[simpits-tech] Motion...

[Joseph Fagner]

As a matter of fact, I got one this weekend and have been playing with it
right up to the point where I had a memory stick go back and a hard drive
failure.  So today has been spent formatting two new hard drives in a mirror
RAID (learned my lesson) and reinstalling windows (I've done this so many
times I'm thinking of opening up my own business).  It's more and more like
the real thing all the time:  More time on maintenance and less time flying.
I wanted realism, but not to this extent.

Jay

-----Original Message-----
From: simpits-tech-admin@simpits.org [mailto:simpits-tech-admin@simpits.org]
On Behalf Of Frank Riedel
Sent: Monday, January 20, 2003 3:59 PM
To: simpits-tech@simpits.org
Subject: Re: [simpits-tech] Motion...

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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