mjbots.com had a week long run where we were completely out of fdcanusbs, which meant that we were also out of all development kits too. Well, a production run just came in:
So now we’ve got everything back in stock once again!
With new python based moteus tview and moteus_tool available, and the new mj5208 motor being included in all the moteus devkits, I figured it was time to update the moteus getting started video. Here it is!
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:
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.
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.
pip3 install moteus_pi3hatThe 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:
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!
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
As a result of all this debugging, I made some general improvements to socketcan support in all the client side moteus tools.
Thanks for everyone on discord’s patience as we worked through these compatibility issues!
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.
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.
Here’s the overview video, with some more shots of it in operation.
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?
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!
To date, all of the development tools for the moteus brushless controller have been available exclusively for Linux based operating systems. I’ve been doing some behind the scenes work, and have gotten to the point where moteus_tool now runs natively on windows and can communicate with moteus controllers using a fdcanusb.
Check out the Windows installer for the latest release:
To make this work, I started from the excellent grailbio/bazel-toolchain, which provides LLVM toolchains for Linux based systems based on the official LLVM pre-compiled binaries. I forked that into mjbots/bazel-toolchain and added Windows support. It isn’t perfect, because the LLVM project only distributes Windows binaries in installer form, and it isn’t possible to extract binaries from them without specialized tooling. So, this version relies on a manually re-packed compressed archive of all the executables.
I also added support for building the libc++ standard library, and using that instead of the MSVC standard library. This let me get c++20 coroutines working with clang on Windows.
All put together, the porting was pretty painless after having a toolchain in place. Just a few #if’s here and there, and I had to write a custom Windows specific console stream, as stdio and stderr do not support asynchronous completion ports on Windows.
Here’s the approximately annual giant video update:
If you’re interested in any of the topics in more detail, I’ve collected links to individual posts for each of the referenced items below.
Thanks for all your support in the last year!
Announcement of moteus r4.3: Production moteus controllers are here!
Automated programming and test setup: Programming and testing moteus controllers
Dynamometer: Measuring torque ripple, Initial dynamometer assembly
Continuous rotation: Unlimited rotations for moteus
The virtual wall control mode: New “stay within” control mode for moteus
Handling magnetic saturation: Dealing with stator magnetic saturation
Discussion of the overall design, and details on individual sub-components:
And the pre-production mk2 servos: Pre-production mk2 servos
fdcanusb: Introduction and bringing it up
power_dist: The failed r2, the closer to working r3, and the final r3.1
pi3hat: Initial announcement, bringing it up, and measuring its performance
Ground truth torque testing: Ground truth torque testing for the qdd100
Skyentific’s telepresence clone: qdd100 telepresence demo
kp and kd tuning: Spring and damping constants
Lower leg updates:
Chassis: The first introduction, and some minor tweaks
Cable conduit changes: New leg cable management
Cartesian coordinate control: Cartesian leg PD controller
Pronking: Successful pronking!
tplot2 and its sub-pieces:
Simulation: Resurrected quadruped simulator
nrf24l01 transceiver and its sub-components
Smooth leg motion: Improved swing trajectory
Balancing
All four feet off the ground: Higher speed gait formulation, and Stable gait sequencing
Improved stand up sequence: quad A1 stand-up sequence part N
Speed records:
