12/23/2014 at 04:08 •
Recently, I've been working on basic motions with Moti; things like shooting over distances, stepping, and braking. This started with comparing different types of braking: regenerative, dynamic, locked anti-phase, and even coasting to see which would stop the motor faster. Regenerative and dynamic braking were pretty much the same, and the best performing. When initiated at full speed, it takes about 15º to come to a stop. Locked anti-phase braking didn't perform well, though I'm sure it could be done better. However it generates an audible buzz at the 500Hz PWM frequency I'm using, and I couldn't stand it...so I quickly moved on. And of course coasting was the worst and was used as a control. So for the moment I'm using dynamic and regenerative braking. This website was helpful for understanding the differences between each.
Before jumping into stepping, I wanted to see how an RC servo controls it's motor, and here I'm talking specifically about the output from the H-Bridge, so I spent some time probing it with my scope. I've uploaded a playlist of these explorations. The TL;DR of the matter is that this was highly useful. Not only did I learn how an RC servo steps, but also how it shoots and decelerates when approaching its destination. I was then able to whip up a step function that produces what appears to be both finely grained, and repeatable steps. I dabbled with shooting, but don't have anything conclusive to report about that yet.
11/30/2014 at 19:49 •
There hasn't been much progress on Moti for a couple of months now as I was busy with teaching and another project. Now that those things are wrapping up, I'm looking forward to getting back to it.
A couple of questions for you. If you had to choose, would you prefer:
1) a few breakout pins and a smaller servo,
2) more breakout pins and a larger servo,
3) more breakout pins that are smaller-pitch (eg. 1.27mm or 2mm instead of the commonly used 2.54mm)?
Lastly, congrats to SatNOGS on winning the Hackaday Prize. It's an awesome project, as were all the finalists.
10/14/2014 at 04:28 •
I spent much of the day getting the driver-level facilities working at their most basic. I've heard this described as bring-up, though it's the first time I've used the term, so I could be misusing it. Anyways, it was a great day, as a number of features were tested, and all worked. Thank god for using monolithic ICs instead of custom designed circuitry. It works just as specified in the documentation. Here's a playlist of a bunch of videos showing what was done.