Time of death: Sunday, 30th April, 4 a.m. After our first real experiments on BallE, one of the transistors from the H bridges controlling the motors burnt on Sunday at 1 a.m. We aren’t sure about the cause underlying this incident: at that time we were varying the acceleration. While stopping the motors, in order to stop them faster we forced the current to 0. This induced a high voltage in the circuit: one transistor burnt and then we weren’t sure the others hadn’t been damaged in the process. Once we figured out what happened, we tried to replace the transistor. As the components on the card were really crowded given the surface (and didn’t satisfy the theoretical constraint of having enough space for the H bridges to cool down) it was hard to extract the transistor and re-solder a new one. We didn’t have the exact replacement so Samuel and Alexis tried to improvise with the transistors we had in stock. The replacement didn’t succeed and at 3 a.m. we had the choice between:
a) redoing the whole mechanics and design for a 2-wheel ballbot
b) picking up another project for the following 4 days until the defense
By choosing option A, we couldn’t guarantee that what happened for one H bridge wouldn’t happen for the others… we barely started our tests with BallE in the final form. BallE wasn’t stable and we needed time to calibrate and perform a broader range of tests. None of us wanted to give up working on BallE. However, we had absolutely no guarantee that we will have succeeded in keeping Ball-E stable for this Friday. We all enjoyed working on this project and we were very emotional about our choice… However, the risk of not having anything stable for our defense was very likely even if we kept working hard on Ball-E.
After a Sunday night full of nightmares, we spent the day thinking of replacement projects that were doable with the hardware we have for ROSE.
The following post will be dedicated to explaining our options and choices. Now, let’s keep a moment of silence for Ball-E…