Coffee Gimbal
SOLIDWORKS Motion Analysis (Version 1)
Final Product Video
I was inspired when browsing for accessories for my camp chair. I saw that Helinox sells a cup holder to augment with their chair.
However, it only held tumbler-style containers and wouldn't work with coffee mugs with handles. Also, the chair ergonomics encourages you to lean back while sitting in it, so I had the idea to create my own clip-on cup holder with passive leveling to prevent my coffee from spilling out when leaning back.
The first version (seen in the SOLIDWORKS motion analysis video) uses an M8 hex cap bolt and a nut as a hinge as I already had the hardware. But even with generous amounts of grease, the 'hinge' would seize up and not freely return to a level position with a load of a full mug.
So, I decided to try using common ball bearings used for skateboarding. I printed the parts with negative clearances for both the bearing and the axle. I fabricated the axle from 3/8" steel rod stock, but the bearing needed to accept an 8mm axle, so I stuck a drill into a vice to make a makeshift lathe. I was able to get the runout to twelve thou. The axle-bearing interface is a transition fit.
The new design with a ball bearing worked much better than with a bolt, especially under an applied load.
Helinox Product
Part machined with 'drill lathe'
The biggest challenge in this project was modeling the black clip-on mount. The chair had complex geometry, and the manufacturer did not supply any dimensions. I used the sketch picture tool in Solidworks to help create the base geometry, which I refined with a ruler and calipers.