# Comments: Motors and Selecting the Right One

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• Member #1698918 / about 2 years ago / 1

Thank you for the explanation, Does the hobby motor the first motor in the demo has 2 poles? I need to know this to calculate the RPM. My hobby motor stall at certain voltage and certain duty cycle and frequency more than 100. In the data sheet shows max voltage 3 and RPM 6600 at 1V. I want to calculate at 3V how many RPM is allowed so i can provide the correct duty cycle at right frequency. RPM = (HZ * 60 * 2) / pole number.

• ccbundy / about 10 years ago / 1

Thank you for excellent descriptions. Agree with member 544838 about 'Ah Ha!' concerning animations. :)

Thought I'd throw in Homopolar motors for inclusion, This is a great science craft for kids! (just make sure everybody wears safety goggles)

http://en.wikipedia.org/wiki/Homopolar_motor

• Member #544838 / about 10 years ago / 1

So where do servo motors sit in the bundle? BTW Fantastic animations, was able to show it in my tutorial and the number of "ah huh" momements with the stepper motor was incredible.

BTW: Efficiency occurs if you can co ordinate repulsion with attraction at the same time, ie therefore the torque produced is effectively doubled as all the windings are effectively "active" and conferring work to the shaft.

Servos aren't bare motors, they're motors with a control, driver, and feedback network. I don't know offhand what kind(s) of motor are used in servos, but I'd guess ordinary brush motors, or perhaps brushless.

• Servos are deserving of their own tutorial (in the works). I want to focus on the types of servos and what to look for.
It's incredible what you can do in modern motor controllers, for simplicity sake, and my sanity, I decided to keep the animations simple. I'm glad the tutorial helped! Making the brushless motor animation really got the concepts to sink in for me.

• Member #500357 / about 10 years ago / 1

I'm using stepper motor in my research and found that stepper motors have low efficiency because the power consumption is not increasing proportionally with the torque applied on the motor. I'm trying to learn more about stepper motor efficiency and how efficient it can be so if any one knows a good source about this topic, please refer me to it. Thanks

• It's a tough topic. At higher speeds, the inductance of the stepper motor windings begins to apply drag on the motor. The cheap way to get around this is to up the voltage but as you see it just reduces the efficiency. I recently found an appnote talking about voltage controlled methods to driving steppers. I am a novice at advanced control methods but this is at least pointing me in the right direction. http://www.st.com/st-web-ui/static/active/en/resource/technical/document/application_note/DM00061093.pdf

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