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  • Linear actuator use in all electric mini-digger

    Discussion in 'The main mechanical design forum' started by MrSquish, Feb 1, 2017.

    1. MrSquish

      MrSquish New Member

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      Hi all,

      I've got this idea in my head of building a mini-loader like a http://www.multione.com/mini-articulated-loaders/ . I'm interested in replacing the hydraulics with linear actuators and wondered if anyone hear could shed some thoughts/advice.

      I'm mostly concerned with the main lifting actuator, I think (although not quite sure) that I could source an actuator with enough Torque and quick enough, but am concerned with potential side loads.
       
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    3. s.weinberg

      s.weinberg Well-Known Member EngineeringClicks Expert

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      You probably don't want your actuator supporting much side load whether it's electric or hydraulic. You'll need a good linear/rotary guidance system to support the loads, and then the actuator just sets position.
       
    4. Dana

      Dana Well-Known Member

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      What are you trying to achieve by going electric? Your reasons will steer some of your choices. The problems I see are cost, keeping contamination out of the leadscrews (unlike a simple rod wiper on a hydraulic cylinder), and position holding (depending on the thread pitch, it may or may not hold position with the power off).
       
    5. MrSquish

      MrSquish New Member

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      My preface to this is that the driveline will also be electric.
      My main reasons by going electric is:
      a) Efficiency - running hydraulics is inefficient as it's continually running a pump.
      b) Servicing - hydraulics require servicing, linear actuators do not.
      c) Simplicity - Electrics are far easier to design and control than hydraulics.
       
    6. MrSquish

      MrSquish New Member

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      Here's a quick sketch up of the main bucket arm.

      I guess my question here is : Given the bucket in position 2, IS there a side load on the actuator?

      Another question is, given a load (in kg) in the bucket, and the length of the arm, and the position of the actuator connected to the arm, how do I calculate the N force required to lift the bucket?
       

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    7. s.weinberg

      s.weinberg Well-Known Member EngineeringClicks Expert

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      There is nothing inherently causing side-load, assuming your actuator is pin-connected at both sides. Having said that, if the load in your bucket is at all unevenly distributed, it's going to try to torque the support, which won't do your actuator any good. Make sure that the support at the pivot is sufficiently rigid that it takes up any torsional or side loads, and not your actuator.

      To calculate the force, take the moment about the pivot point. When they add up to 0, the bucket is balanced. Beyond that, plus some margin for friction, you will have motion. To calculate the moment, you take the force from your bucket (perpendicular to the arm - you will need some basic trig), multiplied by the length of the arm, and subtract the force of the actuator (perpendicular to the arm), multiplied by the distance from the pivot point to where it connects.
       
    8. MrSquish

      MrSquish New Member

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      Thanks so much mate, that's the answer I was after. I'm intending on having two main arms in parallel, so the actuator should be sufficiently protected from the unevenness of the bucket.

      I built up the equation based on your notes, put it in Excel, then noticed that altering the angle made no difference in the result. Then noticed that to find the actuator force requirement, the angle is canceled out in the equation.
       

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