Electromagnet Power Coupling for charing/etc.

Dickens, Thomas P wrote:
>
> One concern I've had with robots recharging is the connection
> to the power; making it an easy connection and a safe connection.
>
> I've thought about using a system like the Sonicare electric
> toothbrushes.
> http://www.sonicare.com/
> http://www.lashoppers.com/sonicare.html
> (Disclaimer: I am not endorsing or promoting Sonicare. Their
> recharging technology just looks interesting for home robotics.)
>
> To recharge the toothbrush you stand the toothbrush up in a
> plugged-in stand. There are no electrical contacts; I assume
> the flow of power is electromagnetic through the plastic case.
> It also does not matter which orientation the toothbrush is in
> (it can go into the base two ways). This would provide a safe,
> easy to connect to recharging station. If anyone has, or knows
> of, a source for old Sonicare toothbrushes and/or rechargers,
> please let me know (I'll pass on the extras to the SRS :^).

It seams simple enough to make one. Its just a transformer with
a wide gap between the windings. Two coils with the primary
hooked to AC and mounted on the charger base, and the secondary
hooked to a bridge rectifier/filter cap circuit will get you an
unregulated power supply on the robot. I think the best topology
would be to have the secondary coil surround the primary, but who
knows. Either way would work. Adding in a ferrous metal core
and back plate to the base side, and cover cap on the robot side
should help to increase the effiency of the transformer. Keeping
the plastic covers and gap between windings as thin as possible
will also help improve effiencies. One can also provide some sort
of interupter circuit to switch on/off the primary coil so it
isn't going when the robot is away, or keeps the robot from
leaving due to magnetic attraction. The only difficult part I see
is the bobin for the secondary coil, but that may be able to be
vacuformed. The covers over the primary and secondary can be
vacuformed over the coils/hardware. The core rod can be a round
iron bar welded to the back plate. The backplate can be a flat
disc of iron. The cap on the robot side can be a iron pipe cap.
Consult transformer design books to figure out the winding turns
and wire size needed for each side to carry the current load you
wish for.

View is a cross section through the center along the axis.
p = Primary winding
s = secondary windings
c = Core metal, should be a ferrous metal suitable for transformer core use.
+, -, | = plastic
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