Far fetched Subject title?
I have this thought for a long time, let me explain.
If you use a parabolic dish to concentrate sunlight it is all good as long as the distance to the hotspot is constant and the parabolic dish is moving to adjust for the constant change of the sun´s position.
If you would use an array of small square mirrors, each mounted on a pan/tilt servo mount with 2 servos a raspberry pi could control those servos and you could concentrate the hotspot at any distance (and also the constantly changing position of the sun could be compensated by the servos, at least to some extent, for full compensation of this the whole array would have to be controlled by a heliostat mount).
There are other uses for this apart from burning random things, cooking with solar for example.
What I do not know is could the servo signal be the same for all mirrors with the pan-tilt mount rotated in the initial calibration of the mirrors with a fixed light source? If not how many servo sets of 2 could a raspberry pi control?
As I wrote, in the beginning, I have this thought for a long time, and I have a raspberry pi, servos, mirrors, tools and could do the build, but unfortunately, I do not have any programming skills.
There are a few large solar power generation facilities that use mirrors to focus sunlight on a central tower. Each mirror has to be independently controlled in order to focus.
I learned how to drive airplanes in the airport next to Solar 1. they have a sample of the pipes they pump brine through to extract energy in the visitors center. it's the size of my palm and as heavy as a car battery. it's as black as a landlords heart, and when lit up it's blinding.
you will want to start with an accurate clock. you will find that GPS is about 1 second behind real time, and it takes some fussing to get it to instrumentation standard
then you need an ephemeris to calculate the position of one particular celestial object; the sun. I chose one that predicts the next days sunrise time and location, so it can point at tomorrows sunrise immediately after sunset:
you need a Mega for the clock, and the solar tracker. both require much RAM. I am waiting on one of these:
fishthing:
Far fetched Subject title?
I have this thought for a long time, let me explain.
If you use a parabolic dish to concentrate sunlight it is all good as long as the distance to the hotspot is constant and the parabolic dish is moving to adjust for the constant change of the sun´s position.
If you would use an array of small square mirrors, each mounted on a pan/tilt servo mount with 2 servos a raspberry pi could control those servos and you could concentrate the hotspot at any distance (and also the constantly changing position of the sun could be compensated by the servos, at least to some extent, for full compensation of this the whole array would have to be controlled by a heliostat mount).
There are other uses for this apart from burning random things, cooking with solar for example.
What I do not know is could the servo signal be the same for all mirrors with the pan-tilt mount rotated in the initial calibration of the mirrors with a fixed light source? If not how many servo sets of 2 could a raspberry pi control?
As I wrote, in the beginning, I have this thought for a long time, and I have a raspberry pi, servos, mirrors, tools and could do the build, but unfortunately, I do not have any programming skills.
Thank you for any input on the topic!
If I understand correctly is that you are suggesting that initially you line up all your mirrors to point at the actual position of the Sun and that after that you want to know if the same signal can be used to control all the servos.
As the Earth rotates once every 24H it appears that the Sun moves across the Sky by 15 degrees every hour. All your servos think that they are at 0 degrees, though in fact they might be pointing in different directions, but yet it seems to me that after 1 hour the pan position of all the mirrors should be 15 degrees.
As far as tilt is concerned all the mirrors in the Death Ray will actually be quite close together. So again I would have thought that as the Sun rises and then falls in the sky the tilt signal sent to each mirror would be the same.
This is an off the cuff response and if anybody wants to shoot it down fell free, I would be interested to know where I have gone wrong.
As far as physically sending the same control signals to mutiple servos at a distance from one another that is a separate issue. You would need to say how many mirrors you would have and the distance betwene them.
aarg:
Maybe, but the enemy can destroy your mirrors before you get that close. Even a baseball bat would be an adequate defense.
But OP wants to change the focus point. In theory anything you throw at it will be evaporated before it gets close enough...
I think RPi is not very good at timing and it will have hard time to control many servos directly. But it has unlimited memory and processing speed compared to Arduino. I think you could use the RPi to do all the processing, time getting, human communicating and use Arduino for servo control. Use some cheap Arduino (or standalone ATMega). IIRC one Arduino can easily control 10 servos and communicate commands from the RPi.
Other problem will be with servo precision and resolution. AFAIK servos have some deadband about the setpoint: if they are close enough they don't move to prevent oscillation.
aarg:
Your "death ray" loses intensity in proportion to the square of the distance. Google "f stop".
Just how does sunlight reflecting off a flat mirror spread?
The sun is 98000000 miles away (about 150 million meters) and the rays are so close to parallel they might as well be. The flat mirror reflection is going to be as parallel as the mirror is flat.
How else could I use a palm sized piece of polished steel to signal people an SOS from miles away?
If the mirrors are in a ring that can be aimed at the sun then they could all tilt inward the same to meet at a desired, changeable focus.
There's a solar power plant in Arizona that uses trough reflectors (need one tilt adjustment for sun path inclination) to heat oil in pipes to heat a big reservoir and run full power generation until about 11PM -- so much for solar only works when the sun is up!
Cooking with solar... there's so many youtube videos showing variants on an insulated box with black insides and a window on front it's not funny. From India one guy used pizza boxes with plastic wrap to cook food for a school without burning any fuel. In Canada one video shows solar cooking a large roast with 10 inches of snow all around, that took hours btw.
I wouldn't mind using a trough heater to heat air in a steel stovepipe. A PC fan could push air in the cool end and an oven at the other end circulate that around the food. Something would have to let cool air in to regulate temperature.
If 1000000 people didn't use gas or electric to cook just 1 day a week, that would save noticeable resources.
I was checking the angle with vertex at sun center and ends at the north and south poles.
It is about 0.005 degrees for ends 7917 miles apart and vertex at 93 million miles.
So what angle when the ends are 10 or 100 meters apart? There's going to be more zeros.
Besides, the sun is 109 Earth diameters wide and light comes to us from the whole disk.
In practical on-Earth terms, sunlight rays are parallel.
The rays from the sun are not parallel. The sun image occupies an area, it is not a point source. So the reflected image diverges with distance. If it was a point source, yes you could play "War of the Worlds".
The apparent average angle of the Sun diameter from Earth is 0.53 degrees with by far most of the light coming from the middle of that.
At 100 feet the total spread is almost 1 foot with the outside half of that being low intensity. Since the mirror is not point wide, the wider it is the less loss there is.
For Practical Purposes the rays are parallel, especially for solar energy where the focus is not insanely remote.
For lab work with equipment made to ivory tower tolerances, mirrors cleaved salt crystal flat aimed near perfectly, no, the sun's rays are not all exactly parallel -- even the ones too close to tell apart.
What is practical for solar energy? If I lose less than 5% total then I've done a good job. Make the mirror smaller or the target wider solves that without a lot of fuss.
We can treat the Sun as a point source for most practical purposes but not for special cases.
Hello, thank you for your thoughts. And very sorry I confused the Arduino with the Raspberry Pi!
I know this would work physically I tried manually with some mirrors, the spot of the mirrors does not degrade visibly, at least not over smaller distances like 50 meters over that normal servo resolution will be an issue for sure. I am not planning on burning enemies either and if it would work for 10 meters it would be good enough for me.
So controlling all sets of servos with the signal of one set would not work, and the Arduino Mega would be able to do 10 so that would be only 5 Mirrors, I was more thinking of a 10x10 row so 100 Mirrors seems not to be possible, probably that´s why nobody built it yet. Maybe in a few years, with different hardware.
I think the microcontroller part is "simple". I think using one Arduino (or any cheap microcontroller you are able to use) per 10 servos generating the pulses and one "brain" than controls them all (either another Arduino or RPi or so) will be relatively cheap and easy compared with the servos and mirrors.
I don't see using servos. They require power all the time and a solar tracker moves slow.
Mirrors on a flat surface tilting up to reflect sunlight can't be packed tight without some shading others. The more off-center the focus and more off-overhead the sun is the worse that gets.
Op might like the GreenPowerScience videos on youtube. They're strictly low-end-science, little math DIY and do some impressive demos. I never saw solar panels kept cool by putting them in water.. in a fishtank.. and compared output to not in the fishtank.
