On 4/19/07, Jiri Slaby <[email protected]> wrote:
Dmitry Torokhov napsal(a):
> I have been thinking about this and I don't think that exporting motor
> data is a good idea, at least not in case of Phantom driver. The fact
> that there are 3 motors is a hardware implementation detail and it
> is not interesting for general application.
Ok, so what about torques (despite it's still something like FF_RAW or motor
descriptor)? It seems not to be so bad called effect name -- not only
phantom uses torques on motors as an unit of force, for example I get this
by quick googling:
http://www.caip.rutgers.edu/~bouzit/lrp/glove.html
They use there some motors with 14 torque values too, so the phantom isn't
the only device which uses this approach.
> My understanding that the end result of controlling these 3 motors
Actually there is also a version with 6 motors :).
> is a force vector (I don't know if there is such english term, this
> is a literal translation from russian) applied to user's hand.
Better say torques vector. You must compute a torque for each place from the
3d (or bigger) vector of forces in different way for each device that exists
-- this means forces are not independent unit, torques are in the meaning of
layer which doesn't care about what is connected above and below it.
> If we are interested in using FF API we need to come up with a way
> to express this effect without exposing implementation details of
> one particular device.
Still, torques are better named raw/motor values, which goes to the device
and I'm sceptic about inventing something class-better than this.
Well, I guess we need to make a decision whether moving this kind of
devices into a force feedback layer is possible or whether every
device needs to have an application specifically tailored to that
particular device.
If we say that it is feasible to plug a device into FF layer then we
must not expose hardware implementation details. That means that
device-sepcific translation between 3d vector of forces into motor
torques must be done by the driver itself.
For devices that require tailored application (for example that glove
- I am not sure how a generic application could control it) old
phantom way of controlling via ioctl will suffice. The device may
still use input layer to report back coordinates.
--
Dmitry
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