I wanted to make a custom Magsafe compatible mount for my car.  So I designed this adapter made with TPU and 3x8mm magnets.  You can use it with the provided simple stand or as a starting point for your own custom mount. 

The magnets need to be inserted all in the same direction. I suggest putting a few in then checking to see if you have the correct orientation by attaching it to your phone before you put them all in.  Two 3x8 magnets get pressed into each circle.  That along with the TPU being a bit grippy make it quite secure for normal use. If you don't print in TPU it doesn't hold the phone as well.

For in the car where there are extra sheer forces from bumps and cornering, I added a socket with corners to keep the phone a little more secure.  I would not suggest using it on a bike, too much impact acceleration.

The magsafe flower is desiged to be printed without supports and is secured to things using the flare bolt and nut which match the chamfer on the flower.