Rowing on a machine is pretty boring. I find that watching a suspenseful movie or TV show is a great way of making it easier for me to meet my cardio goals. Unfortunately, my gym doesn't have TVs, and the rowing machines -- Concept 2 PM4s -- do not have a place for me to put my phone during my workout.

This design is a portable clip-together cradle for a smartphone that will allow you to keep yourself entertained during your rowing session. This was designed around an iPhone 8 and a Concept 2 PM4, but any smartphone that is approximately 67mm wide will likely fit just fine (Fusion 360 files are attached if not), and other Concept 2 models are likely to work too.

I recommend printing this using a durable and (slightly) flexible plastic like PETG.