My first design was to use a liquid crystal shutter to pulse the reflected sunlight. When I contacted the manufacturer of liquid crystal shutters, an engineer there told me it would require too high a voltage to be safely used in a middle-school science project and would be too expensive. So I had to change my design to use a solenoid to tilt the mirror.
My original construction material was medium density fiberboard. Some of the parts of my digitally controlled heliograph were small, and assembling them with screws and glue did not appear to be strong enough to withstand repeated cycling. So I changed to using sheet acrylic (Plexiglass).
During construction, I discovered that the connection between the solenoid and the mirror would require some freedom of movement to avoid pulling itself apart. I eventually added a tiny utility hinge there to allow for the changing alignment angle.