Python HTTP

The ESP32 web server exposes a REST endpoint that accepts JSON commands via HTTP GET. This is the simplest way to control the arm wirelessly from any language or tool that can make HTTP requests.

Endpoint

GET http://<arm-ip>/js?json=<url-encoded-json>

The arm’s IP depends on the WiFi mode:

• AP mode: 192.168.4.1
• STA mode: Assigned by your router (check with {"T":405} over serial)

Python Setup

pip install requests

Basic Usage

import requests
import json
from urllib.parse import quote

ARM_IP = "192.168.4.1"

def send_command(cmd: dict) -> dict | None:
    """Send a JSON command via HTTP and return the response."""
    url = f"http://{ARM_IP}/js?json={quote(json.dumps(cmd))}"
    try:
        resp = requests.get(url, timeout=2)
        return resp.json()
    except (requests.RequestException, json.JSONDecodeError):
        return None

# Move to home
send_command({"T": 100})

# Get position feedback
pos = send_command({"T": 105})
if pos:
    print(f"Position: ({pos['x']:.1f}, {pos['y']:.1f}, {pos['z']:.1f})")

# Move to coordinates
send_command({"T": 104, "x": 200, "y": 50, "z": 150, "t": 1.57, "spd": 0.25})

# Open gripper
send_command({"T": 106, "cmd": 1.57, "spd": 0, "acc": 0})

Pick-and-Place Example

import time

def pick_and_place(pick_x, pick_y, place_x, place_y, height=150, grab_height=50):
    """Pick an object and place it at a new location."""
    # Move above pick position
    send_command({"T": 104, "x": pick_x, "y": pick_y, "z": height, "t": 3.14, "spd": 0.25})
    time.sleep(1)

    # Open gripper
    send_command({"T": 106, "cmd": 1.57, "spd": 0, "acc": 0})
    time.sleep(0.5)

    # Lower to grab
    send_command({"T": 104, "x": pick_x, "y": pick_y, "z": grab_height, "t": 3.14, "spd": 0.15})
    time.sleep(1)

    # Close gripper
    send_command({"T": 106, "cmd": 3.14, "spd": 0, "acc": 0})
    time.sleep(0.5)

    # Lift
    send_command({"T": 104, "x": pick_x, "y": pick_y, "z": height, "t": 3.14, "spd": 0.25})
    time.sleep(1)

    # Move to place position
    send_command({"T": 104, "x": place_x, "y": place_y, "z": height, "t": 3.14, "spd": 0.25})
    time.sleep(1)

    # Lower to place
    send_command({"T": 104, "x": place_x, "y": place_y, "z": grab_height, "t": 3.14, "spd": 0.15})
    time.sleep(1)

    # Release
    send_command({"T": 106, "cmd": 1.57, "spd": 0, "acc": 0})
    time.sleep(0.5)

    # Return to safe height
    send_command({"T": 104, "x": place_x, "y": place_y, "z": height, "t": 3.14, "spd": 0.25})

# Usage
pick_and_place(200, -50, 200, 50)

Using curl

You can also control the arm directly from the command line:

# Home position
curl "http://192.168.4.1/js?json=%7B%22T%22%3A100%7D"

# Get feedback
curl "http://192.168.4.1/js?json=%7B%22T%22%3A105%7D"

# With jq for pretty output
curl -s "http://192.168.4.1/js?json=%7B%22T%22%3A105%7D" | jq .

Rate Limiting

Caution

The ESP32’s async web server handles one request at a time on the command endpoint. Sending requests faster than the arm can process them (roughly every 50ms) can cause dropped commands or timeouts. Add at least 50ms delay between rapid-fire commands.

Session-Based Control

For applications that send many commands, use a requests.Session to reuse the TCP connection:

import requests
import json
from urllib.parse import quote

session = requests.Session()
session.timeout = 2

ARM_IP = "192.168.4.1"

def send(cmd: dict):
    url = f"http://{ARM_IP}/js?json={quote(json.dumps(cmd))}"
    return session.get(url)

Comparing HTTP vs UART

Feature	HTTP	UART
Connection	Wireless (WiFi)	Wired (USB)
Latency	~10-50ms	~5-10ms
Reliability	Network-dependent	Very reliable
Range	WiFi range	Cable length
Multi-client	Yes (multiple browsers)	Single connection
Setup	WiFi config required	Plug and play

Tip

HTTP is better for most applications — it’s wireless, supports multiple clients, and works from any language. Use UART when you need the lowest possible latency or when WiFi isn’t available.

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HTTP control reference from the Waveshare Python HTTP guide and firmware source.