weird movement

[Mohamed Magdy]

hey
I can not solve the weird movement of the robot during following a path
here is a video explaining :https://drive.google.com/open?id=1plN9G ... fXf-UQCHNl

thanks you team coppelia for supporting us .

[coppelia]

Please post the scene, from the video it is very difficult to guess what is wrong.

Cheers

[Mohamed Magdy]

h

[coppelia]

I had a quick look at your robot. The kinematics are too complicated and ill-designed. You have 4 IK groups. Why? Each IK group will be executed sequentially. So there is no simultaneous computation of all constraints as you would have if you had all IK elements inside of a same IK group.
It is really very important to build a tree-like kinematic structure. Each branch that closes needs to close on a non-moving item (i.e. the base of the robot).
Also, using a damped resolution method might help you at first, but it will hide some over-constrain problems you might have.

Cheers

[Mohamed Magdy]

It is really very important to build a tree-like kinematic structure. Each branch that closes needs to close on a non-moving item (i.e. the base of the robot).

Cheers

hey
I think it's impossible to this with hybrid robot because I have the platform which connected in the parallel and serial structure and for that I used dummies as you can see in the scene tree ..please tell me how to do what you are saying !

also

[Mohamed Magdy]

I tried this
base --> revJoint --> revJoint --> prismJoint2 --> revJoint --> platform --> revJoint --> prismJoint 1--> revJoint --> tipA
platform --> revJoint --> prismJoint3 --> revJoint --> tipB
platform --> revJoint --> revJoint --> tipC (at the tip of tool)

--> targetA
--> targetB
but arm 1,3 are also connected with moving item (upper base )which is connected with the base with rev joint

https://drive.google.com/open?id=1TNNSP ... b_Hs-C7Lxd

[coppelia]

That will not work. You really have to create a tree-like structure. Not many trees, but a single tree. Typically something like:

Code: Select all

base -> joint1 -> joint2 -> link1 ->joint3 -> joint4 -> platform -> joint5 -> ...
                                                                 -> joint6 -> ...
                                                                 -> joint7 -> ...
                                                                 -> ...
     -> target1
     -> target2
     -> target3
     -> ...

Cheers

[Mohamed Magdy]

I made a single tree with three branches like in the pic , am I misunderstanding ?

[coppelia]

You have a very comple robot. Describing how to build the kinematic model is therefor complicated. But as stated, the very first thing is to have a single tree. Then you can consider individual tree branches for closing those branches. Have a look at how the models models/robots/non-mobile/ABB IRB 360.ttm and models/robots/non-mobile/adept Quattro 650HS.ttm were made. Also, have a very close look at the various examples located in scenes/ik_fk_simple_examples

Cheers

[Mohamed Magdy]

hey
may I ask another question .
when i use graph to get joint position of Rev_joint 5 ,it shows changing in joint position despite I can see it stationary !!