This is a model of a two-speed transmission of the type you might find in a car. (Except that cars typically have more than two speeds. The principle of operation remains the same as in this simpler model.)
The key feature of an automative transmission is that all the gears are always engaged with each other. When people talk about and inexperienced driver "grinding the gears" of a manual-transmission car, this is not an accurate description of where that horrible sound is coming from. They are actually grinding the dog clutches.
To shift gears in this transmission, you move a clutch plate sideways so that it locks together with one or the other of the two gears on the output shaft. The gears can spin freely on the output shaft: they do not transmit any power directly. But the clutch plate slides on a square section of the output shaft, so when it is coupled to one of the output gears, it transmits power from the gear to the output shaft.
This mechanism is made transparently obvious through the use of transparent gears, transparent clutch plates, all in a transparent housing. You can see how the clutch plates engage with each other edge-on, or even from the end, right through the transparent gears.
An optional Electric Motor Add-on, sold separately, can be installed to replace the manual crank. This kit is available as a stand-alone model, and the core of it is also included in our Radial Engine Car model.
Here are some videos of the model in action. Note that these all show the optional Electric Motor Add-on kit, sold separately. That's mainly because it's easier to demonstrate the shifting action in the videos when I don't also have to crank the model at the same time. It works perfectly fine without the motor, and in some ways the model is more elegant without the wires.
Transmission from the side, showing the shifting action:
Closeup showing the dog clutches from the end, through the blue transparent gears:
Transmission model running while rotating around a complete circle:
Your model will arrive attractively packaged with all the necessary parts (including a screwdriver and two wrenches). The kit screws together in about 45-60 minutes, and does not require any special model-building skills. A detailed, step-by-step assembly video is available on our instructions page.