Spectrum 3847 - Build Blog 2020

I like the way your team thinks. We are going with a PVC pipe as our roller and if we need more grip we will wrap it in electrical tape as we’ve observed it to be extremely sticky with this game piece.

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5236K533 is what we use.


Do you (or anyone else) find this easier to cut than surgical tubing? We have no problem getting 1"ID, 1.5"OD surgical tubing on a 1.25"OD roller but it’s difficult to make clean, square cuts on.

I’ve seen people get fairly clean cuts on it by first sliding the rubber over their stock and then cutting both the round stock and the surgical tubing at the same time, rather then cutting each individually and then joining them.


Not really the edges are always a little uneven, we normally wrap electrical tape around the edges.

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I wonder if we can get cleaner cuts with a jig in the lathe. Cutting it already stretched over roller material is a good idea.

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Although it doesn’t smell the nicest, we simply use a bandsaw. It gives a decent edge, significantly better than cutting by hand.

I imagine a simple lathe setup with a razor blade or rolling blade could work well too.

We’ve been cutting just the rubber (with no supporting roller) on the band saw and are unhappy with the straightness of the edges. Going to try both band saw and lathe with supporting roller inside before trying the silicone or back to urethane like we originally planned and moved away from.

Great ideas, all.

Cutting after it has been installed on the roller makes a significantly better edge in our experience.

Have you guys ever tried the 1-3/8ID one. We’re thinking about it for 1.5” rollers but the issue is the 1-3/8” is 1/16” thick and that concerns me.

We haven’t tried it


The polycarb roller is 1 + 1/8" ID, 1+1/4" OD, but we ordered the 1" ID surgical tubing. Will definitely try using polycarb rollers w/o surgical tubing, and just ordered 1+1/4" ID surgical tubing!


For reference, copious amounts of alcohol makes latex very slippery, but you have a very limited working time before it evaporates. I think both denatured and isopropyl work.

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When using the wire wheel do you spin it perpendicular or parallel to the spline?

We only had the wire cup style one handy, so neither really, it was spinning on top of the shaft and we’d rotate the falcon around to get to every part of the shaft. My guess is you’ll need a little of both to get to the end of the shaft.

Day 24

CAD Updated

The STEP file on GrabCAD has been updated for this week. You can download it here - https://grabcad.com/library/spectrum-3847-2020-ultraviolet-frc-robot-1

Vision Progress

We have made a lot of progress using opensight to be able to track balls and track the rectangle on the loading bay. We are planning to use a limelight for aiming our robot and to have two additional cameras for driver viewing and tracking of balls and the loading bay.

Ball tracking is using a color filter and then selecting only circles.

The rectangle tracking is just normal shape tracking on the retro-reflective tape.



Not sure if this was already asked but are you guys planning on storing any balls in the funnel or will all five be in the conveyor that feeds the shooter?

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All 5 will not fit in our tower. So at least 2 balls will be in the funnel, it’s possible it’s 3, it depends on how nice we can get the balls spaced in the tower.


I’m sure there’s a good reason, but why do you need a camera for both the ball and the loading bay? Also, how will you mount the cameras?

Piggybacking off this, how do you guys deal with the bandwidth limitation with so many cameras? Which feeds to you stream back to the driver station? What software/hardware do you use to compress the video feed?