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JelleB's blog
Posted by JelleB | Mar 21, 2007 @ 09:24 AM | 3,197 Views
GPW came up with an idea in the Stuka thread I had tought about too some time ago; producing sounds though a brushless ESC. Everything needed is there: a microcontroller, more than enough current, a surface that moves proportional to the current (the prop) and FETs to switch that current. The only thing missing would be the software (for the microcontroller) to generate your custom sounds, and a nifty way to let the motor play these sounds and still keep the timing/power in check.
More specifically: the ESC measures the voltage on the loose end of motor connections (the other two are connected to high and low voltage) to determine the zero-crossing of that pole. that determines the speeds of the rotor, after a slight delay the connections are communtated and the next phase begins. Modulating a soundwave over the input current might very well infulence when this zero-crossing occurs.
Another problem to expect is the method used to throttle: The FETs used can only be open ore closed so they are rapidly swichted on and off within one phase to get the required power(PWM for those who like acronyms). This will interfere with your soundwave, but I have no idea how the outcome will be. probably the effect wil get stranger with lower throttle settings (with WOT the FETS should be open for the duration of the phase). Maybe it is possible to use another method than pwm that instead of interfering, uses the soundwave to regulate the throttling.