Hi Brock
You will need some electronics for speed control. A couple of ways to do this.
- vary the voltage applied to the motor in a linear fashion. This could be done simply by using an adjustable regulator (LM317) driving a large series transistor to provide the current. This has some disadvantages. The motor torque at low speed is reduced dramatically. The maximum voltage available for the motor will be supply voltage minus 1.8V, 1.2V for the 317 and 0.6V for the pass transistor base bias. Lastly but not least under low voltage low speed high current conditions the pass transistor will get hot, probably requiring a hefty heat sink.
- PWM control. This would be the preferred method as torque is maintained at low speeds and 1 (or more) mosfet is turned hard on minimising heat generation. If you did not want to use an Arduino or similar to generate PWM there are ready made small DC motor speed controllers out there. I don’t know what Core have in stock along these lines but others have this sort of thing too.
Direction change switching. I would not recommend 2 switches as there is a very real chance both could be ON which I think could short the supply. You would need a DPDT switch centre off. That is ON-OFF-ON to change voltage connection to the motor. That way you cannot have the motor switched both directions at once. Make sure the flywheel diode connects between the misfit drain and positive motor supply with cathode t0 positive motor supply. That way the diode is correct polarity irrespective of which way the motor is connected.
No matter which way you go some electronics are going to be required to control speed or a very large rheostat.
Cheers Bob
