From: prang@ssc-vax.boeing.com (Ron Wanttaja)
Newsgroups: rec.aviation,comp.sys.ibm.pc.games
Subject: Re: PC a step closer to realistic simulator (Thrustmaster)
Summary: Motion simulation
Date: 10 Sep 92 21:40:53 GMT
Organization: Boeing Defense and Space Group, Seattle WA

In article <n=snnvm.hchong@netcom.com>, hchong@netcom.com (Hoi Chong) writes:
> ... and of course a real good PC simulation program, then we have it made. 
> 
> Now, can somebody think of how to simulate directional G's... 

I've put a small amount of thought into that...

Simulating G-forces, of course, is something even the big simulators can't
do.  Changing the direction of the apparent gravity/centrifugal vector is
another thing.  Note that in "normal" flight this vector doesn't change
much... not at all in a coordinated turn, for instance.  The easiest way to
do this is to place the entire cockpit on a pivot and tilt it in the
appropriate direction.  Suprisingly little tilt is needed... just the hint
should be enough.  Ten to 30 degrees, maximum.

There are three traditional ways to get the cab to tilt:

1.  The original Link trainer used a vacuum system connected to four 
bellows rather like concertinas.  Pretty good system, really... plenty of
power, and able to produce some fast movement.  But nowadays, very little
is available off-the-shelf to the home experimenter.  The valves would
probably have to be hand-built, as would the bellows.  The difficulties of
interfacing this organ-builder's nightmare to PC control are left as an
exercise to the student.

2.  Electronic actuators are easier to interface... but getting ones with
the SPEED necessary would be pricy.  Most gear-down an electric motor to
get the power required, but the gearing cuts the response as well.

3.  Hydraulics are the current standard with the big boys.  Tough to do in
the home workshop, though.

Now, there's a fourth way, using a high-tech material:  Nitinol!

Nitinol (also called memory metal) changes length in reponse to temperature.
By using mechanical advantage, it can apply a fairly considerable force.
It's maximum frequency isn't too high, but it's probably sufficient for a
simple simulation.  I've seen a nitinol cross-wire arrangement rigged to
scan a laser-pointer across the wall at a fairly good clip.

Two things make Nitinol ideal for a home-grown simulator:  First, it can be
bought in wire form; the wire itself acts as a resistor.  By hooking a
variable-current power supply to it, you can shorten/lengthen the wire as
desired (within a given range, of course).

Second, its resistance changes linearly with length.  A simple voltmeter
can be calibrated to give a direct readout of position.

So you don't need LVDTs or other methods to determine the current
position... feedback is built right into the system.

It's easy to see how to mount your simulator's cockpit... a cruxiform
base mounted on a center pivot, with springs supporting the arms of the
cross.  Connect nitinol actuators inside each spring, and vary the
current appropriately to get the desired combination of bank/pitch. 

                                          Ron Wanttaja
					  prang@ssc-bee
					  ...rutgers!uw-beaver!ssc-bee!prang
                                          prang@ssc-bee.boeing.com
Newsgroups: rec.aviation