Looking at the photos of a selector frame, I can see 4 panels within the frame that I believe must correspond to the 4 Groups of the selector. I am wondering if the 5 Banks (associated with Brush selection) are all integrated within this one Group panel?I'm thinking this must be the case for a Brush selection to choose a Bank, otherwise some vertical motion would be required. I hope that makes sense.
The brush selection method is actually quite ingenious!Let’s assume a very simple panel frame with only one selector rod on it. On a selector frame, there are 5 banks, plus the commutator bars at the top of the frame. Each of the 5 banks has a brush associated with it, mounted on the selector rod. Each of the 5 brushes that pass over the 5 banks (numbered 0-4) has a trip finger associated with it. During brush selection, the brushes move upwards from their home position a tiny amount--between 1 and 5 clicks, which amounts to an inch or so of travel.
To select brush #0, the rod will move up one click, which puts the 0 brush in line to be tripped by the #0 trip finger as it continues to move upward.
To select brush #1, the rod will move up two clicks, which puts the 1st brush in line to be tripped by the #1 trip finger as it continues to move upward.
To select brush #2, the rod moves up three clicks, which puts the 2nd brush in line to be tripped by the #2 trip finger as it continues to move upward, and so on...
Once the desired brush is in position to be tripped, it stops momentarily, and a magnet engages and rotates the entire trip rod. This rotates all 5 brush tripping fingers about 60 degrees. Once the magnet is engaged, the brush rod starts upwards once again. As the brush continues upward, it drags against the rotated trip finger and “snaps” the brush closed onto the bank terminals.
Here’s the genius part: The height of the trip finger is different for each of the 5 brushes. If the 0th brush is to be tripped, none of the others will be, because they are not at the right height to be engaged by the 4 remaining trip fingers as the brushes move past them. Even though all of the trip fingers rotate to engage the brushes, the remaining brushes will just slide past them without tripping, and they don’t interact with the multiple banks--they’re just along for the ride.
When the call is hung up, and the brush rod returns to its home position, the brushes hit a shelf that they rest on. The shelf resets the tripped brush by pushing the brushes trip arm back to the untripped position, sort of like how you might fold up a pocket knife on the edge of a table before you put it away.
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