[Solved] Powersupply Connection
I see in the videos that powersupplys are not connected to the Audrino but are wired directly to, for example, the motor and the Audrino. Why not connect the power to the Audrino via the jack and power the motor from the Audrino?
Because the Arduino is limited to an absolute max of only 40 mA per pin.
Servos, steppers and motors require more than that to operate, so running them through an Arduino would lead to a short bitter life (and possibly some flames).
The voltage regulator on an Arduino (which is used when you connect to the power jack) has a limited amount of current it can provide, so powering a motor driver from the Arduino's power pin might not provide enough current (especially if the Arduino is also supplying power to other peripherals).
And even if it does provide enough current, the sudden starting or stopping of the motor, or use of PWM, can lead to some voltage transients on the Arduino's power lines, which can cause the Arduino to reset or produce some other glitch. (Using capacitors across the power lines can reduce this effect somewhat.)