[simpits-tech] May the Force Feedback be with you...

[Craig Rochester]

Hi Stig,

The cylinder pressure supplied by the servo driven regulator is whatever your software's algorithm
calls for.  Let's say the force range you want on the grip is 0 to +/- 20 lb.  Your lever is a 5:1
ratio, so you need 0 to +/- 100 lbs output by the spring/cylinder system. Since the cylinder must
compress the spring and supply the force to the stick, the cylinder must put out 200 lbs force.
Let's choose a 2" diam. piston, which has = pi square inches area.  Supply pressure has to be 0 to
200/pi = 64 psi.

You'd set up your control algorithm to output 32 psi for neutral position.  Probably the biggest
weakness of the single cylinder system is the no load condition.  Example: with plane not moving and
operating the stick, the pilot should feel very little force on the stick.  This system would have
to calculate the change in the spring's force as a function of the stick position and apply a
pressure that exactly balances that force.  The algorithm is easy, but I'm not sure how well the rig
could exactly balance the forces.

During flight the system would work fine, any small error in the calculated value of the spring
force would be dominated by the actual force being applied to the stick.

Craig R.


-----Original Message-----
From: simpits-tech-admin@simpits.org
[mailto:simpits-tech-admin@simpits.org]On Behalf Of Stig Joergensen
Sent: Sunday, February 09, 2003 5:41 PM
To: simpits-tech@simpits.org
Subject: RE: [simpits-tech] May the Force Feedback be with you...


but the problem here is you can not adjust pressure required to move the
stick - in this schematics its a constant of the spring, when you fill
the cylinder to 3/4 the amount the back pressure is still the same where
as the pressure to move the stick forward is a function of pressure in
the cylinder.... further more the spring pressure is somewhat linear
where the cylinder pressure is proportional....

/Stig

-----Original Message-----
From: Craig Rochester [mailto:johncraigroch@msn.com]
Sent: 9. februar 2003 23:03
To: simpits-tech@simpits.org
Subject: RE: [simpits-tech] May the Force Feedback be with you...


I think that Marv said it well in his last email.

The simplest design (using air) is a single spring loaded piston driven
by a proportioning valve (servo regulator).  The valve can deliver
whatever pressure you calculate from the sim's outputs.  The resultant
force can be a function of velocity, stick position, trim wheel
position, whatever data you want to use.

Guessing here: IAS, AOA, and stick position would provide most of the
data necessary to calculate the force from the stick.  I don't know how
you'd determine turbulence, but the pneumatics are capable of some
relatively high frequency output.

Craig R.


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