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DC Motors; Gear Box's

  1. Aug 1, 2010 #1
    Ey guys sorry if this is in the wrong area; not too sure but i do mechanical eng and figured it was. Well i hope so lol otherwise i might have selected the wrong course

    We have an assignment coming up, (according to past year students that involves DC motors, gear box's). Wouldn’t mind getting a bit ahead of the pack.
    (Figured its not a assignment question or anything so it didnt belong in the HW area; more after general knowledge. However if it does please move it and sorry for the mistake :))

    Just wondering if anyone can give me a hand with understanding some data sheets and basic stuff.

    "10:1 Gear motor - High Power, 3000 RPM, 0.3 kg-cm"

    First off what does the 10:1 stand for. Im assuming the 10:1 is the gear box ratio.
    -Does the drive shaft coming out of the gear box turn 10 times faster than the motor shaft??? or does the shaft coming out of the gear box turn at 1/10th of the motors shaft RPM???

    I’m assuming this is how fast the drive shaft coming out of the gear box turns at.....??

    Stupid question but if we were to replace this motor with a remote control car's motor, would it go flying away since the wheel would turn 3000 RPM = 50 RPS.??

    0.3 kg-cm
    What does this mean???

    Cheers Trenthan
    Last edited: Aug 1, 2010
  2. jcsd
  3. Aug 1, 2010 #2
    The common way of listing gears is Input RPM : Output RPM.
    So 10:1 would be a reduction ratio.

    It's also common to list the motor speed, but that could be the output speed. Unless there is anything to suggest otherwise in the text i;d assume it was motor output / gearbox input rpm.

    The kg-cg is a torque rating. so an equivilant torque to 300g acting at 1cm. Again this is most likely motor output, but could be shaft output.
  4. Aug 2, 2010 #3
    Thanks Chriss for that help quite abit :)


    stupid question with the kg-cm.

    Lets say i had a 1cm long beam (can think like a cantileaver) which had its centre of mass at the end**

    For case 1 where the COM is 300grams, im assuming it would be able to rotate the beam. Since the torque applied is 0.03Nm (this is the equivalanet of the 0.3kg-cm isnt it??)

    For case 2 where the COM is 3kg would it be able to turn the beam.?? Im assumnig not since its over the 300g-cm stated on the motor.
  5. Aug 2, 2010 #4
    Yep it would be able to turn the 1st case but not the 2nd for the reason you stated.
  6. Aug 2, 2010 #5
    Another silly question.

    I've got a old model car which weigh's ~6kg (just under to be precise). Wouldnt mind changing the motors as abit of an experiement.

    What criteria would be best to look for. I dont want the car to go zoom zoom, slow and steady so if i were to put a cup of coffee on it and drive it over the desk to me it wouldnt spill haha during a long night of study for some entertainment

    All the motors in general ive found from researching on the web seem to have a high RPM and low (kg-cm) stall torque. Or a low RPM and higher stall torque. (Not too sure why it seems theres a relationship or compromise between the two)

    One i found was
    298:1 gear ratio 45 RPM 1.8 kg-cm

    Would the 1.8kg-cm be enough if i was to replace the back two motors with these two?? Not quite sure how to calculate the "torque" the motors would experiance under the model cars 6kg weight.

    If someone can give me a hand or point me in the right direction, more than willing to give it a go :)

    Cheers Trenthan
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