Create Homunculus Brain

You create a box that holds the spirit of a fey, fiend, or celestial. The spirit in the box can see and hear, having 60ft of Darkvision and a passive Perception of 14. The spirit will obey your commands to the best of its ability. When casting the spell, you can include up to 20 non-sentient magical items in the spell. After casting, the spirit will be able to control these items at will, spinning magical motors, activating magical objects, and seeing through enchanted eyes as if they were the spirit's body. If any of the objects require an action, bonus action, or reaction to be used the spirit must spend it to use the item. If any of these objects get farther than 20 feet from the box, their connection to the spirit is lost and it cannot use them. You can recast the spell to add or remove items from the control of the spirit.

This spell is a vital component of building automatons like Steel Defenders and Homunculi. While creating them, you would have cast this spell. A modern automata needs at least 16 magical motors to be fully functional. (If you are a Artificer with a Homonculus Servant or the Battle Smith subclass, you learn this spell for free when you choose those options.)