Saturday, October 20, 2007

Wearable Displays: Some things never change

You'd think that HMDs would change and get cheaper, even if they're not completely mainstream. Remember IO glasses? They're still around, and I don't think the price has dropped. My belief is that QVGA (320x240) is OK for a quick reference monocle design. VGA is the bare minimum for a useful one, and SVGA (800x600) is frankly the required minimum for people to accept a technology. XGA (1024x768) is the right resolution. People expect to achieve such resolution from their main monitors, after all.

If you look at two big HMD online stores, TekGear and VR Realities you'll see a lot of expensive hardware. Some of which has NOT been updated in YEARS. Disappointing, isn't it?

So, what have I found in my own searches recently? Well, 320x240 monochrome NTSC video monocles are cheap and easy to get. Some people are trying OLED HMDs, but they're just as expensive as the older Active Matrix LCDs. That example WAS under $1000, I wonder what happened to cause the price increase?

My personal bet for inexpensive high resolution HMDs come from the DLP and LCOS industries. Both technologies reflect light towards the display instead of blocking it like normal LCDs. DLP uses MEMS moving micromirrors. LCOS uses newer (cheaper?) specially processed silicon. The products from Headplay currently wins in terms of resolution for the price, plus it has oodles of inputs.

One thing I've noticed is how annoying these can be. Many are designed for total immersion. I don't always want that. I think Icuiti is on the right path for "mobile useable display".

Actually, what I'd love to have is a transparent (or Augmented Reality) display that can use my glasses for a screen and put up a simple monochrome image for me. A GPS map would be nice for instance. I'm not wanting a complete overlay, just a portable heads up display. Some systems are made almost like that, but I'm not willing to pay $200 for it, let alone $2000.

HMDs have one issue that's hard to measure. Comfort. Are they comfortable to wear? Am I going to want a bottle of excedrin sitting next to me after I use them for 15 minutes? Once the price comes down that people are willing to pay and you can get enough volume to get a few in stores, this will be a hard question to answer.

Monday, October 08, 2007

Solid machine design: CNC basics and options

Been looking around at parts and pieces for a CNC machine. This structure works for whether the machine is for machining, sensing, or RepRap FDM. Your basic mill/machine will be a three axis machine. X-Y and Z. My preference for linking these machines together is to use the table on an in-out Y axis, then the main gantry left/right for the X axis on the cross member, and the milling head on a Z axis. Easier and capable of "reaching in" is if the milling head moves for Z. If the supports are moved, the mechanics are more complex (as you have to keep the two axes even) but the whole machine is stiffer.

Now, beyond the basic 3 axes, we can add more. One is doing both Z axes options. This lets you reach and achieve stiffness as need be. Rotary axes are the next useful axes. A worm gear based rotary table makes wide circular machining. A horizontal axis lets you work a lathe style mechanic into the system, but you'll need a driver and driven ends.

Many multi-axis systems start adding axes at the cutter instead. This is simpler from a mechanical aspect on larger machines, but always useful. Starting at the Z axis, putting on two more rotary axes to allow for machining withing a hemisphere, and can be very useful. However, a smaller or less forceful cutter is needed. However, you also need a very accurate motion system since you only have 180 or 360 degrees of motion, instead of, say, 1/16" of motion per rotation.

I'm considering a CNC cutter head. Around here, Menards has a low cost rotary tool with flex head. By mounting the flex tool, the cutter head can be kept small and light, allowing for good maneuverability on a small machine. Flat and ball mills can be used with 1/8" shanks, but I'm considering starting out with a carbide or high speed steel Dremel burs. These are more like small mill bits but have 12+ cuts. They also cut at dremel speeds (8000-25000rpm) which is well above what many mill bits are rated for. If a saw is needed, Dremel has some somewhat expensive but neat "EZ Lock" blades that make them quick change and indexable.

More thoughts...