The Matt Hat Kickstarter campaign


I’ve finalized the design of the augmented reality baseball cap – now called theĀ Matt Hat – and it’s available through a Kickstarter campaign. Check it out!

Heritage Health Prize results

A few days ago I attended a talk by the winner of the Heritage Health Prize, and it reminded me that I should document the outcome of my team’s efforts.

My team-mate and I competed under the name Planet Melbourne. We submitted entries up until the first milestone at six months and didn’t make any submissions after that.

This apparently made us a useful reference point during the following milestones. Because the milestone rankings didn’t show scores, movements in a team’s ranking relative to our position gave a rough-and-ready indication of the improvement in their score.

Anyway, our rankings were as follows …

Milestone 1 (6 months): 5th

Milestone 2 (12 months): 5th

Milestone 3 (18 months): 14th

Finish (24 months): 25th

After the initial announcement of the winners, there were a whole bunch of disqualifications. Probably from people competing using multiple accounts. As a result, our final official ranking improved to 17th.

Visor, version 2

I actually got the new head-up display manufactured a few months ago, but haven’t had time to blog about it until now.


Here it is, modelled by my co-worker Scott. Notice the HTC Tatoo held in place with a rubber band. The information appearing on its screen is reflected back off the visor to fill your field of view at a virtual distance of about a metre.


At first glance it looks pretty good, but there are two problems. First, it’s too reflective. I requested aluminium coating on the inside surface at a thickness that would let through 20% of external light, similar to a pair of sunglasses. Unfortunately they coated both sides, so it’s only letting through about 4%. You can sort of see my couch in the background, but it’s faint, so the effect is more virtual reality than augmented reality. Still, that’s easy to fix in the next version.

More serious is the image distortion. I designed the visor using the optics I learned in high school, namely how a parabola can magnify an object and make it appear further away. Well, they lied to me. It turns out parabolic reflectors only work when viewed along the axis, and when they’re viewed off-axis, e.g. from your left and right eyes, the image gets distorted, especially at the edges.

You can see in the picture above how the “22:31″ text is sloping down, and that’s viewed from a camera that was fairly close to the axis. Viewed from your eyes the slope is worse, and, more important, the distortions are different for each eye so the images don’t line up. That makes it impossible to read text.

There’s no good solution to this. I’m writing some ray-tracing software to generate a curved surface that will show a separate image to each eye, but it has drawbacks. Each eye won’t see the entire image, and I suspect it’s going to be fairly sensitive to the position of the eyes relative to the visor.

At least this time I’ve learned a new trick for evaluating a design cheaply. I save the design in STL format, load it into Blender, make it a mirrored surface, and render it with ray tracing. If the reflected checker pattern is undistorted from the two eye positions then I’ve got something that works.

Head-up display update

I’ve been having trouble 3D printing the transparent visor needed for my head-up display. The part sent to me by Shapeways was seriously warped and not at all transparent. So I complained about the warping, and they gave me a credit which I spent on printing the visor in white polished plastic.


The white version let me test the form factor (which seems OK), and I’ll glue some reflective film to the inside to check the optics.


If it passes that test I’ll get it manufactured properly. I’ve found a local prototyping firm who can make the visor using CNC and mirror-coat it using vapour deposition. Not cheap – we’re talking several hundred dollars – but it’ll be done properly.


Seeing this video made me realize that quadcopters are more advanced than I thought, which got me thinking about potential applications. One that came to mind was human-computer interactions.

To interact with someone as an equal we expect them to be at eye level (which is a huge problem for people in wheelchairs), and I assume the same will apply if we ever deal with intelligent machines.

In science fiction the usual solution is to put the intelligence in human-sized robots, such as C-3PO and Robbie the Robot. Smaller robots, such as R2-D2 and Wall-E, are generally portrayed as being child-like and inferior.

However, in his Culture novels, science fiction author Iain M Banks has another approach – small robots that float at eye level. These robots, called drones, range in size from hockey pucks up to rubbish bins, and are usually far more intelligent than the humans they deal with. And I suspect we could build a half-decent drone using existing quadcopter technology.

The intelligence behind the ‘copter would be housed remotely, and the only extra features you’d need on-board would be wireless comms, a decent speaker, a camera, a glowing component to show “emotion”, and centimetre-accuracy navigation. Apart from the centimetre accuracy, that’s mostly stuff you’d find in a cheap smartphone. I’d also like it to carry out “nodding” and “head shaking” manoeuvres, but I assume that’s already possible with quadcopters.

I’d be really interested to see how people interact with a talking quadcopter. Would they actually engage as though it were alive, or would they treat it as just another computer, like a flying automatic teller machine? If they do engage, I could imagine quadcopter drones being used as tour guides and customer service reps.

On an unrelated note, does anyone know why the quadcopter is the dominant design? Surely a tri-copter would be just as stable, and cheaper to manufacture?

Update: I don’t why I ask speculative questions when I can just look up Wikipedia. According to this page four rotors make sense because two of them can be counter-rotating, providing more stability. And they give you three axes of rotational motion, so “nodding” and “head shaking” are definitely possible.


It’s always amazing what obscure products you can buy on eBay. It this case, a 10-pack of assorted sandpaper.


Time to start sanding the visor.

Second part arrives

The transparent visor part arrived yesterday from Shapeways.


It’s not very transparent, but apparently with sanding and polishing it becomes clear. It’s also very fragile – a piece broke off when I tried to attach it to the first part and it had to be glued back on.

Now that I’ve got my hands on the part I can see a few things that need improving.

  1. The visor needs to be thicker. It’s currently 1.2mm thick, and will be difficult to sand and polish without breaking. At least 1.5mm next time.
  2. It needs a shorter focal length. The visor sits too far forward on the brim of the cap and doesn’t really provide fully field-of-view coverage. Shortening the focal length will move it back and increase its curvature, hopefully solving both problems.
  3. The attachment mechanism needs rethinking. The tolerances are too tight – this can be fixed with sanding, but that’s not suitable for mass production. It can fail when the visor material is too fragile. It’s too complex for injection moulding. And it partly obscures the phone’s screen.

Still, I’ll proceed with what I’ve got. Get the visor sanded and polished, then hopefully mirror coated, and see if it works.



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