[simpits-tech] Motion...

[Frank Riedel]

Better use the money for more projectors ;o)

Frank

----- Original Message -----
From: "Joseph Fagner" <crease-guard@attbi.com>
To: <simpits-tech@simpits.org>
Sent: Monday, January 20, 2003 10:36 PM
Subject: RE: [simpits-tech] Motion...


> Good post Gordan, give us a lot to ponder.  I knew motion was much more
> complicated than the simple idea I mentioned, but it has stimulated a lot
of
> good posting.  Seems to me your last point is the most poignant of all:
No
> motion may be the best motion.
>
> Jay
>
> -----Original Message-----
> From: simpits-tech-admin@simpits.org
[mailto:simpits-tech-admin@simpits.org]
> On Behalf Of Gordan Sikic
> Sent: Monday, January 20, 2003 4:13 AM
> To: simpits-tech@simpits.org
> Subject: Re: [simpits-tech] Motion...
>
>    Hi,
>
>  >Think about this for a minute (granted I realize this is probably overly
>  >simplistic and the math is infinitely more complex):  Most software out
>  >there has the 4 axis of data (not to be confused with the axis of evil)
>  >one might need for motion.  Couldn't one just write some software to
>  >read this data and translate that to motion?  The data to which I refer
>  >is (1) pitch and (2) roll  (X and Y axis); via your artificial horizon
>  >instrument.  (3) Yaw (Z axis), via your compass and (4) altitude via the
>  >altimeter.
>  >
>  >
>
> You are right, it's not that simple.
>
> You need angular rates as well as accelerations. Making motion platform
> based on  attitude of the AC would be waste, believe me. Generally
> speaking, with the motion platform one hopes to imitate (inertial)
> accelerations that pilot feels. Simple example acceleration on the
> runway during take-off. During that period pilot feels sustained
> acceleration on his back. The sense of acceleration is imitated by
> rotating the platform slightly backwards, so the weight of the  pilot
> generates the force on the back. That rotational shift is sudden, and
> later the platform is slowly returned to middle position. Thus,
> imitation of just one linear acceleration is achieved completely
> different type of motion: sudden rotation, followed by slow return to
> neutral position. BTW, this is the basic type of operation for
> calculation of required motion platform movement.
>
> In brief, you need output of the state vector from the simulation
> program in order to calculate required motion of the platform.
>
> Other than this, you should think of something completely different:
> Motion platforms are _very_ power hungry, you might easily end up with
> facility which draws couple of  tens of kW of power.
> Yet another problem is safety. Think of the following: it is very easy
> to start the fire in the kitchen with electrical oven of just couple kW
> (or even less), and here you are dealing with much more powerful
equipment.
>
> Yet yet additional problem are foundations, because something must
> support complete construction, and take over complete forces and moments
> generated by the moving platform.
>
> There are many problems, but this doesn't mean that there is no solution
:)
> If you really want to make motion platform, do read appropriate chapter
> in "flight simulation", book that is mentioned few days before. It is
> excellent reading, but be warned that it does not provide us with
> solutions, but presents the problems in very concise way, and just
> guides towards the solution. But in any way it is a "must have" book.
> I've been reading it from the cover to cover and all over again many
> times since 1995 (when I bought it :)
>
> Also check web for motion platforms where you will find some standards
>   you should achieve. one url is www.fokercntroll.com, and the other is
> (if I recall correctly, I'm off line now) www.mug.com.
>
> Personally I'll take following approach:
> Generally, visual system provides low frequency sensations, and use some
> kind of rocking chair to generate high frequency sensations (like
> turbulence, or vibrations, ...). It is also possible co combine it with
> some form of g-suit. This is not as good as well made motion system
> coupled with nice visualization, but it is _much_ better than wrongly
> made motion platform, and in any case  infinitely safer.
>
> And at  the end, one true story:
> (I don't know the details, what kind of  AC, how many degrees of freedom
> in motion platform, nor how many pilots, ... :)
> There was a project of evaluating different algorithms for driving
> motion platform, and within the project many (professional) pilots were
> flying on the simulatior, every flight with different algorithm applied.
> Needles to say that pilots didn't know which algorithm was to be applied
> for any of the flights. After every try, they were asked to describe in
> words how they felt, and to place a numerical mark. After the data were
> analyzed, it turned out that many pilots (more than few, anyway) said
> that the best results were achieved with algorithm "number 5". The funny
> thing was that algorithm in question corresponded to the case where the
> motion platform didn't move at all!  (of course, pilots didn't know that
> fact while "flying")
> This fact presented the problem also. Far to many pilots claimed that
> nonmoving motion algorithm was best, so it had to be explained. The
> explanation was as follows: the visualization was made very well, the
> screen was wide, and clues from visualization contained enough data for
> the brain to construct complete motion. When clues from the motion of
> the platform were added, the brain was confused by the data provided by
> the  platform motion, since it was not able to "correlate" it fully with
> data from the visualization. The result: bad sensation by the pilots :)
>
> I know this was just a bunch of unconnected thoughts but I do hope that
> it helped a bit...
>
> ciao,
>
> Gordan
>
>
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