Re: I'm meeeeeelting!
I've definitely talked about this before, but when working at a UK Polytechnic, we bought, for student projects, remarkably capable six degrees of movement small(ish) robotic arms that moved by using linear actuators driven by motors with infra red sensors on shaft encoders that counted the number of quarter turns. This worked by having an IR emitter and a sensor and a reflector on the shaft made from white plastic that would bounce the light from the emitter back to the sensor four times per full rotation, allowing the micro-controller to count the number of rotations and thus the position of the actuator.
I had just put one of the kits together on a desk by a window, and I was testing it out, and it was working quite successfully, right up until the sun broke through the cloud cover. This flooded the area the robot was in with warm sunlight. Cue the next operation I started, which was an extend to maximum position for all of the actuators, and the arm tried to tie itself up in knots as each of the actuators extended to, and then beyond their maximum position, pulling the robot off the desk, and causing a couple of the switch transistors to pop as the motors got stopped by the safety stops, stalled, and tried to draw more current than the transistor could handle.
Turns out that the white IR reflectors also allowed light from the outside to pass through, and the sunlight swamped the IR sensor, which prevented it from seeing the pulse of IR light from the emitter. This resulted in the motors keeping turning until they were physically stopped!
We talked to the supplier of the arms, and they agreed to replace the motors with the blown driver transistors, and also devised an opaque cover for the shaft encoders to prevent the same thing happening again.
It actually pains me that very few students even considered using these robots, or any of the other goodies we had, to do their final year project (most of them did pure programming projects), and the robots mostly sat in a cupboard until the lab. was decommissioned. If I had still been working, I would have offered to give one of these robots a home rather than seeing them thrown away!