Polycord Pulleys
 

Hey Everyone,

Where do you source your polycord pulleys? We need some that will go onto 1/2 inch hexshaft. Do you just make your own in house? I've done some Google searches but not much luck...

Thanks

Re: Polycord Pulleys
 

Re: Polycord Pulleys
 

Not the polycord itself, but what it sits on.

Thanks

Re: Polycord Pulleys
 

2815 used polycord in 2009 and 2012. Both times, we used some ABS or Delrin rod from McMaster, cut the necessary grooves on a lathe, then broached it for 1/2" hex.

Re: Polycord Pulleys
 

We used a lathe to throw some grooves onto these. http://www.andymark.com/product-p/am-1305.htm

Nowadays I'd just 3d print them

Re: Polycord Pulleys
 

PLA? ABS? Is it strong enough to handle the force?

Re: Polycord Pulleys
 

Are the "necessary grooves" just a semicircle of the correct diameter, or is there more of a trick to it?

Re: Polycord Pulleys
 

If you have access to a 3D Printer you could design and print them.


In 2016 we used PLA Pulleys (with a 10-15% infill) and there were practically indestructible. Through the entire season we only broke one. The one we did break was destroyed by smashing it with a hammer.

Re: Polycord Pulleys
 

As I remember it, we went a little deeper in to ensure enough contact between the drive axle and the cord--but that might be just voodoo for us. You can always wrap a little wedgetop or roughtop around the outside for extra grabbing, if necessary.

I'd definitely keep the width at or below the width of the belt itself, to keep them from walking or having more room to deform and let something by.

Re: Polycord Pulleys
 

We've made a lot of these. It needs to be a deep channel - polycord is sticky and likes walking out if you put any side load on it.

However, consider using flat polycord belting. Round polycord slips even when it's very tight. Flat belting doesn't. And with the belting, you can just build up a high spot on the roller using anything you like - tape, rubber o-rings, etc. and the belt will keep itself straight.

Disclaimer: belt can be much harder to weld than cord.

Mcmaster sells round belt pulleys.
https://www.mcmaster.com/#round-belt-pulleys/=1525gp9

Re: Polycord Pulleys
 

3d printed pulleys work well depending on infill and load. 179 used them to transfer load between the middle to front and back rollers and had to wrap them in duck tape to get enough friction to transfer the load effectively. on 4592 we ran 2 775pros on our intake with quite a bit of compression and found a need to replace a pulley or 2 every match due to cracking however this should not be an issue in most situations as most of ours where broken by hitting other robots and the middle CDF plank. The best solution we found was to run loads of them (i think we ran 7 to 11 depending on the revision of the intake) and be ok with running with a few missing/ broken.

Re: Polycord Pulleys
 

We have been 3d printing custom designed pulleys for prototyping with polycord when the time arises. I can attest to the need for making the grooves deep. The belts will run off the pulley or slip off with side loads if the groove is not deep enough.

The information other people have already posted is a great resource for you as well.

Re: Polycord Pulleys
 

Back in 2012 when my team used polycord belting, we just lathed up some delrin and it worked fine.
I would imagine 3D printing would work just as well if you can; the pullies aren't going to be under particularly high stress.

Haven't seen it mentioned yet, but be aware that over the season, the polycord will stretch and you'll have to have some extra made for replacement. Or have a system to de-tension them between matches to help the lifespan.

Re: Polycord Pulleys
 

One very successful method is sandwiching a banebots wheel between two polycarb discs. I know 1741 used it for their intake this year.

Re: Polycord Pulleys
 

Team 423 used VexPro 3.25" VersaWheels one next to each other as an intake last year. The gap between the treaded parts of the wheels is .370" which is the perfect size to hold in 3/8" poly cord (I think it was 3/8 but it may have been one size smaller). They occasionally would walk into the next groove over if they got a lot of side force but for the most part they worked like a charm. On the other end, we used a piece of PVC tube with slices of a larger PVC tube screwed into it to create grooves. If you don't have access to a lathe or 3D printer, PVC tubing is very versatile and you can find it in almost any hardware store.

Re: Polycord Pulleys
 

If you check out team 188's intake from this year, I believe they put small Colson's on a lathe and cut out a pretty deep groove for the polycord. It looks nice and very effective, though it's probably a bit of an expensive solution if you have access to a lathe or a printer.

Re: Polycord Pulleys
 

3 or 4 years ago my former team needed quite a few of them about dia 3". We had access to a lot of scrap pieces of 1" thick sheet UHMW. We rough sawed them round on a band saw, drilled a dia 1/2" hole, broached it to hex and then mounted the resulting blank on a piece of 1/2 hex shaft chucked up in a lathe. A hex shaft collar held it in place against the chuck jaws. As the UHMW is so soft, we were able to turn them to diameter in one (maybe two) pass. I ground a HSS cutter to profile - radius plus to match the dia of the polycord plus a taper back on each side to encourage the polycord to stay in its slot. Again, because UHMW is so soft, we were able to feed straight in to depth. If I recall, we used 1/4" polycord and went in about 1/2".

Some had to go on a round shaft so we left the hole round, broached a keyway and used a piece of keyed shaft for the mandrel. Some needed a set screw so we left a hub on the pulley and drilled and tapped for a grub screw.

It was cheaper than buying round bar and parting off pieces.

Re: Polycord Pulleys
 

This thread may be of interest. This post describes the method 1712 had used in the past for creating our rollers/pulleys.

Re: Polycord Pulleys
 

They worked decently well for us this year!

Re: Polycord Pulleys
 

We made custom pulleys using some acetal we found at a local plastics company. With several lathes and willing students it took some time but the learning experience was valuable. Not the most efficient process for making polycord pulleys but we liked them. Walking out is an issue but we wrapped some cable in between our pulleys & wheels to fill the space so if they walked out they would still function.

I was a fan of how 188 did theirs. It looks like they just cut a groove into some of the colson wheels from vexpro.

Re: Polycord Pulleys
 

We primarily used aluminum tubing with hex shaft caps pressed into the ends and gum rubber wrapped around the outside. You can wrap the gum rubber around a couple times to get your desired diameter. Make sure to put a hex shaft through both caps while you press the second one in so that they are properly aligned. We used super glue for the gum rubber, and it held well throughout the season. You can also press bearings into the ends if you want a free-spinning roller. All you need machine-wise is a band saw and an arbor press or shop press.

Aluminum Tubing: https://www.mcmaster.com/#89965k741/=152mo6j
Hex Shaft End Caps: https://www.competitionrobotparts.co...oller-end-cap/
Gum Rubber: https://www.mcmaster.com/#93625k158/=152mt6p


We also use small BaneBots wheels partly because they were just lying around in our shop, but mostly because they gave us the right diameter we needed.

BaneBots Wheels: http://www.banebots.com/category/T40P.html

Here's are some pictures of our robot that show our intake and indexer. Hope this helped.

https://drive.google.com/open?id=0B7...Hp2ZFczM0p2UU0
https://drive.google.com/open?id=0B7...mt6OElubzc3X0U
https://drive.google.com/open?id=0B7...lhrUGJiekFFdWc

Re: Polycord Pulleys
 

We used these on our intake: https://www.mcmaster.com/#5234k92/=152mzbr

Once we mounted the rubber tubes on the aluminum inner tubes, we chucked it up in the lathe and took a super sharp razor blade to cut grooves. It worked fairly well for us, but in the future, we'll probably use slightly larger than the 1" aluminum tube because the rubber tube sections tended to walk a bit. To drive the intake from a 0.5" hex shaft, we bought some aluminum .5" hex gears from Vex and turned the teeth off to make them fit inside the tube (we do not have an arbor press or a hex broach, so this was our poor-man's solution). We initially tried a press fit, but I think we resorted to either bolting it or using a roll pin.