Author Topic: Heliostat Project  (Read 33613 times)

Davetech

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Re: Heliostat Project
« Reply #30 on: July 07, 2009, 10:59:17 PM »
"You might have just ruined my good nights sleep though because I'm going to be up all night thinking about it."

Heh... you and me both!

Your half year path representation tells me that the ramp's dimensions might have to change with the season. Unless I can figure a way to make it "seem" to change without actually changing it.  I tried to think what the effect of moving the ramp further away from the vertical axis would be, but it is late and it made my head spin. Guess I need to cut a piece of wood and try it.  Of course the ramp not only needs to be curved vertically but also curved horizontally. Got any curved boards laying around?  :-\

 
________________________________________________

Hmmm... I might have just thought of a way to use a straight board... yep, sleepless night ahead!

« Last Edit: July 07, 2009, 11:02:53 PM by Davetech »


Davetech

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Re: Heliostat Project
« Reply #31 on: July 29, 2009, 03:41:49 PM »
Well, I haven't posted here for 3 weeks because I've been busy with my cnc project.  Now it is on hold until I receive some thick copper clad board that I think (hope) will be thick enough my machine won't cut through it.

Today my eBay wireless doorbells arrived. I've already explored the electronics and found a point that jumps from zero volts to 1.3 volts when the remote button is pushed. That should save me from having to run wires from the collector box to the heliostat.  Now I can keep busy for a little while hacking the remote to be triggered by light hitting LED sensors.

I've checked and each remote will only trigger the sound module it came with, so I'll have two channel capability. I didn't see any dip switches to change the coding. But, what did I expect for $1 plus $4 shipping?  :D






Davetech

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Re: Heliostat Project
« Reply #32 on: July 30, 2009, 02:04:10 AM »
Here's a little more about the wireless doorbell. I'm kind of excited about this because it could have lots of remote control applications and was really easy to do.



Here's the transmitter and receiver opened up and bareing all on my train wreck of a worktable. The receiver/ringer part runs on two AA's. That would be 3 volts with standard batteries but I used NiMH so it was only seeing 2.4 volts... and working.  Since it will be mounted along side the heliostat control board which has the micro on it which needs 5 volts, I wanted to know if it could run at 5.  So I ran the receiver at 5 volts from the bench supply. It was quite happy. The Simpson is set to 15ma full scale. With 5 volts Vcc, the receiver draws a mere 2.5ma  :o   A regular LED draws about 20 to 30ma!  When activated, the current jumps to 5 ma for just a moment and then drops back to 2.5ma.  Clearly, a couple of alkalines would run this thing a long time. Or a small pv panel could run it.  It might have drawn a bit more current had I not disconnected the little speaker. I could have my choice of 24 melodies to listen to every time the heliostat made a correction, but I opted out on that.

As I said in the above post, I found a point in the receiver circuitry that goes high when it receives a signal from the transmitter. With 5 volts Vcc, this point goes to 2.6 volts. It will be a simple matter to run that through an 10k resistor to an input on the micro.





The transmitter runs on 12 volts. The $1 price tag included a 23A 12 volt Alkaline which came with the unit. The transmitter draws zero current on standby and here too, only a very few milliamps when the button is pressed.

Here's the transmitter hacked to be triggered by three water clear gallium phosphate (green) LED's. I have soldered their leads in series and glued them together with a gob of gorilla glue (kind of hard to make out in the picture, but that's what you are looking at). In strong light, they generate .7 volt, enough to forward bias the 2SC945 NPN transistor which then turns on the 2SD837 high gain NPN Darlington transistor. The 2SD837 is a high current device and was overkill, but it was handy and it worked.

This thing is set up so that the battery is disconnected until the button is pressed. The button presses on a micro lever switch, which connects the battery to the circuit, so it was simple to let the Darlington supply the circuit.

I was planning to make a little circuit board for the sensor components, but since it turned out to require so few parts, I just soldered their leads together and will probably mount them in a tube and pot them in resin or epoxy. I'd just gob hot glue all over them if they wern't going to be in the sun. The tube will extend out as a hood and help keep ambient light from affecting the LED's. That's the plan, anyway.

The seller claims the unit will work up to 70 meters.  With NiMH batteries in the receiver, my unit was getting about 100 feet. I think the voltage in the transmitter would have a much larger effect on range. But 100 feet is plenty for what I want (to keep from having to run wires from my solar collector hot box to my heliostat controller).

So. Now you know more than you ever wanted to know about wireless doorbells. Put your thinking cap on and I'll bet you can find a use for it in your project.




Jon

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Re: Heliostat Project
« Reply #33 on: July 30, 2009, 02:40:49 PM »
Thats looks like some good off the shelf material for wireless.  My wife got a solar powered garden light at Family Dollar today, and it switches on/off with the light level on the solar panel (some other units/types have another photo-sensor device near the panel).  That or its parts could be used for sensors, but it's not wireless.

[UPDATE Aug. 5, 09  OOPS , yes it is wireless, a laser, but it's "very narrow" coverage as compared to common radio-wave wireless  :) - I guess thats what I was thinking when I wrote this. ]

« Last Edit: August 05, 2009, 08:09:55 PM by Jon »

Gabriel

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Re: Heliostat Project
« Reply #34 on: July 30, 2009, 06:06:46 PM »
That's a really cool hack of a wireless doorbell. It makes me want to sit down and learn more about electronics so I can do that sort of thing myself.


Jon

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Re: Heliostat Project
« Reply #35 on: July 31, 2009, 12:29:05 PM »
Another option to go wireless is with a laser pointer.  From the sensors, it can "send" a signal to the heliostat that light/no light has been sensed, but it would require more "alignment" than a wireless method, and is prone to some interferences such as people or birds interrupting the light signal, etc.

I guess for any "feedback" aiming system, the light sensors will also have to sense when the Sun changes direction after the afternoon....that is, when it starts to go down or lower in the sky.   A motor will be required to change the direction of the heliostat; probably reverse the direction of the vertical adjust stepper motor.  It might take some kind of "logic gate/electronics" such as a logic chip (maby AND perhaps) or transistors to collect and then signal this condition.
« Last Edit: July 31, 2009, 01:15:58 PM by Jon »

Jon

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Re: Heliostat Project
« Reply #36 on: July 31, 2009, 09:05:07 PM »
Looks like Gabriel's mechanically ganged heliostats can illuminate multiple targets/receivers, and even possibly increase the energy per unit area of any single target/receiver if they reflect all the solar energy to that one spot.

I was also thinking of a way to increase the energy per unit area without any ganged heliostats.  Maby I'm wrong but I'll try to explain.  Given one heliostat, the right side of the mirror will effectively illuminate the right side of the receiver, and the left side of the mirror will effectively illuminate the left side of the receiver.  If the mirror is cut in half, the left side mirror can be adjusted so that its reflected light will overlap the right side light on the receiver.  Hence the illumination or energy there has doubled.   I still need to make a basic experiment of this using two mirrors on a piece of wood, when the Sun ever comes back out, and see if it is possible.

Davetech

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Re: Heliostat Project
« Reply #37 on: August 01, 2009, 04:21:27 AM »

"Another option to go wireless is with a laser pointer."

I tried that.  A couple of months ago I ordered a laser pointer for that very purpose. It puts out red light and is quite powerful. I could clearly see its spot on the trees across the highway in front of my house at night. That's over 150 feet away I'd guess. But I couldn't get any led's to produce electricity from the light. Wrong wavelength I guess. Besides, the laser spot was so small that I couldn't illuminate more than one led at a time unless the group of three was a long way off.    I also tried an infrared receiver from the front panel of a junked vcr, but no joy.  A regular tv remote control might be useful but I had the feeling it might be susceptible to stray infrared.

---

I mounted the sensor components in a tube today and took the whole bread-boarded sensor/transmitter assembly outside and set it atop my solar collector box. I adjusted a mirror to shine on and off the tube and it worked great... for a little while.   Then it quit working. To make a long story short, I finally discovered that the supplied A23 12volt battery was pretty much dead.  Now I think I know why the units were being sold so cheaply. They probably sat in a warehouse for too long (years) and the alkaline batteries bundled with them ran out of shelf life. It was easier and cheaper to just get rid of them on eBay. 

I didn't have any good A23 batteries so I just dug a 12vdc wall wart out of the junk box and will power the the thing with that for testing until I get new batteries. I think a good battery will power the thing for years and I won't have a lossy wall wart wasting electricity in the form of heat 24/7.

---

"I guess for any "feedback" aiming system, the light sensors will also have to sense when the Sun changes direction after the afternoon....that is, when it starts to go down or lower in the sky.   A motor will be required to change the direction of the heliostat; probably reverse the direction of the vertical adjust stepper motor.  It might take some kind of "logic gate/electronics" such as a logic chip (maby AND perhaps) or transistors to collect and then signal this condition."

The little actuator I've built uses a regular pm motor instead of steppers. I've got a whole box of them from scrapped vcr's. And the circuit I've designed is capable of reversing the motor direction. It probably would not be too difficult to do the basic control with some TTL logic but a picaxe micro with its software can be so versatile. In addition, it is dirt cheap. So the plan, at present, is to let a picaxe do the controlling and it can know when and where to go back to the morning position, and maybe through software I can teach it to do an occasional search if the sun is playing hide and seek. But that's further into the future than the end of my nose, so I haven't given it any deep thought.  I tend to learn by doing and I can't do that part yet.




Jon

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Re: Heliostat Project
« Reply #38 on: August 01, 2009, 09:33:36 AM »
I guess laser light would have its problems, but it can be sensed reasonably well with a light dependent resistor (LDR) - sometimes known as a photo-resistor, and maby a photocell also.  I have a vid. on my youtube channel with a laser and LDR.  Thing is also, when I used the LDR, I think there is some "grey areas" of on and off conditions when a simple transistor is used to amplify the light/electric signal received, so someday I'd like to make a voltage comparator circuit or something similar so that the condition of on or off is solid with no grey areas.    Using a microprocessor chip might also not have the problems just described due to its digital nature, rather than analog.  When I get a good burst of energy in me, I begin to make something, until then it's just a dream.


Update of using multiple mirrors:  I did a quick test using two small mirrors, one test in the house with the lightbulbs, and one test outside with the Sun.  The target was just a wall, and I did not test long enough for the Sun to make reasonable changes in its position.  I "focused" the light from each mirror onto the same spot/target, and then moved both the mirrrors a bit together and the lightbeams stayed together (but not at the same target/location for this quick experiment), but I can tell that for this system, once the mirrors are set, that the target cannot change; or at least must be the same distance away if it does,  otherwise the "light beams" won't intersect at the target/receiver.

Update: Aug 4, 09:  A short vid of this concept: 
An Understanding Of Some Heliostat Concepts





« Last Edit: August 03, 2009, 09:33:54 PM by Jon »

Davetech

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Re: Heliostat Project
« Reply #39 on: August 15, 2009, 09:58:12 PM »
My first attempt using led's as sensors used an LM339 dual comparitor and I bumped into the same problems with "grey areas".  Perhaps if the comparitor were followed by a flip-flop...   but, yes, a micro does make the whole system a lot more versatile and easier to configure.



I've gotten a little more done on my project.

Back when I saw it was going to take weeks to get the engraving bits to make my control board, I ordered a picaxe project board. I hate perf- boarding but it is better than nothing. Well, it arrived the other day and I built the controller on it and wired up the door bell receiver to it. I've installed the mechanism and the electronics in an enclosure along with a motorcycle battery and have taken it outside and attached it to my mirror assembly.

The wireless door bell receiver output goes high for about 2 seconds when it is triggered and I thought that was going to be a problem because the mirror would move too far in 2 seconds, but I found that the picaxe could easily handle the problem by just telling the motor to run for 250 milliseconds and then pause for 2000 milliseconds, then check to see if the sensor pin was still high. It works great, with the motor just bumping the mirror about a degree at a time.

Today I tried to learn something about my ramp idea. I took hourly notes on the position my mirror assembly was in to reflect on the collector box and then I cut a piece of wood in a semicircle that I thought was close to what the ramp needed to be like. I needed about six arms to hold everything in place and was having a difficult time with it. Part of the problem was the heat. I can only work a for a while in this heat and then I start feeling my pulse in my temple and my vision whites out in the center. My peripheral vision stays okay, but what I'm looking at is just a big white spot. Then I have to go inside and cool off. So I didn't get near as much done today as I had hoped.

In retrospect, building the electronics on the picaxe project board is probably a good thing because it is something "Everyman" has access to since they are available on eBay. And my goal is to present something that anyone handy with tools and who knows at least how to assemble an electronic kit would be able to build this system for themselves.

redrok

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Re: Heliostat Project
« Reply #40 on: September 14, 2009, 10:41:09 PM »

Hi Davetech;

You asked about using light sensors to track heliostats.
Here are some concepts for you to ponder:

1. There are 2 basic heliostat mounts.
   A. The "Vertical Axis" heliostat mount, Like Gabriel's.
      Alternate names are ALTitude/AZimuth or Pan and Tilt.

     The tracker for these, and others, are the "Inline"
     dual axis trackers. See:
     http://www.redrok.com/neat.htm#US4276872
     See Leo Gerst's heliostats:
     http://www.heliostat.us/
     This tracker is positioned between the mirror and
     receiver and sees the sun back through the mirror.
     It control the motors so the sun is positioned in
     the center.

     There is a problem though. There is another stable
     mirror orientation where the sun is located at the
     edge of the mirror.

    B. The "Receiver Axis" heliostat mount.
      Alternate names are Target Axis.

       This heliostat mount is a bit different. See:
      http://www.redrok.com/heliolighting.htm#receiveraxis
      The main axis, or Receiver Axis, is aimed at the
      receiver. The secondary axis is tilted from the main.

      The dual axis tracker is mounted on a mechanism that
      allows it to aim directly at the sun. The mechanism
      allows the mirror to be aimed in the half angle
      direction. In this case its made with a pair of
      gears. See:
      http://www.redrok.com/heliolighting.htm#recaxgear1
       Cables or pantographs can also do this.
       
      Here is another one:
      http://www.heliotrack.com/

      The tracker for this is not confused by alternate
      orientations as it's always aimed directly at the
      sun. The mirror is kind of dragged along.

An advantage of these types is no computing is required
for operation.

Duane
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Jon

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Re: Heliostat Project
« Reply #41 on: October 06, 2009, 11:01:05 AM »
This is about the feedback method where the light sensors are downrange near the collector/receiver.  Perhaps if the sensors are brought closer, maby a few feet away or so from the mirror, then a wireless sysem might not be needed.   It might affect the accuracy slightly, but it should still work right if it's not to hard to implement.  The light sensors still are to "side" of the reflected light to the target.  When the Sun appears to change position, the reflected light will illuminate the sensors which will turn the motors on to adjust the mirror back into position.  I guess the sensors have to be positioned exactly where needed since a degree off here could mean a foot or two off at the receiver/target.  Downrange, I believe the light from the mirror gets "fuzzy" at the edges so it could be good to have the sensors closer to the mirror.   I think it is also possible to have the light sensors in the reflected light.

One thing to remember about this "heliostat feedback system" is that it is supposed to be/in theory a non cpu/micorprocessor controlled type thing, except for some optional simple logic circuits/ic chips if needed.  Or in short/otherwords there is no timing/guidance method with this system, it simply positions itself with light sensors as things happen.
« Last Edit: November 29, 2009, 06:53:01 PM by Jon »

xqp

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Re: Heliostat Project
« Reply #42 on: November 14, 2009, 05:16:40 PM »
A regular tv remote control might [...] be susceptible to stray infrared.

They will pick up stray infra red, but it's not a problem because the handset transmits a short fast sequence of pulses (a different sequence for each button) and the receiver only reacts to those pulses. The "stray" changes in IR level are very slow so they're easy to filter out. I wouldn't expect it to work too well outside because (on a sunny day) the IR levels are going to be pretty high and the receiver will probably saturate (ie "overload").
Martin

helpmonkey

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Re: Heliostat Project
« Reply #43 on: November 18, 2009, 05:32:00 PM »
Hello Davetech ... helpmonkey from greenwatts... long time ... hope all is well ... sent you a youtube message ... this is a nice thread on heliostats ... very impressed to see Duane from Redrok post here ... I have been trying to make the canuckle into a heliostat for a long time and I have a circuit that I think can do it.. it converts the targets (sun and whatever your aiming at) into voltages and then simply devides the resultant.. I havnt made the final circuit as I am still working on making a single axis work using resistance and I sure could use some help... I will post a link to a schematic if any of you guys are interested or would have some input...

helpmonkey

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Re: Heliostat Project
« Reply #44 on: November 26, 2009, 09:39:53 AM »
here is a link to the first circuit which is a single axis solar tracker ... I think I have the circuit worked out but would welcome any comments and help to improve it. Basically the same circuit will be used for the heliostat but I want to make sure I have the basics covered.
http://www.greenwatts.info/index.php?page=cds-tracker