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Wearable Safety One-Pager — EMG-based PhAI-X1 Assist Control

Audience: Any team running their own EMG → torque code on PhAI-X1 (H10 + XM10) while a person is wearing the suit and applying real assist force. Principle: You are free to design your algorithm, but the guardrails below are non-negotiable. Assist force goes directly into a human leg.

0. One-Line Rule

Never run unverified code in wearable mode — bench-test everything first.

1. Bench First (Required Before Wearing)

With torque output disabled (control_ON = 0 or XM_CTRL_MONITOR), verify the signal, direction, and magnitude first.

  1. Connect the EMG sensor and check the raw / envelope signal with the xm10 tool (Ex.40's 0xF0 channels Raw/Env/Tau) or Live Expressions.
  2. Relax the muscle → resting calibration (BTN1); representative contraction → active calibration (BTN2). Order must be BTN1 → BTN2.
  3. Confirm envelope is ~0 at rest and rises on contraction (increase deadband if noise is high).
  4. Direction check: verify that the intended muscle contraction maps to the intended joint direction (Flexion / Extension) — sign convention is positive(+) = Flexion, negative(−) = Extension.
  5. Left/right check: XM_SetAssistTorque(R, L) takes right first. If in doubt, use XM_SetAssistTorqueRH/LH() to set one side at a time. Reversed left/right can cause a fall.
  6. Gradually increase torque from very small values (e.g., 0.2~0.5 Nm) and observe motor response in the bench-mounted state.
  7. Re-confirm that torque is nearly 0 when relaxed → only then set control_ON = 1.

2. Torque Limits (Do Not Exceed)

Category Value Nature
EMG example default output 1.25 Nm (EMG_MAX_TORQUE_NM 2.5 × scale 0.5) Conservative starting point — recommended starting value
Example soft ceiling 2.5 Nm Saturation inside the example code
XM10 internal hard clamp ±10 Nm Inside the library (libXM_Lib.a) — users cannot change this; inputs above this value saturate
Motor-driver protection 14A / impedance 10A Additional saturation on the H10 side

Set limits conservatively to match the wearer and purpose. Never start with a large value.

3. Emergency Stop Paths (Memorize These)

  • Suit STANDBY button — Physical button on the H10 body. Switching to STANDBY immediately zeroes torque and commands a gentle stop before holding position. This is the fastest stop.
  • Extension cable disconnect / CM link lost — When XM_IsCmConnected() returns false, the firmware automatically switches OFF (torque 0).
  • Cut power — Last resort.

⚠️ A watchdog is not an emergency stop. As of v2.6.0 the XM10 firmware does include a hardware watchdog (IWDG, about 8 seconds), but it exists to recover the board when the firmware hangs — not to protect a person. Eight seconds is a very long time while someone is wearing the suit, and if your code keeps running while commanding the wrong torque, the watchdog never fires at all (the firmware looks perfectly healthy to it).

So a person using one of the paths above is still the primary safety net. A dedicated safety assistant who can reach the stop control must always be present alongside the wearer.

For reference: when a watchdog reset does occur the board reboots and comes back up in MONITOR mode (torque output blocked). What happens after that is decided by your Control_Setup / Control_Loop code.

4. Four Code Sections That Must Not Be Removed

Even when modifying the algorithm in the EMG example, keep the following in place:

  1. Final torque saturation — limit clamp immediately before output.
  2. Zero-torque during calibration — force torque to 0 while calibration is in progress.
  3. Zero-torque on mode exit — in Active_Exit, set torque to 0 and return to XM_SetControlMode(XM_CTRL_MONITOR).
  4. XM_SetControlMode — gate for entering XM_CTRL_CONTROL / returning to MONITOR.

5. Pre-Wear Checklist ✅

  • [ ] Passed bench steps 1–7 (direction, left/right, and magnitude verified)
  • [ ] Starting assist torque is conservative (≈ 1 Nm or less)
  • [ ] Emergency stop path (suit STANDBY) located + safety assistant standing by
  • [ ] Four must-not-remove code sections remain intact
  • [ ] Calibration order BTN1 → BTN2 understood
  • [ ] First motion after donning: small torque / slow speed

6. Monitoring During Wear

  • Use the xm10 tool alone to watch envelope and output torque (the 0xF0 tab for Ex.40) in real time throughout the session. Joint angle is in the same xm10 window under Show 0x20 tab (a 5 Hz table). Connect only one PC program at a time.
  • If torque spikes unexpectedly or fails to return to 0 on relaxation, immediately press suit STANDBY.

This document defines safety guardrails only. Which muscle to read, what intent to infer, and how much assist to apply is your team's design space.