Re: witricity legality?
 

From an engineering viewpoint, it's not a very good idea....wires work so well for carrying electric current. Wireless signal transmission makes sense because the information is what is important, not the power being used by the transmitter. Wireless transmission of power itself is not a very good idea, because it is very inefficient compared to wires (I think the inverse square law has something to do with it?)

It would be fun to experiment with, and as suggested low power applications such as powering custom sensor circuits would be a more suitable application than the drive system, also more likely to be meet the rules.

Re: witricity legality?
 

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

Re: witricity legality?
 

i don't believe that the energy that is lost in the 40% transmission lose is lost to the frame i think that the energy is lost just to space

also the energy from the robot will stil come from the battery no an out side place.


i agree with you that this would be a very sweet science experment (to bad im to old for our counties science fair). but i think this would be the spirt of first to try to put one of these things on a robot

Re: witricity legality?
 

I decided to look into what this year's rules have to say. I found one "debatable" against:I say this is debatable only because the rule is referring to wireless communication, not necessarily energy transfer.

However, it may also be legal:I think, if you made adequate provision for isolating the frame and a wired communication to the RC, you might be able to convince the GDC to allow it. However, I also think they would be more likely to not allow it.

Re: witricity legality?
 

good point it my be legal and possible but in terms of power use, it looks very impossible in practice.

Re: witricity legality?
 

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.

Re: witricity legality?
 

Please provide the rule which would disallow a custom circuit (inverter) that would change DC to a very specific AC frequency. I do not believe you will find one.

Re: witricity legality?
 

There is plenty of energy lost to free space, because the magnetic coupling between the two coils is inefficient. That'll put an upper limit of about 60% on your efficiency considering only the coils.

In addition to that, the stray magnetic fields (of which there will be plenty) will pass through parts of the frame, and those fields will generate currents in anything that's made from a decent electrical conductor, like aluminum or steel. This is not speculation on my part, it's solidly grounded in electromagnetic theory. In fact, it's the same effect that makes your desired power transfer work - the changing magnetic field inducing a current in the metallic wire of the second coil - but it's the stray magnetic field acting somewhere you don't want it to.

I don't think there's anything in FIRST rules prohibiting converting DC to AC, but transmitting it to another point through the air violates the FIRST-only radio rules.

- Steve

Re: witricity legality?
 

JamesBrown already provided it.

<R64> even keeps you from doing it in order to transmit a signal (as opposed to transmitting power).

Re: witricity legality?
 

Just to verify from real life experience, we use AC in one process on our robot this year and have never had any trouble with it in any of our inspections.

-q

Re: witricity legality?
 

Q,

That's wired, though, and not deliberately wireless?

- Steve

Re: witricity legality?
 

As you probably know, we have a data display on the back of our robot. At midwest, the display would go out a lot because the battery voltage often went low when loads were put on it (i.e. traction motors) causing the display to go dim/out. Since the second half of the boilermaker regional, you may have noticed the display now very rarely blanks or dims now.

We put a circuit in line with the power supply to the rear display that takes in the DC voltage from the battery, and runs that into a switching transistor that flips on and off at about 15KHz, generating AC. This high frequency AC goes into one side of a transformer, and comes our the other side at a high voltage. This high voltage is then rectified using diodes, and regulated back down to a (very very clean and stable) 12 volts, while the input can vary anywhere from about 6.0vdc to 18vdc.

If you have any further questions, just come over to our pit in atlanta and ask for Q.

-q

Re: witricity legality?
 

one debate that is poping up every page that i would like to settle is that witricity is not
radio waves
anykind of standard electromagnetic wave (radio, micro, infared, light, UV, Xray, gamma)
it will not be used to control robot
it will not interfere with body
it will not heat up body
the power for the coils will be from the battery not external.

i hope this clears up any future comfusion

Re: witricity legality?
 

Uhhhh... can you tell me which of those is not a 'standard electromagnetic wave'?

Even wires transmit electromagnetic waves... they (wires) just provide a strong suggestion for which way the electrons should go.

-q

Re: witricity legality?
 

Q,
I didn't know about the display, but I follow exactly what you've done and it sounds like you've got a really slick solution to your problem. Nicely done...nice high frequency means small caps at the rectifier output and not a lot of ripple. Probably a lot cheaper and surely more educational than buying a switching power supply. I'll try to stop by when I get a chance.

- Steve