Can Increasing a Spool's Diameter Boost a Motor's RPM?

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Discussion Overview

The discussion revolves around the feasibility of increasing a DC motor's effective RPM by attaching a larger diameter spool to its output shaft. Participants explore the implications of this modification, considering the motor's existing gearing and voltage limitations.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested
  • Conceptual clarification

Main Points Raised

  • Jack inquires whether attaching a larger spool to his 20 rpm motor could effectively increase its RPM to 30.
  • One participant suggests that increasing the diameter of the pulley would speed up the velocity of the belt, potentially increasing the RPM.
  • Jack clarifies that his motor is a geared motor with high torque and is limited to 12 volts DC, which restricts other options like voltage increase.
  • Another participant notes that increasing the diameter of the pulley on the motor axis mechanically gears up the motor, while decreasing the diameter of the pulley on the load could also be an alternative.
  • Jack explains the setup involving a guillotine-style door and a spindle, indicating that he cannot change the internal gearing of the motor.
  • One participant reiterates the suggestion to increase the spool diameter as a solution to Jack's problem.

Areas of Agreement / Disagreement

Participants generally agree that increasing the spool diameter could help achieve a higher effective RPM, but there is no consensus on the exact mechanics or implications of this change, particularly regarding the motor's gearing and limitations.

Contextual Notes

Participants do not resolve the potential effects of increasing the spool diameter on the motor's performance, nor do they clarify the relationship between the motor's gearing and the desired RPM increase.

jsmith24
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Hi all,

I have a small DC motor which turns at 20 rpm. The shaft diameter is 6mm, giving a circumference of 18.85 mm. What I want to do is get an effective rate of 30 rpm. Can I do this by simply attaching a spool or spindle to the motor output shaft with a larger diameter? If so, would it be as simple as increasing the diameter by a factor of 1.5?

Thanks,
Jack
 
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20 rpm! That was not much. Is a gear built-in the motor? Can you change the gear?

But yes: Increasing the diameter of the pulley, you will speed up the velocity of the belt.

Other possibility: Increase the voltage to the motor.
 
Yes, it's a geared motor, sorry! High torque. I'm limited to 12 volts DC, so that's out. I thought it was as simple as increasing the diameter of the shaft (pulley), which would increase the circumference, thereby moving more belt per revolution, effectively increasing the rpm. Thanks!

Jack
 
jsmith24 said:
Yes, it's a geared motor, sorry! High torque. I'm limited to 12 volts DC, so that's out. I thought it was as simple as increasing the diameter of the shaft (pulley), which would increase the circumference, thereby moving more belt per revolution, effectively increasing the rpm. Thanks!

Jack

By increasing the diameter of the pulley (on the motor axis), you are mechanically gearing up the motor. An alternative is to decrease the diameter of the pulley on the load.
 
There's no pulley on the load. It's a simple guillotine-style door. The motor will have a spindle on it, a cord attached to the spindle which will wind up when the motor is forward energized, which, in turn, raises a flat door in a track. When the motor is reverse energized, the spindle reverses, the cord unwinds, the door descends. The problem is that I find 20 rpm (or rather, the amount of cord travel per revolution) too slow. As this was the only motor I found handy, I'm trying to make do. The motor already has plenty of torque to raise the door (which is rather light), so gearing up a bit shouldn't be an issue.

Oh! I forgot to answer part of your question: No, I don't think I can change the internal gearing of the motor.

Thanks!
 
Well, then just increase the diameter of the spool as you suggested in #1.
 

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