Re: [ompl-users] example 6 revolute joint kinematic chain

[Max B. <m.j...@gm...>]

Hi all,

Just to elaborate a bit on my previous mail. One thing that I'm struggling
with is the choice to create a CompoundStateSpace with 6 SO2 StateSpace
Subspaces.
This would give 6 states with an angle, which can represent the six joint
angles. With FK from KDL and the URDF I can make sure to meet the goals and
constraints for the end effector in cartesian space.
Or I could create a SE3 State for the end effector, which has 6DOF and use
IK to find the joint values.

For the first case I am struggling with creating the correct distance and
interpolate functions since the sanity checks are not passing:
Interpolation to midpoint state does not lead to distances that satisfy the
triangle inequality (1.037541 difference)

For the second case I am failing to understand how to implement it such
that I get smooth joint paths out of it, especially for a robot which would
have more than 6 joints and hence computing IK for subsequent samples could
result in non smooth paths.

What would be the best way forward?

Gr Max


*Case 1:*
class KinematicChainSpace : public ob::CompoundStateSpace
{
public:
KinematicChainSpace(unsigned int numLinks, urdf::Model urdfModel,
KDL::Chain kdlChain, Environment *env = NULL)
: ob::CompoundStateSpace(), numLinks_(numLinks), urdfModel_(urdfModel),
kdlChain_(kdlChain), environment_(env)
{
for (unsigned int i = 0; i < numLinks; ++i)
{
addSubspace(ob::StateSpacePtr(new ob::SO2StateSpace()), 1.);
ROS_INFO("Added %i/%i subspace to the KinematicChainSpace.", i, numLinks);
}
lock();
}

*Case 2:*
class KinematicChainSpace : public ob::SE3StateSpace
{
public:
KinematicChainSpace(unsigned int numLinks, urdf::Model urdfModel,
KDL::Chain kdlChain)
: ob::SE3StateSpace(), numLinks_(numLinks), urdfModel_(urdfModel), kdlChain_
(kdlChain)
{
ROS_INFO("Created SE3StateSpace for a %i link robot. ", numLinks);
lock();
}



Op wo 20 mrt. 2019 om 07:08 schreef <m.j...@gm...>:

> Hi all,
>
>
>
> Currently I am trying to use OMPL to create a motion planner for a
> manipulator with 6 revolute joints. I’ve studied the example of the n-link
> in plane robot that is shown in the kinematic chain examples but I’m having
> trouble to create a 6 link revolute robot. Does anyone know of an example
> for a similar robot? Collision avoidance does not have to be included.
>
>
>
> Kind regards,
>
>
>
> Max
>