lördag 24 januari 2015

Designing a virtual reality HMD for smart phones

Update: Design is now available on Thingiverse.

This is supposed to be about software, I know. But without proper hardware it's impossible to write any software. I realized when putting together the Android VR library for jMonkeyEngine 3.0 that I had nothing to test it on.
The quickest solution to that problem would be cutting out a Google Cardboard. I'm not particularly fond of cardboard, however and without it being laser-cut it would look terrible. I have the benefit of owning a 3D-printer (Prusa i3) so I thought I'd have a go at designing my own HMD inspired by the Google Cardboard schematics. They can only be used so far, though, since they're meant to be cut and folded. Using a 3D-printer there are benefits of being able to print complex geometry directly.
I decided to build it in 3 steps, each as simple as possible to avoid overhang problems. The first one would be the cradle where the phone would rest.
I based the measurements around my Samsung Galaxy S4 and tried to design it to allow access to the buttons on the side of the phone as well as the USB and audio. In general, I tried to leave as much space as possible on the sides for different phone types.
Printing time is always an issue with hobby printers, which is why I left the back side open. This and to allow the battery some fresh air. There are holes in it as well (the design anyway. The printer doesn't really make them). These are for if at some point one would like to mimick the Oculus Rift DK2's positional tracking by placing some LED's there.

Next, I went to the piece next to the eyes as the middle part would just be about creating some distance between the lenses and the screen (or so I thought). I happen to have an Oculus Rift DK1 which isn't seeing much use now, so I decided to butcher two of the eye cups for lenses. They are 36mm in diameter, which should give some additional FOV compared to the 25mm recommended for the Google Cardboard. Apart from making good fittings for the lenses the biggest challenge with this piece was making it fit well around the face.

I think I actually spent most of the time making the middle piece. Modelling a good cup for the nose was a big challenge and I've scrapped several prints due to it not being well printed. It's very spacious, and should suit most nose shape and sizes. The other thing with it is that it's slightly wider at the bottom than at the top. This is because I made the piece next to the face slightly more narrow than the phone cradle. In the case I build a Note-sized cradle, this would be even more pronounced.

Below is the current state of the prototype. It's working very well together with the Google Cardboard demos. I can see some 5 mm outside of my S4 screen at the top and bottom, so maybe an S5 would be perfect for these lenses.

I want to have a fitting for a magnet on it as well but I seem to have lost the magnets I bought, for now..
I plan on sharing these as well as a BOM for a complete HMD once I'm happy with the design. Stay tuned for more.

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