But you cannot make energy from their motion, E=MC2 still applies.
They possess "motion without energy"[20]—their apparent motion does not represent conventional kinetic energy.[2
Did you read about the ones they created? they required massive amounts of energy and only exist briefly.
https://en.wikipedia.org/wiki/Time_crystal#Thermodynamics
There is no model of these things where they can be used for a perpetual motion machine. They explicitly say that energy is conserved, as it always it. If you want free energy buy some solar panels or a micro hydro unit, build or buy a biomass gasifier, time crystals and geet engines are not ways to generate energy.
"Tesla envisioned a very long bundle of metal rods, extending from the earth to outer space. The earth is warmer than outer space so heat would be conducted up the bars along with an electric current. Then, all that would be needed is a very long power cord to connect the two ends of the metal bars to a motor. The motor would continue running until the earth was cooled to the temperature of outer space."
that would probably work, but the question is how efficient would it be?
space and earth are about 60 miles apart vertically and a rod of a certain width can only conduct a certain amount of heat.
It would take either some very large rods or many masses of them.
I think we have many places on earth where we can find temperature differentials that are closer together
A lot of people heat their homes with heat pumps that work on a similar principle but by putting pipes into the earth or a body of water where it is warmer.
Thermoelectric generators that generate energy when exposed to different temperatures have been around for a long time, that's a real technology that you can experiment with at home. the problem is they are not that efficient. They are used in cheap 12v electric coolers.
https://www.amazon.com/Thermoelectric-Generator-Peltier-Cooler-Demo/dp/B003FJ6I0Y
none of these things are free energy though, Tesla would be exploiting the energy in the heat of the earth like geothermal plants do now.