polyurethane tubing
 

after seeing some of the designs at our regionals, we would like to redesign our ball - lifting mechanism using the polyurethane tubing. Can anyone make a recommendation on sizing and/or type? We were told to get it from McMaster-Carr.
thanks,
elaine

Re: polyurethane tubing
 

Hope this helps:

http://www.mcmaster.com/#round-belts...-belts/=19dc3a

You most likely want round urethane solid core belting.

Re: polyurethane tubing
 

Team 234 uses McMaster P/N 59725K803. It is kind of expensive, but has lasted two comps with no problems.

In the future, searching may get you a quicker response.

Re: polyurethane tubing
 

We're using the yellow 1/4 inch polyurethane shingle routhane tubing from McMaster. Make sure you buy the barbs that hold them together. Don't pay for the $300 welding kit or try to weld them yourself because you'll have belt failures and it's EXPENSIVE.

We have them cut about 10% shorter per foot to make up for stretch. We also have spans of no more than 1.5 feet between rollers.

We've had 0 belt breaks, so they work :) .

Re: polyurethane tubing
 

The kit is not necessary to weld the belts, it can be accomplished with a lighter, soldering iron hotplate etc, and when done with some care will not break on you

http://www.chiefdelphi.com/media/img...b7b10cca_l.jpg

see also the god of polycord:
http://www.chiefdelphi.com/media/photos/33403
all welded i believe, i'll let Adam chime in on that


yeah...lol its good stuff

Re: polyurethane tubing
 

We've had a few teams come to us and say that they've tried the lighter method and had belts break on them.

Pay a few bucks for the barbs and you'll save yourself time in the build process and stress later.

Re: polyurethane tubing
 

I second what HighLife said - The hollow core 1/4" McMaster-Carr Polyurethane Belting (6567K57) and the associated connectors (6567K22) are the way to go in terms of belting. Quick, easy, and relatively cheap.

(That bit about keeping the spans between rollers short is crucial to note as well - We had a 40" run and the bands flexed too much, even with cutting them shorter)

Re: polyurethane tubing
 

We have spans of about 4 feet (80 total inches of belt) running moon roks from the floor to our top "hopper". On our practice bot, we did the "welding" ourselves. This is with solid core belting. Through hours of practice, we have had no problem with belts breaking. You just have to take your time and give the weld time to set. It can be done.

Re: polyurethane tubing
 

We used the 3/8 inch, clear, hollow core tubing and joined it with the barbs. We have had the barbs pop out, so we added duct tape after that incident, and haven't had any problems since. We are also using 3" diameter plastic pulleys for the 3/8" belting.

I had to manually create a key/set screw hole in 2 of our 4 pulleys on the drive shaft, but it was pretty easy to do, even with a hand drill.

Re: polyurethane tubing
 

mcmaster carr has several smaller sizes in stock and they ship in a day or 2. custom made lengths take about a week.

they recommend an 8 - 10% length reduction from actual dimension to belt, and there is a limitation on belt diameter and roller diameter.

we have been using both styles (our fab and custom made).

Re: polyurethane tubing
 

We used the green belting from McMaster and did the welds with a heat gun. The ones that failed failed long before we put them on the bot. However, knowing what I know now, I'd get the hollow tubing and barbs. It can be installed to replace a broken belt without disassembling your robot. Our runs this year were pretty long and because we wanted to make sure the bands did not flex much, we shortened the band by the recommended 8%. Our bands ended up too tight and placed way too much load on the motor. We probably destroyed a CIM that way.

Re: polyurethane tubing
 

We use an industrial heat gun to weld the tubing together and put it in water to get it to set a little bit faster. You have to let it sit at room temp for 5-10 minutes and then the weld should be as strong as the tubing itself. It's incredible stuff, but I would reccomend experimenting with welding it together.

Re: polyurethane tubing
 

Thanks for listing the part numbers and sorry, forgot to tell you about the span issues. :P

Re: polyurethane tubing
 

We welded them with a 120 watt soldering gun, with a small flat plate bolted to the tip. All welds were 'student destructive tested'.... the students could not pull them apart.

No failures at the welds.

Re: polyurethane tubing
 

We used the Mcmaster-carr hollow 1/4" belting that was mentioned before. It worked well for us and none of the barbs pulled out. I think it was worth it to use the hollow belting because you can run the belts while the rollers are mounted on the robot. With the welded ones, you have to remove all the rollers if one belt snaps for what ever reason. Also, I saw other teams who had solid cord on their 'bots and unless the team used a welding kit or similar, the welds would be blackish/discolored and the heat would deform the belts slightly causing them to bump around and not be as aestetically pleasing. Pretty much the hollow cords look cleaner when done quickly and are easier to adjust. My $.02

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.

Re: polyurethane tubing
 

We used 1/4" hollow tubing from McMaster joined with barbs and we've been very happy with it. We've only had one failure, but that was on a belt that had been used for dozens of hours at a very high speed (it was also stretched a little too...aggressively). For a re-fit, I would HIGHLY recommend the hollow tubing, as if you need to adjust the tension you can easily insert or remove sections of belt in seconds.

Re: polyurethane tubing
 

Team 2228 used the hollow yellow polycord from McMaster with the barbs. Package of 25 was about $5 and we reuse them. The polycord was $1.12 per foot. I second the warning on the amount of stretch you apply. We found 8-10% way too much, particularly if you have a lot of belts loading the motor shaft. We found about 3% did the trick and reduced the motor torque load. I would suggest bearings on the shafts, particularly if you have a lot of belts or stretch them aggressively.

Re: polyurethane tubing
 

Fron Anyheck:

Our feed system uses 50 total (10 sets of 5) of the polyurethane belting o-rings to pick up and transport balls. Over 125 FEET of belts. We're using 1 CIM to drive the feed system. We used the 1/8" belting because we had already made all the rollers for a rubber o-ring sytem that didn't work. You'll recognize the robot from the Bayou Regional, team 2992, the red turreted shooter with the flaming ball on the side. Lots of pics of the belts on the website, http://team2992.com







We run the feed system continuosly and it will hold 12 balls. The balls are controlled with belts on both sides so there is no relative motion between the balls. The belts slip until the "gate" opens and allows the balls to feed the turret. Belts are melted together with a cigarette lighter as described by others. We had no jams or broken belts during the Bayou. We were running the feed system at 2 feet/second (600 RPM on 3/4" diameter rollers) to give us a feed rate of 2 balls/second at the Bayou, we're going to double it for the Championship.

Contact me if you need anything, I'm in Slidell.

Re: polyurethane tubing
 

One aspect I never realized before, this is an upgrade to do at champs. No time to really tweak or test.

I'd go hollow with barbs, cut them long, say, for 3% stretch. Test. Need more stretch? try 3.5%. That's a really easy fix with hollow.


You guys are rookies :ahh: :ahh: :ahh:

Keep up the great work, that's simply fantastic.

Re: polyurethane tubing
 

Using the pheumatic tubing would be a much easier change them trying to weld some belting together. Mcmaster sells the barbs needed to connect the end of the pheumatic tubing.

Re: polyurethane tubing
 

We've got you beat at 220 feet of tubing. ;)

Re: polyurethane tubing
 

We've got you beat at somewhere between 300 and 350 feet. We know the exact amount, but are keeping it secret for now.

We'll be having a guessing game in our pit for a prize.

Re: polyurethane tubing
 

The only problem with the peumatic tubing is it isn't very stretchy, so it would be hard to get it to put enough force into roller to have enough friction so it would actually turn with the roller.

An alternative would be surgical tubing. My team did some prototyping with it and it worked very well. We went with the polyurethane belt instead, but I would still say the surgical tubing is a reasonable option.

Re: polyurethane tubing
 

I have used your own tactics against you and have created a spread sheet that gives me an exact number that may or may not be within the range you have stated. Take that, guessing games that I can never win! :ahh:

Re: polyurethane tubing
 

How do you figure? We have two drive rollers in the center, and coming off of them are tubes going up to upper idler rollers as well as lower idler rollers. We have no issues at all driving them. We specifically used the pneumatic tubing because it does not stretch as much as other types of tubing does.

Re: polyurethane tubing
 

I'd have to agree:D Polyurethane tubing stretches after long use(usually goes back to its original form later) and surgical tubing...it's surgical tubing and is not very fun to watch snap during matches because attaching the ends isn't an exact science.

Re: polyurethane tubing
 

I'm curious to how it would perform at speeds many other teams had their conveyors running at. Also, curious about the relative efficiency.

Did you use stock globe gearboxes? and what was your pitch diameter?

Re: polyurethane tubing
 

They use stock globe motors attached directly to the rollers.

I think that if rollers were run at higher speeds, the pheumatic tubing would be less effective due to the lack of stretch that it has. Probably just end up locking up the motors, or the tubing would be too loose.

Re: polyurethane tubing
 

It doesn't perform at speeds similar to other teams.

The Globe's are unmolested and the rollers are 2 inch od. if I recall.

Re: polyurethane tubing
 

This is interesting to me. My team used 5 foot lengths of the polyurethane belt and it needed to be at least cut 5% shorter to have proper tension. We powered the bottom rollers and had a roller at the top and two more idlers in between. The only problem we seriously encountered in prototyping was not enough tension, and with the pneumatic tubing, we simply could not get that tension. It is also important to keep in mind that we were using and FP with a 6:1 reduction. Our conveyor system was very fast and without proper tension it lends itself to belt slipping. We had 2 inch rollers as well.

Re: polyurethane tubing
 

Thanks so much for all your helpful suggestions!
hope to see some of you at the WPI event in May.
dr. p

Re: polyurethane tubing
 

Our center rollers are powered, so when tension is applied to the top and bottom sets of idlers, they stay true. The only problem we encountered was too MUCH tension. But since we use barb fittings to hold it all together adjustments are very simple.