Continued to work with brushless motors, VESC and ROS. The Differential drive works. 

 just order a tachometer so I can measure the RPM. For low RPM the motors are working quite good. No problem with torque, as i wrote earlier I can't even hold them. So I need to measure how low RPM the motors can handle before calculating gearing further. I will order encoders for absolute rotor positions improving low RPM start and torque. The encoder I am looking at is the AS5047P (which seems to be hard to get) I also looking at the AS5048A which can support 16384 positions per revolution.

Read full post here: http://valify.se/2018/03/24/brushless-motors-vesc-and-ros-second-test/