We are still discussing the point that we will use a wireless transmission or not in order to send power and information from the static card to the blade.
Tonight we tested whether we could send information (and until which frequency) trough ball bearings. We used an engine (12V up to 5500 tpm) on which we attached to ball bearings. We sent a square signal to the outer ring of the first one. It is then supposed to reach the inner ring (that turning with the engine) then to follow a metal stack until the second ball bearing and to cross it from the inner ring to the outer ring and then to be read on the oscilloscope. (and to be compared with the original signal). Up to a frequency of 1 Mhz for the signal, it is perfectly transmitted.(in the condition that we do not have to much vibrations due to the queer rotor) At 10 Mhz (the maximum allowed by our generator in this experimentation) the signal is modified but we can still recognize the information.
The operating condition were definitely not the best as we could obtain moreover we sent information through two ball bearings instead of one. The conclusion is that, at least for sending power, and up to a frequency of 10MHz, transmitting through ball bearing can be a solution.