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DEBUG DC Motor RPM — Parallax Forums

DEBUG DC Motor RPM

NWUpgradesNWUpgrades Posts: 292
edited 2009-05-22 17:40 in BASIC Stamp
I have some DC motors that I have no idea what the specs are on them. Is there any code that could help determine what the RPM is while they are running?

Comments

  • Mike GreenMike Green Posts: 23,101
    edited 2009-05-22 16:03
    It's not so much a matter of code. You need some kind of sensor that would attach to the motor shaft and provide a pulse for each revolution of the shaft. A Stamp could count these pulses with a COUNT statement and display the result converted to RPM.

    Typical sensors for this include using a LED and phototransistor with a little metal or plastic "flag" attached to the motor shaft that interrupts the light beam from the LED or a little magnet attached to the motor shaft and a Hall-effect sensor that produces a pulse whenever the magnet passes next to the sensor.
  • LeonLeon Posts: 7,620
    edited 2009-05-22 17:31
    You can also determine the speed by measuring the back EMF periodically, with the supply to the motor disconnected.

    Leon

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  • NWUpgradesNWUpgrades Posts: 292
    edited 2009-05-22 17:37
    Not sure I understand what you mean.
  • PrettybirdPrettybird Posts: 269
    edited 2009-05-22 17:40
    In the past I have used a small DC motor as a generator and hooked it to a meter. Use a motor with a known RPM and record the voltage. Do the math from there. Tachs in industrial servos are basicly DC motors. Don't know if brushless DC motors will work. This is old school.
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