In order to solve this point :

"we cannot :

• control speed of both wheels when it is rotating is same directions (not under load). In this case, motors reach needed value but quickly speed up until max speed"

We must check :

• under load motherboard closed loop algorithm is fine

But in this case, how can we drive a light robot with this platform?

A solution would be to modify / rewrite motherboard source code (runs on STM32 F103). For now, I have not found any projects about it.