Model Environment Connection: Use joints or drivers?

Hello,
Is it better to use a joint, or a driver with a measure in the model environment
connection?
Or does either method accomplish the same thing? In the pedal demo tutorial,
joints are
used. However in the model I am working on, I have used a combination of joints
and
drivers and it seems to be working properly. I attempted to use all joints but
it ended up
being over or under constrained.

Brent

Hello Brent,

Joints and kinematic measures with drivers are both just constraints
on the model, so if they express the same thing, then there is no
difference. For instance, instead of a spherical joint you can
specify a constraint that two points must have distance equal to zero.

The advantage of “home-made” constraints is that they can express
exactly what you want. For instance, a hip can be very nicely
represented by a spherical joint, so there is no reason to create a
special joint for the hip. But the knee is not really a hinge, so the
standard hinge joint may not be adequate for some applications and
you may have to compose your own. This is where the kinematic
measures with drivers are useful.

In the constraints between the model and the environment you often
end up wanting to describe contact-like conditions like the distance
to a plane being zero. For these cases there may not be a standard
joint that works exactly right, so it can be an advantage to make
your own.

In conclusion: Kinematic measures with drivers is a way to create
tailor-made joints.

Best regards,
John

— In anyscript@yahoogroups.com, “blulrey” <blulrey@…> wrote:
>
> Hello,
> Is it better to use a joint, or a driver with a measure in the
model environment connection?
> Or does either method accomplish the same thing? In the pedal demo
tutorial, joints are
> used. However in the model I am working on, I have used a
combination of joints and
> drivers and it seems to be working properly. I attempted to use
all joints but it ended up
> being over or under constrained.
>
> Brent
>

John,
I suspected that would be the answer (and now I remember you mentioning the knee
joint
example at the seminar). I am, in fact, assigning a distance to a plane between
the human
model and environment model as one of the constraints.

Thank you,
Brent

— In anyscript@yahoogroups.com, “AnyBody Support” <support@…> wrote:
>
> Hello Brent,
>
> Joints and kinematic measures with drivers are both just constraints
> on the model, so if they express the same thing, then there is no
> difference. For instance, instead of a spherical joint you can
> specify a constraint that two points must have distance equal to zero.
>
> The advantage of “home-made” constraints is that they can express
> exactly what you want. For instance, a hip can be very nicely
> represented by a spherical joint, so there is no reason to create a
> special joint for the hip. But the knee is not really a hinge, so the
> standard hinge joint may not be adequate for some applications and
> you may have to compose your own. This is where the kinematic
> measures with drivers are useful.
>
> In the constraints between the model and the environment you often
> end up wanting to describe contact-like conditions like the distance
> to a plane being zero. For these cases there may not be a standard
> joint that works exactly right, so it can be an advantage to make
> your own.
>
> In conclusion: Kinematic measures with drivers is a way to create
> tailor-made joints.
>
> Best regards,
> John
>
> — In anyscript@yahoogroups.com, “blulrey” <blulrey@> wrote:
> >
> > Hello,
> > Is it better to use a joint, or a driver with a measure in the
> model environment connection?
> > Or does either method accomplish the same thing? In the pedal demo
> tutorial, joints are
> > used. However in the model I am working on, I have used a
> combination of joints and
> > drivers and it seems to be working properly. I attempted to use
> all joints but it ended up
> > being over or under constrained.
> >
> > Brent
> >
>