Interesting I assume those are machine lathed. But from what material?
Appears to be some sort of plastic…
Interesting I assume those are machine lathed. But from what material?
I assume delrin, because of the title. 
Photo title says delrin. It’s a good all around plastic that doesn’t wear when using polycords. It’s a bit heavy though.
Wow its sorta like looking for the 7/16’s wrench in the shop. It always appears in the most obvious place.
Is it actually Delrin?
Hope that there is never enough friction generated to melt/burn the Delrin, the fumes/smoke it gives off is like tear gas
Hello all,
These are machined from Delrin 1inch stock.
They weigh about .3lbs each; which we found to be reasonable for the pulleys and a LOT lighter and cleaner then our last solution.
Delrin is pretty stiff stuff and as poly cord pulleys shouldn’t ever experience friction to really melt/burn it.
What is the OD of the grooves? No worries about the rod deflecting under tension?
To go along with Jared’s questions, what diameter round belting (polycord) are you using? If the pulleys are machined from 1" diameter stock, you may be very far below the suggested minimum pulley size.
-Brando
Most polycord has a minimum pulley diameter, and the pulley diameter gets bigger as the cord diameter gets bigger. Exceeding the minimum diameter puts extra load on the motor driving it.
For example, the hollow Yellow Round Urethane belts my team likes to use (McMaster # 6567K56) has a minimum pulley diameter of 1.5". This year we were able to get away with a 1" diameter @ 3% cord stretch, given the gearing & power of the motors we chose. If we used a weaker motor or faster gearing, we would have probably enforced the 1.5" diameter design parameter. We also relaxed the belts overnight and in between competition so they didn’t wear faster than expected.
Just something to keep in mind.
The ID of the pulleys are .64 in.
We are using a smaller diameter then what was recommend but from past experience not have a lot of problems with it.
We are going to put these in later today, and I will report back about any problems.
Doesn’t the hollow round belting flatten out when installed? Have you had trouble with the little connectors coming out?
We have only used the solid round belting but I am wondering if anyone can give a quick pros/cons of solid versus hollow.
- T
No and no.
We have used hollow belts more than a few times and the only times I have have had one separate at the connector was when belts were installed to loosely. They kind of work like finger cuffs, harder you pull the more they hold on.
The only reason we have used hollow belting was because it was easy, no other big reason. They are both great. One advantage to hollow belting is it can be removed and replaced without removing rollers. Solid belting gives you more choices of belt thicknesses and will generally allow smaller roller diameters.
Doesn’t the hollow round belting flatten out when installed? Have you had trouble with the little connectors coming out?
In 2011 when we used 1/4" belting for our claw we had no problems with the connectors, however this year with the 3/16" belting it seemed as if we were always losing at least 1 belt because a connector came undone. I would attribute this to more likely too much tension on the belts but nevertheless something to be aware of.
We also used 1/4 hollow tube and had no issues with connectors.
So my worst fears as been confirmed, the .6 ID of these pulleys make them to flexible. Under the load of 4 cords there is about an 1/8 of an inch of deflection which makes them very stiff to turn. We are switching to 6061-T6 and with an ID of .66.
If you can, go with a much larger OD and use round hollow tube for the roller material.
1.5" diameter x 0.040" to 0.063" wall thickness aluminum tube works great for polycord rollers.
Agreed, in the 1.5" range you can find very nice rubber tubing to slide over the Tube to act as grip as well!
Such as McMaster: McMaster-Carr (comes in black btw :P)
We used 1.25 OD X .060 wall. It allowed us to press in a FR8 Bearings. So we drove one roller and made the rest dead/pressed in bearings.
-RC