E-stop and Docking

FALCON supports an emergency stop (E-stop) feature that brakes the motor in case of an emergency. The E-stop can be triggered by an invalid input signal, a zero input signal, or a dedicated digital input — configured through drvopts and /io/in_estop.

The E-stop sequence consists of two stages: ramp-down braking followed by an optional hold stage.

info

All E-stop related parameters are located in the /estop/ folder.

Ramp-down Stage

The ramp-down stage applies controlled deceleration to bring the motor to a stop.

ramp

Brake ramp exponent. Defines how quickly the motor brakes when E-stop is triggered. Range 0–1.

max_cmd

Maximum brake command during ramp-down. Range 0–1.

voltage_thr [%]

Motor voltage threshold to transition from ramp-down to the hold stage. Set to 0 to disable the hold stage.

Hold Stage

Once the motor voltage drops below voltage_thr, the system enters the hold stage. Three behaviors are available:

• Short circuit brake — if hold_max_cmd is 0, the motor is short-circuited (passive hold).
• Active position hold — if hold_max_cmd is nonzero, a voltage-based position controller is engaged.
• Prop docking — if a reference sensor is connected, the rotor moves to an absolute reference position before holding.

hold_max_cmd

Maximum active voltage drive level for position hold. Set to 0 to disable position hold and use short circuit brake instead.

hold_gain

Position hold controller gain. Higher values produce a faster response but increase the risk of instability.

Prop Docking

For absolute position hold, an external reference sensor (typically a hall sensor that triggers once per mechanical revolution) must be connected. FALCON expects this sensor on the following pins:

Controller class	MSENS signal pin
SC, SL	ENCA/CLK
AM	HALLV

Two readout methods are supported:

• Level mode — the sensor signal stays at a defined level when the prop is at the desired position. Set dock_level_polarity to -1 or +1 to define which level is considered "docked". No angle offset is available.
• Edge mode — the sensor delivers an edge when the rotor passes through a reference point. Set dock_edge_angle to the desired angle offset in revolutions.

homing_speed [ERPM]

Speed limit for finding the reference signal during docking.

dock_edge_angle [REV]

Angle reference for docking after detecting an edge on the dock input. Set to 0 to disable edge mode.

dock_level_polarity

Polarity of the level dock input on MSENS ENCA/CLK. Set to 0 to disable level mode.

States

State	Description
estop_state	E-stop phase: 0 = braking, 1 = docking
dock_hall_input	Debounced dock hall sensor state