# What is the difference between a Rodin coil and a Rodin starship?

I've seen various designs for Rodin coil and a 'Rodin starship'? Are these just regular electromagnets? Or something different? How do they differ from regular electromagnets?

I have never heard the term 'Rodin coil' but what you can see in the linked videos are normal electromagnets. The advantage of these Torodial coils (wikipedia) is that you can built transformers with almost no stray field. The magnetic flux is completely contained within the inside of the windings.

This is relatively easy to understand if you think about a long normal coil and then bend both ends together so that the whole coil is closed.

Such a coil can also be used to compare currents without changing or influencing the circuit too much. You probably have one at home as a Residual-current device to protect you from any current flow from a broken AC device:

The relay 1 cuts off the current flow if the currents through the L and N lines do not cancel each other, which means some other current path to ground.

• Ok, I'm fairly familiar with the devices you've described. Is there no current in the middle of the metal ring though? I've seen videos of magnetic balls rotating in the middle of one of the so-called 'rodin coils'. – Pureferret Jan 30 '12 at 13:12
• @Pureferret: In the ring you might have eddy currents, but no net current flow. At least not in the simple toroidal coil, other designs can of course create interesting field configurations but there is no magic going on here. – Alexander Jan 30 '12 at 13:40
• I'm familiar with the physics of electromagnets. But all the examples I've seen have shown a magnetic field external to the parts labelled 3 and 2 on your diagram. As well as this the magnetic field does not appear to along the rotational axis of 3. See this spinning magnet. Is there something different about the way the wires are coiled, which seems to be at an angle to the ring (3) when viewed from above that makes this happen? – Pureferret Jan 30 '12 at 14:54
• @Pureferret: I only had a quick look at the construction. The constructors website seems to be down (rodinaerodynamics.org), so I can only guess from the youtube videos. The main difference is going from circles around the toroid to long stretched ellipsis plus a some room in between. These two things combined will lead to a big stray field, which can do all kinds of things. For an exact field plot one could use some electromagnetics simulation package. – Alexander Jan 30 '12 at 17:49

## protected by Qmechanic♦May 19 '13 at 21:59

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