About function generators

I need to convert 15v battery voltage to 12v 400hz (roughly).

Using arduino would be overkill.

What is your reccomendation to do this mechanically?

Thank you

Motor-generator.

Paul

Thank you Mr Paul for your answer.

I have googled Motor-generator but only motors show up. Can you clearify please?

Here are some 400Hz motor-generators intended for 60Hz AC. The google search terms were "motor generator 400 hz"

For DC input, look for "400 hz dc to ac converter". You may want a pure sine wave converter like this one, which are more expensive than square wave converters.