ESP-NOW Control

ESP-NOW is a connectionless protocol developed by Espressif that enables direct peer-to-peer communication between ESP32 devices without requiring a WiFi access point. This is ideal for multi-arm coordination, remote controllers, and low-latency wireless control.

Note

ESP-NOW requires WiFi to be running in STA or AP+STA mode. It does not work in AP-only mode.

Concepts

• Leader: The device that sends control commands (can be another RoArm-M2-S or any ESP32)
• Follower: The arm that receives and executes commands
• Broadcast: Send to all followers simultaneously using FF:FF:FF:FF:FF:FF
• Group: Send to multiple registered peers
• Single: Send to one specific peer by MAC address

Setup

1. Get each device’s MAC address

   {"T":302}

2. Configure the follower arm

   Enable broadcast reception (accepts commands from any leader):

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

   Or restrict to a specific leader MAC:

   {"T":300,"mode":0,"mac":"CC:DB:A7:5B:E4:1C"}

3. Configure the leader device

   Set as group leader (sends to all registered followers):

   {"T":301,"mode":1}

   Or as single-target leader:

   {"T":301,"mode":2}

4. Add follower(s) to the leader’s peer list

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

ESP-NOW Modes

Mode	Code	Description
None	0	ESP-NOW disabled
Group Leader	1	Sends commands to all registered peers
Single Leader	2	Sends to one specific follower
Follower	3	Receives and executes commands (default)

Sending Commands

Group Control

Send to all registered peers simultaneously:

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

Parameter	Description
dev	Device type identifier
b, s, e, h	Joint angles (base, shoulder, elbow, hand)
cmd	Command mode: 0 = mirror joint positions, 1 = send JSON command in megs
megs	Message string (JSON command when cmd=1)

Single Device Control

Send to one specific device (or broadcast to all with FF:FF:FF:FF:FF:FF):

{"T":306,"mac":"CC:DB:A7:5B:E4:1C","dev":0,"b":0,"s":0,"e":1.57,"h":1.57,"cmd":0,"megs":"hello!"}

Sending JSON Commands via ESP-NOW

Set cmd to 1 and put the JSON command string in megs:

{"T":306,"mac":"FF:FF:FF:FF:FF:FF","dev":0,"b":0,"s":0,"e":0,"h":0,"cmd":1,"megs":"{\"T\":114,\"led\":255}"}

This turns on the LED on all followers.

Flow-Leader Mode

When the leader is set to mode 1 or 2 with cmd=0, it continuously mirrors its own servo positions to followers. This creates a leader-follower teleoperation setup:

1. Move the leader arm manually (with torque lock off)
2. The follower arm tracks the leader’s movements in real time

Tip

Flow-leader mode with dynamic adaptation (T:112) on the leader creates an intuitive teach pendant — push the leader arm around and the follower copies every movement.

Managing Peers

Add a follower:

{"T":303,"mac":"CC:DB:A7:5C:1C:40"}

Remove a follower:

{"T":304,"mac":"CC:DB:A7:5C:1C:40"}

Caution

The broadcast address FF:FF:FF:FF:FF:FF cannot be in the group peer list. Use it only with single-device control (T:306).

Command Summary

T-Code	Command	Description
300	Broadcast follower config	Enable/disable broadcast reception
301	ESP-NOW mode	Set leader/follower mode
302	Get MAC	Read this device’s MAC address
303	Add follower	Register a peer MAC
304	Remove follower	Unregister a peer MAC
305	Group control	Send to all peers
306	Single control	Send to specific MAC

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ESP-NOW reference from firmware source json_cmd.h and Waveshare Wiki.