Inverse Kinematics Unstable

[mrshifo]

Hello to all,
I'm new with v-rep, I'm trying the inverse kinematics for a mobile robot. I do not understand why it becomes unstable. Can you help me?


http://dropcanvas.com/rsgj0


thanks
andrea

[coppelia]

Hello Andrea,

2 things:

• your kinematic chain is wrongly defined. The base of your chain is base_joint, but it should be basetrack (otherwise base_joint won't be involved in IK resolution)
• the try switching to the Vortex engine. You'll have a stable situation. With the two other engines, you will have to tweak the masses and inertias.

Cheers

[mrshifo]

Thanks for the help,

I already tried to change the mass and inertia is increasing or decreasing but remains unstable you can give me some advice because I want to use BULLET or ODE since vortex stops 20 seconds.

thank you very much
Andrea

[mrshifo]

I partially solved tuning the masses and inertia but when I add a piston (like the model excavator) the kinematic chain becomes unstable why ?

http://dropcanvas.com/wh606

thanks

[coppelia]

You have several IK problems with your mechanism that you first need to solve:

• IK_Group1 that is solving the piston IK needs to be executed after the other IK tasks (since it is not the main task)
• IK_Group1 has the wrong base. IK_Group1 should involve in IK resolution exactly 2 joints, no more.
• the joint Prismatic_joint_piston1 is in passive mode. That doesn't work with IK
• you do not need the damped IK_Group0. When something that is supposed to be stable is not stable, then adding damping is a very bad idea, since you are just covering up a larger problem. Damping in IK should only be used when the constraints cannot exactly be satisfied (e.g. target is out of reach, close to a singularity, etc.).

Cheers

[mrshifo]

I'm sorry,
I tried to edit as you said but the base of the piston does not remain centered with the link1. Can you help?

http://dropcanvas.com/nekvi

thanks