I have just sized the DC motors I want to use (corresponding to my robot and its intended applications - my figures include a 50% uncertainty factor to account for friction in reducers and other losses). Now I need to actually choose the exact motors I want to buy from the manufacturer (I am targeting maxon motors as I am not an expert and want no problem). I have a few down to earth questions about linking the mechanical needs to the electrical characteristics:

  • Maxon states a "nominal voltage" in the characteristic sheets. Is that the voltage you should apply to the motor? This may be a dumb question but I have followed the full maxon e-learning course and read about other tutorials on the web and I could not find this information anywhere. Can anyone who knows about motors confirm?
  • As far as I understand, the nominal torque corresponds to the maximum torque the motor can sustain continuously. So I guess, as a rule of thumb, I should find a motor with a nominal torque = my max torque (after reduction), or around. Right?
  • Also I chose a motor reference (310005 found here) which has a stated power of 60W, as the nominal voltage is 12V, I was expecting to have a nominal current of 5A, but it states 4A. Where am I wrong?
  • The motor I chose has nominal speed = 7630rpm - nominal torque = 51.6mNm. My needs are max speed = 50.42rpm / max torque = 10620 mNm. This means a reduction factor of 151 for speed and 206 for torque. Should I choose a gear closer to 151 or 206?
  • What is the "rated torque" mentioned when choosing a gear? I know my input torque (torque on the motor side) and my output torque (torque on the system side), does that correspond to any of these two?

I have followed some theoretical and practical courses on the web but I find it hard to find answers to my down to earth question...



  • 1
    $\begingroup$ Would you be willing to edit this down to a single question and make several other posts for the rest? You have very good questions here: 1. Should you apply the nominal voltage to the motor? 2. Should you force the motor to apply its nominal torque continuously? 3. Why does 12V * 4A nominal current create a 60W motor instead of 48W? 4. How should I pick my gearing (based on torque/speed needs)? 5. How do I calculate the proper torque for gear selection? (I'd like to upvote these all individually!) $\endgroup$ – Ian Oct 24 '14 at 18:43
  • $\begingroup$ Hello Ian, you are right, it will be cleaner to split the question. I have just done so. Thanks for your input ;) $\endgroup$ – arennuit Oct 26 '14 at 13:42
  • $\begingroup$ Cool. I see that the new questions are #1 #2 #3 #4 #5 $\endgroup$ – Ian Oct 27 '14 at 2:27

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