moveit command for robot arm

Hello. I have a mobile manipulator (husky + ur3) from this site

I have searched a lot to find inverse kinematics for the ur3 robot arm. I found some links, for example this one:here This link is for ur5 and ur10 arms ,but this is not a problem, because its the same for ur3 ,that i use but with different DH parameters and transformation matrix. See the equation (10) -> θ1 atan2(P05y , P05x) +- cos^-1(d4/R) + π/2 These two variables, P05y and P05x are vectors (from the base of the ur3 to the 5th joint) and these variables are expressions that contains parameters such as θ1,θ2,θ3. I computed these two variables with a python code using homogeneous transformation matrix T05 (warning: not T06) and I get:

P05x = 0.08535(-sin(b)sin(c)cos(a) + cos(a)cos(b)cos(c))sin(d) - 0.08535(-sin(b)cos(a)cos(c) - sin(c)cos(a)cos(b))cos(d) + 0.11235sin(a) + 0.21325sin(b)sin(c)cos(a) - 0.21325cos(a)cos(b)cos(c) - 0.24365cos(a)*cos(b)

and

P05y = 0.08535(-sin(a)sin(b)sin(c) + sin(a)cos(b)cos(c))sin(d) - 0.08535(-sin(a)sin(b)cos(c) - sin(a)sin(c)cos(b))cos(d) + 0.21325sin(a)sin(b)sin(c) - 0.21325sin(a)cos(b)cos(c) - 0.24365sin(a)cos(b) - 0.11235*cos(a)

where a=θ1 , b=θ2 and c=θ3 So my question is how can I find θ1 if P05x and P05y are expressions that contains θ1,θ2,θ3 as you can see above ?

Also,because I have lost a month trying to find the 6 equations for ur3 using inverse kinematics (but I will try it later) ,I started using moveit commands with python but I have a problem and I want your help. I run a launch code with husky and ur3 robot in gazebo and then I run a python script: here

and in terminal I see: RuntimeError: Group 'manipulator' was not found. How can I solve it?

So,guys I want your help for my 2 problems (1st: inverse kinematics , 2nd: moveit) Any links (for the first problem) or ideas (for the 1st and 2nd problem) would be appreciated. Thanks.

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