modelling DC brush motor

I want to model a basic DC brush motor in order to get the magnetic force versus the current, the flux, etc. The motor is in the form of this one:

 

I tried it in two different types of analyzes which did not work.

First, I made a transient magnetic 2D analysis. I made a circuit and a model but when there were many errors when I did the solving (for example:

PBEPAV_3 => Error 49, no treated error type
PBCEVL_4 => failed
PBCEVL_3 => Failed
PBERES_3 => failed
FL5RE4   => Command not executed correctly
FL5ERS   => failed
FL5ERS_1 => failed)

 

Afterwards, I made a model of 2D section of a DC brush motor in a magneto static 2D analysis.

In this analysis, I defined the rotor on a different coordinate system so it will be rotated. I wanted to make a magnetic force - angle graph of the rotor (which is the coil in this case), but I get an error because the relative permeability of the coil is close to 1. I defined a mass density to the coil so it won't have the properties of air but it still didn't work.

 

How is the best way to model this DC brush motor, 2D magneto static or transient magnetic 2D analysis? Is there a tutorial for this case? beacuse I did not find..

What caused the errors I have got and how to fix them?

 

Thank you!