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Actuator w/ Feedback for Traction Loss

Discussion in 'DIY Motion Simulator Building Q&A / FAQ' started by Pit, Jun 12, 2014.

  1. stroutmail

    stroutmail Member SimAxe Beta Tester Gold Contributor

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    I've never taken a SCN5 apart, but I suspect they are acme screw type. They do not disclose in their literature and I'm assuming they would say "ball screw" if they were.

    In any machine, Power determines Speed and Force, efficiency considered. Volts time Amps equal power. Speed and Force vary inversely, in other words opposite. You can get more speed by reducing force--you can get more force by reducing speed.

    Linear actuators are simply a motor with a special type of gear type transmission. The ball screw is generally more efficient and expensive than the acme screw. Using a DC motor with a helical, spherical or worm drive, along with a lever is just a motor with another type of "transmission" design.

    In my own humble opinion, you can get the same or better result for less cost using the motor with gear drive and a lever. A linear actuator was designed to push/pull in a straight line in one dimension--like pushing a box off of a conveyor line. A gear motor with lever can be better adapted to the 2 or 3 dimensional movements we see in a Sim. A typical linear actuator has two transmissions, one to reduce the motor speed, and the screw to create the linear movement. The gear motor with lever has only one transmission--the movement after the transmission--rotation to linear movement of the lever is extremely efficient with no friction or heat.

    As far as speed is concerned, a 60 RPM motor rotates at one revolution per second. A 2" or 51 mm long lever arm moves 4 inches in half a revolution. 4 inches in one half second is 8 inches per second or 203 mm per second. Need more force--get a bigger motor, a higher gear reduction (50:1 rather than 40:1) or use a smaller lever. Need more speed, get a lower gear reduction (25:1 rather than 40:1) or a longer lever--plus most likely you will also need a bigger motor. Get a bigger motor and your amps will be higher and the motor controller will cost more.

    BTW, here is a video of a printer running at a speed of 200 mm per second (8 inches per second) Looks about right for a SIM to me. In Japan, there is a saying that cherry blossums and snow flakes fall at 5 centimeters per second---50 mm/sec or 2"/sec is too slow.

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    Last edited: Nov 20, 2014
  2. bsft

    bsft

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    ummmm....we know all that already....
  3. stroutmail

    stroutmail Member SimAxe Beta Tester Gold Contributor

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    Sorry @bsft--but it does depend on who you include in "we". When I first started on the forum--none of these "facts" where known to me. I'm new here and it took many hours of thought and reading to come to my conclusions which of course you with your years of experience already knew. (Should I use a SCN5 or a SCN6--how big a motor should I buy and what type? How many amps will it draw and how hot will it get? How long will it last if I use it a lot? ) Just thinking that sharing our thoughts was part of the community's purpose. Looked like someone was trying to figure out what was the best choice for them. (Based on people using wiper motors, winch motors and different actuators, trying to "source" in different countries all over the world, seems like the decision process is not perfectly straightforward and the principles behind the choice are important.) Perhaps a reference document or tutorial on "Choosing the right Motor or Actuator" might be useful? We all learn differently and I'm one of those dumb ones that needs to understand WHY something works before I can move on to building something.

    I for one am very grateful to everyone who takes the time needed to share what they have learned--even if there is a bit of repeating what I may already know. I learn something from almost every comment and can skim over what seems overly "familiar".
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  4. bsft

    bsft

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    ok, I thought there was a FAQ thread about that, maybe not.
    I do recall in the past when this discussion came up, there was conflicting comments from people between actuators and motors with levers.
    It got more interesting when it came to Arduino coding and comparisons to JRKS.
    @Pit is the ONLY one sim builder I have seen whom has mastered the arduino SMC3 code.
    I will see if I can rattle something up over the weekend...
    Dave.
  5. bsft

    bsft

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    @stroutmail
    Comparison between SCN actuators and 12v 200 watt dc motors

    Shoulder mount configuration

    Using the JRK as a reference.

    SCN5 rated 5-10 kg max, recommended speed without load is 200mm per second

    More like 100-150mm per second as far as I know loaded

    SCN6 rated to 20 kg

    Speed 150mm per second loaded

    @nclabs can correct me on this please

    DC motor with 25:1 gearbox.

    Using 40mm CTC lever and travel of 70mm, approximately 300 mm linear speed per second unloaded

    200-250mm per second loaded

    Using 65 mm CTC lever and travel of approximately 70mm, about 500mm per second linear travel speed.

    350-400mm per second loaded, as found by @eaorobbie.
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  6. nclabs

    nclabs Active Member Gold Contributor

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    SCN5 rated 10 kg max and the speed is 400 mm/s unloaded.
    SCN6 rated 40 kg max with 200 mm/s unloaded.
    Another SCN6 rated 60 kg but with a speed of 100 mm/s unloaded.
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  7. stroutmail

    stroutmail Member SimAxe Beta Tester Gold Contributor

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    This is great...very informative and usefull to any newbe. Only thing missing is the linear force or torque of the DC motor. THANKS
  8. SeatTime

    SeatTime Well-Known Member

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    I have to agree that a worm drive/ lever set up with not too much load, is still a good choice for most SIM builders due to cost, complexity and noise. But a ball screw does have some advantages in efficiency (Worm Gear approx 65% Ball Screw approx 90%) and much less gear binding/friction as the load increases. The full drive output is also directly linear, which is not possible on a motor shaft/lever setup. There although can be some noise as the balls are circulated.
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  9. stroutmail

    stroutmail Member SimAxe Beta Tester Gold Contributor

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    All engineering and design choices are a matter of compromise. A powerful and fast ball screw actuator built for 100% duty cycle is a very efficient thing of beauty, but generally quite expensive. When you try to cheapen a linear actuator it tends to lose it's "beauty" and durability. IMHO.
  10. SeatTime

    SeatTime Well-Known Member

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    Yes, just for one actuator - parts alone (not including motor) have left me with no change from $300. But it will be an interesting experiment:).
  11. bsft

    bsft

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    The only actuators I have are converted Brick Spreader actuators, of which, by chance, I was given.
    http://www.xsimulator.net/community/threads/actuator-2-dof-seat-mover.5065/#post-50916
    they are noisy buggers compared to a DC motor and do move a lot of weight. And they have lasted under the right circumstances.
    Anything will fail with enough abuse, even my actuators are showing signs of bush and bearing wear.
    However, the DC motors have proven themselves to be sufficient for the tasks we put them through,be it less efficiency than an actual actuator.
    @stroutmail , we would all love actuators on our rides, but thats with DIY exists. We cannot afford such items
    We use what we can get or what someone else has spent the time testing to show that a cheaper item does the same job, if not better in performance.
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  12. bsft

    bsft

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    Torque on motors is a curly one depending on what the supplier says.The common 12v 200 watt worm gear motor can have listing of torque from 6NM to 20 NM depending on supplier , even though it may be the same motor.
  13. stroutmail

    stroutmail Member SimAxe Beta Tester Gold Contributor

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    It is complicated. Depends on RPM they decide to "rate" it. Same thing with current. The graph below illustrates. Rated operating point is pretty arbitrary..a guess. An old engineer told me to figure about 50% of stall torque for most uses..using your 45 mm or a 2 inch lever...on a 1/4 hp 200 watt motor...one might claim a force of 40 pounds. (80 in pounds or about 9 nm) Linear actuators have the same issues..their force ratings are quite arbitrary.

    [​IMG]
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  14. bsft

    bsft

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    considering our motors are usually run at 2.5 times to 3 times rated current because of stall current, yes, its hard to get it right.
    We usually have to rely on others using "those" motors/actuators and giving them a go ourselves.
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  15. Delonet

    Delonet New Member

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    Hi, for a good simulator how is the correct speed and the correct course for an linear actuator?