Bus servos

Drive two Feetech ST-series serial bus servos from the browser: drag to command position, read live position / load / voltage / temperature back, and free a joint to hand-pose it (torque off) then re-hold it.

Hardware

• Arduino UNO R4 WiFi or ESP32
• A Waveshare Serial Bus Servo Driver board (or equivalent half-duplex UART adapter), wired to a hardware serial port:
  • UNO R4 WiFi → Serial1 (D0 = RX, D1 = TX)
  • ESP32 → Serial1 or Serial2 (set the pins with configureBus({ rxPin, txPin }))
• Two Feetech STS3215 (or other ST/SMS) servos, daisy-chained on the bus, set to IDs 1 and 2
• A servo power supply (6–7.4 V typical) — not the board's 5 V rail

The STS3215 is the same servo used in the LeRobot SO-100/SO-101 arms.

Setting servo IDs

Servos ship as ID 1. To renumber, put a single servo on the bus, attach it, and call setId(newId) — then repeat one at a time. scan() lists the IDs currently responding on the bus.

Arduino

Install the SCServo library (from the Waveshare Bus Servo Adapter wiki or the Feetech SDK — usually a ZIP, not in the Library Manager), then upload File → Examples → Pardalote → bus-servos. Note the IP the board reports.

Browser

This is a tool — it works out of the box, no code editing:

1. Open index.html in a browser.
2. Type the board's IP into the Board IP row and press Connect.
3. Set the two joints' bus IDs in the Servos row under the display (defaults 1 and 2) — changing an ID reconnects and re-attaches.

The browser remembers the IP and IDs, so next visit it reconnects with one click.

Input	Action
Drag a dial	command that joint's position
Torque buttons or 1 / 2	free that joint (torque off) to pose by hand; press again to re-hold

Notes

• Positions are raw encoder counts, not degrees — ST series is 0–4095 (centre 2048), SC series is 0–1023. write() takes counts; writeDegrees() and .positionDegrees convert (accurate for ST, nominal for SC).
• Limits are enforced by the servo itself. setLimits(min, max) writes the servo's own Min/Max position registers, so the range holds even without the browser in the loop.
• Torque off = teaching by demonstration. disableTorque() lets you move the joint by hand while read() streams the position back — the basis of the record-a-trajectory workflow in projects like LeRobot.
• Calibration: move a joint to its zero pose (torque off), then calibrate() sets that as centre (like LeRobot centring on resolution / 2).