Continuing my alliterating-c tradition of robot names is Cannon, an antweight version of Lolcat. On paper (and in CAD), Cannon looks like it’s going to be a lot of fun.
Here are the specs I have planned out:
- Weapon motor: Turnigy Aerodrive SK3 2826-1240. It is rated at 150W and will provide more than enough weapon power. The old “Beloved Shardy” undercutter I built simply did not have a powerful enough weapon motor, and this one will be sure to suffice!
- Weapon ESC: Thunderbird-18. It’s tried-and-true, and the weapon motor is rated at 16A continuous so a fire seems unlikely right now. Unlikely.
- Battery: Turnigy Nano-tech 3S 460mAh LiPoly. I love the idea of three cells, and in theory, a 460mAh can supply about 14 amps for an entire two-minute fight (throwing out any drops/inefficiencies). I think I will have bigger problems than the battery if the robot requires 14A continuous for two minutes!
- Drive motors: Fingertech Silver Spark 33.3:1 gearmotors.
- Drive ESCs: Fingertech tinyESC v2.1, the same kind used in Lolcat. I can’t say I’m wild about these controllers; I killed five or six of them before I learned that I’d discovered a hardware issue. They now seem to work okay, and I do have to say that Fingertech customer service is phenomenal!
- Weapon: 3.0ish ounce 2.5-inch diameter titanium eggbeater spinning at about 9200rpm. It will be supported by ball bearings and connected to the weapon motor by a urethane belt with a gear ratio of 3:2. The weapon shaft will be hardened S7.
I already ordered some of the parts, and I was actually very impressed by how much higher-quality everything appears. Just look at the packaging.
Actually, just look at the motor and battery!
I do have some small quips with these parts.
- Both the battery and motor are enormous. It’s a good thing I have minuscule drive ESCs because I may have a hard time getting everything to fit, and the body I designed for Cannon is fairly large.
- The brushless magnets don’t feel very strong, though the motors feel very precise when you turn them. My feeling is that I am mistaken and when I actually wire the motor up, I’ll be in for a pleasant surprise.
- The motor wires are small and flimsy.
- The battery came with a JST connector on it. The battery is rated for 25C (11.5A) continuous, 40C (18.4A) burst. JST connectors are rated for 5A. That’s a waste of plastic.
Still, despite my minor complaints, I am happy with my purchase so far. I can’t wait to see that motor spin.
The motor isn’t the only part of Cannon I am excited about. I learned a lot about building eggbeaters well with Lolcat, and I believe most of it will apply in the antweight class as well. For one, protecting your belt is very important. Lolcat’s belt almost got sliced twice at Bot Blast, so I’ll try to get the side rails to cover up the pully. However, the bottom of the side rails is far more important. Tracked Terror kept getting underneath Lolcat and flipping it over. I worry that wedges could do the same with Cannon, but I have devised a fix of sorts.
Notice that the sides are swept back. The beater extends way forward of the front of the supports. I am concerned about what effect this will have on stability. Since the beater, likely the heaviest individual part of the robot, will be centered in front of the support, the entire robot will act even more front-heavy. It could lead to some flipping over on hits; only time will tell. I am also concerned by how small the bottoms of the supports are, but they will be 3/8″-thick UHMW so antweight weapons shouldn’t be able to completely wreck them.
The only way we’ll see how this plays out is in the arena. I will continue to post progress updates on this blog as Cannon comes together.