Re: Interactive Effects

[Johann D. <jo...@Do...>]

On Sat, 26 Jan 2002, Rodrigo Damazio wrote:

> Johann Deneux wrote:
> 
> >
> > About interactive effects: See these effects as functions from something
> > to a force.
> > Position -> Force : That's a spring
> > Velocity -> Force : That's friction (or damping, why does pid define both
> > as different effects ???)
> > Acceleration -> Force : That should be inertia. It's not implemented in
> > I-Force. Actually, Immersion seems to consider this to be the same as
> > friction.
> >
>        I knew this...if you look in Immersion Studio, you'll see you can 
> actually see a graph force vs. {position | velocity | acceleration }...
> 
> >
> >
> > I agree that we should add FF_INERTIA and FF_RAMP, but FF_DAMPER looks
> > pretty useless to me. Unless I missed the point ?
> >
>        Well, I've tried creating some Damper effects - it does make a 
> difference...besides, it's in the specs...

The direct input docs describes these condition types in:
http://msdn.microsoft.com/library/default.asp?url=/library/en-us/dx8_c/directx_cpp/Input/Using/ForceFeedback/EffectConditions.asp
The interesting part is:
"
    *  Friction. The force is applied when the axis is moved and depends
on the defined friction coefficient.
    * Damper. The force increases in proportion to the velocity with which
the user moves the axis.
"
Apparently, the friction does not depend on the speed. And now that I
write it, it hits me: friction is not force = f(Velocity). I should have
known it.
The formula is defined as following:
force.direction = -velocity.direction
force.magnitude = k
Imagine you are pushing a heavy box on the ground. k depends on the type
of the ground, the material of the box and the mass of the box. As those
do not change, k is indeed constant.

I will check again what USBsnoopy says. I seem to recall that for I-Force
devices, friction = damping.

-- 
Johann Deneux