How to create off angled hinges?

Like if I wanted to make swooping car doors
(example: http://www.verticaldoorscanada.com/images/_fer/ferrari-f360-f430-l-lambo-vertical-doors-.jpg)

With angles that aren’t exactly normal x, y, or z, but some weird mix of two angles, how can I set that up? I’ve tried empties and I’ve tried selecting a cylinder that was lined up and then setting the cursor to that location in edit mode and then in object mode setting the origin to the cursor, but it’s not changing the angles of my origin or changing the angles available for my 3D cursor.

First you need to define your custom orientation if you don’t want to use X , Y or Z or the overall normal of the whole door for the rotation

To do so, make a plane, and orient it to fit the custom orientation that will be used by your door
http://i.imgur.com/mqO24iX.jpg

Then change the orientation to Normals :
http://i.imgur.com/5xj35K7.jpg

Now press N to display the property panel and at the Custom Orientation tab , click on the “+” button :
http://i.imgur.com/cF21NKM.jpg

Press F6 to popup the operator menu (or look into the bottom of the toolshelf, to the left of the 3D view) and type the name you want to give to your custom orientation
http://i.imgur.com/9Z8X8wx.jpg

Now that’s done, you’ll notice your custom orientation is now available in the transform orientation drop down menu :
http://i.imgur.com/4nGoMZQ.jpg

From then when you’ll rotate an object, you’ll be able to select the new custom orientation your defined to have this object rotating according to it instead of X/Y/Z or the overall normals X/Y/Z when pressing R then XX or YY or ZZ (pressing 2 time the axis key will make use of the transform orientation you selected, pressing it once will just use the regular X Y or Z)

Remember you can place the cursor where you want to be the center of your rotation , and set the 3D Cursor as the pivot point
http://i.imgur.com/STMQMSL.jpg

I did quick search on Lambo Door Hinge. They are actually really simple two-hinge design. But the hinge needs to be at the right place.

The first hinge is just like regular door hinge. Door opens out horizontally rotating along the vertical hinge line. Only difference is that this hinge sits about 8 inches forward of the door and inside the fender. Door swings out about 25, 30 degrees. That’s the limit. Otherwise hinge bracket will bump into the fender on the inside. This horizontal rotation will get the door away from fender for second rotation.

The second hinge sits between the door and vertical hinge. This hinge rotates the door up with the help of air shock. Air shock is needed to lift the door up. Here is good video of the action and mechanism:

Here is the picture of the hinge parts:

http://i00.i.aliimg.com/wsphoto/v0/1544806744_1/Tansky-90-Degree-Vertical-font-b-Lambo-b-font-font-b-Door-b-font-font-b.jpg

So to simulate this in blender, you need to have the door object with its origin located where it rotate up, the second hinge. And little hinge object where its origin is located at vertical rotation spot. Make the door a child of little door hinge and they to child of the car frame.