Re: polyurethane tubing
 

I would recommend the 1/4" solid core McMaster-Carr Polyurethane Belting. We used it on our robot this year for the first time.

http://www.chiefdelphi.com/media/photos/33401

For all of the people that have had problems with their welded joints failing, I have a feeling that you are not melting the Polyurethane Belting enough. We tried welding with a hobby hot knife and soldering Iron with flat tipped blade, but found that it was only melting the edges of the belting. For the belts on our robot, we used the the blue flame of a candle (the orange flame will char the belt leaving ugly black marks). We then took the hot knife and smoothed the polyurethane that squeezed out of the joint (My mom calls this frosting the joint).

As others have said there is no need to buy a jig. We made our own jig by putting a 1/4" slot in a piece of 1/2" thick aluminum stock. The aluminum acts as a big heat sink too.

We bought a considerable amount of extra belting because we had heard of failures. Fortunately we have had no joints or belts break.

Ryan

Re: polyurethane tubing
 

We used a simple fusing technique and have never had any belts break on us despite attempting very hard to do so. We created a simple mold by drilling a hole through a delrin block then cutting it into two halfves down the center of the hole. We then heated the two ends of the cord with either a lighter or soldering iron, placed it in the mold and applied presurre for about a minute.

Re: polyurethane tubing
 

Welding the solid core takes a little practice to perfect, but once you get it down it will not break. We've found that once you melt the ends together and wait five minutes, if you pull on the joint really hard and it doesn't break, it won't break on your robot.

Re: polyurethane tubing
 

We welded the solid orange polychord with a standard propane torch.

Just melt both ends that you want to connect
Place them in a piece of Angle Aluminum, with the two ends in contact.
Hold for 5-10 minutes till cool.

This resulted in a weld that was strong enough that two people doing tug-of-war could not rip it.

The welds might not be the prettiest, but they work amazingly, and don't jump off of our pulley's

If I remember correctly, the polychord on our bot had a tension of somewhere more than 30%. (I think I remember it being 35%, but I might be wrong.)

Re: polyurethane tubing
 

We used the orange solid core from McMaster, heated both ends up with and clamped it with an old ribbon cable crimper that had some small angle added to it. to keep things lined up.

Re: polyurethane tubing
 

Here are some intersting tables on Rounthane. Notice that you can see the extra load the stretching will put on your motor, which guided us into our new conveyor motor setup for Atlanta. Previously, we just guestimated everything with conjectures that a motor would or would not work. This data, PINK's recommendation, and the lack of necessity to weld the belting are all of the reasons we're redoing our conveyor with it for Atlanta.

Quick question though -- is the polyurethane cord on McMaster the same as the Rounthane? Usually mcmaster mentions the brand name, if there is one, in the product details.

Re: polyurethane tubing
 

If you are attending nationals, you can find 744 SHark Attack. We used a lot of belting this year and Ralph, our electrical lead, is an expert belter. He does almost all the belting at him company. Feel free to stop by, we melt them simply and they have not broken for us yet.:D

Re: polyurethane tubing
 

My team used the 1/4 inch clear polyurethane tubing from mcmaster. I constructed a welder out of these parts listed:

Materials:
-one 6-inch piece of KOP C-Channel(cut out notches on each side where the holes are lined up so that the belt can be taken out once it is welded)
-squirt bottle WITH WATER!
-Heat gun
-pair of nice channel locks
-piece of flat bar(used for rolling the belting to create smooth weld)

Process:
1: cut an access whole on each side of the c-channel so that each end of the belting can touch and be pulled out with ease(when it is connected).
2:Have one person hold each side of the belting slightly spaced apart while another uses the heat gun to start a slight melt on each side of the belting(person holding the belts might need some gloves if you have sensitive hands :D )
3: As the belts start to look "melty", push them together and continue to heat to the point when the ends of the belt reach its melting point, then remove the heat.
4: Use channel locks to squeeze the belting smooth and squirt with water to cool it down so it can retain its shape.
5: Place belting on flat surface and roll it with the flatbar(works nicely if it's cold), I usually rolled in once forward, and once back.
6; Now, brag (graciously) about how successful a weld you have without spending 300-400$ on a belt welder:D :D :D

We were able to weld 30 belts in about 45 minutes(including a snack break). It might take a few tries to master, but the welds will turn out really nice, almost as if you bought a welder to do it for you.

Re: polyurethane tubing
 

I have no experience with this material. Does its texture allow some slip on the balls, to avoid jamming them together when they are 'queued' in your conveyor systems.

We used rubber surgical tube and it had nothing but grip, so we had to keep the balls spaced out well to avoid jams.

I wanted to find a semi-slippery material to re-work the belt system just for the experience.

Re: polyurethane tubing
 

we found that the 1/4" hollow core worked quite nicely and could be asssembled in place. that might be my choice for quick fixes and retrofits.

Jason

my first post from a cell phone... isn't technology coool?

Re: polyurethane tubing
 

This stuff is excellent as semi-slip material. It isn't grippy like rubber surgical tubing, but the problem is that it may not pick up as quickly (in my experience-we put tread on our bottom rollers to aid pick up). You can pretty much jam balls down our hopper and then pull them out just as easily.

Going back to the welding discussion, 766 used the yellow hollow cord this year, and we just welded it together with a heat gun. We held the ends in the heat until they melted slightly and put them together when melted, waited for cooling and dremeled (with that sanding attachment) the surrounding blobs off. In two regionals we've never had any loop break.

Technology is cool!

Re: polyurethane tubing
 

I just changed my usertitle thanks to your inspiriration Aren.


Well, pretty much; I don't see any reason not to do solid core. We bought our 1/4" for $0.60 a foot, just try to beat that with prewelded or the barbed kind.

In terms of welding, we just use a soldering gun with a flat tip, and initially used a jig that was thick aluminum plate with a 1/4" groove. We would've done all that way but found just the jig from the welding kit on ebay for $50. The jig made it easier to keep the waste material consistent, and made the process faster. With 74 belts per robot, and changing center to centers along with stretch several times, it added up.

Our process has always been this. Cut to the length we desire (we made an excel where we put in waste material, desired stretch, and pulley Center to center... it spits out what length to cut to) melt the ends nicely, squeeze together (same process for both plate and jig). We end up with a good deal of excess material around the weld, we initially trimmed it with dykes, but in a moment of laziness I found a belt sander with fine grit works GREAT.

I've strength tested every belt welded myself, the kids think it's because I'm fearless, I think it's because I'm stupid. So far, only ones with obviously poor welding have broken, and only 2-3 at that. As shown by Billfred, I tested HARD; usually by stepping on one end and pulling up with both arms.



Sooooo. In other words, we'd do the same thing in the future.

Re: polyurethane tubing
 

Another material to keep in mind for belting this late in the game, is pneumatics tubing. We kit sized tubing, and connected it to itself with barbs. We haven't had a single failure, and if somehow we ever ran out of tubing, replacement tube wouldn't be hard to come by!

Re: polyurethane tubing
 

Yeah, pretty much what AdamHeard said, except for the spreadsheet.

Re: polyurethane tubing
 

For size, you shouldn't need anything thicker than 3/8, my team used 5/16 and it is proabably what I'd recommend. A hot plate is what I would recommend for attaching them. If you need to fix them while they are on the bot I'd use heat gun. Most people say let it cool off before you put tension on, this is very good advice. Try not to stretch before it is completely cooled down, probably about 1/2 an hour to an hour. If it's in the heat of competition, get some Dust Off, and spray the belt, it should decrease the cooling time exponentially. I'd use PVC pipe for the rollers. Get some Sched 80 2 or 3 inch Diameter, and cut about a 1/8 inch groove everywhere that you want the belt to go. Then I'd take a piece of PVC whose ID is the same as the original one's OD and put two thin pieces on either side of each groove to further prevent slipping.