I've worked with automation systems that used carousels, both sequential operation and random access. The big problem with them is that most stations failed to do any routine maintenance on the mechanics; occasional cleaning of the tray assemblies with denatured alcohol followed a light coat of silicone spray on the surfaces that slid against each other did wonders to keep the trays moving smoothly, which avoided 99% of the jams.
I've also worked at stations with Instacarts. They were easy to program but had quirks of their own. If the ground connection wasn't perfect, if any static electricity discharged to them all 48 trays would fire simultaneously. I know of one station (not one I worked for) that had multiple Instacarts, all of which would repeatedly do that "trick" during lightning storms. And since all 48 trays shared a common audio bus, that would create quite a cacophony if the Instacart was on-air when it happened ... a lesser version would happen if the "stop" tone didn't get recognized and another tray in the same unit was playing. But the biggest headache was if you ever needed to set the azimuth on them, as every tray had to be set individually; ditto demagnetizing the heads ... 48 of those, too.
One station had the Schafer replacement for the carousel ... Audiofile. Three columns of 16 trays, each column with its own head assembly which moved up and down as needed. Advantage: You could play a cart each from all three columns in the same stopset, or sometimes repeat if there was enough time for a cart to recue and the assembly to move to another tray. Disadvantage: They really needed routine maintenance, which required removing the faceplate and all 48 trays, then cleaning the post that the assembly moved up and down and a light coat of spray silicone.
There is an Audiofile underneath the carousel in this rack:
And there were other variants, notably the IGM Go-Cart, which was sort of like a carousel but moved the tray assembly around using rubber wheels along a track. Those could have up to 78 trays in them (and I saw one with that maximum number of trays in an automation system once). The other was the predecessor to the carousel, the Gates 55, which was a column of 55 trays, taking up an entire rack, accessed sequentially from top to bottom, then back to the top. It was infamous for occasionally not completely returning a tray to the "out" position, then demolishing the cart edge as it attempted to move the playback assembly anyway.
This automation system had multiple Go-Carts (the two leftmost look like full 78-tray units to me):
Here's a pic of a Gates 55 (it's the unit
not wearing the minidress
):