Poly Cord
 

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.

Re: Poly Cord
 

Look up urethane belt on mcmaster.

Re: Poly Cord
 

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

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

HTH

Re: Poly Cord
 

From McMaster-Carr: link

This is what we used in Lunacy.

Re: Poly Cord
 

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).

Re: Poly Cord
 

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?

Re: Poly Cord
 

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.

Re: Poly Cord
 

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

Re: Poly Cord
 

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.

Re: Poly Cord
 

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.)

Re: Poly Cord
 

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

Re: Poly Cord
 

Same here

Re: Poly Cord
 

Oh...it's called "Urethane Round Belting", not poly cord.

Re: Poly Cord
 

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)

Re: Poly Cord
 

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.

Re: Poly Cord
 

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.

Re: Poly Cord
 

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

Re: Poly Cord
 

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

Re: Poly Cord
 

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.

Re: Poly Cord
 

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?

Re: Poly Cord
 

Our team has used hollow poly cord a couple of times.

1) You can do either. In the past we have generally stacked pulleys (either COTS from McMaster/SDP-SI or homemade), but a single roller with multiple grooves can be a more elegant solution. I have seen various plastics (UHMW and ABS mostly) turned into roller/pulleys on a lathe, and that works well for many.

2) We have only ever had problems with barbed connections when people got lazy and made poor quality cuts. As long as you make sharp, flush cuts and fully insert the barbs, you will have no issues.

Re: Poly Cord
 

we used the custom made ones. There are about 30 on our Lunacy robot (4 different lengths). we still use the robot for demos. none have broken.

I think we used either the 1/4 or 5/16th diameter.

Re: Poly Cord
 

We're seriously considering using the round belting for a mechanism this year. One of the ideas I have in mind I either saw or heard about in the past, is to use something like 1.5" nominal ABS sewer pipe, and put short sections of 2" pipe, split lengthwise to make it just a little smaller, over the 1.5" pipe, leaving a short gap wherever a bolt goes. The outer pipe sections could be screwed to the inner one. The inner pipe would be supported at the ends by caps with bearing holes bored in the center, and a sprocket would be screwed to one end of the pipe.

Re: Poly Cord
 

Our lunacy bot used in house constructed PVC rollers (schedule 80) where the endcaps were drilled out to accept bearings and then it was glued together. To act as guides we sliced sections of PVC that had an inner diameter the same size as the outer diameter of the roller and glued them in place.

Last years roller claw used COTS aluminum rollers that someone found on McMaster.

Do be mindful of the span of your plastic rollers if you use them and how much tension they are under.

Re: Poly Cord
 

The coolest solution we ever came up with was to take a piece of thin wall aluminum tubing and mount four roller bearings on the robot and sit the tube on top of them. You can do it upside down too, the polycord pulls the tube against the bearings. We used the lexan "fingers" you can see to hole the belting in place, we never had a problem and in retrospect they could've been much smaller.

Picture

Re: Poly Cord
 

That's a neat idea! You could use just about any kind of tubing with that design, as long as you can figure out how to drive it. Would another section of poly cord work as the drive system from the motor?

Re: Poly Cord
 

Our team was considering using surgical tubing instead of polycord to pick up balls. Would this work?

Re: Poly Cord
 

This is what we did here. PVC center, larger diameter PVC outer. Caps in the ends with bearings inserted.

http://www.chiefdelphi.com/media/photos/33017

Re: Poly Cord
 

We did essentially the same thing as 234 in 2009, but with a different size PVC. Here's the best picture I could find where you can really see what's happening.

http://www.chiefdelphi.com/media/photos/32480

Re: Poly Cord
 

We essentially did the same as 234 and what Sean posted.

I would look at thin wall aluminum piping in your application for rigidity. The amount of tension on those belts tends to bend PVC over longer lengths. We put in a plug that sat in the middle of our PVC pipes to help keep the pipe itself from bending. It mitigated the problem, but if I were to do it again, I'd go aluminum.

-Brando

Re: Poly Cord
 

Yep. That's how we did it, and how we drove almost all of our prototypes. :)

Re: Poly Cord
 

Yeah I think it will. We used surgical tubing on our 2009 robot. The great thing about surgical tubing is its ability to stretch a lot which makes it pretty easy to work with because you don't have to cut it very precisely but it is tough to join the ends together. We used a plastic version of the McMaster connector and added some super glue. The bad thing about surgical tubing is that it did seem to wear out quite a bit and I think we had to replace it once at each event we attended.

We are going to try out some solid 1/4" Polycord this year. It looks like great stuff. I just hope that it lives up to its acclaim.

Re: Poly Cord
 

Polycord is GREAT never wears out and if you join it properly it will stay together forever.
Trick
Cut the cord 5% under length and cut the ends at a long angle. Then. Take a piece of aluminum and clamp it in a vice. Have someone hold a propane torch against one side and press the ends of the cord against the other side until you see it melt a good bit. Remove them from the heat and press them together. Hold them together until the joint cools. You get probably 90 percent of the joint strength in 10 minutes but for best results let them sit overnight before streching.
Bruce

Re: Poly Cord
 

Can verify all of this, but for a 2009 ball intake system, with very long belts, stretch was much more of an issue than with solid systems. Retension belts about every event or so.

Re: Poly Cord
 

Did you use a drive pulley manufactured for poly cord belts, or make one? It looks like some of the drive belts are made out of a piece of pvc pipe with spacers or something similar. It looks like it could get pricy quick to buy multiple drive pulleys.

Re: Poly Cord
 

We found that this worked even better when you took a block of metal and drilled a hole to match the cord diameter, cut it in half and used it to clamp the polycord at the joint. Then you don't end up with misshapen joints.

Re: Poly Cord
 

Urethane belting was a fantastic find. We've used it every year since 2008 for various mechanisms with no failures, solid core mostly 1/4". You can easily make your own pulleys cutting a 'V' groove on a lathe (no need to make a round groove, a V works great.)

One important hint: You should NOT USE A FLAME as the fumes from burning urethane are toxic. Use a heat gun (expose only the ends to the heat) or soldering iron. The ends will get molten, push them together in the corner of an 'L' angle and wait for it to cool. Start long, you can trim a bit out later if needed.

Re: Poly Cord
 

Chris, to clarify, did you use the clear O-Ring style urethane belting shown here?

Re: Poly Cord
 

We're considering running 1/4" solid or hollow on smaller diameter pulleys than what is recommended in McMaster? For instance 1.5 inch rather than the recommended 2 inch for the 1/4 solid.

Has anyone tried that and been successful ......or had issues with connections failing?

Re: Poly Cord
 

In FRC, you can run polycord around smaller diameter pulleys/rollers than is recommended without any problems.

These cited minimum values are for long-term operation, and FRC robots literally only see dozens of hours of run time over the course of a season. Over the lifespan of a FRC robot, running polycord over rollers 0.5" to 0.75" below the minimum recommended values shouldn't cause any problems as long as the polycord was fused together properly.

Re: Poly Cord
 

welding is defiantly the way to go.

use a heat gun to melt the ends stick them together and run water over it. in 30 secs it will be ready for use. idk why other teams say wait hrs its not like glue its molten plastic once it cools its ready to go.

Re: Poly Cord
 

Squirrel - check out pvc pipe. There is a schedule 80 pipe who's id is the same as the od on a schedule 40. You can cut small pieces of the 80, then force them over the 40 to act as guides. I believe is was 3" or around there for the schedule 40. In this way, you don't have to even use fasteners or glue. Just the friction holds it very well.

Re: Poly Cord
 

Neat idea...we'll see if we need it. For now we have a comb thing working reasonably well.

http://www.youtube.com/watch?v=KB9IiNlYZm8

Re: Poly Cord
 

We used this to build the prototype -
http://www.mcmaster.com/#about-belts/=fwr5sl

And the ones referenced at the top once we had the final design and dimensions.

Re: Poly Cord
 

For Lunacy, we used 1-5/8 OD PVC with 1/4" belting, slightly smaller than recommended.

We took the couplers for joining sections of the pipe and cut them in half and used them as spacers for the belts.