[adrian_b]

Even if you do not have a motor but just a single charged sphere, at its surface there will be an electric field increasing with the charge.

At a certain charge value, and at a not very large one, the surface electric field will exceed the breakdown field of air and a corona discharge will start.

See St. Elmo's fire.

https://en.wikipedia.org/wiki/St._Elmo%27s_fire

So unfortunately the idea of using the repulsion forces does not work.

To prevent the discharges, the entire environment around the 2 charged moving parts would have to also be charged with the same sign, but then the repulsion forces between your parts would be balanced by the repulsion forces from the surrounding medium.

[modeless]

Thanks for the patient explanations! You could immerse the thing in insulating liquid, maybe inside a rubber pouch, would that not be enough?

[adrian_b]

High-voltage equipment, e.g. high-voltage transformers, is indeed immersed in insulating fluids, either in special insulating oils or in the gas sulfur hexafluoride, which is more convenient than liquid oil.

This increases several times the breakdown field compared to air but it is not enough to reach similar energy densities like with magnetic fields.

To give some numbers, the air breakdown field is around 3 MV/m, while the maximum magnetic field in a motor might be up to 2 Tesla.

The ratio of the energy densities is the square of the ratio between the product of the magnetic field with the speed of light and the electric field, i.e. the square of (2 x 3 x 10^8) / (3 x 10^6), so 200 squared, i.e. 40 thousands.

Even if you increase the breakdown field 10 times, which is quite hard to achieve with fluids, the magnetic field would give forces much, much higher at a given size.

[ben_w]

For a bit, but if you keep raising the voltage you find the electric breakdown happing on the outside surface of the robot (or whatever’s using the electric field muscle) instead of where you put the insulation.