Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Gearbox torque?

  1. May 24, 2009 #1
    gearbox torque?!?

    Hi, I don't know much about mechanics and I'm trying to build a mechanism to drive a set of syringes, and I need to buy a gearbox motor to drive the syringe shaft forward and back. the syringe needs to be driven 70mm, and i'm going to attach a rack and gear to the motor to get this motion. however, because of the hydraulics, it actually requires quite a bit of force, and i don't know what gearbox motor will be strong enough to drive it. i didn't know how to measure how much force i need so i put weights on the shaft and it needs 2.5kg to drive forward at a good speed. (it doesn't have to be incredibly fast but i don't want it to be terribly slow either).

    could anyone recommend a motor that will be strong enough to drive it at a good pace??
    or tell me what information and numbers to look for in the data sheet??

    thanks so much!!
  2. jcsd
  3. May 24, 2009 #2
    Re: gearbox torque?!?

    the speed i want to drive it at is 10mm/sec
  4. May 24, 2009 #3
    Re: gearbox torque?!?

    U need to buy high torque and low rpm motor to drive the shaft
  5. May 24, 2009 #4
    Re: gearbox torque?!?

    Buy the brushless motor under the specification
    Power: 200 Watts
    *.RPM/Volt (KV): 1000
    *.Continuous Current: 6-15A
    *.Burst Current: 19A*
  6. May 24, 2009 #5
    Re: gearbox torque?!?

    A 70 mm stroke at 10 mm/sec sounds straight forward. The required power is
    P = F dx/dt = 2.5 Kg x 9.81 m/sec2 x 10 mm/sec x 1 m/1000 mm = 0.25 Newton-meters/sec = 0.25 joules/sec = 0.25 watts
    So probably a 1 or 2 watt motor will suffice. A stepping motor turning a lead screw is one approach. 70 mm will be 55 turns on a 1/4-20 pitch screw. You can either count digital motor steps or use limit switches at the ends. 10 mm/sec will be about 8 turns/sec. A direct drive 480 RPM stepper motor on a 1/4-20 lead screw will work. The control electronics will be less if you use a DC gear motor geared down to 480 RPM with limit switches.
  7. May 25, 2009 #6


    User Avatar
    Gold Member

    Re: gearbox torque?!?

    I don't know anything about steppers, but I definitely agree with Bob about the lead screws. You just can't beat those suckers for power and smooth movement. I use them for all sorts of stuff. They're incredibly easy to make, as well. Just take some threaded rod (or a bolt for short strokes) with a matching nut, and connect the nut to the thing that you want to move.
  8. May 25, 2009 #7

    Ranger Mike

    User Avatar
    Science Advisor
    Gold Member

    Re: gearbox torque?!?

    McMaster Carr on web. they got everything. motors, lead screws, metal, wire etc...
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook