I'm a veteran programmer new to the electro/mechanical world and unfamiliar with the terminology and what's already available. I have a single motor that I would like to use to drive a carousel or an elevator (these are very small models measured in inches). I would like to be able to switch between operating either of them so that only one of them is being driven at any time. I have been searching online for the terms "single motor" and "multiple transmission/gears" and other similar terms with no success. Now I have an idea on how to make this happen via swapping gears but I'm pretty sure this must be common so I'm wondering if someone could point me in the right direction; I would hate to reinvent the wheel.
Let me just state the obvious: Use two motors. Now hear me out on this one!
There is a saying that "If all you have is a hammer, then everything looks like a nail". Meaning, people tend to view their problems based on the tools or abilities that they have. If they have a hammer, then they will hit their problems into submission. This approach can be both good and bad.
It's good in the sense that you will often find a solution that you have the ability to accomplish.
It is bad in the sense that you asked a mechanical question in an electrical engineering site. You are going to get answers that prefer electrical engineering solutions.
That being said: Gears are hard. Building mechanical systems based on gears is hard. Building one-off mechanical systems in your basement is super hard. The reason for this is that mechanical systems are very "tweaky". You have to factor in things like the flexing of material, the tolerances of your fabrication method, the ability to get parts in the sizes that you need and the price that is reasonable. Doing any of this with gears brings the level of difficulty higher. I wouldn't even consider making something like this without a 3-D printer, CNC machine, or laser cutter-- especially if you want it to be small and elegant/unobtrusive.
Even if you can build it, will it work on your first try? Tenth try? Is it going to be reliable? Durable? Is it going to be noisy? Electronics are not so hard, especially if you are just driving a simple motor(s).
Which is more difficult: getting, mounting, and controlling a second motor or making a complex mechanical thing with gears and stuff?
If I were building this, I would use two motors. According to FedEx, my 3-D printer should arrive here tomorrow and I have been studying gears and stuff for the past month-- and even then I would still use two motors. But then again, I'm an electrical engineer.
Planetary gears are used in electric cars to solve the problem of a gasoline engine and an electric engine driving the same wheels. Regardless of what solution you use, you need a mechanical way to describe how to split the torque between the carousel or the elevator. The easiest way to do that is a second motor. If you need to run only one at a time, you could use a clutch, but I don't see this as any simpler than two motors.
I really see no reason to use one motor. To have enough torque to move both loads you will need a bigger motor and a complex transmission. Two smaller motors should work as well, and your transmission is a pair of wires.
One of my old VCRs used a single motor to operate everything but the spinning head. When the motor was driven in one direction, it would rotate a cam that would connect or disconnect other mechanical assemblies; when it was driven in the other direction it would operate the selected assembly. One could use such an approach to connect the motor to "elevator up", "elevator down", or "carousel spin".