FRC 95 2018 Build Thread

The SUMPRODUCT function is an even simpler way of doing this math.

Latest CAD screen shot. The tower is coming together, as is a 4-bar linkage to move our cube collector. Still outstanding is the cube collector geometry, which has been subject to pervasive prototyping; the spool assembly for the lift; and our solution to climbing, which has finally left the concept phase.

How tall is your robot? It was brought to my attention by 3005 to watch for Center of Gravity on the Cable Protectors and the Ramp, and while the height limit is 55 inches, a SCALE with OWNERSHIP is only 48 inches of clearance.

Great looking build. I noticed the Pneumatics on the underside of your robot. We were thinking the same. If those were for CLIMBING from direct contact with the PLATFORM, Q134 of the Q&A was explicit in the clarification for CLIMBING.

Fully closed-down it is 54in. Right now everything is modeled to provide maximum height when extended, but we intend to shorten down the elevator once all components are modeled and we can be sure of our maximum attainable height. We intend to be able to deliver cubes onto a SCALE without OWNERSHIP, perhaps even on top of a first row of cubes.

Those images are from our pre-season drive base and those air cylinders are used as brakes. They do not lift the robot enough to violate any rules.

This is always one of, if not my favorite, threads of the year. It’s very cool to see some of our design choices echoed. Do you guys intend on climbing? We are attempting to implement a similar POWER CUBE elevator system but have encountered packaging woes with what we’ve referred to as a “buddy climber”. I’m fairly certain we can climb on our own but we’d absolutely love to bring another machine with us.

Thanks! It’s always nice to hear that our work is appreciated.

We have a climbing plan that we just conceived of yesterday. It’s higher-risk than we normally tackle, so we’re going to get the core capabilities of our robot designed first, namely ground-loading CUBES and scoring in all SCALE positions, while leaving the space we think we need open for the climb mechanisms. Then we’re planning on designing the climb stuff soon-ish.

We anticipate that a good cube-handler will be competitive at a Week 1 event (our first) and that we’ll have time to finalize our climbing mechanisms before our second event in Week 3. Hopefully we get into our Week 5 wait-list event and have time fine-tune everything in competition.

Chassis parts arrived last night!

Progressive Manufacturing does some stellar work!

CAD for the balance of the cube handling and scoring components is complete, at least for the first iteration!

What diameter are those intake wheels? They look quite large!

We’re starting from ~5in and will wrap a little more material around it. The friction material is TBD.

Couple questions:

  1. Will you be incorporating a disc brake into your elevator?

  2. Have you ever used F4 Silicone tape? As per your previous comment you are still playing with different grip materials and I’d suggest trying it.

  3. Your hole pattern seems quite large (unless I’m mistaken it looks 1/4), do you choose to rivet/bolt with larger fasteners and lower quantity instead?

  4. Will you be getting things powdered/painted? :slight_smile:

  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: https://www.homedepot.com/s/Rust-Oleum%20Painter’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.