Author Topic: Heliostat Design(s) [Work in Progress]  (Read 17648 times)

Bob101

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Re: Heliostat Design(s) [Work in Progress]
« Reply #15 on: December 12, 2012, 05:10:09 PM »
That's really interesting Paul L.

I came across Jeremy Blum's tutorials earlier and found them very useful but I had no idea he was working on anything like this!

Their design is very similar to mine actually. I notice that they are using an accelerometer to determine the angle of the panel, something I had considere. However, my machine actually uses the hall sensors in the motors and knowledge of the gearing system to determine the panel's angle.

Love their use of a carjack. It's brilliant in its simplicity.


Gabriel

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Re: Heliostat Design(s) [Work in Progress]
« Reply #16 on: January 08, 2013, 08:00:17 PM »
Hey Everybody,

It's been quiet on the forums lately, so I figured that I would do a quick post of a new heliostat design that I have been considering.

If you look closely in the attached pictures, you'll notice that this design moves differently than most others that you see.
Using this Wikipedia link as reference, you'll see that instead of having "pitch" and "yaw" like normal (where pitch = altitude and yaw = azimuth) this design has pitch and "roll."

This changes the math in the program some, but I think I already have it figured out. I actually didn't realize this when the idea first popped into my head, and it wasn't until I started experimenting with it in CAD that I realized that the Sun Tracking / Heliostat Program wouldn't work without modification.

Anyway, some of the reasons that I like this design are because it seems to be relatively easy to make, the structure for the mirrors is built into it the machine, and you can focus them if needed, and it seems like it would be sturdy.

That is one issue that I have with the first design I posted. It seems like it would be hard to build a strong one with basic materials, tools, and skills.


I've already attempted to make the gear boxes for this machine, but after a lot of effort still didn't turn out with something that I liked. It's obviously going to take some practice to make these things. :)


Paul L

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Re: Heliostat Design(s) [Work in Progress]
« Reply #17 on: January 09, 2013, 11:59:13 PM »
Happy New Years Everyone!!

    I'm still thinking about heliostat design too.  I've been interested in tensegritys for awhile and have often thought that it would be great to combine both heliostats and tensegritys.  I was delighted to find someone else, Kevin Varner, had the same idea in 1982.  I came across his patent here

http://www.google.com/patents?id=0SI2AAAAEBAJ&printsec=abstract&zoom=4#v=onepage&q&f=false

Since I couldn't make heads of tails of it, other than the fact that it is lightweight and cheap, I tried to contact him.  After a little e-stalking, couldn't find his email, but I did find his brothers', who I asked to forward my email.  Hopefully he'll be in contact soon, and maybe could offer some insights on how to build a light, rigid support system....

 

 

Gabriel

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Re: Heliostat Design(s) [Work in Progress]
« Reply #18 on: January 10, 2013, 05:48:18 PM »
Hi Paul,

I have always been interested in tensegrity type structures, but had never considered them for a heliostat design before. The patent link definitely looks confusing. I can't say that I really understand it myself, but I think that it uses the same axes of rotation as the heliostat design that I just posted.

If you're able to put this together, then kudos to you. :)


Paul L

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Re: Heliostat Design(s) [Work in Progress]
« Reply #19 on: January 18, 2013, 04:10:39 PM »
So I went over the tensegrity patent and thought I might throw a miniature version together just to see if I had the basic priciple down.  I've uploaded a short video below.  Eventually, if this were to work, I might consider flipping the whole thing on its edge; instant heliostat totem!  It would take up less space in the yard too.  The setup I have in the video looks complicated, but in actuality, was pretty easy to put together and took roughly 40 min.   
 
I'm having trouble though with the azimuth tracking - I haven't put anything together yet because from what I can tell just by looking at drawings, the patent design just wouldn't work.  The "Bail", which I've circled in the picture, moves along a wire, supposedly adjusting the mirrors azimuth.  Am I crazy, or would this work?  In any case, I'd rather use a different mode of getting the mirrors to move along their azimuth axis, but as to how, I'm not sure.  If anyone has any ideas don't be shy about sharing.  Otherwise, I'll be dustbining this setup.

I am one of the lucky few that has one of Gabriel's SunHarvester shields, along with three driver power boards, and have just finished soldering on all the screw terminals yesterday.  I've hooked everything up and it's all working very nicely, though I've run out of wire to hook up my last pair of stepper motors.  Nonetheless, I've got four motors running - enough for two heliostats, and I can't say enough about how I am impressed with the whole affair.  Especially the joystick control and the ability to switch between target groups.  And the button to set the time precisely is an excellent addition as well.  Setup is fairly straightforward too (though I did have to go and watch his demonstration video again to figure out how to enable joystick control) .  If anyone is thinking about ordering a SunHarvester Shield, do it.

Tensegrity Heliostat
« Last Edit: January 18, 2013, 04:13:59 PM by Paul L »


Gabriel

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Re: Heliostat Design(s) [Work in Progress]
« Reply #20 on: January 18, 2013, 05:51:19 PM »
I'm impressed that you did that in 40 minutes. It definitely would have taken me a lot longer.


I'm having trouble though with the azimuth tracking - I haven't put anything together yet because from what I can tell just by looking at drawings, the patent design just wouldn't work.


That's actually what I was referring to in my previous post. It's not rotating along the azimuth, so if you try to use the current Arduino Sun Harvester Program, V097_e, it won't have any hope at all of tracking correctly.

I think I have the math for it figured out though, and it wouldn't be hard to try it out.

If anybody is interested in trying it,

Go to the "functions" tab and find the function named "FindHeliostatAltAndAz".


Inside the function, find this code
Code: [Select]
  machinealt=to_deg(asin(z/dist));
  machineaz=to_deg(atan2(y*-1,x));

and replace it with this code.

Code: [Select]
  x=x/dist;
  y=y/dist;
  z=z/dist;
 
  float tempx=x;
  x=y*-1;
  y=tempx;
 
  machinealt =  90 + (-atan2(y,z)*(180/pi));//actually pitch
  machineaz = asin(x)*(180/pi);//actually roll

That should, I think, make the program work with "pitch and roll" type heliostats.

Keep in mind that this is just a quick hack of the program, so a lot of things will be mislabeled since they shouldn't really be called "azimuth" or "altitude" any more.


The first heliostat I ever built was a "pitch and roll" type heliostat. I was absolutely clueless of that fact though until I just recently started experimenting with different heliostat designs.

I built both of these heliostats, and neither one worked. I double checked everything in what was then a PC based program, but I couldn't figure out what was wrong.
http://www.cerebralmeltdown.com/projects/heliostat_num1/default.htm
http://www.cerebralmeltdown.com/heliostatprojects/heliostat_num2/default.htm

Then I built this heliostat, and it magically started working.
http://www.cerebralmeltdown.com/heliostatprojects/heliostat_num3/default.htm

All of these years, and I finally realized what was wrong!

Now that I look at the design, it doesn't look half bad. The Pros are that the weight is equally balanced, so you wouldn't need very large stepper motors, and that you essentially have an "unlimited" range of motion. The Cons are that you have to figure out new dimensions for different sized mirrors and also that it would be a little trickier to set up correctly since you have to deal with two "posts" to hold it in place.






Now that those Sun Harvester Shields are in the hands of a little more than half a dozen people, hopefully we'll start seeing more and more designs popping up.

Paul L

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Re: Heliostat Design(s) [Work in Progress]
« Reply #21 on: January 18, 2013, 09:28:54 PM »
And now time for something completely different...

I was trying to think of ways to get my azimuth rotation for the previously mentioned tensegrity setup when I realized that I could use hydraulics.  Then I though, well, why use gears at all for any setup?  Hydraulics kinda make sense - I haven't done any comparison pricewise, but tubing might cost less than all the wiring we'd need to run power to each of the steppers on each of the machines.  Additionally, the steppers and circuitry could be kept in inside, protected from the elements.   Check out these videos to get an idea of where I'm going with this...

DIY Syringe Pump Fix


Engineering Project - Syringe Accurate Hydraulic Crane


and finally, this beauty:   http://iaus.com/StudioFiles/AniHydro/AniHydro.html

« Last Edit: January 18, 2013, 09:33:26 PM by Paul L »

Jim McMillan

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Re: Heliostat Design(s) [Work in Progress]
« Reply #22 on: January 19, 2013, 12:13:15 AM »
Cool stuff. I wonder what kind of precision one could get by using a hydraulic ram driven by a stepper motor connected to a positive displacement pump...

dlaing

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Re: Heliostat Design(s) [Work in Progress]
« Reply #23 on: January 24, 2013, 01:16:04 PM »
Could you equate the "pitch and roll" type heliostat to an equatorial telescope mount? If so, the pitch stepper motor (similar to declination) would only need to make a few steps each day, compensating for orbital motion.

Would a "pitch and roll" heliostat then be able to use less power? The pitch motor could be turned off for large amounts of time between steps, assuming the heliostat is self-locking. But the roll motor is probably making more steps, so it might even out.

It might even be possible to build a heliostat with only one stepper motor. If you went out every day to fix the pitch manually, or every few days, if you have a large target.

Gabriel

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Re: Heliostat Design(s) [Work in Progress]
« Reply #24 on: January 25, 2013, 10:51:53 AM »
Hi dlaing, and welcome to the forums!

I'm not very familiar with equatorial type telescope mounts, so I'm not sure if they are the same or not.

The "single axis heliostat" is an idea that I've heard mentioned in various places around the net. I've always been skeptical of it though because despite all the talk I've never seen anybody build one.

I have, out of necessity really, written a simulator that graphs the angles required of these heliostats to reflect the light at the required target. At some point, I really need to clean up the code and upload it so that everyone can experiment with it, but that's for another time.

Anyway, after some experimentation, it looks like for this to work you would not only have to change the pitch manually but also you would have to use a different target altitude every day too to compensate for the sun's declination.

It seems that in order for the pitch to require essentially zero adjustment over the course of one day, you would also need to adjust the target's altitude according to this formula.
targetalt = 90 - latitude - sun's declination
The azimuth would also have to be zero, or at least close to it.
Considering that the sun's declination fluctuates by roughly 47 degrees over the course of the year, the target would have to be moved  quite a bit every day, depending on how far it is from the heliostat of course.

So I guess you could technically make it work in certain circumstances. I guess it just doesn't work quite like most people expect though, which is probably why you don't ever really see them.

Strictly speaking though, the amount of power required to run a heliostat is extremely tiny compared to the amount of power you get back out of it. I'm currently experimenting with a kilowatt meter to get a rough idea of how much a heliostat might use. Hopefully I'll have something posted soon.

dlaing

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Re: Heliostat Design(s) [Work in Progress]
« Reply #25 on: January 27, 2013, 10:45:15 AM »
Thanks for running the numbers for this. I'm not surprised it doesn't work, like you said someone would likely have built one already.

The simulator would be very interesting to see.  Is it a standalone program, or one written in matlab?

If we could quantify the power usage of the two heliostat types, then we might as well choose the more efficient geometry.

Gabriel

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Re: Heliostat Design(s) [Work in Progress]
« Reply #26 on: January 27, 2013, 02:32:38 PM »
The program is written in MatLab. I think it is simple enough though that it would run in something like FreeMat or Octave which anybody can use. Mostly the script is just a mess right now, which is why I haven't gotten around to uploading it yet. I'll try and hurry up and clean it up though since it would be useful for everyone to have.

The geometry technically wouldn't change the efficiency. The mirror normal vector still points the same direction in both cases, it just travels a different "path" to get there. Although I suppose certain geometries are prone to shade parts of the mirror during certain times of the day just because of how their structures must be built.

dlaing

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Re: Heliostat Design(s) [Work in Progress]
« Reply #27 on: January 28, 2013, 09:16:26 AM »
I did a little more research and there appears to be a working single axis heliostat.
http://www.solare-bruecke.org/English/scheffler_e-Dateien/scheffler_e.htm
They appear to have the primary axis of rotation on the line between the heliostat and the target and the target azimuth is at 0. Does that mean the trick that the mirror cannot be in line with the primary axis of rotation? And it appears that the two axes aren't orthogonal. If you have time to run another simulation, I would be interested in the results.

I was refering to electrical efficiency, not solar efficiency, but I didn't say so explicitly. Sorry for the confusion.
« Last Edit: January 28, 2013, 11:01:29 PM by dlaing »

Gabriel

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Re: Heliostat Design(s) [Work in Progress]
« Reply #28 on: January 30, 2013, 02:04:32 PM »
Oh, this design actually makes a little more sense. I guess this is more in line with what you originally mentioned. From what I've read at least, you do have to use a target azimuth of zero, but I believe that you can use any target altitude that you want. You would have have to change the tilt of the mirror frequently though. In the document you gave, they referred instead to changing the shape of the parabola.

Incidentally, this type of machine is often called a coelostat.

The simulation I wrote wouldn't work with this since it is a slightly different design from the other heliostats I have experimented with. I'm sure that it would work though.


I did some testing with my Kilowatt Meter, and found that my heliostat circuit would use about 0.03KWH per day. Just to make sure that I would over estimate instead of underestimate, my example day was the longest of the year, summer solstice.
I'm sure that I could get the power usage significantly lower by using a faster speed and acceleration too. There are other variables that could be tweaked too. For example, changing the design of the machine so that it is well balanced and doesn't required much power from the stepper motors to move it would help. Adding a simple light sensor so that the machine only moves on sunny days would also help.

Anyway, 0.03KWH per day is 10.95KWH per year. Assuming a price of 10 cents per KWH, it would cost about $1.10 to run this heliostat for an entire year. This is like I said just a rough estimate, and I think I could get it down a lot lower than that even.

trevarthan

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Re: Heliostat Design(s) [Work in Progress]
« Reply #29 on: April 02, 2013, 08:54:51 AM »
You guys seem to be suffering from the same problem I have: lack of a MakerBot or similar 3d printer.