Polycord on tote intake: recipe for disaster?

[Leav]

Our initial mockup for a horizontal roller gripper calls for about 14 small wheels (7 for each side) in order to get the shape we want, and when you consider that they all need to be powered, it starts looking slightly ridiculous.

One alternative we have considered is using polycord or double sided timing belts, but our small amount of experience with these items on an intake has us worried that they will ride out of the pulleys if any vertical forces are involved.


This is a valid concern, right?

Any examples of polycord intakes which could stand up to axial loads? maybe we're missing an obvious way to keep them in their groove


Thanks!

[Amar Shah]

Make sure the grooves are decently sized. Assuming you are using round polycord, a semicircle of the same diameter as the polycord should provide good security.

[Ian Curtis]

We have found that polycord does a pretty garbage job of gripping to the totes. If you are using polycord, one thing I've seen used with grooves in the past is to to use a "comb" on the backside of the loop where they aren't touching gamepieces to keep them in line.

See this picture for an example.1276's 2009 robot

[IKE]

I concur with Ian. Without the comb, they will walk out of pulley grooves. Even with a comb, they still have a good chance. Flat belt can be a bit more stable if you put a small crown under the center of the shaft.

[Squeakypig]

Just remember to tension it every 6". At least that is our experience, some say you can get away with more, I don't trust them.

[Kevin Leonard]

We've had success with polycord intakes in the past by making our own pulleys for the cord to ride along.
Additionally, in our 2013 intake, we used the polycord like a chain or a belt between the sets of wheels. This made it so it all rotated unless the disc couldn't push further up in our hopper, in which case the polycord would break traction with the pulleys and not destroy the discs.

We don't plan on using any polycord in our rollers this year, but best of luck to you!

[pmangels17]

In 2012 we used polycord to move the basketballs through our robot, and we made our rollers out or 2" (IIRC) PVC pipe that we bolted to the driven shaft, using PVC endcaps drilled out in the center to keep the rollers concentric with the shafts. Then we cut small rings out of the endcaps and slid those to where we wanted the belts on our pulleys, to create guides on the rollers. You might have decent luck using some sort of similar system, perhaps also putting tread on the PVC to grip the totes better at the front and then use gaps in the tread to align the polycord.

I can't comment on how well the polycord grips the totes, but it had a decent grip on the rollers when properly tensioned. Hope this helps, good luck!

[Chris Endres]

We subtract 10% of the total length on poly cord. Example: slacked length needed = 10in, cut and weld a 9in piece. I wouldn't recommend super long segments (<20"). Also, we use custom pulleys, they work like a charm. Remember, poly cord is meant to slip a little. If you don't want slip, use belts or chain.

[Leav]

Thanks for the input everyone. We decided to go with wheels on the input and keeping the polycord for the pulleys that will drive the wheels.

Hopefully this will eliminate any possibility of polycord climbing out since there should be no side forces.