An attempt at open firmware for the myCobot280 from Elephant Robotics, with a serial console interface.
| Demo1 | Demo2 | Rainbow |
|---|---|---|
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This is an initial attempt at open firmware, and requires modifying your myCobot280. You should not attempt this unless you are comfortable performing each step. Moveover, the firmware is experimental and largely untested and unverified -- its use (or misuse) may cause harm to person or property.
Moreover, robotics (in specific), and electronics (in general) can be dangerous. The myCobot280 is suprisingly powerful, and also needs to be very firmly anchored to some stationary base. You should have a setup that includes some method (like an emergency stop button) of instantly being able to disconnect the power to the robot instantly if something goes wrong.
No warranty of any kind is provided -- use at your own risk.
The myCobot280 is an inexpensive robot arm sold by Elephant Robotics. It has great promise for a variety of applications (including research), but I struggled getting the firmware or Python APIs working on both the Raspberry Pi and M5 versions. This is an attempt at writing open firmware for the controller, to get around the issues I was struggling with.
The myCobot280 is a 6-axis device. From disassembly, as best as I can infer:
- The first 5 servos are STS3215 or compatible
- The end-effector servo appears to be a STS3032, supporting continuous 360 degree rotation
- There is a microcontroller (the "atom") provided in the end effector, which includes a display and some GPIO
- Everything appears controlled by a shared Serial Servo Bus.
The Waveshare ESP32 Serial Bus Servo Driver that I purchased came with open source firmware, but this appeared to be primarily for controlling "SC" type servos, and had unexpected behavior when using "ST" type servos (though their firmware does appear to support these, with modification).
The firmware in this repository is indended for the waveshare controller, but is designed specifically for the myCobot280.
This firmware is intended for use with the inexpensive WaveShare "Servo Driver with ESP32".
It requires modifying the myCobot280 by unplugging the servo in the base from the native controller (e.g. Raspberry Pi) and plugging it into the WaveShare ESP32 controller.
Using an appropriate power supply is required. The supply that came with my myCobot280 was labelled as 8.4V, while the cobot appears to have a supply in the base that lowers this voltage a bit. The 8.4V supply appeared to work for me, but it's not clear whether this might overvoltage any of the servos (particularly the Feetech STS3032 that appears to be in the last stage).
The WaveShare driver can be flashed with the firmware using the Arduino IDE. The board setting appears to be "ESP32 Dev Board", with "PSRAM" set to enabled.
The firmware is controlled over the ESP32 serial port using a serial console. You can either manually enter commands, or connect to it using your favorite programming language (e.g. Python) and send commands.
At start-up, the firmware scans for servos by pinging them, and holding ("torquing") any servos that it finds at their current position. The output on the serial console looks something like this:
Firmware name: OPEN_COBOT280
Firmware version: 0.1
Servo 0: No Response
Servo 1: Found
Servo 2: Found
Servo 3: Found
Servo 4: Found
Servo 5: Found
Servo 6: Found
Servo 7: No Response
Servo 8: No Response
Servo 9: No Response
OK
The OK signifies that the console is now available to take commands, as seen below.
The available commands are as follows (this can be displayed by typing "help" into the serial console):
Commands Description Example
----------------------------------------------------------------------------------------------------
Queue commands
move servoId position speed accel Queue a move command move 1 1024 1000 100
qoff servoId Queue an untorque command qoff 1
qtorque servoId Queue a torque command qtorque 1
go Execute queued move commands go
clearqueue Reset the move queue clearqueue
Instant commands
off Turn all servos off off
torque Torque (turn on) servos torque
stop Stop all servos in position stop
ping Detect/ping all servos ping
rgb r g b Set color on ATOM display rgb 0 255 0
Demos
rainbow Rainbow on ATOM display rainbow
center Move all servos to 2048 center
demo1 Move all servos back/forth demo1
demo2 Move all servos back/forth demo2
Informational commands
queue Display all queued moves queue
status Display all servo information status
status-tsv As above, but in TSV format status-tsv
version Display firmware version version
help Display this message help
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You may first wish to verify that the firmware can find all the servos, as expected. Type status (enter), and something like the following should appear, showing each of the servos and the most recently read information from them:
Servo Status
servo:1 exist:1 error:0 position:2048 speed:0 load:0 voltage:84 current:1544 temp:33 mode:81 isMoving:0
servo:2 exist:1 error:0 position:2051 speed:0 load:0 voltage:84 current:1544 temp:34 mode:81 isMoving:0
servo:3 exist:1 error:0 position:2046 speed:0 load:0 voltage:84 current:1544 temp:35 mode:81 isMoving:0
servo:4 exist:1 error:0 position:2051 speed:0 load:33 voltage:82 current:1544 temp:43 mode:81 isMoving:0
servo:5 exist:1 error:0 position:2041 speed:0 load:1088 voltage:77 current:1544 temp:71 mode:81 isMoving:0
servo:6 exist:1 error:0 position:2051 speed:0 load:27 voltage:81 current:1544 temp:45 mode:81 isMoving:0
There is also a version of this command, status-csv, that outputs the status information in a delimited format, for easy parsing:
servoId,doesExist,errorState,currentPosition,currentSpeed,load,voltage,current,temp,mode,isMoving
1,1,0,2048,0,0,84,0,33,81,0
2,1,0,2051,0,0,84,0,34,81,0
3,1,0,2046,0,0,84,0,35,81,0
4,1,0,2051,0,33,81,0,43,81,0
5,1,0,2041,0,1088,83,0,70,81,0
6,1,0,2051,0,27,85,0,45,81,0
OK
A first command to run (that doesn't involve any motion) is rainbow. This will show a rainbow colour pattern on the ATOM display.
Two motion demos similar to the official myCobot280 demos are provided. The demo1 command moves each axis of the arm back and forth, one at a time. The demo2 command moves the arm in between some curled-up ball positions. center brings the arm to approximately center position, and both demo1 and demo2 perform this before beginning their demos.
Nominally, motion commands are queued to the motors (using the move) command, then those queued commands are send to the motors after sending the go command.
For example, let's move one of the motors toward the end of the effector by sending:
move 5 500 1000 100
This queues a move for servo 5, moving to position 500, at speed 1000 and acceleration 100. The firmware will then respond with a message that this motion has been queued:
servo:5 isValid:1 torque:1 justTorque:0 position:500 speed:1000 acceleration:100
Added move request to queue.
OK
Each servo can hold only a single queued motion at a time, and if you queue another move to that servo (before a go command), it will overwrite whatever is currently in the queue for that servo. We can see whatever is in the current queue by using the queue command:
Servo 0 no request
Servo 1 no request
Servo 2 no request
Servo 3 no request
Servo 4 no request
Servo 5 servo:5 isValid:1 torque:1 justTorque:0 position:500 speed:1000 acceleration:100
Servo 6 no request
Servo 7 no request
Servo 8 no request
Servo 9 no request
OK
This shows that only a single servo has a queued motion. To run the motion, type go.
The command off will send the release command to all identified servos.
Similarly, the command torque will send the torque command to all identified servos, holding them in place.
The stop command quickly releases then torques each identified servo, effectively holding it in its current position.
When initialized, the firmware pings all expected servos. If all expected servos don't respond to the ping, you should likely discontinue using the robot and see if there's a failure, since you may see unexpected behavior.
You can always re-ping (i.e. re-discover) servos using the ping command, which should see output like the following:
Servo 0: No Response
Servo 1: Found
Servo 2: Found
Servo 3: Found
Servo 4: Found
Servo 5: Found
Servo 6: Found
Servo 7: No Response
Servo 8: No Response
Servo 9: No Response
OK
If you have an end effector added, you may see more servos than just the 6 on the stock cobot.
Currently, the only supported ATOM command is setting the colour of the display. This can be accomplished using the rgb command, which takes the red, green, and blue (0-255) settings as arguments. For example, setting the display to green can happen using the command: rgb 0 255 0.
The rainbow command cycles through the colours on the atom display.
Q: What is the servo position unit? A: This is a good question. As near as I have inferred, the range is 0-4096, with what should be considered a danger zone towards either end as the robot reaches the limits of its range of motion.
Q: What are the speed and acceleration units?
A: This is also a good question, and I have no idea. A speed of 1000 and acceleration of 100 seem modestly fast.
Comments, questions, bug reports, and cool use-cases are welcome.
For bug reports or issues, please use the Github issue tab.
Contact information: Dr. Peter Jansen <pajansen@arizona.edu>.
Web: https://cognitiveai.org/
Twitter: https://twitter.com/peterjansen_ai
Please cite the following:
This work is licensed under the BSD 3-Clause license:
Copyright 2023 Peter Jansen
Redistribution and use in source and binary forms, with or without modification, are permitted provided that the following conditions are met:
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