Arm Prototyping Today

Today was pretty standard - went to the soldering seminar, and then hit the shop around 3:00. The day was spent prototyping our arm design.

Our arm is passive - we have no motors or actuators attached to it. The concept is pretty basic - small, light balsa wood strips are mounted to a rotational bearing that is centred in the robot, mounted 45cm up. On the end of the arm, elastic bands are used to both stabilize it (preventing unwanted bouncing etc.) and as the restoring force of the arm. When the arm impacts the pole, it will rotate out of the way without applying a large magnitude of force on the drive base, allowing it to continue to drive straight. Then when past the pole, the elastics will snap the arm back into place, without the reverberation that would accompany a spring loaded system. 

After trying a couple of different elastic materials, including a coarser elastic tubing and flat bungie cord like material, I resorted to the trusty rubber band. Both of the more robust materials didn't deform enough and put too much force on the arm. After playing around with the configuration, I found that attaching the rubber bands below the arm, at approximately 38 cm above the ground, was the optimal place. 

I also played around with some scrap plexiglass, to get the feel for how fabricating the case for our circuitry would be. I learned not to drill too close to the edges, and to be careful not to screw it down too tight - both can cause cracking. I think I'm going to pick up some green plexiglass this weekend - it'll match the wheels :D

Also, our battery and encoders came in today! A very successful lab session for sure.