Polycord Pulleys

[Cothron Theiss]

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.

[George C]

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.

[Lil' Lavery]

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

[gerthworm]

Originally Posted by Max Boord

3d printed pulleys work well depending on infill and load.

They worked decently well for us this year!

[BrendanB]

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.

[hectorcastillo]

Originally Posted by TheRozb

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

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

[Michael Hill]

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.