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rpm vs torque for actuator build

Discussion in 'DIY Motion Simulator Building Q&A / FAQ' started by Mortisedsnail36, Mar 10, 2020.

  1. Mortisedsnail36

    Mortisedsnail36 New Member

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    ok so my understanding is the goal is to move a min of 4 inch a sec while loaded. now most servos are rated at 3000 rpm if lead was 2mm that would be almost 4inch a sec unloaded. now say we went to a 6000rpm servo and a lead of 1mm would results be the same but torque output multiplied by the reduction in lead. none of this is taking into account ramp up speed or anything. I'm just trying to figure out if I should aim for rpm based or straight torque base build for an actuator. also is there any easy way to figure lifting capability of a setup in theory.
  2. Ads Master

    Ads Master

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  3. Gadget999

    Gadget999 Active Member

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    do you want a ballscrew actuator, a chain / belt drive or a lever arm ?
  4. adgun

    adgun Active Member

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    1 watt is 1 newton with a speed of 1 meter a second.
    actuator speed 100mm a second ,so 1 watt will give 10 newton minus screw efficenty
    ballscrew efficienty is 90% so every watt will give 9 newton force
  5. Mortisedsnail36

    Mortisedsnail36 New Member

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    I'm just want raw figures as if it were direct drive. I'm figuring less lead more lifing power and more lead less lifting power. based on vertical load. and how rotational torque translates into lbs lifted vs the amount of lead to the amount of speed.
  6. adgun

    adgun Active Member

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    it stays the same what pitch you use, its the speed that counts!
    also with rotation its the same rpm with lever lenght gives the speed
    you can make nm from newton every watt
    4,5 newton is 1 lbs
  7. Agosky

    Agosky New Member SimAxe Beta Tester Gold Contributor

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    You can’t think ”rpm based or torque based”, you need to know required velocity and force and start from there.
    Power = torque x rpm = force x velocity.
    So if your lead drops from 2 to 1, you get only half speed but double force. In your first example, 3000rpm servo 2mm lead versus 6000rpm servo 1mm lead. If those servos have equal torque then your force doubles and speed stays the same, BUT with equal torque that 6000rpm servo has double amount of power also. With a constant amount of power you can only trade force for velocity or vice versa. So as you said, ”less lead more lifing power and more lead less lifting power”.

    Needed torque for ballscrew:
    Torque = Force x Lead / (2 x PI x eff)
    Linear force of ballscrew:
    Force = Torque x 2 x PI x eff / Lead
    Should work with SI or imperial units: in-lbs, lbs, and inches, or N-m, N, and meters.
    Efficiency 0,90 should be close.