Like with the fdcanusb, I built a programming and test fixture for the moteus controllers. The basic setup is similar to the fdcanusb. I have a raspberry pi with a touchscreen connected via USB to a number of peripherals. In this case, there is a STM32 programmer, a fdcanusb, and a label printer. Here though, unlike with the fdcanusb fixture, I wanted to be able to test the drive stage of the controllers and the encoders too.
This post will be short, because it is just re-implementing the functionality I had in my turrets version 1 and 2, but this time using the raspberry pi as the master controller and two moteus controllers on each gimbal axis.
I have the raspberry pi running the primary control loop at 400Hz. At each time step it reads the IMU from the pi3 hat, and reads the current state of each servo (although it doesn’t actually use the servo state at the moment). It then runs a simple PID control loop on each axis, aiming to achieve a desired position and rate, which results in a torque command that is sent to each servo. Here’s the video proof!
To date, I’ve used the moteus controllers exclusively for joints in dynamic quadrupedal robots. However, they are a relatively general purpose controller when you need something that is compact with an integrated magnetic encoder. For the v3 of my Mech Warfare turret I’m using the moteus controllers in a slightly new configuration, with a gimbal motor, one for each of the pitch and yaw axes.
From an electrical perspective, gimbal motors are not that all that different from regularly wound brushless outrunners. The primary difference being that they are wound with a much higher winding resistance. That enables them to be driven with a much lower current, at the expense of a lower maximum angular velocity. In this case, I’m using the GM3506 from iFlight which has a winding resistance of 6 ohms, that results in working currents being on the order of 2A maximum.
Developing the moteus brushless servo controller has been a very long journey, and while it isn’t over yet I have a reached a significant milestone. The first batch of production moteus controllers are now available for general purchase at mjbots.com and shipment worldwide for $119 USD each!
I’ll repeat some of the specifications here:
Simultaneously, I’ve got development kits available that give you everything you need to start developing software for the moteus controller out of the box: moteus r4.3 developer kit
