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Building a Better Mouse Trap.

Discussion in 'DIY Motion Simulator Building Q&A / FAQ' started by SeatTime, Mar 6, 2018.

  1. SeatTime

    SeatTime Well-Known Member

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    My Motion Simulator:
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    Motion Simulators - How real can we go? (Designing a Better Mouse Trap :)):
    So what am I taking about?..Please note that the following is just my thoughts on this matter, although you cannot fight physics. I'm also not rubbishing anyone's rig, as they all still work quite well for what they are.
    To explain what I'm attempting to do, lets first look at the current state of play in regards to simulators and go over some of their main Advantages/Disadvantages.

    Basically we currently use three types:



      • Seat Mover - where only the seat moves (normally the seat is on a Universal joint) - this has the following Advantage/Disadvantages (Adv/DisAdv):



        • Adv: Fast/low latency - due to low mass.
        • Adv: As the seat is moving and the control are stationary, there is a difference in relationship between the controls and seat which mimics the movement felt in the real world Ie The driver being moved around in their seat in relation to the Car/Planes controls though G-Forces - although this in itself limits the amount of movement that the sim can do before this difference becomes/feels unnatural.
        • DisAdv: The Sim as explained above is limited in movement and therefore the amount of G-Forces it can simulate.
        • DisAdv: Obviously with only small movements the simulation of extended G-Forces via gravity is very limited.
        • DisAdv: Washout Issues: As for any motion Seat the issue with managing 'return to home position movement' after a motion event - This can often be felt as an abnormal movement with the effect being normally reduced via well written/setup washout algorithms which come with their own issues.
        • DisAdv: Nausea: Any unnatural movement - Ie using roll for sway, or pitch for surge, washout issues, or not using roll/pitch can change what the driver is seeing, as opposed to what they are feeling, which can upset the balance systems of some people and cause nausea. Note that as the Seat mover normally uses only small movements the likely hood of someone getting sick is less. Although well synchronized low latency motion has been shown to reduce motion sickness.



      • Full Frame - As it name implies, here we move the whole frame, anything from 2 to 6DOF. Irrespective of the DOF the Adv/DisAdv are similar. Note: Sometimes members mix both a Seat Mover siting on further DOFs full frame moving tables/rigs to get some advantages from both systems.



        • Adv: Both the seat and the controls move in unison making it feel more natural when the sim moves through larger movements (Aircraft/Roller Coaster) - although care must be taken with too much movement in a balanced (seat siting on a Universal Joint) rig due to the often incorrect roll center.
        • Adv: When compared to a standard Seat Mover, with each addition of an actual DOF the motion becomes more natural.
        • Adv: As larger movements are realistically possible, more Extended G-Forces via Gravity can be simulated.
        • DisAdv: Depending on the mass of the Rig there can be some increased latency when compared to a Seat Mover.
        • DisAdv: There is limited/no natural difference in relationship of the Driver to his controls from Gs (Driver moving in his seat from G-forces), as can be simulated in a seat mover.
        • DisAdv: Washout issues: See above - same as Seatmover.
        • DisAdv: Nausea: See above - same as Seatmover, although with bigger movements come larger chances of nausea



      • Pressure Systems: These act against the Body of the Sim Driver, simulating the G-Forces that would be felt. There a few types, but for this explanation I will stick to what is normally used today Eg G-Force Paddles and Seat Tensioners. These can be used by themselves, or as a part of a motion system. Adv/DisAdv are as follows:
    G-Seat

    Seat Harness Tensioner




        • Adv: Can simulate extended G-Forces without the use of gravity.
        • Adv: Low latency due to the low mass of the paddles or belts.
        • Adv: Can simulate more G-Forces then is usually possible via gravity alone.
        • Adv: Works well with a motion seat in layering more forces with what is being produced by that motion system - Ie. With a motion seat it can also produce a combination of forces that are not able to be produced by a motion seat alone Eg. Simulating opposite centrifugal forces when entering a roll in an Aircraft, or on a NASCAR high banked track.
        • DisAdv: Often limited in the pressure that can be applied when compared to what would be felt in a real Car/Plane etc.
        • DisAdv: As the paddles/Tensioners need to push against the body of the driver opposite to what the direction of force actually is, it can move the driver in an incorrect direction of what is wanted for a natural difference in relationship with the controls Note: This is although normally quite a small movement, but will get worse as the force trying to be simulated is increased.
    So, Looking back at the above - What would be a better solution in simulating a real Car/Plane/Roller coaster?
    As an example lets look at the Sway and Surge DOFs and what we do now to simulate each one:

    Sway:



      • Via 'Rolling' the rig left or right. This works in a limited manner by using initially inertia and then a small amount of gravity for any extended sway force. Unfortunately this is often still felt as a roll (the human body normally has a lifetime of experience standing up) especially when it is extended and if you also want to impart actually simulated roll then the two can often cancel each other out, as they are working in opposite directions EG Car - on a High Banked NASCAR track, or Plane - Rolling into a turn. This can also impart some latency into the simulation depending on the inertia involved and amount of roll used.
      • Via moving the rig in a horizontal direction. This is a more natural sway movement which feels like it should for the initial inertia movement, but for any extended sway forces it just does not work and there is the issue of washout - 'returning to home'.
      • Via A combination of both Rolling and horizontal movement - Works better, but your still taking away from any natural roll of the simulator and the body always knows ;).
      • Washout Issues: Any Sway/Roll movement has to return at a one stage to it's 'home' position, which without some very well written/setup washout algorithms, will be felt as a fast movement of the sim in a very unnatural opposite direction.
      • Nausea Issues: Well Synchronised low latency motion has been shown to reduce motion sickness, but if you are displaying a rolling/pitching plane, or car on a banked circuit and the rig is not not moving in the same way, don't be surprised if someone may get sick ;).
    Surge:



      • Via Pitching the rig forward or back. This works in a limited manner by using initially inertia and then a small amount of gravity for any extended sway force similar to sway, but unfortunately with the same issues of unnatural movement and the cancellation with any pitch DOF.
      • Via moving the rig in a horizontal direction. This is a more natural surge movement, which feels like it should for the initial inertia movement, but for any extended pitch forces it just does not work - and there is the issue of Washout 'returning to home'.
      • Via A combination of both Pitching and horizontal movement - Works better, but your still taking away from any natural pitch of the simulator and the body always knows ;).
      • Washout Issues: Any surge/pitch movement has to return at a one stage to it's 'home' position, which without some very well written/setup washout algorithms, will be felt as a fast movement of the sim in a very unnatural opposite direction.
      • Nausea Issues: Well Synchronized low latency motion has been shown to reduce motion sickness, but if you are displaying a pitching plane, or car on a car going up and sown a big hill and the rig is not doing that don't be surprised if someone may get sick ;).
    Is there a better Solution for a more realistic Simulator?
    Lets look at what actually happens to a driver/pilot when they are sitting in their seat and the car/plane is in motion or it is accelerating or decelerating

    When the Car/Plane makes a change in direction, accelerates, or decelerates the body of the driver wants to keep going/staying in the direction/position it was in due to the laws of physics. So the car say turns left and seat turns left and in turn forces the drivers body to turn left. Basically the driver body is thrown into the side of the seat/harness - if it was not there he would keep on going :). So for a simulation to be reallyrealistic especially for extended forces, it is really the Body of the driver who needs to be often in motion for any sway/surge/heave event not always the Sim rig. By moving the driver into or away from the seat, the forces are more natural as with the G-seat there is no washout required and the moving relationship between the driver/pilot and his controls is more natural. The possibility of simulating higher G-forces - (especially extended) than a normal sim is also possible.

    Forces in an Airplane

    [​IMG]

    So simply, that is the pretense of my new pressure/motion system Ie. The driver will be moved independently of the rig/seat for force events with high force :), which will be added into my 6DOF/Harness Tensioner rig - as there are some forces and orientations that these still do well. Now built and running see https://www.xsimulator.net/community/threads/seattimes-sims.11757/ Near bottom of page - 'New Rig'.
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    Last edited: Aug 5, 2018
  2. PiaMan

    PiaMan Active Member

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    I like where you're going and can't wait to see how you've come up with to exert these pressure forces on the driver. I've been needing a new sim project as otherwise I was going to have to get into RC cars/simulator driving for that project going on. Luckily another hobby took over for the meantime.

    following along for your progress..... thanks for the brainstorming out loud and informative post
  3. SeatTime

    SeatTime Well-Known Member

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    My Motion Simulator:
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    I've actually already done it - works great. It uses a vest, off rig actuators and bowden cables.
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    Last edited: Mar 7, 2018
  4. FargusFaustmeister

    FargusFaustmeister Member

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    For the linear motions (sway and surge) you make a good point about extended sensations. How about adding a 360 degree platform so if you're doing a long turn you get the initial sway and then the platform spins, not even necessarily very fast, to create an "extended g-force" simulation. What you'd basically be doing is creating an eccentric load, and the spin could maybe provide enough force to trick the brain. Doesn't need to be all that much either. Get a brush slip ring and (somehow lol) mount all of your electronics onboard the sim platform (balance rotation weight around the central axis for mechanical ease) and you've got 360 degree freedom.

    Take that with a grain of salt as I've not had a chance to develop any intuition with simulated forces, but that's what I'd investigate. Combine with a low-power seatbelt actuator and pure linear sway and surge and I think you could have a pretty good long-force sim.
  5. SeatTime

    SeatTime Well-Known Member

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    My Motion Simulator:
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    Maybe that would work and I did look into it, although your body would only be off-centered by a small amount to generate any force. Eg Sit in a office chair and spin - that is all you are going to get ;). For me it would have been way more complex/expensive with 360 custom software, slip rings etc, likely problematic with VR and finally, I don't have the room :). But don't let me get in your way if you want to try it out :).
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  6. FargusFaustmeister

    FargusFaustmeister Member

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    If you were to spin without offsetting the sitting position from the center of rotation then you would only feel like you were spinning, but adding a moment arm would create an acceleration (tangential) that, coupled with the mass, would create a force acting in whatever direction you wanted to simulate.

    I've got a bunch of notes on this that I'd like to dig up to offer a more scientific justification for my absurd ponderations, but thanks for the encouragement none the less :)
  7. ferslash

    ferslash Active Member

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    so... how are you thinking you can achieve your design... you said 6dof harness tensioner? am i right?
    if so, how would you implement it? i have been thinking about all your post... but i have not an smart solution :D
    fer
  8. SeatTime

    SeatTime Well-Known Member

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    My Motion Simulator:
    AC motor, Motion platform
    I already have a 6DOF, so it does not need to do everything, but see my thread for more info about both systems.
    https://www.xsimulator.net/community/threads/seattimes-sims.11757/
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  9. noorbeast

    noorbeast VR Tassie Devil Staff Member Moderator Race Director

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