A part of the review has been auto-translated.
The wheels don´t spin, the way the wheels are proposed to be mounted is not good. Of course, I left a couple of millimeters so that the wheels can turn, but the tension of the chain pulls the wheels, coming to rub part of the wheel (the part towards the chassis) with the chassis and, because of that, friction is created, which prevents rotate, creating a lot of resistance to the movement of the track. Of course, I didn´t tight too much the nuts. The solution: I used 6 screws m4 x 50 philips screwdriver type, 6 m4 nuts, and 6 m4 retention nuts. 1) Pass the screw through the weel 2) Screw in the normal nut, until 3 mm before reach the wheel 3) Pass the screw through the chassis 4) Squeeze the m4 retention nut, until both nuts stay tight, then use a tool to thight a little more the normal nut. That way, the wheels are free to spin