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I have a demo that spins a motor, but the leads on my motor broke. I happen to have another motor lying around that I'd like to swap in, but it's of a different type. Here's my circuit:

Spin Motor Spin from Node-Ardx

This is the old (broken) motor: https://www.sparkfun.com/products/11696. It has an operating voltage range of 1.0 to 3.0V DC and a no load speed of 6600±10% RPM (@1.0V DC, 110mA).

The new motor that I'd like to use is part of this kit: https://www.sparkfun.com/products/12866. It's a 6VDC motor with a No Load Speed of 90±10rpm and a No Load Current of 190mA(max.250mA).

I'm running this off a Sparkfun Redboard, which is UNO R3 compatible.

Can I swap in the new motor without any circuit changes? Will I have to add additional power for the new motor? Or should I change the circuit with a larger resistor or something else?

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  • The board runs off USB, so 5v, I think. – KatieK Nov 12 '14 at 19:04
  • You really shouldn't be running motors off the Arduino's power supply to begin with. The new motor's higher voltage rating suggests that at the same voltage it may actually draw less current than the low voltage motor did - but it may also fail to spin. – Chris Stratton Nov 12 '14 at 21:31
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Regarding voltage, I think there should be no problem as the datasheet for your replacement motor specifies a "suggested voltage 4.5V DC".

However, be careful that there is another important value in motor datasheets: the stall current.

Simply stated, this is the current consumed by the motor when it tries to rotate but is unable to, due to its too low torque in comparison with the effort needed for rotation, e.g. if it tries to rotate the wheel of a robot that is too heavy.

The original motor has a stall current of 0.8A according to its datasheet (you can get it from the link you provided).

Your replacement motor has 1A according to the link you provided.

These 200mA can make a big difference for the transistor used in your circuit, a P2N2222A.

Indeed, that transistor is specified to switch a maximum of 600mA current at the collector.

So in the best case, the motor will run correctly without load, but if you provide some load that makes it stall, then the transistor will raise temperature (you could sense that by approaching your finger) and ultimately would get toasted.

Please also note that some poorly designed motors may consume a current near the stall current, due to internal friction (I have already almost grilled a transistor this way...)

So my answer is:

  • you can do it for a simple experiment with no load on the motor
  • if you really want to do something with the motor, take another transistor with a higher Ic current
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  • Great answer! This motor does work in a pinch so I can get my demo done; it's a little wimpy but does spin. Thanks for explaining the robustness / torque factor! – KatieK Nov 14 '14 at 23:33

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