thanks for chiming in and for your kind words, I appreciate your comments and your interest in the project.
Here are my thoughts on the servos discussion in this thread:
- Cheap (~$120) linear servos are slow and generally underpowered. If they have control circuitry, that would be closed source. Alan - I looked and haven't found anything in that space. Let me know if you have something that fits.
- A typical large hobby servo would have something like "Operating Speed: 0.13sec / 60 degrees (6.0V no load)" in the specs - fast enough to control an airplane model. My servos are fast - about 0.5 second for full stroke. I am in complete control of torque - by choosing the motor, gearbox and pulley dimensions.
- Movement precision in my case isn't a major requirement (as Chris noticed), although my servos are doing fine in that department. R/C PWM so far fits fine (1000us range with 10us noise is still a 1% precision, and RPi Hat or Teensy Pulse Position Library do much better). If my servo doesn't reach its setpoint in 3 seconds, I cut off motor power. This trick sacrifices SOME precision, but saves motors and H-Bridges. No matter how I torture the servos, they run cold.
- My control circuit is a typical Arduino thing that has many connectivity options (R/C PWM, I2C, Serial) and it is completely open for tinkering. Whole servo is $25 (motor) + $10 (BT-2 H-Bridge) + $3 (Arduino Nano) + $3 (sensor). Note the magnetic rotation sensor for feedback - its stability and precision is amazing, I won't use POTs ever again. Also, those automotive motors are made to last, and under normal load are quite reliable.
Overall, I highly recommend playing with the concept of self-made servos. It isn't hard, and it opens many possibilities. There are now brushless motor based servos, they are the future for robots.
Carl: our projects are indeed similar, although at the moment I put a lot of emphasis on PH4 autopilot, running on RPi 3 with a custom hat (Navio2 inspired). You can see it in the robot "skull" in the photos. I gave a 30-minute presentation at the RSSC.org meeting about my plans and the basic use of the autopilot and QGroundStation - https://youtu.be/UAVATDUWX7Y?list=PLUEDYYT2aLNMpZigEr-VQspI149PWWbnc&t=3885
Most of what we need can be achieved by autopilot alone, but you know how much fun it is to tinker with Jetson Nano and its two eyeballs. And yes, Hollywood scenario is always on my mind, and I already call my lawnmower "Crazed Rhino", although it doesn't deserve this and is so far well tamed. :-)
Anyway, thanks once again - and keep making good robots!