Input Priority System
The Input Priority System is a feature that enables the use of both CAN bus and serial (DShot/PWM) signalling simultaneously.
The input priority system enables:
- Both CAN and serial signals to be actively read for throttle control allowing the unit to fallback to a backup signal if the primary signal is lost.
- Either CAN or serial signalling to be used without needing to first configure the unit.
- Telemetry and configuration can be used on a signal even when that signal is not being used for throttle control. E.g. DroneCAN telemetry and configuration are still enabled even if only DShot throttle is accepted.
Signal Priorities
- For a respective signal type (CAN bus or serial) a priority of primary or secondary, or no priority, can be assigned.
- By default CAN bus is the primary signal type and serial is the secondary signal type.
- If the primary signal type is acquired it will take precedence over the secondary signal and will control the throttle, if the primary signal type is not available or the signal quality is poor the secondary signal will be used if available.
The unit must be configured with a primary signal type. Having a secondary signal is not mandatory. Two signal types cannot have the same priority.
Conditions For Switching Signals
The signal health of each active signal type is tracked, if the signal health drops below an acceptable threshold or if no valid throttle is received for the signal timeout duration (default 500ms) the motor controller will attempt to fallback to a lower priority signal. If a higher priority signal than the currently active signal is in good health and available the motor controller will switch to the higher priority signal.
The unit will fall back to a lower priority signal if the current signal is degraded or times out, the diagram below demonstrates the current signal timing out.
If a higher priority signal than the current signal is available and in good health the unit will switch to it, as shown in the diagram below.
Losing a lower priority signal will not affect operations as shown in the diagram below.
Minor dropouts or degredations of signal quality within acceptable ranges will not lead to a switch of signals as shown in the diagram below.
Signal Loss
Signal loss will occur when no valid signal from any of the active signal types is received for the signal timeout duration (500ms default).
The below diagram demonstrates signal loss when only one signal is being used.
The below diagram demonstrates signal loss when multiple signals are in use.
Arming
DroneCAN supports an additional arming mechanism as described below. This will only affect whether the DroneCAN signal is considered armed and will not affect serial signalling. Therefore, this message will only have an effect whilst the DroneCAN signal is the active signal type.
Configuration Considerations
Require Signal Armed to Fallback
It is recommended that when using multiple signal types in a fallback scenario to enable the βRequire Signal Armed to Fallbackβ setting, this will prevent the unit switching to a disarmed signal which could lead to an unwanted disarm event during motor drive.
It is highly recommended to enable 'Require Signal Armed to Fallback' when using fallback signalling if 'DroneCAN Require Armed Msg' is enabled.
The diagram below demonstrates how the primary signal is only switched to after it is armed.
Require All Signals to Arm
To ensure that all communication methods are operating correctly before beginning operation the βRequire All Signals to Armβ setting can be enabled, this will require all signals to meet arming conditions after start-up before the motor will drive.
The diagram below demonstrates the requirements to arm the unit when 'Require All Signals to Arm' is enabled.
PWM Acquisition
When using fallback signalling, the conditions to acquire/re-acquire a PWM signal are different. To acquire, a series of zero throttle pulses must be received OR a series of pulses within 10% of the current throttle value (if another signal is active) must be received. This enables reliable re-acquisition in fallback scenarios.
The diagram below indicates the ranges in which a PWM signal will acquire when using multiple signals.
