[Dr_C2]

I saw on a separate thread on the slotracer.online forum another discussion around brushless motors so thought it might be useful to share my understanding.

1/ Standard brushless motors and their controllers use a three-wire set-up. This setup is sensorless in so far as the motor doesn’t have any in-built position sensors. However, rotation of the motor does require that the motor controller can determine motor position. This is done my measuring the back-EMF on each of the three motor phases. This approach works extremely well except at very low speeds. This is not a concern for R/C model aeroplanes where there is never a requirement to run propellors at very low rpm.

2/ R/C cars are a different matter, and as Kevan mentioned earlier, there is a ‘cogging’ effect when trying to drive sensorless brushless motors at low speeds. Technically this is because the EMFs induced are too small to measure at these low rpm.

3/ The solution is of course to move to sensored brushless motors which typically have three Hall sensors embedded inside the motor. These motors have the normal three current carrying wires plus a separate power bus for the Hall sensors and additionally three output signals which correspond to each of the three Hall sensors.

4/ My working assumption is that we will require sensored brushless motors for digital slotcar applications.

The brushless motor in my earlier post is indeed a sensored brushless motor and the slotcar drives smoothly at low speeds, intermediate speeds and at high speed.

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