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Is there enough torque in the motor for the system?

  1. Jun 25, 2015 #1
    Good morning,

    I have little problem here and I've come here with hopes of a solution!
    I'm currently messing with a rotary to linear pressure cycling system. The size of the air cylinder has already been decided and I'm simply trying to design around it.

    Here are the specifics! I've added a picture of the rough model.


    Starting from left to right...

    The motor I'm thinking of is the....

    Ampflow A28-400

    Torque @ 1100 RPM = 177.01 in*lb.

    1st Spur Gear (Pinion)

    Radius : .3 in
    17 teeth

    2nd Spur

    Radius: 3.5 in
    120 teeth

    Rectangle bar attached to the spur gear and rod clevis(w/ pin)

    Length : 5 in

    Air cylinder

    Produces a force of 459 lbs @ 100 psi
    Stroke 6"
    Diameter 2.5"


    Torque from Air Cylinder ONLY.

    I want to see if the torque supplied by the current motor is enough if I wanted to cycle 250 psi.

    Force(Air cylinder @ 250 psi)

    [F = P*pi*(d^2/4)]

    F = (250 lb/in^2)(3.14)(2.5^2/4) = 1227 lbs (Needed to move)

    Torque needed @ 250 psi (w/ rectangle bar)

    [T = F * d]

    T = (1227 lb)(5 in) = 6135 lbs ( This is where I believe I'm totally off.)


    Torque from MOTOR w/ GEARs

    Find the force from motor to spur 1

    [F1 = T1/r1]

    F = 177.01 in*lb/.3 in = 590.03 lbs

    Find torque in spur 2

    [T2 = F1 * r2]

    T2 = (590.03 lbs)(3.5 in) = 2065.00 lbs

    From my calculations, there is no way this motor can do its job but the numbers seem crazy high to me. Am I performing these calculations correctly? If so, would there be anything you guys can suggest?

    Thank you for your future assistance!

    Last edited: Jun 25, 2015
  2. jcsd
  3. Jun 26, 2015 #2


    User Avatar
    Gold Member

    Your equation T = F*d is wrong. Torque is force times radius, but that is only the beginning of your difficulties.

    You need to make a proper kinematic and dynamic analysis of this device, remembering that the cylinder pressure is not 250 psi all the time at all. You need to put together a P-V diagram for your cycle, all for energy storage in the moving parts, and write the complete system equation of motion. Only then will you be anywhere close to evaluating the suitability of the motor.
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