Hardware setup and first-motion checklist

This guide assumes a four-servo hobby arm and an Arduino Uno or Nano. Servo wire colors vary, so verify the datasheet before applying power.

Wiring

Joint	Arduino signal	Servo power	Servo ground
Base	D3	External regulated 5–6 V	Common ground
Shoulder	D5	External regulated 5–6 V	Common ground
Elbow	D6	External regulated 5–6 V	Common ground
Gripper	D9	External regulated 5–6 V	Common ground
Hardware interlock	D7 to GND through NC switch	—	Arduino GND

                  +---------------- servo V+
5–6 V supply + ---+---------------- servo V+
                  +---------------- servo V+
                  +---------------- servo V+

Supply GND --------+---------------- servo GND ×4
                   +---------------- Arduino GND

Arduino D3/D5/D6/D9 ---------------- servo signal ×4
Arduino D7 -------- normally-closed interlock -------- GND

The D7 interlock is a logic-level secondary stop. The primary emergency stop should be a normally-closed, latching switch that physically interrupts servo power. Do not route servo current through a small signal switch.

Power sizing

Use the servo datasheets’ stall-current values. Size the supply and wiring for the sum of all possible simultaneous stall currents, with margin. Never power four servos from the Arduino 5 V pin or USB port.

Mechanical calibration

1. Disconnect servo horns from the arm links and remove the gripper load.
2. Upload firmware/calibration/calibration.ino.
3. Open Serial Monitor at 115200 baud with no line ending.
4. Press 1–4 to select a joint. Use + and - one degree at a time.
5. Record the first angles before binding or collision at each end.
6. Choose a neutral home angle and reinstall each horn without forcing the link.
7. Put the measured conservative values into LOW_LIMITS, HIGH_LIMITS, and HOME in firmware/robot_arm/robot_arm.ino.
8. Upload the main firmware only after all four joints are calibrated.

Leave at least 5–10 degrees of margin from every observed mechanical endpoint.

First-motion test

• Arm is clamped to a stable surface.
• Workspace is clear; nobody is inside the motion envelope.
• External supply polarity and common ground were checked with a meter.
• Latching power emergency stop cuts servo power and is within reach.
• D7 interlock reports open when pressed.
• Calibration sketch was tested one unloaded joint at a time.
• Host bridge starts in mock mode and rejects out-of-range commands.
• Real bridge starts with --serial and a bearer token.
• First real move changes only one joint by 5 degrees at low speed.
• stop detaches outputs; the five-second watchdog also detaches them.

Suggested first command after adjusting the project’s home values:

armctl arm
armctl move --base 95 --duration-ms 2000
armctl stop

If the servo chatters, overheats, draws excessive current, moves in the wrong direction, or approaches a hard stop, cut servo power immediately.

What software cannot verify

The repository tests can validate command schemas and software limits. They cannot verify polarity, supply capacity, physical clearances, horn alignment, real emergency-stop operation, or the correct limits for a specific arm.