PointConstraint in IAA tool

[Ruoli Wang]

Hi,

I am tring other PointConstraint in IAA tool, but there are some erros loading setup file.

Exception:
Invalid point constraint body1 (Unassigned) specified in Constraint
right_foot_contact

I suspected there are something different than RollingOnSurfaceConstraint to specify contact body, which is not described in the Guidebook. Anyone know how to amend it?
Thank you,

<PointConstraint name="right_foot_contact">
<!--Specify to disable constraint by default-->
<isDisabled> true </isDisabled>
<rolling_body> calcn_r </rolling_body>
<!--Specify the body containing the surface (plane) that the rolling body rolls on.-->
<surface_body> ground </surface_body>
<!--surface's normal dirction defined in the surface body-->
<surface_normal> 0.00000000 1.00000000 0.00000000 </surface_normal>
<!--surface's height in the direction of the normal in the surface body-->
<surface_height> 0 </surface_height>
<friction_coefficient> 0.75000000 </friction_coefficient>
<!--A guess at the area of contact approximated by a circle-->
<contact_radius> 0.01000000 </contact_radius>
</PointConstraint>

[Ayman Habib]

Hi Ruoli,

The error message suggests that the name of the body_1 of the PointConstraint is not specified (or doesn't correspond to a name of an actual body in your model). You'll need to specify that in the XML file. A PointConstraint enforces that two points on two different bodies to be coincident so both body_1, body_2 and the corresponding locations need to be populated.

Code: Select all

<PointConstraint> <isDisabled>false</isDisabled> 
<body_1>Unassigned</body_1> 
<body_2>Unassigned</body_2> 
<location_body_1>0 0 0</location_body_1> 
<location_body_2>0 0 0</location_body_2> 
</PointConstraint> 

Hope this helps,
-Ayman

[Ruoli Wang]

Hi Ayman,

Thank you for the quick reply.

I am still not so sure about how to assign locations of the two points. In the foot-ground contact, the contact point is moving along the COP path. How should I implement this?

I have tried using [0,0,0], it seems work. But not sure why? [0,0,0] should be the origin point of the body segment?

Thank you,

Ruoli

[Ayman Habib]

Hi Ruoli,

Sorry about the confusion, but it appears that IAA assumes that the constraint is applied at the center of pressure so you shouldn't need to specify locations (or they get ignored by the IAA code anyway as far as I can tell).

Please file a bug report (documentation) so that we can make this clear in the documentation of IAA in the user's guide for the next release.

Hope this helps,
-Ayman