how to slow down an electric pulley ?

Discussion in 'FAQs' started by fran1942, May 1, 2006.

  1. fran1942

    fran1942 Member

    Hello, I am a real newbie when it comes to electrical mechanics etc, so I be really happy for some help.
    I have a Tamiya electric pulley unit set up to form an aerial tramway.
    The trouble is that when I connect a battery to the electric motor, it runs too fast. The RPM of the motor is too much for a realistic tramway.
    I am using the smallest battery that will power the motor. It is a 1.5volt battery.
    I know gearing would normally be the answer, but there is not room for additional gears on the Tamiya kit and it is all custom built. I have my small pulley wheels driving the large pulley wheel, but the speed is just too fast.
    Can I buy some sort of power regulator to slow down the electric motor ?
    If I bought a smaller electric motor would that have lower RPM ?

    Any ideas would be most welcome.
    Thank you.
  2. liven_letdie

    liven_letdie Member

    You can do a couple of things, however i am no expert so do your homework first. You can get a potentiometer (pot) which would be a current control/speed control (imagine a volume knob on a stereo). Or you could make a small circuit board with resistors to give one speed. Im sure others will have better ideas, but its a place to start!

  3. ezdays

    ezdays Out AZ way

    Boy, you're getting way down there on voltage at 1.5 volts, but if that's too much, you might get by with adding a resistor in series with the supply voltage. What size? That's going to depend on how much current the motor takes running a full speed. If you have any resistors available, you might try a small value first, like maybe 50 ohms, and go up in value until you get the right speed. What that does is lower the voltage to the motor and it should lower the speed.

    If you had any specs on the motor, then we could be more precise in the resistor value range. See if there isn't any voltage and current data stamped on the motor or instruction sheet.
  4. fran1942

    fran1942 Member

    thanks very much for that. It seems a ceramic resistor will do the trick.
    Excellent advice. I am off to electrical wholesalers right now to pick one up.

    Thanks guys.
  5. pgandw

    pgandw Active Member

    In lieu of specs on the motor, you will have to do some experimentation. You need to determine what is the lowest voltage the motor will run at satisfactorially, and what voltage gives your tram the speed you want. Use a variable DC source ( a good power pack) and voltmeter for these tests. Hopefully, the motor will run properly at a slow enough speed to meet your requirements.

    What type of battery did you use? D, C, AA, AAA (all are 1.5V)? If you used one of the smaller batteries, and the motor still went too fast and didn't drain the battery immediately, then that is an indication the motor is probably a high efficiency, low current motor. It will take a higher value resistor than some other motors - probably somewhere around 7-10 ohms. The good thing about a low current motor is that the resistor rating only needs to be 1/4 watt.

    If the motor will not run reliably at less than 1 volt, you are going to have to increase the mechanical reduction - either gear or pulley - or find a lower RPM motor. Typically, the smaller the motor, the higher the RPM - but there are other factors here too. Using a motor rated at 3 volts instead of 1.5, even though having the same top RPM, might give more control.

    Hope this helps.
  6. Dick Elmore

    Dick Elmore Member

    sign1 Tie a knot in the cord. That will slow down the electrons and make the motor turn slower. eh eh eh.

    Texas Chief
  7. cidchase

    cidchase Active Member

    A power-pack with accel/decel would give you better control. I think you could still use the resistor in series to get better resolution (more travel) on the speed control knob.
  8. johnny b

    johnny b Member

    Is there anyway to change the pulley size itself to something bigger. Or modify it ? A bigger pulley or wheel would make the overall operating speed slower. The bigger the wheel or pulley the slower it will go. No matter what the voltage and speed of the motor. Just an idea though.
  9. zedob

    zedob Member

    post a pic if you can
  10. jim currie

    jim currie Active Member

    Dick that will cause the B+ to over load.:D :D
  11. kf4jqd

    kf4jqd Active Member

    Just a simple law of mechanical physic's. The larger the pully wheel, the slower it will run. The smaller of the pully wheel, the faster it will run. There is a mathimatical equation to determine the size to speed ratio, but it has been over 10 years ago using it! :(

  12. jim currie

    jim currie Active Member

    as i remember it goes like this the RPM of the motor times the diameter of the driver divided by the diameter of the driven 100rpm *10 inchres = 1000/20 =50 rpm.

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