Stock ATOM protocol

This page describes Elephant’s stock ATOM firmware (v7.2). It is not installed now, but the backup can restore it. pymycobot, myStudio and ROS use this protocol. The full command list, cross-checked between Elephant’s English and Chinese documentation and pymycobot, is in Stock protocol commands.

Frame format

FE FE <LEN> <CMD> <data...> FA        LEN = number of data bytes + 2

Commands that were used

Code	Command	Notes
0x02	SOFTWARE_VERSION	Reply 0x48 = v7.2
0x12	IS_POWER_ON	Fast reply, no bus traffic
0x20	GET_ANGLES	int16 big-endian, angle × 100
0x22	SEND_ANGLES	6 × int16 + speed (%)
0x23	GET_COORDS	x, y, z (0.1 mm), rx, ry, rz (0.01°)
0x52 / 0x53	SET / GET_SERVO_DATA	One servo register, one byte. The two-byte mode gave wrong values.
0x6A	SET_COLOR	LED matrix, no bus traffic

What the stock firmware does on the bus

• GET_ANGLES and GET_COORDS: a PING to ID 7 (the gripper, which gets no reply without a gripper), then one SYNC READ of 15 bytes at register 56 from servos 1–6. The ATOM then converts the result. get_coords runs the forward kinematics on the ATOM.
• SEND_ANGLES: one SYNC WRITE at register 41 for all servos: acceleration 50, goal position, goal time 0, and a goal speed proportional to each joint’s distance (≈3.34 steps/s per degree at speed 30, minimum 300). The servos then move by themselves. The firmware does not interpolate.
• When idle, the stock firmware does not use the bus.

Problems seen

• After a series of status queries starting at GET_ROBOT_STATUS (0x19), which this firmware does not support, the ATOM stopped replying to all commands. The servos were not affected. A power cycle cleared it.
• Before that, the ATOM acknowledged send_angle but wrote nothing to the bus. The cause is not known.

LED colours

See LED matrix signals.