Comment by jcims | Hacker News Reader

Comment by jcims | Hacker News Reader

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A speaker is a precision open-loop voice coil that precisely translates input current to force that displaces a membrane. A laser galvanometer is a precision closed-loop voice coil that translates input voltage to a specific position/displacement. The mechanical components to ensure repeatability and the electrical components that 'close the loop' are what generally make them (much) more expensive than speakers.

Picking off a mosquito will require positional accuracy of say 1mm. If you want a range of 10 meters you're going to need positional accuracy of ~.1 milliradian. Most galvos have a rotational range of .3-.5 radians, so you're not going to need extreme positional accuracy relative to what's on the market. A controller, pair of quality 16 bit dacs, galvo hardware and decent power supply should be adequate. I have some of the cheap $300 ebay 2-axis galvos and those are not sufficient. You're going to need a step up and are easily getting into the thousand dollar range for the galvos alone.

Why not use the same system that laser printers use with rotating mirrors and precisely timed laser pulses. I’m not sure how accurate you could get it over 10m but it would be massively cheaper and could use parts and electronics that are already produced at scale. Cheaper means you could take more of a shot gun approach to make up for any loss of accuracy.

That would definitely work if you just wanted to shoot any bug out of the sky. Probably have to use a more powerful laser to dump enough energy into the wings to damage them.

The system in the article uses reflections from a continuous illumination by the laser to identify the insect. Basically just translates to an audio signature that can be used to to see if it’s a mosquito and even if it’s a male or female.

It should be a lot more tricky with a very short illumination by scanning laser.

What about adding more scanning lasers to get a better measurement of the location? That could also be your power increase by firing multiple lasers at the same spot. Might be safer too since each individual laser would be lower power and the dangerous spot would be localized to where the beams cross.

You are asking too much of the galvanometer, and not enough of the system it is part of. Do your own muscles satisfy your requirements? Muscles no different can put a basketball in a hoop from half-court, blind.

The return signal from progessively-focusing beam can provide the closed-loop control needed.

This actually isn't asking much of the galvanometer. Commercial systems are generally 20-24 bits and have resolution in the 10-20 microradians range...100-1000 times more precise than we need.

But ultimately the control system has nothing more than input voltage to the galvanometers to steer them, and depending on the source of inaccuracy they may or may not be able to overcome it.

When the goal is a gadget you can afford to deploy, system design is where you need to get your accuracy.

Fast, close-to-linear response over a short range can be cheap; the overall linearity you get from your $1000 gadgets is unnecessary. Fixed calibration targets could help compensate for broad nonlinearity and also drift from, e.g., temperature variation. Varying focus as you home on the target with a spiral path forgives a lot of initial inaccuracy. The system could refine its response curves with each kill, to home in faster; calibration targets might not be needed if unfocused illumination is forgiving enough.

It doesn't need a 100% kill rate in the first 10 minutes. Indeed, in a usefully big volume it gets plenty of attempts on each target. So, there is plenty of time for the system to tune itself to its own hardware.

You seem very knowledgeable about engineering these types of solutions. What is your background?

The reason I ask is because after seeing the OP video (which is remarkable) I am left thinking that in terms of getting a cheap MVP to the market maybe a ballistic system of some sort would be preferable.

Take the same approach of using a high speed camera but using a pneumatic launcher shoot a handful of grains of sand at high speed. There are obvious downsides to this approach but the risk to human health is lower. Thoughts?

Not the person you asked but you'd probably be better served by looking at ways to stick with directed energy but find ways to converge it at that point so that the energy density +/- a few feet from the target is safe. Like a lower power version of this https://youtu.be/WAI7Lu4UFi4?t=825 basically long distance frying of ants with a magnifying glass.

Sand grains suffer from a large surface area relative to their mass, so their speed would drop off very quickly. I have one of those bug-a-salt guns and they kinda suck at anything more than 10 feet (also bugs seem to be pretty resilient to that kind of damage). Obviously you could make one that is more precise but I feel like there would be a lot of new variables to deal with.

Some kind of beam steering ultrasonic setup might work as well (although probably expensive) If you can get 10-15 transducers to pop off a precisely timed 5W burst of say 60kHz sound such that they constructively interfere at the critter, you might be able to get them to disassemble in air without any moving parts on your rig.

That seems like a winning strategy: an array of ultrasonic transducers could both detect and range the bug, and then you just play back a loud impulse spike with the same phase delays as you heard. No moving parts, no misses, no calculations. If the spike is short enough, you physically can't damage anybody's ears.

Maybe you only deafen them, so they die of old age without mating.

I once priced out an array of half-inch-sized ultrasonic transducers. Seems like they were astonishingly cheap... like under $.50 each? Plus $.50 microcontrollers and a drive transistor for the spike. Maybe an FPGA running parallel convolutions?

I took a degree in engineering decades ago, but I have had this in the back my mind even longer. I haven't done anything with it, but have finally begun dinking with microcontrollers.

I would expect a sandblast to be worse to get in your eye than a flash of light. So, you would still need good large-body sensors. You would need to lead the target, another complication, and it would be hard to know how close you had got. The ones that miss would keep going and come down somewhere, although not fast. The range would be very limited because of how fast the grains would slow down -- drag goes by the area, but kinetic energy by the mass, hence volume, so smaller projectiles lose it very fast.

Great points. I was coming from the mindset of DIYing an open source solution rather than building a marketable product. I've been building a portable 50W CO2 burning system for marking outdoor items and all of the above has been from my experience with the tradeoffs of components you can buy off the shelf. If you were to design the system from the ground up there is a lot of fat you can trim and leverage the overall system design to compensate for shortcomings in individual components.

To me the largest engineering challenge is actually the identification step, where you'd need to get sufficient return to positively identify the critter. Would be interesting to see how they pull this all together.

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