Poly Cord

FIRST General Forum
1

Where is the best place to get the poly cord that a lot of people used in 2006?

Also:
How well did it work in roller system for picking up the balls in the 2006 game? I was not around for that game to much.

2

Look up urethane belt on mcmaster.

3

http://www.durabelt.com/roundoringinfo.php

This is the company that makes the stuff. Look for distributors in your area or on-line.

HTH

4

From McMaster-Carr: link

This is what we used in Lunacy.

5

We ordered ours from McMaster. It worked well. There are some guidelines on measurements and what to order and if you follow that it worked very well. (There is a recommended stretch).

6

Do you guys order specific lengths or do you order extra and cut to length? If you do the latter then do you use those quick connect fittings or do you weld them together?

7

we used it in 2009 and ordered extra to cut to length (built 4 duplicate robots that year that were all a little off from each other). to hold them together we welded them with a lighter and then used a sander to shave off the excess bumps that formed from pressing the two ends together. if you go with welding the ends let the cord sit for a couple hours after heating to let it fully set.

the extra was used to whip the engineer in charge of designing the robot because of how much “fun” it was to put on the robot.

8

We have used the same technique on all our robots using round or flat polycord. (04, 06, 08, 09, 11)

9

We used the solid polycord from McMaster in 2009. We created a jig and purposed an old soldering iron as the heating element to fuse the ends together, as was previously stated the stretch factor is important.

10

We used a piece of steel angle as a jig, clamping the two ends together. We used a creme brulee torch (a small butane torch) to heat the pieces together. As was pointed out earlier, they then need time to cool completely before they are used. Also, be really careful when you sand or cut off any bubbles or bumps. I recommend practicing on a few short bits. One of our mentors and one student became very adept at the welding, so we had one of them do it whenever we replaced the cord.

Side note: If you use polycord that needs welding, you are going to want to have a bunch of replacement lengths already welded when you go to competition. (In general no open flames allowed in the pit area.)

11

We used hollow with connectors for Lunacy and never had a single failure.

12

Same here

13

Oh…it’s called “Urethane Round Belting”, not poly cord.

14

The recommended stretch 10% is pretty overkill in my experience with the 3/8 solid. If you have more than three or four belts it takes a huge lever arm to get things to line up, and you take a huge performance hit from the all the friction in your bearings. We found 5% much easier to work with, and we even did 3% with no difficulties. (Though as a precaution we shipped the robot with the 3% belts removed so they didn’t stretch over time)

15

My team used solid core round belting belting material in Aim High and it worked very well for us, but it was a BEAR to melt together. In Lunacy we switched to the hollow core tube belting and used the metal barbs that came with it, and that worked just as good, no failures.

There’s a big discussion about the use of polyurethane round belting here if you’re interested.

16

What OD’s did you guys use in the hollow and solid applications? I would think somewhere around 1/4" would be sufficient but then again I’ve never used them before.

17

Yeah 1/4" is what we used. It’s the standard cheap yet effective stuff you can get from McMaster and other places

18

Are there advantages/disadvantages to using solid as opposed to hollow tubing or vise versa?

19

Speaking as someone who was on a team which had little trouble with the solid core, I think the hollow core with connectors is the way to go.

  1. Easier to work with at competition (don’t need heat source)
  2. Less time consuming (no waiting for cooling)
    We used the solid core largely because we had some, tried and it worked. So we had no reason to try the hollow. I have no idea if one of the two variations is more robust than the other.
20

Thanks everyone for the info concerning the “polycord”. I will be placing an order for the 1/4" hollow Urethane Round Belting and barbed connectors.
Two more questions:

  1. These round belts in are normally used multiple loops. So, are you machining custom rollers with multiple grooves, or are you stacking off-the-shelf pulleys? Is there a material of choice for the rollers. I suppose aluminum, UHMW polyethylene, or even wood could be used.
  2. If we use the barbed connectors, are these actually reliable? Has anyone tried melting the ends in addition to the connectors? Is this overkill?