Big Disk Energy Post-event report: Franklin Institute 2018

Big Disk Energy went 0-2 at Franklin Institute, mostly due to CG and electronics issues. Although I intended for this robot to deal massive hits, I did not fully anticipate the forces that the electronics would see because I thought the softer UHMW frame would dampen any hits the robot gives or takes. That was not the case, the frame was far too rigid to preform this function. I did not put any other mechanism in the robot to dampen the shock the electronics see so in the first fight, after a minute of bouncing around the arena, the pads on the output terminals of the weapon ESC tore off from the inertia of the ESC.

In BDE's inaugural match, it had to go against Silent Spring, one of the most successful robots in the northeast. After a few blade to blade hits, Silent Spring was able to remove both of the snap wheels from BDE after I made a bad move and exposed the wheels. The snap hubs immediately fell off, leaving me to question their reliability. I kept the blade spinning and due to the gyroscopic forces from the weapon and the torque of the hub motor, the blade kept spinning and hitting the arena floor and walls, shooting BDE around the arena. After about a minute of flying around, the pads tore off of my weapon ESC, disabling it. BDE was then counted out.


In BDE's second match, it had to fight Squishy, a robot built by another member of the WPI Robotics Club. After breaking the weapon ESC in the first match, I realized that I forgot to bring the spare motor controller and frantically looked for a replacement. This proved to be difficult due to the size constraints from the frame and because it had to be able to work on 6s. I could not find a replacement ESC but was then shown that the top layer of fiberglass could be scratched away on the broken ESC, revealing an internal copper trace that could be soldered to. I successfully repaired the weapon ESC just before the match started and quickly plugged everything back together. I, however, accidentally plugged the weapon PWM connector in the receiver backwards. Squishy also had some electronics issues with the weapon but was able to get them fixed before the match.

Later in this match the snap hubs failed a second time, and a wheel fell off without being hit, then Squishy tore the other one off. BDE was counted out and Squishy won the match.


BDE was able to be fully repaired from the second match by flipping the weapon PWM connector and re-tightening the snap hub setscrews. At the end of the event, there was a 3lb rumble that BDE participated in. At the beginning of the match, I spun the weapon up but was quickly forced into the wall by a wedge. BDE bounced off of two walls, put a gouge in the arena wall, then on the final hit both motors shot out of the robot. That mesh is made out of 1/8" thick steel! 


Overall, I was satisfied with BDE's initial performance. The weapon module and blade design worked exactly as I wanted. I added holes in the side of the robot in the initial design for a plate to prevent the motors from coming out but after testing with the motors glued in, I thought that the glue would hold up. the next version will have the plates to prevent the motors from coming out. The snap hubs failed in both matches so the wheels will be changed to the Botkits D2 wheels. The Botkits wheels are about 3x heavier but are far more reliable because the wheel is bolted on to the hub and the hub uses a clamp mount to the motor shaft, grabbing along a wider area with more force. The ESC will stay the same but will have to be mounted better and the leads will have to be battle hardened for shock resistance.

The main problem with BDE at this event, however, was the poor CG placement. Due to the heavy weapon module and blade, the CG of this robot is very close to the front, meaning that there is more weight on the bolt dragging on the ground than the wheels. This makes the robot turn slowly and get very little traction in reverse, causing a slow reverse acceleration. The focus of the design for the next version of BDE is going to be making it drive better by creating a new frame with better motor and electronics placement for a more favorable CG, putting more weight on the wheels.

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