Title: The Phoenix Rises Date: 2012-11-12
After designing and building a 3lb combat robot in 4 weeks for the Atlanta Mini Marker Fair (AMMF), I was coerced (read: accepted an invitation from Jamison) to go to GMX two weeks later for another competition. Now given that MowBot’s performance was good at the last competition but spotty with the weapon not working consistently, I felt the need to redesign and rebuild in the 2 weeks I had before the competition.
So here I go again. A complete redesign and rebuild in half the time as the original design and build. (Spoiler: I don’t get much sleep)
There were a couple of design flaws that I looked at from the first build:
Weapon Support Structure
There was way too much friction heating and a severe lack of constraints throughout the weapon drive system that caused a lot of vibration and slow ramp up speed. The weapon was virtually ineffective because of this.
Solution: Direct drive the the weapon off the motor. This calls for an increased support system using a thrust bearing, transfer shaft that bolts to the can of the motor, and a drive plate to attach the weapon.
The weapon had a very weak torsional structure given that the main component was aluminum that bends fairly easily (check the pictures from after the competition at AMMF). The teeth were not near as hard as I thought they were and didn’t get the desired bite and destruction that was expected of it.
Solution: Weapon shape redesign, material hardening. I redesigned the shape of the weapon electing to make the entire thing out of S7 tool steel instead of the just the teeth. We did not realize this before but the S7 we had bought was just annealed and not hardened giving it a hardness of HRC20 instead of the ~HRC50 we were looking for.
Corners on the chassis
The corners where the armor met on the chassis got bent down in the rumble at AMMF by Dominant Mode and lifted the base up enough for my wheels to not contact the ground anymore making me unable to move.
Solution: reenforced corners. I left the angled armor on one of the sides and flattened the other so that the corner would be backed by the aluminum frame. I also switched to 1075 steel for the armor plating that was hardened and then tempered to turn it into spring steel.
After a late night drive up to Tennessee, some early morning assembly work, and just over 2 hours of sleep, the 6 of us who had come walked into GMX. The competition was a lot of fun with a good showing from all the robots. The new hardened armor got it’s test and held up remarkably well taking just scratches and not yielding. There was a large hit taken by one of the corners that bent all 4 aluminum rails of the chassis (redesign not successful). Luckily a hammer was able to correct the damage. The whole team be brought had trouble throughout the day with motor controllers failing, motors tearing themselves apart, and switches turning off in the middle of matches but the team helped with each repair, most of them being on robots that were not our own.
During the semi-final match I noticed some wires starting to stick out of the bottom of the chassis. The match ended in a win for MowBot but after I drop out of the area there was a small spark and fire started to come out of the bottom of my robot. After a quick use of the fire extinguisher, a trip outside, and a battery swap, MowBot was reborn as The Phenix clad with a new white finish from its ashy rebirth. It went on to loose the final and do well in the rumble taking hit after hit and earning a valiant second place at GMX.
All in all a great weekend and a lot of lessons learned. Always keep a fire extinguisher near by…