(4) -> I'm indeed using N20 motors. More precisely, I bough those in 12V/60rpm version : https://fr.aliexpress.com/item/4000274747864.html?gatewayAdapt=glo2fra&spm=a2g0o.9042311.0.0.27426c37E5t7rD Usually, I'm not that fond of non specified components, but it's hard to find that light motors (I already had 2 N20 at home, which worked well), and cost is a critical aspect of the robot, because in real use, there will be a huge risk of loosing the robot due to pilot errors (maybe 10% per operation). As there are 16 motors (8 for the elastics of the arms, 8 for the wheels, it makes a significant part of the cost)