Abstract: A motor speed controller for use with dc motors, such as found in model (slot) cars, is provided by a plurality of pairs of oppositely-poled voltage-sensitive threshold conduction devices which are selectively connected so as to be controllably inserted between a source of operating voltage and the dc motor. In a preferred embodiment of the invention, the voltage-sensitive threshold conduction devices advantageously comprise a series connection of diode bridges which are sequentially included in the energizing path of the motor.Furthermore, the controller provides a speed sensitive brake function by controllably connecting at least one voltage-sensitive threshold conduction device across the windings of the dc motor. When so connected, this allows the voltage generated by the spinning motor to cause the voltage-sensitive threshold conduction device to be conductive until the motor speed slows to the point that the generated voltage no longer causes the device to conduct.