Garmin Varia/GoPro combo underseat hinged mounting plate

There are a bunch of things people typically want to mount rearward facing on their bikes (mountain or road). Most of the vendor mounts use a 20mm M3 spacing for the actual mount (GoPro or Garmin for instance). Most bike saddles have a pari of M5 bolts under the rear of the saddle which makes a good mount point. This mount uses a 55mm long M5 socket head bolt (I used partial threading) and a captive M5 nut to form the hinge (the hinge clearance is only 0.5mm so you might need a slight sanding of the mating surfaces to get easy hinging). I put a very tiny dab of CA glue to hold that nut into place. In addition because I hate threading into plastic as a reliable thing, I use captive nuts on the mounting plate as well (both the Garmin and GoPro models take a countersunk M3 bolt so the holes are clearance rather than Tap size). This model prints well SLA or FDM (I printed mine in the blue tough resin) but the Prusament CF PC Blend would do equally well here (you need a small amount of flex for the hinge to lock and to absorb vibration). Note the slots for the M5 bolts for the saddle are slots rather than holes as I discovered each saddle frame is close but not exactly the same spacing.

I used 2 different mounts (and the plate allows rotation of the mount in any 90 degree orientation for your use case) and since this is not really a “remix” but rather a whole newly designed mount to use their vendor mounts, I am linking to their actual mounts.:

https://www.printables.com/model/111239-garmin-varia-blendr-adapter (Garmin quarter-turn mount)
and
https://grabcad.com/library/garmin-gopro-camera-mount-dzino-1 (GoPro mount)

As always I am including the STEP files for those that want to customize their own print. It was created in OnShape CAD.