FRC 95 2018 Build Thread

  1. Nope. The stall load on the 775s to hold position isn’t very large.
  2. No, I will take a look at it, thanks! Do you have a suggested vendor?
  3. Yes. The holes you see are 0.201, clearance for a #10, or 0.272, press-fit for a #10-32 PEM nut. The chassis design is frozen (on day 3-4 of build) long before we know what all of our mechanisms will look like, so we put a 1in pattern on top of each frame rail and work with that.
  4. We’re going to talk with a local PC’er, if that doesn’t work out we’ll spray paint them again.

We’ve bought the silicone tape from ACE Hardware, in the plumbing section, before. It is very grippy, but tends to roll back/double up after a lot of use. And it isn’t cheap.

Has prototyping yielded good results from the overhead roller? Any issues with the cube just doing a backflip?

Thanks for the tip.

Yes, it has. I have a few videos to post tonight. The top roller is mounted on a swing arm, so when the cube flips the roller just follows the cube until the cube is eventually acquired (<1s).

On a related note:

Our roller construction has been fun and interesting. We have traditionally machined metal inserts and used metal tubes to create rollers. This year, we wanted something lighter, cheaper, faster to make, and easier to replace. Well… we figured out a solution that we’re really happy with:

In final form we’re going to use a lighter wheel than a Colson and hose clamps to secure the sheet metal to the wheel, but the same general construction technique. This roller took about 10 minutes to cut on our sheet metal shears, roll-bend, and zip-tie in place. We’re then attaching a() friction material(s) to the outside with electrical tape.

It’s really interesting to see other teams’ season processes! This year our team is attempting to improve ourselves in several areas, including overall quality and aesthetics. I noticed you mentioned your team has spray painted your parts before. Since we’re planning on doing the same this year, would you have any advice for spray painting aluminum?

James, any reason to use metal for roller tubes instead of plastics? I had good success last year with a 3" OD polycarbonate tube for an intake. Stuffed the motor right inside it. Reasonably light and should be more resistant to damage than the aluminum (flex vs deform).

Might even be able to get away with 3d printed plugs.

This is actually the one thing that we get the most questions on, so it will be good to get the answers out publicly!

  1. Prep your parts well. We thoroughly de-grease our parts with acetone. IPA will work well too. Degrease twice at least. This improves the chemical bonding of the paint.

  2. Rough(ish) surfaces hold paint better than glossy surfaces. A quick sanding with 300-600 grit sandpaper will let the paint ‘bite’ into the metal more effectively. This improves the mechanical bonding of the paint.

  3. Control your spray environment. Keep dust down, extract paint fumes and over-spray, keep temperatures warm or hot (70-80F+).

  4. Lay your parts out horizontally. I know, you can paint both sides if you hang the parts vertically. Don’t, unless you’re good at spraying paint. You’ll get many fewer, or no, drips if the parts are horizontal.

  5. Prime. Get an etching or metal primer from the same manufacturer as your paint and apply a coat before painting. Match the color of the primer to the paint. White primer for light colors or thin-coverage colors like red.

  6. Paint! Get a good quality shaker can, spray handle for the can, and go to town. Don’t be afraid to practice, but practice with a comparable substrate. Spraying on cardboard is not the same as aluminum, so the practice isn’t as useful. If you move fast you can hold the can quite close to the aluminum and get great coverage in 1-2 passes. Don’t *start *spraying on the part, always be moving when spraying on the part, keep the nozzle at the same angle and distance to the part during each spray pass. Follow all instructions on how often to reapply coats as needed.

We used Rust-Oleum Painter’s Touch 2X and loved it. See:’s%20Touch%202X?NCNI-5 with the comparable primers.

I had instruction from an auto-body painter friend of mind and taught my students how to spray paint from what I learned (that is to say the manual technique of spraying). It’s hard to describe through text, perhaps we’ll take a video of it when we go to paint some parts.


Good question… because we had not considered using plastic! The shop that we work in stocks sheet aluminum (0.030in-0.250) so that’s our default go-to.

I think we’ll try skinning the wheels in polycarbonate as an iteration/weight reduction effort.

I still can’t wrap my brain around motor-in-roller designs. Do you have a good rendering or diagram that shows how this black-magic works?

Here’s an image of 558’s in 2014 off the TBA blog:

Drost more or less has it covered. The big trick is realizing that the tube spins around the motor and then it starts to make a bit more sense. If you think of it as the hex shaft going into a broached plug in the tube then realize you’re just moving that mounting point in a bit it seems to work for me.

I’d post a pic of the one I did last year but i’m pretty sure it’s EXACTLY the 558 one because I talked to Foss about it and ended up ordering the same tube of MCM. The only issue we had was holding the tube in our band saw to cut it cleanly, the tube wanted to collapse. In the end we just used a hacksaw.

Awesome, thanks guys! That looks like a great packaging option. We will take a look at it.

We’ve been working on a narrow-ish intake to avoid any issues in picking up two cubes, but that still had a wide ‘target’ for the driver to hit. Conflicting requirements, right? Great.

We’ve got something that works pretty well in a variety of power cube orientations and can pull in a cube even if only 10% or so of the cube is initally engaged.

See: and

We’re also pursuing a multi-axle intake design. More refined prototypes are being made tonight, hopefully we’ll have some more results tonight.

Thank you for the spray paint instructions! We’re considering also trying to start painting parts of our robot this year.

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Our Mk2 roller collector, something a bit more robot-sized, was unsuccessful last night. Power cubes would tip and jam instead of sliding into the collector or tipping and rolling in. We need to figure out what let our Mk1 collector work that isn’t present in our Mk2 collector… A setback, but one we can overcome I’m sure.

By robot sized do you mean smaller wheels? Or did you shorten your prototype to account for the 16" maximum extension?

We made it a few inches narrower, 15in vs 18in, the roller has a shorter pivot arm, 6in vs 8in, and the floor pan is a little thicker. .25in vs .1in. A few other things are a little different i’m sure.

Bad science practice changing multiple variables at once… welcome to build season!

I would also recommend wearing a respirator and goggles to catch any stray paint, even with a fume extractor.

This thread has been interesting so far, and I look forward to future progress reports!

Hey James, awesome thread as always.
From your CAD it looks like your elevator is being mounted straight to your bellypan (brainpan?)? Am I missing something?
Also definitely keep us updated on the over-the-top cube collector, because I really like that style and just haven’t had a chance to prototype it.

Yes. Even a 3/4 paper mask does wonders at keeping spray out of your respiratory system. I suggest cleaning safety glasses/goggles with IPA or paint thinner (mineral spirits) immediately after spraying to keep them clean.

We have not modeled triangulation for the tower yet as it is heavily influenced by the ramp design that is still in progress. We are confident that we can find a solution given the grid of holes on the deck.

So as a non-mechanical mentor, I didn’t know about the FRC Design Calculator. In case there’s anyone else looking for it, I think it’s available here:

Just be sure that your cleaning solution won’t affect the structural integrity of the glasses/goggles. My safety glasses once got coated with small spots of paint from an electric sprayer. 70% isopropanol removed the spots completely.