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  1. #1
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    Question Motion Simulator Syncronization Issues

    Hi everybody. This is my first post on this forum. I'm hoping since this is an enthusiast site someone out there will have encountered the same issues I have. First let me provide a background of the simulator.

    I am in the process of building a motion simulator (2DOF). I am currently running Flight Simulator X as the simulation software. The base is fully hydraulic and the cockpit sits on top of a bidirectional plate. The hydraulics are linked to the yoke so pull/push will move the cockpit up/down and twisting the yoke provides movement side to side.

    Potentiometers are installed on each axis and hooked up to a Leo Bodnar Interface board which is recognized in FSX as a controller.

    My issue is that the cockpit movement is NOT synchronous with the visual display, especially on the ailerons axis. There is a significant delay between me moving the yoke (cockpit) and it's visual representation on screen.

    Note this simulator is entirely active. There is no feedback from the simulator back into the cockpit to control motion. The pilot dictates every move. I've been through the aircraft config and .AIR file a countless times. Some settings help but it is not exact.

    So my question is, is there a way to sync my control movement with what displays on screen? I appreciate any help!

    **Please see my attached pictures for further clarification**
    Attached Images Attached Images

  2. Thanks KenK thanked for this post
  3. #2
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    Re: Motion Simulator Syncronization Issues

    Hi,

    The hydraulics are linked to the yoke so pull/push will move the cockpit up/down and twisting the yoke provides movement side to side.
    When you say this, is that you are controlling the base movement with
    the yoke and yoke column?

    In this way you don't get the movement correct.

    First, the platform is not meant to represent the angles of pitch and
    bank of the aircraft only, but its accelerations. You have much math
    evolved, and in some situations, for example, in an stall, the plane can do a thing
    totally different from the yoke command.

    You need to act your hydraulics by the software (what you seem
    to call feedback, but its not). This is the only way to get it correct.

    Sorry if I don't know your post correctly.
    Diego

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    Re: Motion Simulator Syncronization Issues

    Hi, you`re sure its not mechanical?
    maybe your flow of oil is to slow, or the pressure is to low.
    it could be even be the actuators.
    regards Henk

  5. #4
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    Re: Motion Simulator Syncronization Issues

    Hi Dabbigu:

    Your mechanical setup looks great. I am thinking of doing the same thing with Pitch only to simulate gravity during T.O. and R.Thrust. I have flown actual simulators (TBP and Citation ) and these two forces seem to be the most pre-dominant to me.

    After you apply pitch and roll with the yoke there will be some delay for hydraulics to react and another for FSX to react. Another thing which affects all this is roll rate. A C150 will roll slower than an F16 so the hydraulics may benefit from some accumulators and proportional controllers (now its getting complicated). I agree with the direct feedback from FSX idea. FSUIPC (FSX) probably has a direct value for Pitch and Roll which can be used to drive a proportional valve directly. This may still give you some delay between yoke input and platform roll but should be better.
    Dont forget those E-stops and Hyd E-dumps.


    I need to find some U-joints .

    Nice setup !!!!

    Regards Ken K

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    Re: Motion Simulator Syncronization Issues

    Another thing which affects all this is roll rate
    Even for the same aircraft, roll rate will vary with some things.

    I agree with the direct feedback from FSX idea
    This is not feedback. But this is the only way to get a simulation motion
    platform and not a toy.

    The feedback is from the position and velocity from the cylinders to the
    controller, so creating a closed loop system, that will eliminate any
    delays or positional errors (of course if the flow is sufficient).

    FSUIPC (FSX) probably has a direct value for Pitch and Roll
    Of course it have, but this is not the only values used for driving the platform, and really not for the proportional valve. This should be used
    for calculating the platform position, and then sending to the controller,
    that receiving the actual platform position and speeds, calculate the
    proportional valve position.

    You cant extract take off and Landing accelerations from pitch and roll
    information, but from the linear acceleration on this axis (I forget the name).

  7. #6
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    Re: Motion Simulator Syncronization Issues

    DIEGOCN you are correct and definately a hydraulic expert.

    For accurate motion the FSUIPC Pitch and Roll signals must be used along with the cylinder position and speed. Some servo amps provide all these functions with integrated proportional ,integral ,derivative controls. You could probably buy the servo and valve as a matched system for your application. Depends on how much you want to spend.

    In my case I just used pitch to simulate gravity. About 45 degrees nose up pushes you back in the seat at takeoff and 20 degrees nose down slides you out of the seat for reverse thrust. It used a one-shot timer that triggered a valve on for a few seconds at TO. and RT. The effect was pretty convincing. I was not really trying to simulate actual acceleration.
    My budget is too small.


    Regards to all
    Ken K

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    Re: Motion Simulator Syncronization Issues

    DIEGOCN you are correct and definately a hydraulic expert.
    Thank you, but really it is not even my area of work

    The controller ( servo amp ) could be doing with a PIC micro-controller,
    very good and cheap, or ARM micro-controllers too, and you can
    implement a PID algorithm, as you said.

    What should be expensive is the proportional valve.

    I opted for pneumatic because of the costs, maintenance and caution required
    by hydraulics, and for some advantages pneumatic has over hydraulic for
    this type of application.

    Anyway pneumatic proportional valves are really expensive too, so I use
    a hybrid system, that I'm projecting yet.

    In my case I just used pitch to simulate gravity
    Yes this is how it is commonly doing, but when connected to the simulator, the information
    extracted is not the pitch, but the acceleration of the aircraft in this direction,
    that the motion controller software apply like you do, in the pitch axis of the platform.

    Of course the software combines the pitch and roll too, and get all
    the positions and accelerations on the axis of the platform.

    Uhm, on FSX you don't need FSUIPC to extract that information
    from the simulator

    Thanks,
    Diego

  9. #8
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    Thumbs up Re: Motion Simulator Syncronization Issues

    Guys, thank you for the feedback thus far! I understand I will contantly be "chasing" the plane on screen (visual display) with my manual movements of the cockpit since there is no feedback back into the motion base.

    To further clarify, with modifications to the aircraft configuration files and FSUIPC have attained a pretty convincing flight experience. Movement along the y-axis (elevator) is prtty much spot on, and changes register instantly. Throttle, rudder pedals, and trim wheel ar also programmed in and wrked near flawlessly.

    The x-axis (ailerons) is a different story. There is an almost 3 second lag from when I move the yoke before the plane moves left and right.

    Any thoughts on getting the ailerons reasonably more acurate? Once again I truely appreciate your time and help!

  10. #9
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    Re: Motion Simulator Syncronization Issues

    Editing the air file, as you may know, you are modifying characteristics of
    simulation of the aircraft, so it gets more distant than the real aircraft.

    The "pretty convincing flight experience", can be true referred to the
    "synchronization" ( I don't think its so correct because the two are not
    even trying to synchronize ), but not to the model of flight of the aircraft.

    If you want a "synchronized" system, you will need to control the
    motion platform from the simulator, and send feedback to the controller.

  11. #10
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    Thumbs up Re: Motion Simulator Syncronization Issues

    Guys, I just purchased a PhidgetInterfaceKit 8/8/8. Judging from the pictures I posted and description of my current setup, what additional parts would I need to add/replace on my hydraulic base to allow feedback from the software back into the base? Thanks again!

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