Edit: Check the post Collin made in the comments for fact corrections.

For my senior year I was fortunate enough to join a really great and well run FRC program, More Robotics. Here’s “where it all began” and where I got inspired to pursue engineering as a career instead of typing all day as a CS major. I did not do that much mechanical design on 1714, as I had better teammates, but I did help with the game strategy and ultimately got hooked around competition time. I was very much in over my head, and I called the game exactly wrong (continuing a streak that only ended in 2010), but it was a great year for me.

Anyway, I might as well show you the bot and stuff.

More Robotics 09

It kind of sort of looks like HOT before they made mods and became the best bot ever.

It’s a bit hard to visualize the robot because of the entirely polycarbonate construction, so here is a picture with some balls.

Here are some balls.

Here are some balls.

Basically, if HOT’s robot were one ball wide, it would work a lot like 1714. The front hopper holds about 3-4 balls gravity fed and the belt system can hold 6 balls if carefully managed (which it was, our operator was pretty good). The main design was that we wanted to be able to shoot from long range, on moving targets, quickly. We also wanted to avoid jams at all costs, hence the single track of balls. The all polycarbonate construction is because we worked out of our awesome sponsor’s plastic fabrication shop, American Acrylics. The robots also look fantastic and cool this way.

I’d like to emphasize I didn’t do much design work here, so any “wow you guys rocked gg chris” comments should be directed toward the other students of 1714.

Building with polycarbonate

Before 2010 (when 1714 got a CNC machine for LARGE sheets of polycarbonate), we got really creative with our fabrication. We primarily build with 1/4, and 3/8ths polycarbonate sheet, using 1/8th for shielding and non structural parts of the robot. Polycarbonate can easily be cut on a table or band saw, can be drilled into like most parts, and can be routed out like wood. Like sheet metal, using it in the right application can make for a decently rigid robot, and with Lunacy a rock solid metal frame wasn’t a huge priority anyway. So we made everything out of it.

The chassis is made up of 3/8ths polycarbonate sidewalls, all bolted together, with 1/8″ top and bottom covers for electronics. Pretty simple stuff. Some lightening holes here and there. Occasionally we’d make a bearing block out of some 3/8ths material and shove a bearing in there to support the shafts. We used the BB planetaries from 2007 with a supported shaft for the back wheels, and window motors with a large overgear in the front. The idea was that if the front wheels were spinning fast enough to “break loose” we could turn faster… I don’t know if that actually worked very well, but no one uses the Window motors anyway. We installed encoders to match the speeds of the wheels, since it’s not like either were torque limited.

The cool part was the ball tower. We needed a large load bearing structure but with a large lightening pattern. We had a laser cutter and lots of 1/4″ thick acrylic, so we prototyped with that and using some wood as spacers (where the polycarbonate “standoffs” are now). Once we got a design that worked, we cut the exact same hole pattern out but with huge filleted square sections all over. We then taped and secured the acrylic to 1/4″ polycarbonate, cut out a rough hole in the polycarbonate for each lightening square, and then used a hand router for the rest. It was a REALLY cool process and it made for clean, precision cuts. The other two sides of the ball tower were made with some 3/8″ lightened polycarbonate, and then we had a superstructure. (Can you tell this is the part I worked on a lot?)

The turret was the creation of our manipulator captain. The turret base was laser cut UHMW Polyethelene, which is fairly self lubricating. A large gear profile was cut in one of the layers of the turret; this gear mated with a smaller laser cut gear mounted to a Globe motor in order to rotate the turret. It was a simple, fairly low friction solution with the minor downside of making it hard to mount a vertical wheel in place. Instead two horizontal wheels were used for a bit more range, coupled to a CIM with some Poly Cord (polyurethane belting). We couldn’t “curve” shots but we had a turret and doubling the wheels used made our exit velocity pretty high. Before we modified the robot, we could make 20+ foot shots. Not accurately, mind you… We threw one of the shitty Mabuchi motors on a little “kicker” to get that last ball out of the turret and into the shooter.

Design Roadblocks

Our season had a lot of troubles. We initially pursued an Archimedes screw based design. Now a lot of teams say they have Archimedes screws, but actually have helixes or whatever. We pursued actually building an Archimedes screw, with the path spinning and everything. Unfortunately we failed to notice 1726’s cool videos online with the screw’s inside spinning, but not the outside rails the balls roll up on! Whoops. We scrapped the screw and went with the belts.

Our shooter was great… at long range. What wasn’t great was camera tracking. We were kind of counting on tracking goals and shooting long range. Nope. We also had traction control issues. Mainly instead of a PID loop, we had a fairly laggy system that would ramp up to the input specified, then check the input only after that. We also didn’t check if the wheels spun too fast at all, so we had not a very good system! We basically spent the first regional driving around and being a target. We missed eliminations entirely.

Oh, another problem: At short range we’d be running the motor incredibly slowly, but even at some of the lowest PWMs we had the shooter was still shooting a bit far.

Anyhow, we fixed both those issues with the addition of an AM Planetary to the CIM as well as new code with zero traction control whatsoever! We lost shooting range we no longer cared about and became a turreted flumper.

Competitive Success

So, yeah, did you know I won 1714’s first regional? 😛

I’m just kidding, I was just the drive coach so I didn’t actually accomplish anything. But yeah, 1714 went from missing eliminations to the first overall selection at Minnesota. While one could take that as a snide remark regarding the strength of the Minnesota Regional, we actually improved a lot. In one of our best qualifier matches, with the three best bots in the competition on one blowout, high score alliance, we scored 23 balls. Granted, it’s because no one in Minnesota bothered to starve balls, but still. We got better. I got a bit better at communicating to the drivers, the drivers handled the upgraded bot amazingly, and with the entire team behind us we got 1714’s first regional win. It also was one of the last regoinals won by a then-rookie alliance captain, 2826.

The reasons we managed to go from terrible to competitive are twofold. First, continuous improvement. We saw what was wrong with the robot and changed it. Second, we were fast. Our belt drive was coupled to a CIM and Toughbox. Our belts were moving at around 6 feet per second. We scored our starting 7 in a second. Because we could score so quickly, it helped to make up for our low capacity and ball output. Who cares if you’re a double wide dumper if you can only spit out 2 or 3 balls a second? Speed is EVERYTHING and this is proof.

It’s too bad we didn’t build a dumper, huh.

Things this design taught me:

  • Whatever you do, do it quickly.
  • The shotgun approach is sometimes the simple and elegant solution.
  • Asking for help isn’t a bad idea. What if we sent 1726 an e-mail?
  • Don’t rely on a solution you don’t know will work (camera tracking was SO reliable this year…)

Conclusion

This robot inspired me. 😀

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