I am trying to design a suitcase that will be able to generate electricity using the kinetic energy generating by the rotation of the wheels. Each wheel will have a motor on it. When the wheel spins, it will use the motor as a generator to create electricity that will then go and charge a battery in the suitcase. Think of the battery as a portable charger to charge your devices. The problem i am having is that when I have the two wheels running at about 5 mph on a treadmill ( i know its a bit fast) in parallel, i am only getting 1 Volt when it is hooked up to the lead. With no load, i am generating about 5 volts. That is what i would like to be getting with a load... So i am wondering.... How many motors, or of what kind, do I need to get the output to be 5 Volts under load?