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I am trying to drive a small motor using (software emulated PWM) from a Pi like device. I'm following a circuit that looks like this:L https://www.instructables.com/id/Raspberry-Pi-GPIO-Circuits-Controlling-High-Powere/

Main differences are: My power source is a 3.74 LIPO battery, and my load is a motor, not an LED.

When I turn the GPIO pin fully on (not even PWM at this point), I don't get the full speed of the motor.

I'm not really sure what I am missing in my understanding.

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  • $\begingroup$ what happens when you connect the motor directly to the battery? $\endgroup$
    – jsotola
    Feb 7, 2020 at 22:12
  • $\begingroup$ Full speed ahead! $\endgroup$
    – jgauthier
    Feb 7, 2020 at 22:39
  • $\begingroup$ What are the specs of the motor and transistor? $\endgroup$
    – Ben
    Feb 12, 2020 at 1:24

1 Answer 1

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Transistors have voltage drop too! Try measuring all voltages. What is the nominal voltage for the motor?

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  • $\begingroup$ Welcome to Robotics Rig Tig. Thanks for your answer but we are looking for comprehensive answers that provide some explanation and context. Very short answers cannot do this, so please edit your answer to explain why it is right, ideally with citations. Answers that don't include explanations may be removed. Also, questions to clarify the original post should be made in comments. $\endgroup$
    – Ben
    Feb 8, 2020 at 21:57
  • $\begingroup$ Sorry, @Ben. Android app does not allow new person to add comments, only answer. But I can add a comment to my answer. I suggest either make my answer a comment, or remove it. Bottom line for OP, measure, test, learn, measure, test, learn. When you go to write up all your measurements and tests, you'll probably have a light-bulb moment! $\endgroup$
    – user24605
    Feb 9, 2020 at 1:49
  • $\begingroup$ Thanks @RigTig. You're probably right. The .7 V drop from the transistor is probably making a significant difference here. $\endgroup$
    – jgauthier
    Feb 9, 2020 at 16:36

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