Author Topic: Solar latitude zenith crossing inducing operational hemisphere reversal.  (Read 7770 times)

tradewinds

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I haven't seen this topic discussed about the tracking program, if it has been, I apologize.
My array will be located at Latitude 19.539879, between the tropic of Cancer and the equator. Thus the array will experience a solar latitude zenith between May 18th and May 19th and need to mechanically track inversely as if it were moved into the Southern hemisphere. Between July 26th and 27th the solar latitude zenith will occur once again and the tracking would resume back to Northern hemisphere operating conditions.
Does this software program automatically accommodate latitude zenith crossings and reverse the stepper motor commands to accommodate the necessary operating direction reversals? Nearly 20% of the year, my array will need to track Northerly.
Thanks,
 Mike 
« Last Edit: December 14, 2013, 01:43:09 AM by tradewinds »


tradewinds

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I just ordered one of the Sun Harvesters and a wind protection switch, seems you're out of limit switches.
Which of the currently available Arduino boards would be recommend for use with the sun tracker setup? I'm looking at buying a few of them accompanied by a few other accessories for other projects such as an automated hydroponics system, etc. Seems there's several things I can use these micro-controllers for.


Gabriel

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Hi Mike,

I'm not sure if I understand the first question right, but it sounds like your machine will have to tilt back further in the altitude direction to compensate for the fact that your machine probably isn't able to move far enough along the azimuth to point at the sun during certain months. Is that the right idea?
"Out of the box", the program won't calculate altitude angles past 90 degrees from the horizon, but I don't think that it would be very difficult to change that if needed. It would be a good problem to address because I can see how that would be a problem for people closer to the equator. Do you know what the physical movement restrictions are for your machine? It might be possible to have the program automatically figure out the best way to orient the machine based on those values.

For the best Arduino question, the quick answer is that either the Arduino Uno or the Arduino Mega 2560 would be best. Or at least, those are the two that I have tested.
The in depth info for this question is at this link. http://www.cerebralmeltdown.com/sun-harvester-shield-documentation/

I didn't realize that I was so low on limit switches. I'll have to order more. For a machine as large as yours though, you may consider using something more robust anyway. The ones that I've been selling are mainly for smallish machines.
If I can find a couple of extra limits around, I'll throw them in the package.

Thanks for the order!
« Last Edit: December 15, 2013, 10:31:02 AM by Gabriel »

tradewinds

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Hello Gabriel,
       My machine isn't yet complete but will have around 144 degrees vertical/elevation articulation from pointing 18 degrees above the southern horizon to pointing straight up (90 degrees) and backwards down to 18 degrees above the northern horizon. It's vertical pointing limitations are only set by the frame restrictions. Unfortunately, the slewing drive can rotate it into self destruction without limit switches. ::)

      It's east west restrictions are only defined by how many times the internal wiring can be rotated before twisting apart. If the leads where brushes on a rotating contact plate, it could rotate east/west and around again indefinitely : 8) .

      So yes, my question was whether or not the program was capable of inverting the stepper motor functions when our latitudes  solar zenith had been crossed. I believe we've about 20% of the year when the sun is to our north when at latitude +19. From what you've expressed, it isn't yet capable of the scenario. Sounds like some added programming maybe necessary? Perhaps I should call it a "latitudinal equinoctial" crossing or "latitudinal equinox"? Thus far I haven t found the "accepted term" for this event unless its one the previously mentioned. I like "latitudinal equinox" but I see there's also a "Subsolar point".

      For others to understand - If a tracking machine were at the equator; half the year it would be pointing north and the other half the year it points southerly... that sort of thing. Within the tropics (between the tropic of Cancer (latitude +23.5) and Capricorn (latitude -23.5)) solar tracking machines will need to point beyond straight up to backwards and at least straight up for a couple minutes a year if right on one of the two tropic latitudes. So the closer your machine is to the equator within the tropics (Capricorn and Cancer) the closer you get to having to track half the year north and other half south equally. So when the sun crosses your latitude (not longitude) it means your east west controller needs to reverse its motion as well as your elevation controller, otherwise the machine will track opposite and be ineffective.     
« Last Edit: December 18, 2013, 01:48:09 AM by tradewinds »

tradewinds

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Hello again Gabriel,
      No rush on the switches for me, I'm close to the ocean and will need to rustle up something that's sealed. This is a very corrosive environment I live in... but it's warm all year round so the trade off is worth it for me. I've just finished fabricating the tubing steel truss's for the array platform and have them on the axle for alignment and unification as a single platform/rack. I'm still a couple weeks away from completing the base support frame and such and also need to add and cast concrete counter balances. I'm currently in the process of selecting compatible steppers for the slewing drives. The smallest of the slewing drives will require above 4.5 NM torque which puts them in the Nema 34 class stepper motors. I'm also facing an oddball 12mm keyslot hollow input shaft on that slewing drive, so it looks like a trip over to my local machinist to shave down the shaft that arrives in the stepper I select.  Unfortunately I don't think your motor controllers will have the power to drive the steppers I need so I'm having to hunt them down also. Lot's more online shopping ahead.
BTW... Thank-you for your help on this subject.
~Mike
« Last Edit: December 17, 2013, 11:59:22 PM by tradewinds »


Gabriel

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Hi Mike,

"Sounds like some added programming maybe necessary? " Yeah most likely. Of course, if you did go with brushes on a rotating contact plate then you wouldn't need to change anything in the program, although you probably wouldn't get the most efficient travel paths on the machine. I don't think the reprogramming would be very difficult. I can take a look at it when you get to that point.

I did throw a couple of extra used limit switches in the package. You can at least use them to do some bench testing.

The machine that is closest to yours in size is Sid's. You might be able to use the same Driver Boards that he did.
http://www.cerebralmeltdown.com/2011/07/19/sids-solar-panel-sun-tracking-machine/

Gabriel

tradewinds

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Hello Gabriel,
      I guess it's good timing for me on this purchase.
      I found a Holiday sale on a particular combination purchase, though one of the motors is a wee more torque than is necessary, but I took  the plunge and ordered and will have a couple of the following stepper drivers http://www.wantmotor.com/ProductsView.asp?id=256&pid=82. I also ended up with their Nema 42 steppers rated at 30Nm that were part of the sale - model 110BYGH201-001 http://www.wantmotor.com/ProductsView.asp?id=174&pid=80. Plus a breakout board that I'd assume is not necessary for this application? I'll have to have a shaft milled down for my elevation slewing drive and probably buy one of the 110BYGH150-001 23Nm steppers for that purpose. That will leave me with a spare 110BYGH201-001 stepper. This system should be capable of fast motion for the evening park and wind positioning if nothing else.
      I'll upload some pictures of the build after I get a little further along.

     

Paul L

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Hey tradewinds,

    I'm thinking about splurging and treating myself to a dual axis slewing drive for Christmas.  Just out of curiosity, where did you get yours from and for how much?  I'm thinking about ordering from china (roughly $200 for their smallest 3" model), but then there's all the hastle in figuring out how to get it over here to Canada.  At the end of the day, it looks like shipping will be more than the drive itself, which is a little disappointing.  Suggestions?

Cheers,

Paul

tradewinds

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Aloha Paul,
      I purchased my PVE3 slewing drive directly through H-Fang. Yes, shipping is expensive but for me it's even more expensive (the shipping cost exceeded the cost of the slewing drive). The last one shipped from China to mainland USA over near the East coast for customs and then all the way back West - across the mainland and then down here to Hawaii. No direct deliveries to Hawaii from out of country due to stupid customs regulations. 
    Yours would be more direct. I spoke with Andy for my order. "Andy" <chuanhui@h-fang.com.cn>. I would contact H-Fang directly and avoid Aliexpress/etc. if possible. I'm sure Andy can give you a quote with shipping and the detailed information about the particular drive you're looking at. Sounds like you're after the SDE3 model.  Here's a link to that slewing drive line on their website. http://www.h-fang.com.cn/product.aspx?Cateid=13 ALSO: You may want to discuss input shaft types and mounting matches to the stepper motors you'll use. They can put in modified screws to accept your drive shaft etc. The 3" slewing drives need around 20Nm input torque which puts them in the Nema 42 class stepper motors. 
     
Aloha,
 Mike
« Last Edit: December 26, 2013, 04:19:20 PM by tradewinds »

tradewinds

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Hello Gabriel,
      I'm not familiar with the sun harvesters signal output polarity values etc and the stepper driver cards inputs from your store are not exactly the same as the inputs on the stepper drives I have for my motors.
      Attached are the input values for my stepper drivers and I'm curious as to the proper wiring between them and the Sun Harvester Shield. I'd rather not mix-up the connections.
Here's the stepper driver .pdf if needed... I had to open it up to get the manufacturer information so I could find the .pdf file on it.
http://www.bsjd.com/Uploadfiles/jishu/2011080311393215779.pdf
ALSO: I'm going to make a slip ring (because the type I need is not available off the shelf) so the final azimuth function will be 360+ (unlimited).   
Thanks,
 Mike
« Last Edit: December 26, 2013, 08:30:21 PM by tradewinds »

Paul L

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Re: Solar latitude zenith crossing inducing operational hemisphere reversal.
« Reply #10 on: December 26, 2013, 05:24:42 PM »
Thanks tradewinds!

   Yes, that's the model I've been looking at, and I have been in contact with "Andy" at H-fang.  I wanted to stick with NEMA 23 motors since they're cheaper and I already have a bunch, but it looks like I'll have to get some additional reduction planetary gearboxes to get more torque out of them to run the slewing drives.  H-fang will provide them, but it bumps up the price to just under $700  - a number my wife finds unacceptable  - and I haven't even told her about shipping yet!  ::)  I may have to put this idea on hold for awhile....

tradewinds

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Re: Solar latitude zenith crossing inducing operational hemisphere reversal.
« Reply #11 on: December 26, 2013, 07:30:58 PM »
Aloha Paul,
      I had nothing here in the line of steppers and looked into smaller steppers with planetary gearboxes and the cost was a wash for me so I went NEMA 42 but found a few excellent deals with shipping. I actually ended up with 4 new NEMA 42 steppers (2 smaller ones I ordered separately for the price of 1 and shipping). I ended up with 3 drivers (they sent an extra driver for some unknown reason) all of it was $800 and some change. Another driver will cost me another $150 (to complete a set for another build) but I have a suspicion I can get one cheaper through the manufacturer. The 3 drivers I received had some of the print wiped off them with acetone I suspect. Out of curiosity I opened one up to see if I could find what they were trying to hide at Wantai and found the manufacturers website address stamped on the PCB which is what I suspect they wiped off with acetone from the exterior cases. http://www.bsjd.com/en/products.asp They appear to be geared to sell direct to the public.
Wantai, Longs and Leadshine etc all appear to use the same manufacturer.

       
 
« Last Edit: December 26, 2013, 07:36:31 PM by tradewinds »

Gabriel

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Re: Solar latitude zenith crossing inducing operational hemisphere reversal.
« Reply #12 on: December 27, 2013, 08:49:37 PM »
Hi Mike,

To answer your earlier question, it looks like PU, DR, and (I think) MF are the inputs that you are interested in. It seems that all of the ones marked "-" are supposed to go to GND on the shield.
PU+ goes to STEP.
DR+ goes to DIR.
MF+ goes to En (or at least I'm assuming that "Motor Free" means that this pin turns of the motors)
I would assume that the breakout board you mentioned earlier would make it easier to make this connections.

I've also been looking at different slip ring ideas for making my own. The way my heliostat design is set up, a slip ring will probably be the easiest way to keep that altitude limit switch wires from getting tangled.

Hope that helps,
Gabriel

tradewinds

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Re: Solar latitude zenith crossing inducing operational hemisphere reversal.
« Reply #13 on: December 28, 2013, 07:55:23 PM »
Aloha Gabriel,
       Slip rings... After doing substantial research on the topic and considering the application and its physical parameter usages I came to the conclusion that the use of sealed or shielded bearings is more than likely the best route. They offer several advantages, one being that they offer brushless operation and the other is the simplification of the build. To make them more effective and to reduce the demand of conductivity through the rollers (balls, needle/rods) , removal of the shield or seal should be carefully preformed and extraction of the factory grease is in order. After cleaning out the factory grease repacking them with highly conductive lubricant and replacing the seal/shield. The build is fairly easy to explain textually. Use of 2 nonconductive cylinders, One cylinder allowing the OD of the bearing to fit within the ID of the cylinder and the other cylinder OD allowing the ID of the bearing to slip around it. By drilling holes and tapping them through the larger cylinder in three opposing locations around the bearings desired position allows for clamping of the bearing within the desired fixed location of the outer cylinder. The all-thread or bolt provided to clamp the bearings within also provide for the fixed external terminal locations. To install the inner connectors there are a few differing ways to accomplish that. One is to put hole through the inner cylinder at each bearing location and to place a stripped wire end through the inside of the hole and sliding the bearing over it, effectively making contact (use of a conductive grease is a good idea between the pinched wire and the inner bearing surface. Another way is to use all-thread or nut and bolt opposite to that of the exterior clamping method and this obviously requires a large bearing so that the work can preformed within the inner cylinder. Obviously an insulator is placed between each bearing. Simple and effective. Here's a similar slip ring build - http://stephanschulz.ca/sts/howto/slipring.html

 I've already ordered bearing that are 100mm OD that will slide nicely into a 4" schedule 40 PVC pipe and the ID of the bearings 55mm that will slide loosely around a 1.5" schedule 40 PVC pipe. Cheap price for the bearings too... $9 each. Strike that, they just went on sale $8.10 each now. http://www.ebay.com/itm/150403597128?ssPageName=STRK:MEWNX:IT&_trksid=p3984.m1497.l2648   

The driver wiring... so the sun harvester shield board signals through its Positive polarity. That's what I needed to know. Negative signaling really looked odd to me on the driver images and I've never seen it indicated that way in my former electronics days. But one never knows for certain until the question is answered. ;)  Thanks

Aloha,
Mike
« Last Edit: December 28, 2013, 09:40:47 PM by tradewinds »

tradewinds

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Re: Solar latitude zenith crossing inducing operational hemisphere reversal.
« Reply #14 on: December 29, 2013, 05:39:40 PM »
BTW... I am aware that a bearing is not a good choice for most common applications of a slip ring. But for a solar tracker application, the bearing is subjected to a near dead rest state at all times. Therefore any noise upon the channels would be intermittent and negligible at most assuming they could even be measured. If the bearing is packed with conductive grease, it's effectiveness should be staller offering a great deal of amp capacity. Electric track powered vehicles (mining cars) use their loaded wheel bearings as slip rings in the same method for conducting electricity to their motors.