User Manual

Brushless Motor Connections and Operation
128 Advanced Digital Motor Controller User Manual V2.1, December 3, 2020
very slow speed. Nevertheless, there are many applications (e.g., fans, pumps, watercraft
thrusters) that do not require high torque at very low speed.
Important Notice
Do not use sensorless commutation if torque is required at start or at very low
speed. Always use sensored motors when driving wheels. Sensorless works best
for driving propellers or fans.
Sensorless Parameters
The following parameters need to be tuned for trapezoidal sensorless to work optimally.
• Startup Frequency (SSF): This is minimum frequency (electrical Hz) at which the
motor will always try to commutate during motor start or when slowed down.
• Back EMF Integrator Limit (SVT): This defines the threshold at which the integrated
back-EMF of a given phase will trigger the commutation.
• Back EMF Coupling Constant (BECC): In case of non-ideal back-EMF waveforms,
this number is required to compensate for back-EMF coupling due to other two
phases.
The “Startup Frequency (Hz)” is set to 10Hz by default. This frequency works for practical-
ly all motors. Some motors with high friction, heavy load and/or high inertia may not start
at all, or start unreliably. If this occurs, try different Startup Frequency values.
In the sensorless mode the motor will spin regardless of the phase wiring order. If the
motor spin in the opposite direction than the one desired, swap any two of the three mo-
tor wires, or change the motor direction to Inverted in the motor configuration..
The number of poles setting is not necessary in order for the motor to run. The number
of poles is only used to measure the motor’s rotation speed. Enter a negative number of
poles in order to change the speed polarity and count direction.
Sensorless PWM Frequency
PWM Frequency is variable when operating in sensorless mode. At startup and very low
speeds, the applied PWM Frequency is 6kHz. As the motor speeds up, the PWM Fre-
quency is automatically increased up to 45kHz max. These settings work in practically all
conditions and should be left unchanged
Sensorless Auto-tuning
An auto-tuning mechanism is provided for determining the BECC and SVT values. Beware
that the motor will reach maximum speed during calibration/auto-tuning. The auto-tuning
sequence lasts around one minute.
Make sure the controller is configured in open loop. Then, from the Diagnostics tab of
the Roborun+ Utility, click on the “Motor/Sensor Setup” button from the diagnostics tab
of the Roborun+ Utility. The motor will ramp up to two different speeds. If motor fails to
start, or starts unreliably, it may be necessary to adjust the Startup Frequency. See “Sen-
sorless Parameters” section above.