B Simple yet effective way to reliably control the DC Motor speed?

AI Thread Summary
To effectively control the speed of a 5-V DC motor for a stroboscope project, using Pulse Width Modulation (PWM) is recommended over series resistors, which can limit current and torque, leading to inconsistent speeds. A simple solution is to implement a buck regulator, which can adjust the output voltage and is available for under $5. This method allows for precise speed adjustments necessary for stroboscope applications. Additionally, using a potentiometer or a wire-wound rheostat can provide fine control over the motor speed. Overall, PWM and adjustable voltage regulators are the most reliable methods for achieving consistent motor speed control.
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Is there a reliable way to control the speed of the DC motor used in this stroboscope model? Should different resistors be used?
As a part of our physics high-school self-study, we are making a stroboscope. We have a small 5-V DC motor that powers the strobe disk.

strobe-motor.jpg

It works as expected, but, clearly, the motor makes the disk spin at a constant speed. Is there an easy, but effective and reliable way to control its speed? I don't mind joining some resistors in series if resistors can do the job (no variable resistor needed). If resistors is indeed the way to go (I don't think so), should I empirically decide the values of the resistors (or, should I employ Ohm's law)?
 
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Don't use series resistors to drop the drive voltage. Instead, learn about how to use Pulse Width Modulation (PWM) to control the DC motor speed... :smile:
 
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The speed of an unloaded DC motor is determined by the supply voltage. The torque of the motor is determined by the current. If you use a series resistor, you will be limiting the current and therefore torque, so it will tend to wander in speed.

As berkeman pointed out, PWM should be used to regulate the speed by changing the duty cycle. A cheap and easy way to do that is to use a simple "buck regulator", which will be PWM on the inside. Take a look on the web for a cheap "DC-DC adjustable voltage buck regulator". That should cost you less than about $5.
Adjust the speed of the motor by adjusting the regulator output voltage to the motor.
https://www.ebay.com.au/itm/394143426291
 
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