Thursday, July 25, 2013

Cake Slice and PA Bot Blast 2013

Hi Charles, I'm writing a blog post.


Part of my joy of moving up to MIT was the fact that I was now in prime vicinity of a more lively roboting community. In the Northeast region, we have well established competitions like the Franklin Institute of Motorama.

Another regular event in Pennsylvania was PA Bot Blast, held in Bloomsburg every July. My friend Aaron fan from the Georgia Tech Invention Studio convinced me to go, so I convinced my long time bot buddy Charles Guan to make the trip with me. We created enough hoobaloo in MITERS to spawn a small team and soon we had an entire van committed to go. Hence fourth it was time to get prepared as the date loomed closer and closer.

DDT was definitely going. The new version was completed in late 2012 after Dragon Con in preparation for GMX robot battles where it went undefeated and unscathed. The only work I needed/wanted to do on him was trim the through bolts that hold the frame halves together. This way, the robot was actually invertable.

I hope heating those screws don't melt the nylocks

I was previously intending to bring Cake, my old Beetleweight made in 2010/2011, but I had lent it out to some friend going to Robogames and it returned to me... missing a few things.

Without a waterjet, there was no hopes of finishing the parts needed to make it competitive or solid. Time to move on.

Instead I opted to make a joke bot. Lets design a wedge with absolutely insane speed for the sole purpose of box rushing people and maybe decking them into the wall. No way it would win, but it would be extremely entertaining to watch and drive.

I grabbed a pair of 280-sized motors from my spares bin. These motors were surplus back from Florida but had some serious power. First indicator of this were EXTERNAL BRUSH HOUSINGS WITH HUGE CONTACTS. This is of course opposed to the dinky precious metal springs that daintily drape over the commutator. I knew this motor had some serious current carrying capabilities.

And they did. They drew 3 amps no load.

To make the robot a tad more reasonable I mated these motors to the 10:1 gearboxes of the ever popular "1000 RPM Gearmotors". First I had to remove the pinions from the old motors. Then I had to secure them to the new splined shafts of the surplus motors. Historically, we know that a press fit simply isnt enough for these motors since their monstrous torque essentially reams out the pinion if any excessive load is on the shaft (i.e. robot weight). I remedied the problem by complimenting the press with a flux and solder treatment.

With the drive motors finished, I began arranging the parts to develop a chassis design. While a traditional wedge could have worked, I felt it was to boring. Some creative arrangement later turned up an old friend of a robot: the dustpan.

3D printing frames is cheating

By this time, we only had two days left until the event. The only option was to 3D print the frame on the IDC's Dimension 1200es ABS FDM printer. It saved a lot of time on parts machining but it also introduced some headaches of its own along the way.

Robot taking shape! Control electronics were selected to hopefully run the powerful motors. I whipped out my 9 year old Scorpion HX esc for the drives, and pulled an orange RX for the control. It was then I discovered the esc was not enough to handle those surplus motor hacks. Sad day. I suppose we will have to compromise with a Pololu 4.41:1 HP gearmotor.

The wheels were leftover Banebots 40A durometer wheels with a hex bore. I made hubs from some metric hex stock center drilled for the 4mm motor shafts, drilled to hold a 6-32 set screw, and pressed into the BB wheels.


so far so good

To save some time on printing, I elected to make the dustpan bottom from a thin sheet of garolite. This sheet would be held on the bottom using adhesives.

It was decided that this robot, being made from parts of the robot cake, would refer to its inheritance in some way. Also being a wedge shape, I decided to name it Cake Slice. It would be a part (or slice if you prefer) of Cake, while having a slice-like shape. So brilliant, I know.

Apparently I don't have any finished photos :(

On the Friday evening two hours before our departure, I came home hoping to test drive the robot. Unfortunately I left my transmitter on and was unable to practice with the robot. Its first match would also serve as a driving test.

Game Day

Five hours of Miku later, we arrive at a waffle house and meet Aaron for a 4am meal. From there we venture down the last hour to the Columbia Mall in Bloomsburg to see the wonderful new arena that Jeremy and his parents had put up.

THIS IS IT. jk, test box

builders watching the robot being tested outside the test box

okay, the new arena seriously

omg prizes! best trophies in the US
Being the first builders that morning (we better have after camping out in the parking lot), we picked prime seating in a center row, right above a power outlet.

Aaron's robot ,"Final Exam" without hat

My two robots DDT and Cake Slice. Washers taped to the front to prevent wheelies

delran-bumble:a stepper motor drive robot from out MIT crew

threecoil: an innovative flywheel 4-bar flipper robot

Alex Hone's stuff
After a smooth check-in and drivers meeting, it was time to begin the fray. Leggo robots!
DDT vs Slim Pickens
DDT drew the first match of the event against a sheet metal wedge. Slim was based off a viper kit if I recall correctly, and added some extra steel to strengthen the front plate from my horizontal blows. Unfortunately for him, DDT doesnt attack the body as much as he punishes the corners of any robot. DDT ripped and bent up the front wedge enough to high-center Slim and he tapped out.

Cake Slice vs TTI Wedge
Titan Tech Industries is developing a series of modular robot kits for interested persons. In this Bot Blast, they are debuting their wedge kit, which looks like a sloped Weta without an active weapon. By this, I mean a classic cheese wedge shape with UHMW wheel guards bend around the frame. My only concerns were CS's tendency to lift up when he charges the opponent. I would need to get a running start to keep the drive aggressive and the front end down.

What ended up happening was completely unexpected. I actually stripped the gears running around the box. When I opened them up, it appears the boxes were design to have about 1/5 gear face contact. Ugh. So terrible engineering. If you buy these ever, remember to remove some of the spacers on the intermediate stages to get better contact.

DDT vs Speed Bump
Nooooo! I have to fight one of our own :( Speed bump was a low wedge bot made from the donated frame of a fellow bot builder. It was less than an inch tall, and features a gaussian cross-section double wedge. The top was made of a plastic found in 3-ring binders and I was a bit afraid of blasting through it and hitting the lithium battery.

Luckily, there were no fires. The match was also far more difficult than I had imagined. The low angle of the wedge and the flexibility of the binder material made it early impossible to get a bite. My only good shots were the aluminum sides. After a few taps late into the match, Speedy was high-centered and tapped out.

Cake Slice vs Speed Bump

DDT vs Dust Pandemonium
Now I have to fight the style robot i was originally famous for: the dustpan. Pandemonium was a custom made CF almost-unibody with a meanacing thresher type weapon protruding from the front. He would charge opponents, capture them in the dustpan, and gnaw on their frames with the thresher. As long as I kept my blade out front, I knew I would be able to stay out of the pan and away from the weapon.

When the match began, he charged straight at me figuring he would not be able to maneuver around my blade. I hit straight into the gut of the dustpan and luckily hit a seam. That one hit penetrated into his electronics and gave me the fastest KO at 15 seconds.

Cake Slice vs Guildenstern
Guildenstern is a vertical bar spinner what didn't alarm me at first. But it turns out the bar is asymmetrical, made of steel, and packs quite a punch as seen in its previous matches. For Cake Slice, this would pose a problem  because he could probably easily punch through the front wall and hit my gooey insides.

I added a layer of padding on the inside wall to dampen any blows just in case. I was mainly hoping I could suspend his frame using the dustpan pontoons. This was actually feasible since unlike many other vertical spinners, Guildenstern lacked anti-wedge devices. Either way, all strategies soon went kaput when I lost a drive side early on.


It appears layered ABS is easily ablated. No throwing hits though

DDT vs Ripto
Ripto is the classic vertical disk design of a talented builder and driver Kyle Singer. He scaled down his beetleweight for this competition to enter this antweight version. He also has gone through thus far undefeated. I knew there would be no mistakes allowed in this match. I could not allow any wasted movement since Kyle could easily capitalize on my gyro dances. I would need to aim for a disabling hit or weapon kill early on.

I think I was lucky my first hit. Taking out the drive made things easy for me in that he couldn't hit me in my instability. After that, it went downhill for him. I was able to sneak in behind him and chop up his o-ring wheels.

DDT vs Ripto (finals)
Same strategy with a little more desperation. This time, it was for the infamous Bot Blast light tree trophy! The hits were far better this time but the result was the same. This version of DDT is an absolute keeper!

Before the finals!

Unhappy bearing trying to escape
Cake Slice did was Cake Slice was supposed to do. But DDT performed flawlessly going 5 wins and 0 losses. The match against Dust Pandemonium also went in as the quickest knockout. Below is a shot of DDT and his spoils of war.

DDT and his spoils of war