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What fast linear actuator would you use?

Discussion in 'DIY Motion Simulator Projects' started by Antidamage, Oct 6, 2015.

  1. Antidamage

    Antidamage New Member

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    So there's this old video here:

    He's using actuators from a hospital bed. They seem to move pretty fast. I've looked around and the fastest I actuators I can find are about 20mm/s, which seems way too slow. I found ONE other example of a fast actuator capable of 9 inches in a second, which seems more like what I'm after but I wasn't able to source it.

    Have any of you looked into this before?

    Since I haven't done the maths - what sort of Newtons do the normal pinion-mounted 2DoF motion rigs require?
  2. Antidamage

    Antidamage New Member

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    Sorry, I should add that I did find one by Progressive Automations that's 11 pounds/9 inches per second or 33 pounds/3 inches per second. Forums won't let me link to it, but does that seem strong enough?
  3. bsft

    bsft

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    @Antidamage , unfortunately you will not be able to do links until after 10 posts, I think. So unless perhaps, you can copy paste info, its a bit hard to say.
    Back to needed load to shift a sim, thats a broad area.
    Short story long, shoulder mount seat mover is the best leverage and will move a reasonable heavy person.
    As for actuators, again, grey area. The SCN5 is the favourite, but I think you are pushing you luck with an over 110kg driver, SCN6 move more weight, but are restricted to speed.
    Also, with actuators, get a LOADED speed, its usually a lot slower than quoted.
    Now, about actuators, @nclabs , is the best to advise overall.
    The only experience I have is with DC motors and JRK control boards, but its been shown that a 200 watt worm gear DC motor will rival a SCN in movement and speed.
    What ID suggest is if you have a frame design in mind, then start a new thread with that and we can advise from there.
    Also, if you dont mind tinkering and want to say a quid, look at the options of DC motors and the variious controllers around as well as have a dig through the threads,
    Cheers, David.
  4. Antidamage

    Antidamage New Member

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    I've had a good look at what everyone is doing with worm gear motors but the range of motion seems less than ideal. How are you guys finding the limited range when it comes to VR?
  5. bsft

    bsft

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    define "range of motion less than ideal"
    Theres a few VR guys here @noorbeast and @dontcarefilmer should be able to advise.
  6. Antidamage

    Antidamage New Member

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    "Less than ideal" being you only get a couple of inches of lift in each direction. Can anyone comment on how it "feels"?
  7. bsft

    bsft

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    others I am sure will comment.
    Its an immersion thing, its a mind trick, having motion suit a video game gives you the impression you are under greater forces and or inclines than what the seat/frame is actually moving for.
    Using rift on a motion sim would be very immersive and the rift is immersive enough without motion.
    I actually only use screens and 14 builds, later, 2 hire machines (seat movers with screens) over 100 players , 10 professional drivers playing as well, the degree of lift or angle is not overly needed although others will correct me. If professional drivers comment that is "feels" like they are under forces, even with 8 deg total lean on a frame, then the immersion is right.
    i can tell you, even with a poorly seat mover, I feel a heck of a lot more. The pitch of the car going over a jump, I anticipate hitting the ground. When the car goes into a roll from a slide of track, there is a split second feeling you are going to go over with it. The bumps, I can feel the gravel in dirt3 and then almost every wooden slat going across a bridge.
    If you can, look up to see if there is any local motion sim places you can go have a play on, or give us your location and there may be a sim guy near you that you can go have a play on their sim.
    Cheers, David.
    • Agree Agree x 4
  8. Antidamage

    Antidamage New Member

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    Interesting. Well, it doesn't seem too expensive to give that route a go. Thank you for the feedback!
  9. Antidamage

    Antidamage New Member

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    I'm in Auckland NZ (just by chance, the same as the guy in the video I posted). Is there anyone from around here on this forum?
  10. bsft

    bsft

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  11. Antidamage

    Antidamage New Member

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    If anyone is and they want to try my rift with their config, I'm down for a weekend of insanity!
  12. noorbeast

    noorbeast VR Tassie Devil Staff Member Moderator Race Director

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    Warning, a very long answer to a seemingly simple question, but then again try explaining how VR feels, and what technically is required for realistic VR presence, to someone who knows nothing about it and has no frame of reference to hang their understanding on.

    You have a Rift so let me start with that as a reference point you are familiar with, or more specifically what makes for 'bad VR' as a basis to better appreciate the nuances of VR and motion simulation.

    Bad VR can have its genesis in hardware and/or software. Basically if what you are seeing differs from what your brain expects then is can be disorienting, or even make you sick. Presence, your mind accepting something as real even though it knows it is not, is somewhat of the VR holy grail. But there are real limitations, FOV, resolution, locomotion, realistic input, poor graphics throughput are just some of those limitations. Thankfully we can exploit the weaknesses of human perception to minimise such limitation, see for example the excellent keynote by Michael Abrash earlier this year (starts at 42:15).



    At the moment VR, particularly the first generation consumer VR, is somewhat of a compromise. The FOV is limited, the graphics frame rate and throughput is limited by currently available hardware and drivers, there is no universal solution for locomotion, the CV1 Rift won't even launch with dedicated VR specific input, largely based on the assumption that there is not enough content to take advantage of it right away, hence it warrants a longer development gestation period. But that does not mean that even first gen VR can't be compelling.

    Let me suggest that the very best developer/consumer VR experience of presence available right now is seated, where the controls match what is being simulated, where haptics fit your brain's expectations. In other words I consider a cockpit based VR experience with high end peripherals, sound and complementary haptics is the most reliable experience of presence. It does not mean you can't have other types of triggers for presence, say with Light and Magic demos, but rather that the more you have contributing to and complementing the experience the easier presence is to elicit as a response.

    @bsft is spot on in describing motion simulation as 'a mind trick'. Like with VR all consumer grade motion simulators make compromises and exploit human perception, because it is not affordable or practical to try and replicate G-forces. Tricking the brain in simulating G-forces, not replicating them, and how good or bad that is depends on the design, speed and practical limitations of any given simulator.

    Given the real limitations of physics, cost and other practicalities I consider that in VR the axis travel distance is far less important than the haptic quality of the movement. To give an example, if you try and use large amounts of sway in VR to simulate G-forces in a car, then it will likely feel very unrealistic. First because the tactile feeling is all wrong in VR, as your body does not move like that in a real car, and second because very large axis movements are likely to result in latency, and latency is one of the biggest VR presence killers.

    Even a 2DOF motion simulator can be very effective in VR, particularly in a driving simulation with high quality peripherals and surround sound. The wheel, pedals and their feedback feel right, the movement can be dialed in to provide a range of cues that are as powerful as those provided by VR itself, and which compliment each other. Interesting, as motion simulation veterans like @eaorobbie have found it is better to trade large axis movements in a motion profile for more precision when used with VR and if you think about my sway example it is not really hard to understand why.

    Car based VR/motion simulation is not that hard to do well, flight based is far more challenging as it brings into play the very real limitation of our motion rigs when used in conjunction with 360 degree simulation. While it does not replicate G-forces even a 2 DOF can hep trick the brain for flight simulation, particularly when used in conjunction with VR. @value1 made it possible to do pitch and roll more realistically for VR in the FSX/P3D plugin and @Archie has detailed how to go about making the most of exploiting human perception on a 2DOF for flight profiles in FSX/P3D: http://www.xsimulator.net/community/faq/prepar3d-guide-to-realistic-motion-settings.144/

    Like with VR your brain can suspend disbelief and accept you are doing a loop or roll, even though you do not have real G-forces acting on your body. I would suggest doing that well, particularly in VR, does not really rely on large axis movements but more on the subtle combination of complimentary haptics, sound and sight.

    So for me making the most of a motion simulator is very similar to what you do in VR, focus on the things that most easily trick your brain. That can lead to thinking about things differently. Surge on my compact sim is designed to move the controls relative to the user, rather than the whole simulator, because I am interested in the haptics of simulating sustained surge. My haptic harness attaches to the the sim with the lap belt and not the traditional shoulder straps with springs, as I use actual heave. That way the harness still feels like it tightens and loosens with bumps in a realistic manner but is not as affected by pitch, though I do exploit the curve my assisted heave knee travels through to have the harness also tighten and loosen in response to surge.

    As VR is still so new there is still a long way to go in working out how best to use it for different types of motion simulators, which makes it a ton of fun to use and explore both.
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  13. Antidamage

    Antidamage New Member

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    It sounds like you're suggesting we do our best to make a bump simulator. I'm all for accurate tactile feedback but this isn't a new field - if you have the money, actuators are the way to go. Forty years of simulation can't and shouldn't be disregarded. Why would I get rid of my g-force simulator in favour of a bump simulator when I can make both? Both ideas are on the table.
    • Disagree Disagree x 1
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  14. noorbeast

    noorbeast VR Tassie Devil Staff Member Moderator Race Director

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    I am not suggesting you get rid of a simulator, nor that it be a bump simulator, just set it up to best advantage for VR.

    That is not dumping motion simulation experience but refining it based on some understanding of the compromises made for both VR and motion simulation. It really does not matter if it is a 2DOF or 6DOF Stewart rig. What I am suggesting is that for VR it is better to aim for fast accurate motion Vs large axis movements, which may look impressive, but really are not that accurate. The best experience is further enhanced by high quality peripherals, transducers and sound, which all compliment the illusion. And it is an illusion with any consumer grade motion simulator. At best a consumer style simulator could momentarily pull perhaps 2-2.5 Gs. Nothing like what an actual race car or fighter jet does.

    The speed and movement accuracy of a simulator is more important than how that is achieved. A decent 200W DC powered worm drive sim can be faster than say SCN5 or 6 actuators, at a far lower price point, it is horses for courses depending on money, design and expectations. Generally the speed needed is a bit subjective and is significantly affected by design choices, but general wisdom suggests between 200-700mm/s and that is influenced by many factors: http://www.xsimulator.net/community/faq/calculating-basic-linear-speed-and-forces.89/

    Hard core motion sim racers would consider the Youtube video you linked to be way too slow and it would be even worse for VR as the latency would be significant. You may get away with something like that for gentle flight sims, but even there the motion profile would need a lot of refinement to give precise and smooth experiences.
    Last edited: Oct 6, 2015
  15. Boomslangnz

    Boomslangnz Active Member SimAxe Beta Tester Gold Contributor

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    nah sorry I'm in Christchurch
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  16. nclabs

    nclabs Active Member Gold Contributor

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    I totally agree with @noorbeast , I used the same principles for my simulators. You need to feel a fast and precise movement with your body to match closely what your eyes are seeing, and if you do this wrong, you will have a very bad and confused VR experience. With my sim I can stay in VR for hours with no issues at all. I've some video for you: and now I'm waiting to gather everything I need for the new simulator! :D
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  17. bsft

    bsft

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    "bump simulator".....ok then......
    Tell that to 99% of the people here and the at least 10 professional drivers I have had on my desk racer "bump" simulators,
    asterix & obelix!.jpg
    @Antidamage , you said "Why would I get rid of my g-force simulator" , do you have an existing simulator?
    now I am curious.....
    • Agree Agree x 2
  18. Archie

    Archie Eternal tinkerer

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    I'm in the FAQ? Awesome!! :thumbs
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  19. Antidamage

    Antidamage New Member

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    I call it a bump simulator because the sensation you're experiencing isn't as much "I've reached X angle and am experiencing Y forces" as "I've begun moving in X direction". So the key feature of a worm drive is responsiveness. There is no arguing that you're not going to reach a 45 degree offset (representing 1g of lateral acceleration) with what most people are using at the moment. I'd counter that a fast actuator will give you the same sensation and ultimately provide slightly more of the g-forces you want to experience due to the improved range.

    So let's assume actuators have latency and speed problems (I disagree with this, I've found some VERY fast actuators, 10 inches/second fast) and worm drives have range problems. There's no denying that while the extra range on an actuator is a diminishing return, it doesn't diminish until it's quite a way beyond what the arm on a rotary shaft can do. I would also counter that even worm drives have enough latency to be a problem sickness-wise.

    So why not combine both? You have a long-range slow response positioning system and a short-range fast response system. Why not add pneumatics into the platform? They have no mid-state but they're REALLY fast and really cheap. In fact, I'd question having a motion simulator capable of being that violent. I don't really want to experience hitting a wall at 200km/h, but it'd be nice to have a bigger range of g-forces available.

    In the end, it's all a question of how much you can afford to throw at the motors you're using. I presume everyone has seen this by now as well:



    So far I've been really impressed with what everyone has done and it's my fallback plan, but there has to be room to do something new. I guess this is the wrong place to ask about new ideas though.
  20. Nick Moxley

    Nick Moxley Well-Known Member

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    Actuator, No thanks. I dont feel like having a permanently mounted Birds nest with 100 little birdies SCREAMING TO HIGH HELL in my ears. DC motor's are Cheap, Effective and overall Do the job just fine. If you want an Amusement ride, Go to the Amusement park. Nuff said.


    As other's have stated, Its not the big SLUSHY movements that translate to Immersion, But rather VERY fast Precise movements. Until you've experienced it for yourself, I can understand the confusion. But you've gotten the answer From All us Owner's. We're not pulling your leg, we Speak the Truth, Plain and Simple.
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