Thanks Mat, didn't know the thing about the magnets.
Haven't measured the current by now, as I don't own such a device.
But what I can tell is, that in the default setting, the pololus were set in the configuration tool to 12A max current, which was not enough to lift me back up from a far left or right position. I set them now to 18A, and now it's working.
I'm not sure if this is really the true value that goes out to the motors, as it seems quite high to me, but I'm not very good with all this electronical stuff.
Anyway, it's a good idea. I'll get an amp measure device from a friend to see what's really getting on.
In the end I'm already thinking about getting myself a pair of this ones, what do you think?
http://www.motiondynamics.com.au/worm-drive-motor-12v-24v-200w-180-rpm-20nm-torque.html