PMTH3 was a very interesting project to work on. I worked on it at home over the summer. I had pretty much no machine shop access so I had to design around that.

I spend quite a large amount of time on the CAD model, checking tolerances, and adding every single nut and bolt and came up with this:

I had learned a lot from the disaster of PMTH2 and aimed to fix all the pitfalls.

First, NEW DRIVE MOTORS. This used the 1000 rpm kitbots motors, coupled with Fingertech wheels and hubs for the perfect match up. I’ve never had any drive issues since.

I also wasn’t satisfied with how hard PMTH2 hit. This was a result of two things. First, the drum had difficulty getting under opponents to hit them into the air; instead it just hit them forward, resulting in the same issue that plagues horizontal spinners. PMTH3 had optional wedglets in the front to aid in guiding opponents into the disk.

The next fix to hitting was in the shape of the weapon. PMTH3 uses what is called a single tooth disk, or STD. The blade is asymmetric, but still balanced giving the maximum amount of time for the opponent to move into the blade, and gives me the most “bite”. This allows PMTH3 to hit it’s opponent with about half of an inch of AR500 (super hard tank steel) as opposed to just the tip of the drum.


The last major change was the addition of the little ears on the weapon rails. These allowed PMTH3 to drive even while inverted. I could then self right by driving into a wall with the blade spinning.

PMTH3 was also designed to be super easy to fabricate. I asked a friend at school to waterjet the parts for me, and so about a week later, I had a box of parts show up to my door. I also opted for using real engineering principles and opted for needles roller bearings, along with thrust bearings to constrain the blade.

Because of the waterjet T-nut design, I was able to assemble the robot in one day! All the pieces fit together perfectly and so it was time for testing!

PMTH3’s blade had so much inertia and was spinning so fast that by turning really quickly, I could get the robot to “gyro dance” and lift up one side of the robot.

Finally it was time for it’s debut competition (One day before going back to school in the fall)!

Unfortunately, it also didn’t do as well as I had expected.

In my first match, I was fighting an overhead saw robot (saw blade on an arm) so I didn’t think too much of it. Typically the saws are incapable of cutting through aluminum and so they’re pretty rare nowadays. Boy was this not the case.

In the first 30 seconds of the match, the other robot Splatter cornered me, sliced straight through my top plate and my battery connector. Needless to say I couldn’t move after that. (excuse the slowmo video)

My next match was against a big block of styrofoam and I won (lolz)

During my last fight of the night (unfortunately no video), I was paired up against a pretty vicious drum spinner. We exchanged some good first hits, but the shaft collars that held my shaft in place got knocked off and I ended up losing my weapon.

Luckily PMTH3 didn’t sustain any real damage (besides the cut in the top plate) so it can still run again.


Overall record – 1-2              (Getting better!)