30 lb Rebound!

After finishing the newest version of my 12lber and being absolutely satisfied with it, I decided it was finally time to make it back to the big leagues and build a new featherweight!

I hadn’t built one of these since the joint effort with Jared of PMTH, a robot made out of a cast iron skillet.

Of course, my new featherweight would have to be a scaled version of Ricochet!

Photo Apr 22, 6 16 24 PM

First step: Big ole pile of waterjet parts.

As always I like to try to standardize the thickness of my frame to keep everything simple, and with the aspect ratio of my design, it works out that the frame should be about constant thickness. In this case, the robot is made out of 7/16″ 6061 which I found as leftover stock from the Hyperloop team!

The top and bottom plates are made out of leftover Sawblaze 1/8″ Ti which should be plenty strong, even to keep Megatron out!

For drive train, I decided to use P60s, with prop drive 42-38s, aiming for a top speed of around 15mph. This is way overkill but it compensates for another issue, the weapon motor…

Photo Jan 28, 3 36 35 PM

Unfortunately, the Prop Drive 50-60 that I elected to use was a bit underpowered. I had a desired top speed for the blade which determined my gearing, but it took around 7 seconds to get the blade spun up. Luckily the drivetrain allows me to zip around my opponents in the 7 seconds it takes to spin up. Once the robot’s spun up the first time, there’s no stopping that blade! It stores a theoretical 8kJ of energy!

Photo May 05, 5 14 50 PM

Some lazy mill work. I just assembled the box and through hole drilled the mounting holes.

The central weapon hub. Both needle rollers press into this piece which goes through the entire blade and keeps the weapon load evenly distributed on both bearings. The post is actually tapers to compensate for the waterjet taper in the blade.

The blade is actually made out of 2 pieces of 1/2″ AR500 welded together. Unfortunately it was difficult to source a small piece of 1″ thick AR so I opted for this setup which also serves as a valuable test for the bigger bots! In order to keep the heat treat on the hitting end, I made sure to keep the tip of the blade cold, and only welded in strategic places around the blade. I ground a bevel in the blade to allow for better weld penetration.


Photo May 05, 10 06 58 PM

The assembled robot! The wedge is welded very similarly to my 12lber and the only change before my first competition was to dual up on the wheels for more traction (it does burnouts!). Overall this build was extremely pleasant and 30lb Rebound is ready to throw opponents into the ceiling!


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