Category Archives: robots

new product day: mj5208 brushless motor

Welcome to the newest mjbots.com product, the mj5208:

This is a high quality 5208 sized 330Kv wound brushless motor with short pigtails intended to connect to moteus controllers. All the moteus devkits as of last week are shipping using this motor instead of the previous “semi-random” motor.

Specifications:

  • Peak torque: 1.7 Nm
  • Mass (with wires): 193g
  • Peak power: 600W
  • Kv: 330
  • Dimensions: 63x25mm

There are two bolt patterns on the output, a 3x M3 17mm diameter one, and a 2x M3 pattern spaced at 12mm. The stator side has a 4x M3 pattern spaced at 25mm radially and a 3x M2.5 spaced at 32mm. The axle protrudes a few mm from the stator, making it easy to adhere the diametric magnets needed for moteus.

New cross-platform moteus tools!

After receiving many requests via youtube, discord, and email, I’ve finally gone ahead, bitten the bullet, and updated all of the moteus tools to be pure python and work in a cross platform manner. Now, the only thing you need to do to install pre-compiled versions of tview and moteus tool on most* platforms is:

pip3 install moteus_gui
python3 -m moteus_gui.tview    # (or maybe just tview)
python3 -m moteus.moteus_tool  # (or maybe just moteus_tool)

I’ve personally tested these on Linux, Windows, and Raspberry Pi, and others have at least verified basic operation on Macs. Python 3.7 or greater is required.

….

But wait, there’s more!

Now, both moteus_tool, tview, and the python bindings more generally can use python-can as a transport. That means tview can now be used with socketcan, pcan, and a bunch of other options. To one up that, most users won’t have to even specify any command line options, as tview and moteus tool will automatically select a fdcanusb or python-can depending upon what is available.

I’ll be updating the devkit introduction video soon, although the commands in there will largely continue working for the time being.

Errata

  • Neither pypi or piwheels has pyside2 for the Raspberry Pi, but it is packaged in Raspberry Pi OS. You can follow the instructions in git to find a recipe that works.
  • To use the pi3hat, you need to also do pip3 install moteus_pi3hat

New product day: moteus heat spreader

The moteus controller is capable of a lot of instantaneous power. However, to fully make use of that power, you’ll need to keep the mosfets cool on the board. moteus has two mechanisms for that:

  1. A heatsink can be mounted to the bottom side of the PCB between the board and the motor. This is most useful when integrated into a servo motor, and the servo housing can be used as a heatsink.
  2. Mounted to the top of the board, attaching to the MOSFETS directly.

In addition to the MOSFETs, the gate driver chip, the DRV8323 can produce large amounts of heat, especially when the controller is run at a higher voltage, like the 44V that the moteus r4.5 supports.

Getting the heat out of all those irregularly spaced components on the top can be tricky, thus mjbots.com now has the moteus heat spreader:

This precision machined and stylish black anodized aluminum piece fits over the top of the PCB and mounts flush against both the MOSFETs and the DRV8323 to ensure optimal heat dissipation from all components. It can be used as-is, or with an additional heat sink fixed to the flat upper surface.

Don’t hesitate to ask any questions in the mjbots discord!

moteus and socketcan

Various users have been trying to use lower-cost Raspberry Pi CAN-FD adapters for the moteus controller for some time (like this one from Seeed), but have had problems getting communication to work. I buckled down and went to debug the problem, discovering that the root of the issue was that the linux kernel socketcan subsystem calculates very sub-optimal CAN timings for the 5Mbps bitrate that moteus uses. This results in the adapters being unable to receive frames sent at the actual 5Mbps rate, but instead only slightly slower.

The solution is to manually specify the bus timings when configuring the socketcan link. This makes the MCP2518FD boards work, and also PEAK-CAN-FD USB adapters (and probably every other socketcan CAN-FD adapter) work as well. You can find the timings linked in the moteus reference documentation: https://github.com/mjbots/moteus/blob/main/docs/reference.md#bit-timings

General socketcan improvements

As a result of all this debugging, I made some general improvements to socketcan support in all the client side moteus tools.

  1. There is now a documented commandline for invoking moteus_tool from socketcan: https://github.com/mjbots/moteus/blob/main/docs/reference.md#moteus_tool-configuration
  2. I released moteus and moteus_pi3hat 0.2.0 to pypi. These provide socketcan interfaces for python, transparently using them if no fdcanusb or pi3hat peripherals are found.

Thanks for everyone on discord’s patience as we worked through these compatibility issues!

Automated wire stripper and cutter

Over the Thanksgiving day holiday, I knew I had a bunch of harnesses to build. Rather than being a good corporate steward and actually building them, I instead built a machine to automate the first of the 3 time consuming parts of the harness construction: wire cutting and stripping.

This was just thrown together from two cosmetically damaged moteus devkits, a Raspberry Pi 3 an old development version of a pi3hat, a hand wire stripper, two synthetic rubber bands, an off the shelf 24V supply, and a bunch of 3d printed parts.

Why?

Simple automated wire management at the DIY level is not new. It’s been done many, many, many times before. YouTube has decided that every day I need to see someone else’s take on the problem. Look down in the resources at the bottom for my collection of alternate solutions.

What differentiates this version is (1) I built it most from junk parts I had around, (2) since it uses brushless motors it can be both very fast and very precise. Here’s a clip of it executing a few cycles where it strips 3mm from the front end, pre-cuts 3mm from the other end, then cuts the wire to a total length of 5cm. The overall cycle time for all operations is around 1s per wire for the 30cm wires I needed right now.

By replacing the guides and doing some tuning, it should be capable of managing wire between 30 AWG and 18 AWG, although to date I’ve only tested it on 26 AWG.

It did take a bit longer than the weekend — I printed a second revision of everything early the following week, then waited for a panel mount switch to make the power supply look more professional.

Video

Here’s the overview video, with some more shots of it in operation.

Resources

The BOM, .3mf’s and source code are in github at https://github.com/jpieper/bstrip. There is a hackaday page here for discussion: https://hackaday.io/project/176211-bstrip-wire-cutstrip

Maybe someone else will find it useful?

Other DIY-style solutions

pip3 install moteus

I’m excited to announce new python bindings for communicating with moteus controllers! A simple example from the README:

import asyncio
import math
import moteus

async def main():
  c = moteus.Controller()
  print(await c.set_position(position=math.nan, query=True))
  await asyncio.sleep(1.0)

asyncio.run(main())

This code will try to locate an fdcanusb on your host and use it to communicate with controller with ID 1. All of those details can be customized through code depending upon how you construct things. The library is pure python, although it doesn’t work on Windows currently because it relies on an asyncio aware pyserial wrapper that doesn’t work there.

At the same time, there is a parallel python library “moteus-pi3hat” which only has an armv7l package. This provides an identical API for working with the pi3hat on a Raspberry Pi. It lets you configure which controllers are attached to which bus (by default it assumes everything is on bus #1). After setting that up you can use an identical API to command and monitor the controllers.

Thanks to everyone in discord who helped test!

mjbots repository reorganization

In the spirit of “most of your users are yet to come”, I’ve gone through a moderate re-organization of some of the mjbots github repositories to make them more usable and sensible.

The biggest change is that mjbots/moteus has had a history rewrite and a directory structure re-organization. The current development (and default branch) is now “main”. The biggest changes:

  • Proprietary pdfs have been removed
  • All hardware which isn’t related to the moteus PCB has been removed
  • The firmware source has moved from “moteus/” to “fw/
  • The client side utilities moteus_tool and tview have moved to the “utils/” directory
  • There is now a “lib/” directory which houses client side libraries

Second, mjbots/power_dist is a new public repository that houses the power_dist board firmware and software.

Third, the hardware and software for the quad A1 is now located at mjbots/quad. This repository is rewritten to remove all things that are not quad related, and also to remove proprietary pdfs.

If you have questions about where things are, don’t hesitate to ask in the mjbots discord!

New tool day: Pace ADS200

I’ve muddled along for a long time soldering with a little Weller WES50. I’ve done a lot of work with it, but given how many SMD boards I’m doing with big ground planes and tiny components, I needed something a bit more capable. Enter the Pace ADS200 from tequipment:

Made in the USA, with 120W of power and a wide range of tip selection it has been an incredible upgrade. All those soldering jobs which were painful before are so much easier, and I don’t even have all the tips I wanted for different jobs yet. I also have the MiniTweez, but don’t yet have the tips that will let me show that off. I’ll try to post some soldering videos in the not too distant future.

Pocket NC windowed machining

When I first acquired my Pocket NC v2-50, I was planning on using it for rapid prototyping of small aluminum parts. I figured with 5 axes, I could do many things with a single setup just clamping from the bottom. However, I was initially thwarted in that plan and had to resort to more creative workholding solutions due to two problems.

First was the vice that came with the Pocket NC. It is serviceable, but provides very little clamping force if you want to hold something that is tall and skinny. For now, while it isn’t ideal, I’m making good progress with the wcubed vise.

Second was the range of Z travel. As shipped by Pocket NC, in order to reach the center of rotation, tools have to stick out something like 35mm. If you want to go beyond, that adds even more. This was a problem, as there aren’t that many tools that can achieve a reasonable material removal rate while sticking out that far, if they can do so at all. This, I’ve finally resolved with this Pocket NC “Q-Tip”:

With that modification, I got an extra ~15mm of travel, which means that I can reach the center of rotation with only 18mm of stickout which is completely reasonable for this class of tools.

Now I can finally “window” machine parts out of a few maximally sized generic blocks of stock with only a single setup. I’ve got 3.5″x3.5″ stock in a variety of thicknesses, which lets me do just about anything, if slowly, without having to worry about workholding.

That’s what it started with

And some video showing the cutting: