The Mendocino motor is a solar-powered magnetically suspended electric motor. It floats in the air with virtually no friction thanks to the magnetic suspension. The solar cells on the outside of the motor drive solenoids inside the motor, which, combined with another magnet in the lower frame, allow for zero-friction rotation around the motor's axis. This functional principle of a power-generating solar cell had already been discovered in the U.S. in 1954. A free-floating motor with magnetic suspension in horizontal position was not developed before 1992 by Larry Spring – in a town in California, USA, called Mendocino.
Functionality and structure
The body of the solar motor is a 12-sided cylinder which has solar cells on each of its 12 side plates. Inside the body, there are six solenoids which are supplied with power generated by the solar cells.
For every winding, two opposite solar cell rows are connected in parallel. For each side plate, three solar cells are connected in series in order to increase the magnetic force of the connected solenoids inside the body. The solar cells facing the light supply the respective solenoid with power and generate a magnetic field which is repelled by the correspondingly polarized field magnet. This repulsive force (also known as Lorentz force) puts the solar motor into a rotational motion. The solar cells facing the light turn away from the light, the next solar cells move into the light – and the motor spins smoothly.
Thanks to the shaft magnets which are located on the ends of the shaft, the solar motor floats over four supporting magnets which are attached to the lower frame. It only has one slight contact point to prevent it from losing balance to the side. The fifth magnet in the lower frame causes the motor to turn, triggered by the repulsive force of magnetic poles with equal polarization. The functionality of the Mendocino motor requires magnetic suspension because the motor can only generate a very low drive torque. Magnetic suspension considerably reduces friction.
Optical rotation measurement
With this motor, the speed signal is generated without contact by a wenglor retro-refl ex light barrier type K1R87PCT2 and then transmitted to a summation meter. This means that the motor floats without any friction apart from the tip contact (ceramic ball). As a result, up to 100,000,000 rotations are counted per year. All components are visible and their functionality is clear. The advantage of this probably unique motor is that it rotates very smoothly thanks to its twelve surfaces, can start independently even with little ambient light (tealight or dull daylight indoors) and it could spin for decades.
Text: Wolfram Glatthar, Fabian Repetz Pictures: Wolfram Glatthar, Heather Brown (Larry Spring)