Archive for June 24th, 2011
Having had many bike helmet mirrors disintegrate over the miles and years, I’ve had a background project bubbling along to build something more durable. Whether that’s feasible or not remains to be seen, but here’s another go at it.
These doodles aren’t workable, either, but they convert the ball joint into two orthogonal rotating joints that could be 3D printed with some attention to detail.
The general idea:
- An ordinary inspection mirror has most of the tricky bits
- An azimuth-elevation mount aligns the shaft relative to the helmet
- The mirror shaft extends to put the mirror forward of your eye
- The existing mirror ball joint aligns the mirror relative to your eye
What’s not to like:
- Exposed screw heads
- Off-center, hard-to-grip adjustments
- Probably not printable without support due to all the bearing surfaces and cutouts and suchlike
A few more days of doodling produced something that seems better. The az-el joint axes and the mirror shaft axis now meet at a common point, so the mirror shaft moves as the radius of a sphere. The elevation screw hides behind the azimuth mount, out of the way, which makes it awkward to adjust the tension.
The helmet mount plate must be concave to more-or-less match the helmet curvature. I’ve been securing mirrors using double-sided foam tape to good effect, but it requires a fairly large pad to provide enough adhesive force.
Two glue joints make everything buildable and should have basically the same strength as the parts themselves. The helmet plate builds concave face up. The az and el mounts build with the bearings upward, as do the mating surfaces on the other parts. Maybe the screws need actual nuts embedded in the mating parts, in which case there may be problems.
The setscrew holding the mirror shaft can crush the tube; I think they’re thin brass, at best. Putting a stud screw on the end will hold the shaft in place, leaving the setscrew to prevent rotation. Perhaps the stud can reinforce the tube.
What’s not to like:
- Many parts (but all buildable at once)
- It sticks out too far from the side of the helmet
- Ugly on a stick
But maybe something will come of it.