Work of our members

A Motorised Sundial

Below is a photograph of a sundial which has, in its centre, a surface parallel to the Earth's axis.

At the top and bottom of the surface are two sets of solar cells, four sets total.
These four series of cells are connected in a balanced circuit.

In addition, there are strips fitted perpendicularly to the axis, and, some way out, there are two more strips that are again parallel to the axis of the earth.
These strips may or may not cast their shadows on the solar cells.

This construction may turn about the axis, driven by a small motor which derives its power from the solar cells.

In the photograph, the central plane is about east-west, but any starting position is possible.

When the sun rises, the east cells will generate more voltage that the west ones, because the latter will be in the shadow of the strips.
The voltage difference will power the motor, which will in turn drive the array until both sets of cells are in full sunlight.
That will be when the polar surface is perpendicular to the sun, the only position in which no solar cell receives any shadow from the strips.

At that moment, the net voltage from the cells is zero, and the motor stops.

As the sun moves on, the more distant strip will cast its shadow on one side of the solar cells and the motor starts turning again, until the surface is again square to the sun.

The result of all this is that the centre array keeps tracking the sun, and its motion may be used to indicate the time.
In practice, this sundial tracks within the minute.

When the sun sets, the process halts and the sundial remains stationary, until the sun rises again the next day and the game repeats, just as with any sundial.

What if it is cloudy?
That will also stop the array from turning. But as soon as sunshine returns, the sundial will align itself into the sun again.