Robot Strategy

So you've got a copy of the rules and asked questions to clarify them -- time to start designing the robot? Lifters, dumpers, belts, vision algorithms? Nope! First you have to consider strategy. You can design the best ball shooter in the competition, but if it turns out that the competition favors shoveling and dumping balls en masse you won't accumulate many points.

Original Strategy Meeting

(Note that some of these conclusions are incorrect and many changed before/while we made our robot) The first thing we did (after the info meeting, before maslab even started) was discuss strategy. By discussing possible scoring strategies, we quickly concluded that robots should only score in the center of the tower and that the reliability with which the robot could score in the center of the tower was the robot's most important quality. Correspondingly, we figured that the 200 point bonus for clearing the field was not that important (despite the big number); it was only the value of 4 balls in the tower and could easily be prevented if the opponent dumped a single ball over the wall in the last 10-20 seconds of the match.

In terms of collecting balls, we decided that the ball-dispensing button (henceforth referred to as the cyan button, although the online rules might still say that it is green) was the most efficient method of collecting balls. We figured that both robots would rush to find and press the button, positioning themselves so the released balls fell directly into a storage container. Even with a 20 second delay between button presses the robot collects a ball every 5 seconds -- a hard feat to match collecting the balls that are already scattered across the field.

Then we discussed mechanisms for accomplishing these strategies. At this point we watched a lot of videos of previous competitions -- past Maslab teams have committed a lot of time testing out designs for us, and the least we could do is take advantage of it. (Well, perhaps they were just making their own robots, but we can still benefit from their work). We chose an omni-drive to make it easy to line up with the tower (run into the tower then move sideways), a dumper (with a very large storage area) sized to line up with the center of the tower, and a roller + belt system to collect balls (from the ground or from the ball dispenser) and lift them into the dumper.

What was wrong and what changed later

First of all, we were slightly mistaken about the rules. We had thought that the towers bottomed out at the ground, leaving a lot of space for balls, but there was actually a raised floor that significantly limited the number of balls that fit in each section. But we were still correct that scoring in the center of the tower was critical to winning. The 200 point bonus for clearing the field was irrelevant, but not (as we thought) because opponent robots would prevent it from happening. In the final competition, even the best robots couldn't quite clear the field of balls. Lesson for the future: don't overestimate the robots. Maslab's challenge is hard; the robots won't be as good as you expect!

We later talked to a MechEE non team member who talked us out of using belts (they're too unreliable). With his help we tried to design a four-bar linkage but couldn't get the dimensions to work (the tower was too far up and out from the robot) and switched to an elevator.

We also talked to Maslab TAs who told us that previous teams had tried omni-wheels but they hadn't turned out to be that useful. We switched back to normal wheels with the plan of using PID control to aim at the tower.

Robot Design

Mechanical Design

CADing

It's a good idea. I taught myself to use SolidWorks over winter break -- if you're reading this before IAP you should too.

Collisions with walls

Robots get stuck on walls. A lot. Either by getting lost in a corner or by hitting a pole/wall without triggering bump sensors. You need to think about this before you design your robot -- how will you keep your robot from suffering such a fate? We designed the robot to be surrounded by bump sensors (front-left, front-right, back-left, back-right) such that it couldn't hit the wall without a sensor triggering. Of course the final robot didn't have these sensors... but more on that later. They're a good idea.

Assembly

We designed the robot to be assembled with slots and tabs held together by screws (see picture). It worked well and was easy to assemble, but it took a while to CAD (perhaps saving time overall, though). It also imposed the requirement that most/all parts be laser cut. This is a good idea, but make sure it is possible. And that you have someone on your team who can laser cut; we had 3 or 4 laser cutting plans fall through for various reasons. Be really sure you can laser cut if that's how you want to make your robot.

Materials

Maslab ran out of acrylic and we were forced to find other materials for the final iteration of the robot. We discovered medium density fiberboard (MDF), which costs about $5 for a 2x4 .25" thick sheet at Home Depot. It is strong enough and easy to machine. Maslab staff: you should consider using it instead of acrylic next year. Maslab students: you should consider using it regardless. One note on laser cutting: the Architecture department didn't want to laser cut MDF for some reason, but MITERS was willing to (they love MDF and say you can use similar settings to plywood (just cut slightly slower to be safe)). The laser-cut MDF came out a lot nicer than the acrylic and we could easily machine it by hand as necessary afterwards.

Jamming

Just as your robot can jam on walls, moving parts an also jam on parts of the robot. Be aware of this and design around it. Our lifter didn't end up working because it jammed on its sliders and we were unable to fix it in time. Of course we did have time problems... but try to design around it anyway.

Electronics and wiring

This can get kind of messy. You should design in space for electronics in the CAD and, if possible, make zip tie holes for wire routing. It will make your life so much better! We did this, at least to some extent, and a Maslab TA told us we had the neatest wire of all the robots.

Code Design

Performance

Conclusions and Suggestions

Team forming

overall strategy mechanical design and sensors software design overall performance conclusions/suggestions for future teams

Team Ten/Final Paper

Contents