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Actuator Build

Discussion in 'General Talk' started by Brayden Reiland, Jan 13, 2020.

  1. Brayden Reiland

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    Hello,

    Im currently trying to build a syringe pump with one of the main parts of the project being a ball screw linear actuator . Im curious to know how exactly one comes up with a value for the maximum for the system can supply. For example I'm looking at the C-Beam linear actuator. In the specifications if says that they Max force is 26lb. Id like to know what determines this force value. Is it have to due with the size of the motor, or the lead screw. All responses are much appreciated.
     
  2. Peter Van Der Walt

    Peter Van Der Walt OpenBuilds Team
    Staff Member Moderator Project Maker Builder Resident Builder

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    Most critical factors for outright force:
    - Ball/Leadscrew pitch: Finer pitch = slower but higher torque
    - Stepper motor, higher torque motor = higher torque
    - Stepper driver - decent driver (for example DQ542MA Stepper Motor Driver, not a little Allegro breakout for example)
     
  3. Rob Taylor

    Rob Taylor Veteran
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    Motor winding diameter and wire gauge both directly affect input torque. 3A through a NEMA 23 will give you less torque than 3A through a NEMA 34 because T = F.d. The screw itself is a mechanical ramp conversion with an integral "gear" ratio based on thread pitch and diameter. It also has friction. Not much for a ball screw, a fair bit for a lead screw. The rigidity of the overall system- screw diameter, nut fastening, end bearings, etc. also affects how much usable force it can convert.

    This doesn't mean that larger motors are inherently better for all projects though. That extra diameter has more momentum, and that can be a problem in a lightweight, high-speed system. For a syringe pump, probably not a problem though.

    Basically, the same considerations as any other mechanical conversion system. Just gotta think through the sequence of applied forces. There are online calculators for this though.
     
  4. Brayden Reiland

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    Okay so that being said, if I was looking for a larger force output by the C-Beam actuator id have to add larger motor and change the lead screw? The reason is that the system that im trying to duplicate needs about 120-150lbf in order to achieve what I need. Is this something that can be done with the open builds systems?
     
  5. Rob Taylor

    Rob Taylor Veteran
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    You're limited in the screw diameter you can use inside a C-Beam because of the nut size. 16mm ballscrew nut housings are quite large. Leadscrew nuts are smaller, but really need a decent #2 grease to get a good performance out of them which could be an issue in a clean (or dusty/gritty) environment. Ballscrews like way oil, a little easier to manage. Look up the calculators, they simplify things a lot. Just "lead screw force calculator" or something.

    Remember it's also possible to put a motor through a planetary or worm reducer and then actuate a rack and pinion or screw from there.

    The length of the extrusion will also factor into its total load capacity as well. I probably wouldn't go more than 1000mm at 150lb, but that's more a guess than anything.
     
  6. Brayden Reiland

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    This application is quite small, with only needing about 110mm of stroke. That being said do you think this is something that the C-Beam actuator can work in this application, or something a little more beefier needs to be looked at.
     
  7. Rob Taylor

    Rob Taylor Veteran
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    The C-Beam Actuator as-is? Perhaps, with such a short stroke. A C-Beam based actuator in general, maybe a 12 or 15mm leadscrew? I don't see why not. Personally I'd probably go for a double-linear-shaft rather than anything on V-wheels, because of the torque inherent to the force offsets. C-Beam is plenty strong for the frame though.
     

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