Friday, November 23, 2012


Aug 31-Sep 4, 2012 - My very first Dragon*Con, and Robot Battle. Belated as it is, let me share a few of the things I learned about building my first antweight robot.

Don't use motors encased in plastic for your competition robots.
Don't skimp on good wheels.
Learn to drive.
You can't beat real-time combat experience in improving your robot design skills.

Above: Before leaving for Atlanta, GA.

Above: Final design.


To build a working 1lb antweight robot that would compete in the Robot Microbattles, a 3 hour competition on the 2nd to last day of D*Con.

Kuroneko-bot - The Design Process

Kuroneko-bot (or 'Black Cat' -bot) actually started out in its initial design phase as a bunny (jokingly). This was actually my first time designing a robot, and after actually participating in a robot battle, I gained a lot of insight in how to build my next robot. But for my initial design, I had a few criterion in mind:

1) When flipped over, it should still be able to move.
2) It should be able to slide, or wedge, its way underneath the opponent.
3) It should be as flat and low as possible while still maintaining a wedge shape.
4) There should be front 'claws' that would act as 'redshirts' or 'decoys' to any sharp rotational objects. (<--my feeble, amateurish attempt at thinking about dealing the opponent robot. I was more worried about making it run than how it would handle a fight. In hindsight, I should have given a little more thought to how I should buff up my robot's defense or attack - the better robots had either brilliant defense or brilliant weapons, or both!)

Above: Online whiteboard collab brainstorming. See the bunny ears?

After sketching it out on paper to get a better idea of scale, I used Solidworks to create a CAD model for her. This is what it looked like after using black-box placeholders for the battery, receiver, ESCs (electronic speed controller), and motors.

Above: Kuroneko-bot in Solidworks.

Mounts were designed around two Tamiya mini-motors (12 speed) to provide more structural support. These little Tamiya motors allowed you to configure your own gearbox. Besides those 3-D printed mounts, everything else was scrounged up from already existing parts from MITERS, which is why the initial wheels where mismatched and dog-eared. This also constrained my initial design of keeping it as flat and low as possible, since I had to build around the parts - not optimal, but it still managed to work.

Above: Scale of the motors.

Above: Top motor mounts on.

Above: With everything fitted in - a tangle of wires!

At this point, I did a quick test run. It ran, but the bot slid everywhere, and I had trouble controlling it. I had attributed it to the slippery floor and the mismatched felt-like wheels that picked up all the grime on the floor, and resulted in different ground-clearances when attached to the bot. After a minute of continuous driving, I noticed it start to spin in circles, as if one wheel was not responding. Like a noob, I continued to gun the controls, trying to see if it was just something that had stuck underneath the wheels and continuing to keep it running at full speed would free the wheel.


Luckily, it hadn't escalated to visible smoke (always a bad sign) before I found out! After taking it apart (the first of many, many dismantlements), I had noticed nothing wrong except that both motors were really warm and smelled burnt, and one of them was locked up and dead. It would take another two motors and a bit more tweaking before I would figure out the reason.

Since I didn't have any spare motors at hand, I decided to worry about this issue after we were in GA. So I packed up Kuroneko-bot, and drove down with Adam and Charles, which was an adventure by itself (consisting of mostly Vocaloid Miku songs, Gangnam-styling down an empty night road, and my first time driving for over two years and over 3-4 hours continuously). ROAD TRIPS! :D

STAGE 2: Invention Studio @ Georgia Tech, Atlanta, GA
After arriving in Atlanta, I went and bought more of the same Tamiya motors I had built the mount around. These took almost no time to assemble, since I had memorized the gear ratio I had used before and the kit assembly was familiar now. But after reassembling Kuroneko-bot at the Invention Studio and giving it another test run for another good few minutes, those motors went immediately dead as well. Opening Kuroneko-bot up again, both motors smelled burnt and one motor was found dead. After inspecting the case a bit, I discovered that the plastic around the motor shaft (the little stick protruding out of the little motor can the kit provided) was melting and deforming, and thus causing the motor to misbehave.

The next day, I bought a Double Gearbox Kit (Tamiya again), bought new flight wheels to replace the mismatched wheels I had brought up from MITERS and quickly 3-D printed new wheel hubs for them.

Above: Final assembly.

Above: Final assembly with the cover on. Does it look like a cat now?

Above: Added hack-weight on the bottom to make my robot heavier.

STAGE 3: Robot Minibattles, Dragon*Con, Atlanta, GA

There were 3 robot competitions at D*C: ones for sumo-bots, 1lb (antweights) and 3lb (beetleweights) robots, and 15lb and 30lb robots. I participated in the antweight category, but if you have the chance to go and can't make it to the lighter-weight category fights, the main Robot Battles competition is the one you should gun for. Lots of great robots, fan favorites, and exciting battles!

Above: The antweight and beetleweight stage.

Above: The much larger stage and open-air arena of the main Robot Battles.
(I did not participate in this)

In terms of how I did... Haha. My performance was sub-optimal, but still a good learning experience. Kuroneko-bot came to weigh 0.986lbs, the heaviest in its category, and I drove it while wearing a maid's outfit.

Above: See the maid? Yeah... that was me.

The first round was a draw, and ended with one of the motors seizing up from the plastic casing melting around the shaft. We had to do a quick operation to make the shaft opening bigger. But while opening up the melted motor cases to make the shaft hold bigger, we also learned too late that we had accidentally rotated the motor case before reassembling the motor. Since that caused it to change its orientation, and thus how my controller controlled which direction the robot would go, I had to open it up again to make adjustments. The second round ended with one of Kuroneko-bot's motors dying and the other seizing up for the continuous full-throttling - the opponent had pushed it out of the ring to score its win. There were 15 minutes between each round, but boy, were those seconds hectic and nerve-wracking  Nothing can replace the experience of an on-the-fly maintenance of a competition robot, since it either works or it doesn't.

One of the most exciting matches of the beetleweight division ended with one robot erupting in a cloud of smoke. Luckily it wasn't from the batteries!

Above: Smoke in the covered robot arena!

Lessons Learned:
-Tamiya motor plastic cases melt extraordinarily easily 
-Motors were probably overvoltaged (check the model's rating!)
-Make sure of the motor's orientation before complete reassembly
-Don't gun your controls

In the end, I opened up Kuroneko-bot so many times, not only did I get really fast at disassembling and reassembling it, I pretty much stripped almost every screw holding the top plate on by the end of the competition. For more sustainable robots, try to invest in fasteners that do not require screws in 3D printed parts! Also in hindsight, this project should have been started much earlier, which would have allotted me time to find suitable parts and not design around parts.


The rest of D*C weekend was spent chilling with friends, new and old, going to some panels, and experiencing Atlanta (more specifically, Atlanta traffic and every road that had 'Peachtree' in it - Peachtree St, Peachtree Ave, Peachtree Rd, Peachtree Blvd, and on and on). All in all, my time spent in Atlanta was awesome! There was, however, a webcomic panel I went to that honestly disappointed me.75% of the panel were jokes and random questions, and about only the last 25% of the panel and questions had real content. Then again, perhaps all the good question-askers had intended to stay silent in the back, hoping for the actual content to answer our concerns. Maybe what we needed to do was sit more up front and ask more aggressively. I did manage to catch some of the panelists on the way out and got my questions answered, however, which ended up as very useful advice!

D*C is huge! This was the largest convention I've been to by far - crowded, claustrophobic at times, busy, exhausting, and full of fun. Thanks for a great time, D*C!

Above: Me photobombing a pic of an Iron-man cosplayer.
The helmet/mask could flip up to reveal his face.

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