Poly Cord

[Ian Curtis]

Originally Posted by squirrel

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?

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

[Drivencrazy]

Originally Posted by DoctorMagazine

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

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.

[Bruceb]

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

[Chris is me]

Originally Posted by Jared341

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.

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.

[chadr03]

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.

[Ninja_Bait]

Originally Posted by Bruceb

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

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.

[JCharlton]

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.

[David Hoff]

Originally Posted by Chris Fultz

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.

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

[waddell]

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?

[artdutra04]

Originally Posted by waddell

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?

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.

[cmwilson13]

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.

[Tom Line]

Originally Posted by squirrel

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.

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.

[MrForbes]

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

[Chris Fultz]

Originally Posted by David Hoff

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

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.

[Chris Fultz]

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.