I have been constructing a persistence display. For this display, a PCB is twirled at high speeds, about 1800 rpm. In an earlier thread,
https://www.eevblog.com/forum/projects/smt-pcbs-subjected-to-torsion-and-high-g-forces/msg3076319/#msg3076319I asked about the PCB that was shaking itself to pieces. I remade it and I am glad to report that now, after adding a 1/4 inch thick aluminum back plate, adding cutouts for the brush tabs, and moving the microcontroller onto the opposite side from the tabs, it is no longer popping the chips off the board. So, good times.
But now I am having another problem that perhaps the hive mind could help with. I have a diagram of it which I have attached to this message. My original idea for transmitting power to the PCB is to use the scheme where there are two tabs at the edge of the PCB where brushes attach. These brushes would be strips of metal, and there is a commutator ring which these metal strips brush against. The commutator ring is split into positive and negative halves. The two brushes are connected to a full-wave bridge rectifier. Each rotation, the polarity reverses and back. When the polarity reverses, the change is detected by a comparator and triggers the timer on the microcontroller. This is how I orignally intended to detect the position of the PCB so that I know how to time the LEDs. I chose this scheme rather than using a hall effect sensor because I thought it would not require any proprietary hall effect sensor chip that might be hard to get in the future.
In retrospect, this is a terrible idea, mostly because the contact with the ring is made at a large radius where the speed of the contact is very high. Instead it should be done at the axle. Instead, I was thinking of building the slip ring on the axle, like any sane person would, and then using the carbon brushes from a power tool to contact the axle. Are there any electromechanical wizards who have experience building slip rings? I was thinking of perhaps trying to use the slip ring from an alternator. Perhaps there's a method of detecting the axle position that uses a standard Hall effect sensor or a standard photocell interruptor type scheme? I would like this device to not just be a one-off if possible.