Bipolar Build for Motorama 2004

The Design and Parts

I had been pretty much religously watching BattleBots on TV and Season 5 had recently ended. I was always impressed with a particular lightweight shell spinner named Ziggo. It's not unlikely that I was impressed because it was ahead of its time, retiring opponents and winning competitions. I read up as much as I could on the bot and how it was created and decided to try to make a 30 pound version. This is a little humorous because Ziggo was actually a 60 pound bot modeled after Jamie Hyneman's Blendo. You may recognize the name from his work on MythBusters. Blendo was the first bot judged too dangerous to compete I think, which naturally drew in the builder of Ziggo.

I started working on Bipolar by looking at other 30 pound bots and what weapon motors they used. Almost all of them were using the now-extinct EV Warrior motors. I decided to get the slightly more powerful (as a pair) and significantly more expensive Astroflight Cobalt 940 motors. It looks like they don't sell these anymore either. They were $175 apiece, and I needed two of them to get the slight power boost that I wanted over the EV Warrior motor that cost a mere $22. They are lighter, but somehow it didn't even occur to me that I was being an idiot. The motor controller I picked was a Thor Spin Controller for around $200. This was done so I could have proportional weapon control instead of using a big relay system for $30 that would only allow me to have on/off control. Ah well...

I also decided to use a Vantec RDFR23 speed controller instead of a pair of Victor 883's because it was a little smaller and lighter. This was one place were I made a good choice. The Vantec never failed me and five years later I sold it to Jerry, another builder who now does combat robot birthday parties. He is one of the guys I met at the Robot Club & Grille for the first time I ever saw these things in person. His encouraging and positive attitude is a big part of why I'm doing this today.

The drive motors were Team Whyachi T-Boxes. They were also $170 apiece, plus $27 for each wheel and $26 for the wheel hex shaft. Again, I'm not sure why I didn't just get the $20 drill motors that everybody else was using (and is still using today). As you can imagine, the build got pretty expensive pretty quickly. So far I've wasted around $500 in parts that were too fancy for my own good...

The batteries in the original bot were... uh... plentiful. I had found the Team Tentacle Torque Calculator and determined that I needed about 2000mAH of battery for the drive system to last a hard 5 minutes. Rather than thinking "hmmm I wonder if the fights will be 3 or 5 minutes?" I decided to get a pair of 1700 mAH nimh packs for the drive. Each one was around a pound and because they charge slowly, I decided to get three pairs to be sure I could always have a fresh pack if I had three matches in a row that were only the 20 minute guaranteed time apart. It didn't occur to me that that was not likely to ever happen, or that I would have so much drive battery power that it wouldn't matter if it did. The weapon pack was the biggest single pack I could find - a 3600mAH pack of NiCd cells. This was another purchase that served me well - in fact I was still using these same nicad cells at motorama 2009!

I had another company that has since disappeared, make the weapon pulley and weapon mount for me. The pulley had a seat for a single Timken Tapered Roller Bearing. I thought that would be enough to hold the shell on the 1" shaft. I'm not sure why I thought it would be after I pressed it in with my hand and held it there with duct tape... In the end it didn't matter much.

The Shell

The shell was a cooking wok from The Wok Shop, the same place Ziggo's shell came from. I thought it would be plenty strong - after all, the 60 pounder used one! I failed to notice how much additional metal was added to the wok to make it strong enough to compete with. It turns out that he added about 15 pounds of steel to the 22" wok that Ziggo used. I added maybe 2 pounds to the 24" wok that I was using... ugh. I had the metal shop teacher at school help me plasma cut the bottom of the wok out and weld in a .25" thick mild steel plate for the 5" diameter top. I can't remember how I got the holes in the plate but I'm sure he did most of the work. They lined up so-so and I ended up reaming them out quite a bit to get the four shell bolts to fit. I welded a tiny .25" square mild steel ring around the bottom of the shell to make it stiffer and thought I would be fine. A friend of mine cut some 4140 I got from Mcmaster-Carr into giant triangular teeth and welded them on for me. In the end the shell was like 11 pounds.

The Assembly

Parts started arriving sometime in the fall of 2003 I think. I had no idea how to connect wires together or even how bolts were classified. I knew there were big bolts and small bolts, but had no idea about thread pitches or head styles. I didn't have a car so I used whatever hardware I could find on my dad's workshop shelves. That meant some of the screws were #8, some were #10, some were .25". The head styles differed from slotted buttons to hex heads. I think I even had a couple of toilet seat bolts in there because they had really flat heads. I had no idea what I was doing at all.

I was so excited to mess with the parts that I took a cardboard soup-can tray and made a baseplate out of it. I bolted the drive gearboxes in with a couple of random screws and tape. The rest of the guts were mostly taped in as well. It sagged and dragged on the ground some, but the drivetrain alone wasn't very heavy so the box held up ok. I took it out in the driveway and drove it a little. It actually worked ok. I thought I'd be cool and see how fast it could spin in place though... The battery flew out of the bot and the wires pulled out of the connector. I was able to press them back in but it was pretty scary when it happened. It's a miracle I was able to get the thing to work without having any idea what I was doing. I am amazed I didn't smoke anything or start a fire. I wish I had a picture of this prototype.

I took my graph paper model and tried to make a 1:1 scale drawing on a piece of poster board. Mechanical Drawing was the class that I struggled in more than any other in high school though, and the baseplate was rotated 45 degrees to allow the wheels to have outboard supports so I didn't have a straight edge to measure from. It was kind of a struggle but eventually I got something going.

I drew the diamond shape on a piece of the original plate that I got for the heavyweight baseplate (hah, like that was going to be thick enough... I'm using it in my 12 pounder now!). My dad helped me use the circular saw to cut the sub-square out and I started trying to install parts. I decided it would be a good idea to electrically isolate all of the components from the plate by covering it with a piece of cardboard. Shhh... it was cut from a Beast Lite box... I started putting components on the plate by blindly laying them on and trying to wrap pieces of galvanized steel stripping over them with bolts. I never had any idea how I was going to mount the parts before I just started trying to do so. That was a mistake.

Once I had the front assembled, I realized that one of my batteries was laying down on its side while the other was up on its end. I had run out of space because I didn't actually intend to lay either one down until I was doing the assembly. If you look at the paper drawing, both battery squares were narrow. Oh well, they sorta fit. The mounts were seriously questionable but the bots pretty much stunk back then so it was ok. I added the battery and mounted the weapon block and motors to create the final layout. Much additional work was done to mount and protect the weapon battery, but then I had to wire the thing.

Just like the metalworking, I had no real idea what I was doing with the wiring. I made the drive wires all 14 gauge because a friend of my dad's said that should hold the 30A that the drivetrain could draw. I made the weapon battery wires as big as they allowed when I ordered the pack - 8 gauge wire with 75A powerpole connectors. The 75A powerpole connectors are like 3" x 2" x 1" when you connect them in pairs - absolutely monstrous. Fortunately, the design was so crappy I had lots of space. I somehow managed to get all the wires run to all the parts without blowing anything up. I had some 10 gauge wire for the weapon battery to plug into because I couldn't find any 8 gauge, so it was a big waste to use 8 gauge wire in the first place for the battery. I somehow managed to make ok connections everywhere and the bot powered up the first time. None of the weapon mechanics were set up but all of the electronics were working.

By this time I think it was around mid January 2004. I installed the weapon pulley and tried to get the urethane flat belts to go on. I was able to get them onto the little tiny drive rollers I was using for weapon motor pulleys but was never happy with them. I had to mess around a long time to get the belts the right length. After a couple of weeks I got it together and did a halfhearted spinup in my garage against a cardboard box in my garage. I thought it was awesome but it probably only spun about 150 RPM or so. Then I took it to the post office to see what it weighed...

Oh Crap!... it was around 33 pounds and I only had 2 weeks until we left for the competition. I started looking for places I could drill holes to save weight. I didn't want to drill any in the baseplate if I could help it because I didn't want to take the electronics off of it. It was such a nightmare to assemble in the first place that I couldn't bear to disassemble and reassemble it. I decided to get a 1" twist drill from one of my dad's friends (yes, not a hole saw, a standard Silver and Deming drill bit). I started drilling holes in the shell and after I was done I had managed to lose about .75 pounds. I started cutting all of the hardware down as much as possible and getting rid of everything that wasn't vital. I managed to get rid of another pound or so that way. Eventually, about four days before leaving for Harrisburgh I decided I had to remove one of the two drive batteries to make weight. I did that and then packed my stuff.

When all was said and done I named the robot BiPolar because it had two big hammers on opposite "poles". I joked at the competition that the name was chosen because I was never sure what mood it was in: sometimes it would work and other times it would refuse to. It could change at a moment's notice. The bot was a tremendous lesson in project management, resource control, realism, and lack of budgeting. In the end I still consider it a success because of how much I learned. The weapon didn't work for anything but I did end up winning my first fight of all time somehow. The other guy's wheels unthreaded from the drill motors he was using. Ha! I guess the extra $300 I spent on a fancy drivetrain was worth it after all...NOT. I met a bunch of nice, helpful people and came up with a brand new design for the next version of the weapon based on a bot named Neotier. Check out the Event Report for a significantly more detailed narrative of what happened.