I have a device with parts inside. What I would like to do is at some point show the inside part without "opening" the device, but I don't want to mess around with shaders and transparency. Is there a way to show this part kind of inside the device, but control the opacity so that it is visible from the outside? I know this can be done in compositing, but I am not familiar with compositing. Similar to the way the engine and chassis are represented in the picture.
Transparency is easy if you use the video editor: Render two images, one of the part of the car you want to be transparent and one of the parts you want to reveal.
Then take those images and put them on the video\picture lines. (Go to your files to drag and drop the picture) Make sure the part of the car that turns transparent is on top!
Then find the opacity setting of the top picture and key frame it where you want the reveal to start and end, making sure to key frame the reduced amount of opacity where it ends.
If you plan to render a sequence of fancy turns with the camera, render two videos and follow the same process.