You can build an inverter with a small 60rpm DC motor. The motor turns a disk with 4 brushes, 2 on each side of the disk. The disk is a sandwich of two conductors separated by an insulator. One of the brushes on each side contacts the respective conductor, and the other brush contacts an outer band. Each sector of the band has a resistance. The resistance is selected so that as the motor spins the disk, the outer brush on each side contacts the resistive sectors, and it creates a sinusoid. The signal is then fed into a transformer to create120VAC. This arrangement runs off of a 12V car battery or a DC generator.
Disk Sector Resistances
OHMS one side opposite side 9:00 transition transition10:00 1M open 11:00 10k open 12:00 0 open 1:00 10k open 2:00 1M open 3:00 transition transition 4:00 open 1M 5:00 open 10k 6:00 open 0 7:00 open 10k 8:00 open 1M
Output voltage is between two conductor brushes. The first brush goes to 12V through a 100 ohm resistor The opposite brush goes to ground through a 100 ohm resistor. The first band brush goes directly to 12V The opposite band brush goes to ground.