Poly Cord

[Ian Curtis]

Originally Posted by Chris Fultz

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).

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)

[Tom I]

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.

[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.

[Drivencrazy]

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.

[Tom I]

Originally Posted by Drivencrazy

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.

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

[RoboCat2005]

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

[mathking]

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.

[JellyMan]

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?

[Jared Russell]

Originally Posted by JellyMan

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?

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.

[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.

[MrForbes]

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.

[Phyrxes]

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.

[Ian Curtis]

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.

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

[MrForbes]

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?

[DoctorMagazine]

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