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Rotating tubeand spring

  1. Jul 21, 2011 #1
    I am trying to design a certain mechanism. It is basically a rotating tube(a DC motor is driving it) attached to a motor at one end. There is a spring attached to just about the midpoint of the rectangular tube. The tube will spin and start stretching the spring. once it reaches the other side, the motor will cut out and the force of the spring will rotate the tube back to its original position. The whole point is for the tube to hit a ball on its way back. If I have a certain motor with these specs:

    · Torque @ Max Efficiency: 127 oz-in.@12VDC
    · Torque @ Stall: 368 oz-in.@12VDC
    · Gear train damage can occur if stalled (locked)
    · .240” (6mm) Diameter Shaft
    · No load current: 45mA
    · No load current @ Max Efficiency: 95mA (12V)
    · No load speed: 10 RPM
    · No load speed @ Max Efficiency: 7.96 RPM
    · Gear ratio: 300:1
    · Motor size: 1.30"Dia. x 1.015"L
    · Gear size: 1.45"Dia. x .985"L
    · Shaft size: 0.24" (6mm) Dia. x 0.715"L
    · Weight: 0.2813 lbs. (4.5 oz.)
    · DC reversible motors
    · Solder type terminal
    · High torque construction
    · Oil bearing design for long service life
    · Insulation resistance: 10 MOhm
    · Dielectric Strength: 300VDC

    then how can I determine what the max load rate of the spring can be, as well as the amount of force the ball will be hit by? The rectangular tube is 10 inches by 1 inch by 1 inch and hollow on the inside. Thickness is about 1/16". It is made out of aluminum. I'm including a picture of what it looks like.. The spring will be mounted a little bit lower than the pivot point of the tube so that it will rotate the tube all the way around. I apologize for the crappy paint =) Any help you guys could offer would be greatly appreciated =)


    Attached Files:

  2. jcsd
  3. Jul 22, 2011 #2
    Getting a lot of views but no responses... Initially I was going to treat this as a dynamics problem... But now I see it more as a statics problem since I'm focusing on stall torque. Overall, I do not want to damage the motor but I still want to place maximum force on the ball... I understand that the force of the spring can vary depending on the placement in reference to the pivot point and mounting point on the tube.
  4. Jul 23, 2011 #3
    I'm not sure exactly what you're having trouble with.

    Maximum load rate of the spring? You mean the rate of change of force on the spring while it's being loaded by the motor? I don't want to think too hard about that in case it's not what you're after.

    You can't determine the force on the ball from this. The force will vary during the contact time, and will depend on the elasticity and mass of the ball.

    Do you want to maximize the speed of the ball? In that case you should maximize the impulse applied to it, not the force.

    By the way, it'd make it easier for people to read if you removed unnecessary information like the solder terminals and insulation resistance.
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