JSON Command Reference

Every command sent to the RoArm-M2-S is a JSON object with a T (type) field that identifies the operation. This reference is sourced directly from the firmware’s json_cmd.h header file — the authoritative definition of all supported commands.

Commands can be sent over serial UART (115200 baud), HTTP (/js?json=...), or ESP-NOW.

Safety

T:0 — Emergency Stop

Immediately halts all motion.

{"T":0}

T:999 — Reset Emergency Flag

Clears the emergency stop state so the arm can accept motion commands again.

{"T":999}

EoAT Configuration

T:1 — EoAT Type

Switch between gripper and wrist end-effector modes.

{"T":1,"mode":0}

`mode`	Type
0	Gripper
1	Wrist

T:2 — EoAT Assembly

Configure the physical dimensions of the installed end-effector for correct kinematics.

{"T":2,"pos":3,"ea":0,"eb":20}

Parameter	Description
`pos`	Mount position: 0=edge, 1=D-3.2, 2=D-4.2, 3=D-10.2
`ea`	Extension A length (mm)
`eb`	Extension B length (mm)

Arm Control

T:100 — Move to Init Position

Moves all joints to default position without interpolation.

{"T":100}

T:101 — Single Joint Control (Radians)

Move one joint to a specific angle in radians.

{"T":101,"joint":1,"rad":0,"spd":0,"acc":10}

`joint`	Name	+ Direction
1	Base	Left
2	Shoulder	Down
3	Elbow	Down
4	End-effector	Grab/down

T:102 — All Joints Control (Radians)

Move all joints simultaneously. Angles in radians (180° = π).

{"T":102,"base":0,"shoulder":0,"elbow":1.57,"hand":1.57,"spd":0,"acc":10}

T:103 — Single Axis Control (Cartesian)

Move along one Cartesian axis.

{"T":103,"axis":2,"pos":0,"spd":0.25}

`axis`	Default (mm)	Description
1 (x)	235.11	Forward/backward
2 (y)	0	Left/right
3 (z)	234.79	Up/down
4 (t)	1.57 rad	End-effector angle

T:104 — XYZT Goal Control

Move to Cartesian position with interpolation (smooth motion).

{"T":104,"x":235,"y":0,"z":234,"t":3.14,"spd":0.25}

T:1041 — XYZT Direct Control

Move to Cartesian position without interpolation (fastest path).

{"T":1041,"x":235,"y":0,"z":234,"t":3.14}

T:105 — Position Feedback

Read current position and torque values.

{"T":105}

Returns: x, y, z, t, torB, torS, torE

T:106 — End-Effector Hand Control

Control the gripper/wrist angle in radians.

{"T":106,"cmd":1.57,"spd":0,"acc":0}

`cmd` value	Action
1.57	Release/open
3.14	Grab/close

T:107 — Grab Torque

Set maximum grip force.

{"T":107,"tor":200}

Range: 0–1000.

T:108 — Set Joint PID

Adjust P and I gains for a specific joint.

{"T":108,"joint":3,"p":16,"i":0}

Defaults: P=16, I=8 (with PID mode on for RoArm-M2).

T:109 — Reset PID

Reset all PID parameters to factory defaults.

{"T":109}

T:110 — Set New X-Axis

Redefine the forward direction of the coordinate frame.

{"T":110,"xAxisAngle":0}

T:111 — Delay

Insert a delay (used in mission sequences).

{"T":111,"cmd":3000}

cmd is the delay in milliseconds.

T:112 — Dynamic External Force Adaptation

Enable/disable compliance mode with per-joint torque limits.

Start:

{"T":112,"mode":1,"b":60,"s":110,"e":50,"h":50}

Stop:

{"T":112,"mode":0,"b":1000,"s":1000,"e":1000,"h":1000}

T:113 — 12V Switch Control

Control the two 12V switched outputs (PWM).

{"T":113,"pwm_a":-255,"pwm_b":-255}

Range: -255 to +255 (0 = off).

T:114 — LED Light Control

Control the onboard LED brightness.

{"T":114,"led":255}

Range: 0 (off) to 255 (max).

T:115 — Switch Off

Turn off all switched outputs.

{"T":115}

T:121 — Single Joint Control (Degrees)

Move one joint to a specific angle in degrees.

{"T":121,"joint":1,"angle":0,"spd":10,"acc":10}

Max acceleration: 22.5 deg/s².

T:122 — All Joints Control (Degrees)

Move all joints simultaneously. Angles in degrees.

{"T":122,"b":0,"s":0,"e":90,"h":180,"spd":10,"acc":10}

T:123 — Constant Control

Continuous motion along an axis (for jogging).

{"T":123,"m":0,"axis":0,"cmd":0,"spd":3}

`m`	Mode
0	Angle
1	XYZT

`cmd`	Action
0	Stop
1	Increase
2	Decrease

File System

T:200 — Scan Files

List all files in flash storage.

{"T":200}

T:201 — Create File

{"T":201,"name":"file.txt","content":"content here"}

T:202 — Read File

{"T":202,"name":"file.txt"}

T:203 — Delete File

{"T":203,"name":"file.txt"}

T:204 — Append Line

{"T":204,"name":"file.txt","content":"new line"}

T:205 — Insert Line

{"T":205,"name":"file.txt","lineNum":3,"content":"inserted"}

T:206 — Replace Line

{"T":206,"name":"file.txt","lineNum":3,"content":"replaced"}

T:207 — Read Line

{"T":207,"name":"file.txt","lineNum":3}

T:208 — Delete Line

{"T":208,"name":"file.txt","lineNum":3}

T:210 — Torque Lock Control

Enable or disable servo torque.

{"T":210,"cmd":1}

`cmd`	State
0	Off (arm goes limp)
1	On (servos hold position)

Mission Control

T:220 — Create Mission

{"T":220,"name":"mission_a","intro":"description here"}

T:221 — Read Mission Content

{"T":221,"name":"mission_a"}

T:222 — Append Step (JSON)

{"T":222,"name":"mission_a","step":"{\"T\":104,\"x\":235,\"y\":0,\"z\":234,\"t\":3.14,\"spd\":0.25}"}

T:223 — Append Step (Feedback)

Record the current arm position as a step.

{"T":223,"name":"mission_a","spd":0.25}

T:224 — Append Delay

{"T":224,"name":"mission_a","delay":3000}

T:225 — Insert Step (JSON)

{"T":225,"name":"mission_a","stepNum":3,"step":"{\"T\":104,\"x\":235,\"y\":0,\"z\":234,\"t\":3.14,\"spd\":0.25}"}

T:226 — Insert Step (Feedback)

{"T":226,"name":"mission_a","stepNum":3,"spd":0.25}

T:227 — Insert Delay

{"T":227,"stepNum":3,"delay":3000}

T:228 — Replace Step (JSON)

{"T":228,"name":"mission_a","stepNum":3,"step":"{\"T\":114,\"led\":255}"}

T:229 — Replace Step (Feedback)

{"T":229,"name":"mission_a","stepNum":3,"spd":0.25}

T:230 — Replace with Delay

{"T":230,"name":"mission_a","stepNum":3,"delay":3000}

T:231 — Delete Step

{"T":231,"name":"mission_a","stepNum":3}

T:241 — Move to Step

Navigate the arm to a specific step’s position.

{"T":241,"name":"mission_a","stepNum":3}

T:242 — Play Mission

Execute a mission with a repeat count. Use -1 for infinite loop.

{"T":242,"name":"mission_a","times":3}

ESP-NOW

T:300 — Broadcast Follower Config

{"T":300,"mode":1}

Mode 1: accept broadcast. Mode 0 + mac: whitelist a specific leader.

T:301 — ESP-NOW Mode Config

{"T":301,"mode":3}

`mode`	Role
0	Disabled
1	Group leader
2	Single leader
3	Follower (default)

T:302 — Get MAC Address

{"T":302}

T:303 — Add Follower

{"T":303,"mac":"CC:DB:A7:5B:E4:1C"}

T:304 — Remove Follower

{"T":304,"mac":"CC:DB:A7:5B:E4:1C"}

T:305 — Group Control

Send to all registered peers.

{"T":305,"dev":0,"b":0,"s":0,"e":1.57,"h":1.57,"cmd":0,"megs":"hello!"}

T:306 — Single Device Control

Send to specific MAC or broadcast.

{"T":306,"mac":"FF:FF:FF:FF:FF:FF","dev":0,"b":0,"s":0,"e":1.57,"h":1.57,"cmd":0,"megs":"hello!"}

WiFi

T:401 — WiFi Mode on Boot

{"T":401,"cmd":3}

`cmd`	Mode
0	Off
1	AP
2	STA
3	AP+STA

T:402 — Set AP Credentials

{"T":402,"ssid":"RoArm-M2","password":"12345678"}

T:403 — Set STA Credentials

{"T":403,"ssid":"YourNetwork","password":"YourPassword"}

T:404 — Set AP+STA Credentials

{"T":404,"ap_ssid":"RoArm-M2","ap_password":"12345678","sta_ssid":"YourNetwork","sta_password":"YourPassword"}

T:405 — Get WiFi Info

{"T":405}

T:406 — Save WiFi Config (from status)

{"T":406}

T:407 — Save WiFi Config (from input)

{"T":407,"mode":3,"ap_ssid":"RoArm-M2","ap_password":"12345678","sta_ssid":"YourNetwork","sta_password":"YourPassword"}

T:408 — Disconnect WiFi

{"T":408}

Servo Settings

T:501 — Change Servo ID

{"T":501,"raw":1,"new":11}

T:502 — Set Middle Position

Define the current position as the servo’s center (middle) point.

{"T":502,"id":11}

T:503 — Set Servo PID

{"T":503,"id":14,"p":16}

System

T:600 — Reboot

{"T":600}

T:601 — Free Flash Space

{"T":601}

T:602 — Boot Mission Info

Check if a mission is configured to run at startup.

{"T":602}

T:603 — Reset Boot Mission

Clear the boot mission so nothing runs at startup.

{"T":603}

T:604 — Clear NVS

Clear non-volatile storage. Useful for WiFi recovery.

{"T":604}

T:605 — Debug Output Control

{"T":605,"cmd":1}

`cmd`	Behavior
0	Silent
1	Debug info (default)
2	Flow feedback

Command reference sourced from firmware json_cmd.h (January 2025 release). Waveshare GitHub.