VRC1414: Sack Attack Season Blog

Just like last year, VRC1414 has been blogging its entire journey since we began our Sack Attack efforts in May. Since we just reached a significant milestone of “mechanically complete” today (almost a month earlier than last year), I thought this would be a good time to share here:

Some quick facts before you dig into the details on the blog:

  1. We’ve grown from 1 team as rookies to three teams this year.
  2. We’ve decided to use a “collective design process” this year where all three teams brainstorm, design, and work together to complete “the” design with one of our robots, then “build out” the other two while optimization takes place. (if you follow all of our posts through from May, this gets explained more fully)
  3. We do not reach to the high goal - that decision is documented in the blog.
  4. Our drivetrain is exactly the same as last year except two motors now power our sideways motion in the “H-Drive” instead of one. Just like we predicted, this gets us to top velocity more quickly
  5. Lift ratio on the 4-bar linkage (which was inspired by many NZ designs from last year) is 7:1
  6. “FRC-Style” roller uses longer threaded beams (2, 5" beams connected together) covered in no-slip pad, connected to the gears you see
  7. The mouth opening for the accumulator if of flexible with, tensioned on either side by latex tubing.
  8. We do NOT use any high strength motors in this design and because of our extensive testing this robot runs well beyond a single match time on a single battery.
  9. There is still some optimization and programming work to do, but we won’t be changing much from what you see.

The blog, thus far, contains entries that span May-present. Feel free to read, use ideas, ask questions, etc. We’re going to do our best to update the blog as close to weekly as we can between now and our first event in November.

We’ve had a blast to this point - these sacks because of mass and HIGHLY variable shape have really provided a big design challenge. Good luck to all Sack Attack teams this year.

It looks like you have had some great success so far!

Some questions…

How wide is your intake? About 11"? It looks like your intake works really well.
How many sacks can you hopper hold?

Your robot looks really clean - it does seem like the low, tight roller works better than some of the tread systems I’ve seen lately. Is that polycarb plate rubbing the foam, or slightly above it? Is is acting as a skirt to keep sacks from getting under the robot?

I LOVE the paint! Looks very very cool :slight_smile:

  • Andrew

what is the material on the intake roller? I couldn’t tell…

Looks and runs awesome.

-Nick

It’s non-slip mat that is differently colored than the type VEX sells I think.

I had thought it was mesh.

Do you guys plan on trying a “chainsaw” roller (like 24C’s) or something similar to fix the top roller issue os spitting sacks back out the top?

One of our team members thought that sticking a piece of metal or lexan at an angle above the intake should keep them from coming out the top. Hopefully the angle of the metal or lexan should let the sacks slide back into the hopper.

Rre

I had thought of that too but, it would have to be done really well because if there were any gap between the roller and the metal or if your roller were too grippy, your intake would be likely to jam

This is exactly what happened with our intake. We’re going to remove the bar and let them come out, and let the roller suck rogue sacks back in again.

You could always try something like on 24C’s original robot, that might fix your problem altogether so you won’t need to compensate for it while driving

Yes - just a little wider than two sacks

Way more than we ever anticipate lifting at once. The pile of five is likely to be the most we try to hold at one time in a match.

Right now is seems like it may be an “issue” that could negatively affect us, but we need to run/practice more to see if it really is. If we need to address it, we’ll likely start with a simple polycarbonate guard, test and go from there. Follow the blog into Sept to see what happens with it.

Others had the answer right. No-slip pad. It comes in colors at Walmart.

Can it descore? And how did you make the roller? Under the no-slip pad are there stand offs, or is it lexan tubing?

stand offs

We’re still optimizing and iterating our polycarb usage. The flat polycarb sheet that runs across the chassisand prevents the polycarb “ramp” from digging in the foam works really well, but when the arm is up the falt shhet becomes a place where sacks get stuck easily. So, we working on other solutions as we speak and hope to have that ironed out soon. Watch the blog for updates

The problem is, we’re using 6" wheel legs on our intake, and it would be very hard to turn them into a chainsaw. And we don’t really want to change to a chain/sprocket roller, because our wheel-leg roller descores really well.