting (especially using thin poly cord), you will need extra rollers in the middle. Or you can just use some thin 1/4" AL rod to support the belts from flexing inward too much. Belting takes a lot of tweaking and babying to work perfectly.

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

Has anyone tested the green rough type belting vs. the orange or clear not-as-rough types? Any opinions on either of them?

Also, from everyone's testing, what seems to be a good minimum spacing between your belts for this year's game?