Motion Simulator Syncronization Issues

[dabiggiu]

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**

[diegocn]

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? :o

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

[kermit]

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

[KenK]

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

[diegocn]

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).

[KenK]

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

[diegocn]

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

[dabiggiu]

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!

[diegocn]

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.

[dabiggiu]

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!

[diegocn]

Please, call it Motion Platform, not feedback :)

With this interface, from what you don't have some things, like
analog output. In general, you need to use a microcontroler,
as the interface between the computer and the platform will have
some delay for a PID controller.

The most expensive part should be the proportional directional hydraulic
valve, this valve can control the flow of the fluid precisely. You can try
controlling proportional manual valve with an electronic device, like
a motor, but I don't know if the cost is compensating, and some
other things.

You will need to detect the actuator position, and send it to the
PID controller ( that is feedback ).

Its not a simple thing, then you can start reading some things like:
- PID control loop
- Closed loop control
- Proportional hydraulics

You can try using a simple directional hydraulic valve, and switch it fast,
with variable duty cycle, but you need some other knowledge first.

Diego