Thanks to my move last December, all the in-progress work on my direction-finding extra-sensory belt went into the dump. Now that I’m settled into the new place, I’d like to go back to work on the project. Here’s the thoughtlog for today.
I’ve had something of an epiphany. Vibrating motors might not be the best mechanism, if I want to maximize runtime and minimize noise. Better, perhaps, would be a series of inflatable air-bladders. The air would most simply be provided by a compressed cartridge. To direct the air, I’d want one solenoid valve per bladder for inlet.
As density of CO2 is 1.9769g/L at STP, a 12g CO2 cartridge contains about 6L. They cost about $0.65 in bulk. It should also be possible to use larger or refillable cartridges to improve running time.
Latex bladders are relatively simple to fabricate at home, acc to eHow.
Electronic solenoid valves would be used to direct the air to a specific bladder. Mead has a series that look suitable.
The general idea would be to use four bladders: one each for belly, back, left and right sides. The firmware would wake up once a second (might need to tune the interval) and inject the bladder(s) facing north with a quantity of CO2. The bladder(s) would gradually leak, likely remaining only 1/2-1/3 full in time for the next air charge. If they were completely sealed, an additional set of valves would be required to empty them; this would increase battery load and equipment cost, but conserve CO2.
Assuming the bladder would contain 1 cubic centimeter of CO2, and one bladder was filled per cycle, a single cartridge would provide 6,000 cycles, or about 1h40m. That’s not going to work. I want at least twelve hours out of a single charge, so I’d need about 90g of CO2. I found a source for 88g CO2 cartridges for $6.50 each, no idea of scale. How big are those? They’re expensive, but in the right area for capacity. Also found refillable tanks rated for 4500 PSI that might work, but those are definitely too big: they’d add “backpack” to the list of hardware for the belt.
I think CO2 or HPA might be too much work to be worthwhile. I’ll look into pumps later. For now, chore time.
Thoughts?
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