Thread: witricity legality?
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Unread 28-03-2008, 14:20
Matt H. Matt H. is offline
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Re: witricity legality?
Quote:
Originally Posted by stj_1533 View Post
A couple things to note...

You'll need a way to convert the DC of the battery to AC in the transmitting coil. Not hard to do, but it'll hurt the efficiency. You also have to match the resonant frequencies of the transmitting and receiving coils, and match the frequency of the DC to AC inverter to those. A little harder to do, but still possible, with patience and a little research.

The power is transmitted much like it is between the two windings of a transformer - the changing magnetic field generated by the transmitting resonator passes through the receiving resonator and generates a voltage there. The difference is that the magnetic field is not in the least bit confined, which is what the ferrite core of a transformer does. What'll happen is that that changing magnetic field you generate will induce currents in every loop of metal within its range, particularly the robot chassis, manipulator, neighboring robots, metal field elements, belt buckles, tools in the pit, hoop-shaped body piercings, whatever happens to be around. It can really wreak havoc on your electronics. Plus, metals get hot really fast when you induce currents in them. And, the more power you try to transmit, the greater the volume the magnetic field takes up, so more things draw power away from your transmitter.

Then, at the receiving end of the power transmission system, you'll need to rectify the AC back to DC. If you're going to run a sensor with it, you'll need to regulate the supply.

Hang on...if you run a sensor this way, you'll have to get the data back to the RC...with a wire, since other radios on the robot are prohibited.

In short, assuming this might by some stretch be legal, then trying this on a robot will at best waste power, and at worst cause enough heating in the chassis (large current in a thin piece of metal) to catch something on fire. Hmmmm, maybe that could be your science project - ignite a sheet of paper wirelessly.

BTW, one problem with Tesla's demonstration with the fluorescent tube is that there was no easy way to confine the volume which the fields operated in - if your neighbor's transmitter was on, your lights were on. It still needed quite a lot of work to be practical.

It sounds like something really cool to tinker with, and pretty inexpensive, but there's a lot that's got to happen before it's practical and safe for use on a robot. Have fun with it.

- Steve
It is most definitely illegal to make a custom circuit to convert the DC power provided by the battery into AC power require for inductance. While in theory DC induction could work the coils quickly become magnetically saturated and therefore not useable. Because you can not provide a source of AC power on the robot (or a custom inverter to convert the battery power) you can not use such a method to power your robot.

Now let's talk about eddy currents. The M.I.T. experiments you cite did not involve numerous large metal objects such as robots. The large magnetic fields involved in transmitting electricity wirelessly will create millions of small whirling currents in an AL frame causing it to heat and sapping energy from the motors. It's an amazing and innovative idea, but it will be several years before it reaches fruition.