Scalextric motor control
The standard Scalextric hand controller uses a wire wound potentiometer for speed control. This works by controlling current supplied to the slot car.
To give reasonable speed control over the whole range of the controller trigger, the resistance of the potentiometer needs to be of the order of the resistance of the motor winding. This means that at slow speeds, the potentiometer is still passing a sizable current, heating up the potentiometer and wasting energy. Historically, the use of series resistance has been an important means of controlling motors (and lamps such as those used in stage lighting). Modern power electronics provide a much more efficient means of controlling motors such as those used in train locomotives. Efficiency is particularly important in battery powered motors such as electric cars to extend the vehicle range.
Most electronic speed controllers operate by providing current pulses to the motor. A variety of terms are used for this such as pulse width modulation, chopper control, phase angle control and burst fire control. All work by controlling the average current by switching it on and off and adjusting the ratio of on time to off time. For DC operated systems, pulse width modulation is an excellent method of speed control
40106 PWM controller
The following diagram shows a variable mark-space ratio astable controlling a power MOSFET. D1 and D2 provide different charge and discharge paths for C1 depending on the setting of VR1
40106 based PWM controller
Graph showing the effect on the duty cycle of changing the setting of VR1 (from slow speed to full speed)
CircuitWizard simulation files
Download 40106 PWM controller. To switch on graph, select the view menu > graph
Download 40106 PWM controller with motor. To switch on graph, select the view menu > graph
PCBs
PCBs are available for PWM controllers:
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