As an off-season project my team is working on a foam ball shooter and we are now looking at making a conveyor similar to what a lot of other teams have made for ball games in the past. We have plenty of good ideas for how to design something like this, but not much experiences with the parts that comprise one.
The top questions I have are
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[li]What are some common grippy belts that are used, and where can I buy them? Polycord? Like this?
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[li]What about this flat stuff Miss Daisy used?
[/li][li]Knowing names, durometers, and sources will help.
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[li]How do people keep belts from wandering on the roller?
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[li]Miss Daisy’s machine has small black wraps of (electrical tape??) on the roller. Does this work by emulating a Crowned Pulley?
[/li][li]What are the spacers in between the cords seen on 254’s robot and so many others? A name or link would be great.
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Any additional tips or tricks that other teams have picked up over the years would be great. We are building a shooter in order to get experience with something we haven’t tried before, so any experiences or lessons learned from you all would be great to have.
It’s just flat polycord. McMaster carries both kinds in several different sizes, simply go to belts –> flat/round belts –> set material to urethane.
Miss Daisy’s machine has small black wraps of (electrical tape??) on the roller. Does this work by emulating a Crowned Pulley?
Yes. 469 did the same in 2013. We put an o-ring under the tape to get more of a crown.
Our rookie robot (Rebound Rumble) had a polycord elevator/conveyor to pick the balls up from the floor, raise them about two feet, then laterally another foot or so to drop it into the trigger cup (a PVC end cap mounted on a pneumatic cylinder), which would then lift the balls into the shooter wheels. We did both runs from the same motor, running (IIRC) four strands of polycord vertically and three horizontally. Thes ran on shafts with notches made by gluing short segments of foam tubing (insulation, I believe) with even shorter gaps between them. The polycord ran behind the balls on the lift and under the balls on the lateral run. We had sheet plastic (lexan?) as the opposite wall for the balls to roll up and over.
You can also use surgical tubing instead of polycord, we used it in 2009 and 2012, worked great both times. Spacers in between each band will keep them from going anywhere, just hold them in place using a locking collar.
That is a great resource! Does anyone know what those particular spacers are? A larger plastic roller on top of the under roller?
I imagine we could just 3D print something that would work well but I would be interested to see what is available.
Depending on the ID of your surgical tubing, you can actually get pretty good results by using a short length of pneumatic tubing as a press-in insert to the ends of the surgical tubing. Works pretty well for these sorts of applications, though there are other ways to do it.
Though I’m definitely sold on flat belting after playing around with it the last few seasons. Just a bit of electrical tape around your roller to make a crown and the belts will self-center.
We’ve found that a bit of glue and pneumatic tubing works well. Put glue inside each end of the surgical tubing, then slide those ends over a piece of pneumatic tubing (a 1 inch long piece should do just fine). Let dry and it will hold, as long as it’s not stretched an outrageous amount.
Just want to point out that while the belts do self-track to the center of the crown, it’s definitely not going to stay there under any sort of side load. Be prepared to be realigning belts between matches.
1987 Broncobots had a kick@$$ conveyor belt system this past year (kinda reminded me of what 1986 Titanium did in 2013 with their full court shooter :P) but I believed it was a surgical tubing type conveyor with pulleys at each end to keep it in line and to control the flow of boxes. See it folded up. Roughtop is also REALLY grippy (we used it on my FTC team I help mentor last year and literally wore down the tile flooring during a mis-programmed auton.
so here is another question, what diameter rollers do you all like to use? I know that there are minimum diameters for the different thicknesses of polycord, but I have never fell upon a standard roller diameter that seemed to work better than others.
We did something pretty small (about 1") for our 2012 robot. This was our rookie year, limited budget, and we spent most of it on registration and shifters. The diameter was selected so that we got the right speed for one of the motor/gearbox combinations we had (I believe it was a window motor).
IIRC, slightly more than 1.9" (OD of Sc40 1.5" PVC).
Going into further detail, we then wrap the 1.5" PVC with shelf liner. We create our spacers/grooves by using rings of 2" PVC over that assembly.
We used this approach in 2009, 2012 and 2013, and were largely happy with it. We still get some amount of wandering polycord, but it’s not really a big deal.
