Some time ago I wrote about using the wcubed vise for the Pocket NC. While I don’t end up using it very often any more, mostly because I rarely work with rectangular stock, it can be useful from time to time. Unfortunately, it is no longer manufactured. In case anyone is interested in replicating it, I’ve taken at least a minimal stab at modeling it up based on measurements of my unit along with necessary hardware as picked from McMaster. I suspect the model should be good enough to get something that works.

Being a switch mode 3 phase motor driver, the moteus controller changes the current flowing through the phases of a motor by rapidly switching the phase terminals between the positive input voltage and the input ground. The control of this switching is denoted “pulse width modulation”, or PWM for short. To date, the rate at which it has switched has been fixed in firmware at 40kHz. As of release 2022-03-12, this can now be altered anywhere between 15kHz and 60kHz to better optimize peak power capability, control bandwidth, maximum speed, and heat generation.

With the r4.8 release of moteus, a not-yet-announced feature was included – the ability to have an off-board primary encoder! It didn’t get announced at the time, because the connectors necessary to populate the board were not obtainable. In fact, that is still the case, but I’ve located a substitute part which works well enough, so here we go!

Theory

The moteus controller uses an absolute magnetic encoder to determine the relationship between the rotor and stator of the motor at each given instant. That allows it to produce torque in the motor at any speed, from standstill to the maximum possible speed. Until now, the only magnetic encoder that was supported is the one mounted to the backside of the board. This is largely acceptable, as moteus is intended to be used in integrated applications.

Now that 64 bit Raspberry Pi OS is a real thing, I finally got around to updating the pi3hat libraries. Now, as of pypi 0.3.20, you can use the pi3hat library to run console only or graphical tview on the most recent Raspberry Pi OS!

With the Artisan’s Asylum closed for a relocation, I’ve been without access to a manual lathe for a while. Fortunately, import mini-lathes aren’t that hard to come by!

This is a Sieg C4 derivative from Little Machine Shop, which was about the largest machine I could reasonably move into my basement.

It isn’t as rigid as the Colchester at AA was, but it does have power feed and power cross feed which both work just fine. I’ve run into a few minor quality issues, and the spindle runout isn’t great, but it should do for my needs.

The most recent moteus firmware release, 2021-12-03, added not one, but two new control modes for less common applications. Previously, mentioned was the “voltage_control_mode” for using gimbal style high resistance motors without changing the sense resistors. In this post, I’ll describe a similarly named, but very different mode “fixed voltage mode” for operating brushless motors as if they were a stepper motor.

For some applications, you don’t care about torque control, or about power consumption at all. Traditionally you would use a stepper motor in those applications, with a correspondingly less expensive stepper motor driver. However, in some cases you may still want to have high rate trajectory control, CAN based telemetry, or have already standardized on moteus controllers for other moving parts of your solution. There are two new options that can be used in such situations: