Motors

 Brakes and Auto Brake in Brushless Motors

How do brakes work?

In both brushed and brushless motors brakes are achieved by connecting the pick up braids together. This makes the motor act like a dynamo and slows itself down quickly. This is called "Dynamic braking".    

Some motors give more braking than others.  How can you maximise dynamic braking from whatever motor you are using?   Less resistance in circuit means more braking current and stronger braking.  That means low resistance in the hand controller and thick track wire give more braking.  What about the connections between the motor and the car’s pick ups and the motor?   The lead wires have some resistance, but typically this is  insignificant.  Brushless motors need an Ecom in the car, well designed Ecoms give very little reduction in braking.

Try spinning the rear wheels of brushless and brushed motored slot cars and you’ll notice brushless has much less friction.  That’s not surprising as there’s no brush friction in brushed motors.  What difference does that make on track?   Brushless motors typically produce less braking so are normally driven with full or almost full dynamic braking.  Brushless roll a lot further once they’ve deslotted but this can be reduced by using “auto-brakes”  ( see below).    Brushed motors such as group 12 often produce far too much braking with full dynamic braking, and are often driven with "anti brakes" or dynamic brakes disconnected .... that’s pretty well unknown with brushless.

In brushed motors the commutator switches the voltages produced by the armature windings to produce the braking current which goes back to the controller.  With brushless motors the Ecom (electronic commutator) switches the voltages produced by the stator windings to produce the braking current.   That only works as long as  the motor is rotating fast enough to produce sufficient voltage to make the Ecom work.  Below that speed no braking current goes back to the controller and the dynamic breaking disappears.  Fortunately “fast enough” is well below normal racing speed.  This can be observed when braking to a stop.   We could go into the detail of how the Ecoms do it, but that’s outside the scope of this article.

Auto Brakes

When cars deslot. there is no connection to the controller.  Of course  no braking current means no dynamic braking. That is often cited as a reason for larger accidents when brushless cars deslot  leading to bigger crashes and more cars in difficult to marshal positions.  In Ecoms with “auto brakes”  the braking current flows through the Ecom when the car has deslotted so there is dynamic braking even when the car is out of the slot.    Here’s  a couple of examples of ecoms with auto brakes.

© Copyright British Slot Car Racing Association 2025   Photos copyright C.Frost    All rights reserved

Latvian Auto- Brake ecom

Front and back views

Prototype ecom with auto- brakes.

This example is being evaluated for use in the BSCRA brushless INTRO 32 class which is due for introduction in 2026