A Magnetic-Gravitational Motor

Introduction

This is another quite old idea, which could have been designed as a purely mechanical device. But it is probably easier to understand initially as a combined magnetic-gravitational device.

Fig 1. Weights suspended by springs in a wheel

Introductory design

Suppose a wheel is made as shown in Figure 1, where a number of weights (red) are suspended by tension springs (blue) between the rim and the center of a wheel centered at point P. Then the locus of the weights will be very approximately a circle (purple) centered at a lower point, O.

Obviously the weights in this wheel will be balanced overall, and so the wheel will have no tendency to turn.

Fig 2. A fixed magnet repels magnetic, spring-suspended weights,
on one side of the wheel only

A magnetic modification

Now suppose the weights have been made as magnets, and another fixed, radially magnetised repelling, semicircular magnet (orange) is added on one side of the wheel, as shown in Figure 2. Then the locus of the magnet-weights will be as shown by the purple curve in Figure 2, i.e. they will be raised just before and after they have crossed the vertical centerline.

In this design, with the magnet-weights suspended by springs as they are, it would be reasonable to expect that the repulsive force on each moving magnet tending to turn the wheel back as it rises just before top center would not be very much greater than the similar repulsive force on each magnet tending to turn the wheel forwards as it rises just after bottom center.

So, on the one hand, the magnet-weights fall through a greater height on the descending side, and this should cause the wheel to turn. On the other hand, it could be argued that as the descending magnet-weights complete their fall, there will only be a net exchange of gravitational potential energy to spring stored energy (where there was no such net exchange before), which will be enough to ensure that the wheel won't turn.

Resonance

However, something else can also be done:— wherever weights are combined with springs, mass-spring resonance can be made to occur.

Modelling — summary

In Figure 1, assume the weights are 0.5 kg each, at approximately 0.125m radius from O. The springs between the weights and the rim, and the center P of the wheel are:—

Unstretched length Lo = 0.05m
Max. stretched length Ln = 0.4m
Max. force Fn = 11.445N
Spring constant k = 32.7N/m

(In Figure 1, the weights are shown in their correct positions for the above data, for a stationary or very slowly turning wheel of 0.25m radius and distance OP of 0.05m).

With the wheel stationary, we then add a force radially outwards from O of 8.177N on the top weight, and allow it to rise to its natural position for this, at very nearly 0.25m above O. (This is similar to Figure 2, but with greater displacement). We then remove this artificial force, and rotate the wheel clockwise at a steady 8.0888 rad/s. Then (radial) centrifugal force of 8.177N will replace the artificial force. Then, as the wheel rotates, approximately one half-cycle of mass-spring resonance per half-revolution of the wheel will occur. At the bottom of its fall each weight has dropped to slightly over 0.323m below O, i.e. well below its natural position for a 8.177N radial force. (And so its spring to P could then raise it to well above that natural radial position on the ascending side).

No energy gain

However, I have not found any overall energy gain from this approach. The old question "Where does the (extra) energy come from?" applies here. Even with mass-spring resonance occurring, there is just an exchange of energy between different forms, i.e. kinetic, potential, spring stored energy, and rotational energy of the wheel. As for forces of magnetic repulsion, in this device the magnets could just as well have been replaced by mechanical components, e.g. compression springs.

Can we be more creative?

So, we'll have to be more creative about how we use permanent magnets, if we hope to gain any net energy from them. More on this next.