Motor drive & motor selection for solar tracker
ajit.nayak87
Posts: 76
Dear all,
I am trying to build worm gear based single axis solar tracker for worm gear box. I need some guide line choosing proper worm gear & motor drive for application. These are step i explored so far.if someone not agree please requested to give idea with proper links to understand it better.
http://www.sunflowerenergyinc.com/Slewing_Drive_-_032511_-_REV.03.pdf
General equations for worm gear & motor
1)efficiency= (output Power of Worm gear/ Input Power of WormGear) = Po/PInput
2)Output power =P0=(2*pi*Output speed*output torque)/60
Output power in Kw
Output speed in rev/min
output torque in Nm
3)Input power = PInput=(2*pi*Input speed*Input torque)/60
Input power in Kw
Input speed in rev/min
Input torque in Nm
4)Net Torque= Toutput+TInput+Tholding =0
In order to drive 250Kw plant ; assume 15kw per row I have 16 rows with 1 column.
Worm gear has to Drive 16 rows with coupling with single column item
each panel weighs 20Kg ; 60 panel per row-> 60*20kg=1200Kg
Each row structural weight around = 700Kg
Net weight alone = 1900Kg per Row
so load on worm gear might be 1900*16=30400Kg
These are basic step involved here. Now i based on above thing how can i calculate the exact motor & motor drive here. Need some specific relation here.
I am trying to build worm gear based single axis solar tracker for worm gear box. I need some guide line choosing proper worm gear & motor drive for application. These are step i explored so far.if someone not agree please requested to give idea with proper links to understand it better.
http://www.sunflowerenergyinc.com/Slewing_Drive_-_032511_-_REV.03.pdf
General equations for worm gear & motor
1)efficiency= (output Power of Worm gear/ Input Power of WormGear) = Po/PInput
2)Output power =P0=(2*pi*Output speed*output torque)/60
Output power in Kw
Output speed in rev/min
output torque in Nm
3)Input power = PInput=(2*pi*Input speed*Input torque)/60
Input power in Kw
Input speed in rev/min
Input torque in Nm
4)Net Torque= Toutput+TInput+Tholding =0
In order to drive 250Kw plant ; assume 15kw per row I have 16 rows with 1 column.
Worm gear has to Drive 16 rows with coupling with single column item
each panel weighs 20Kg ; 60 panel per row-> 60*20kg=1200Kg
Each row structural weight around = 700Kg
Net weight alone = 1900Kg per Row
so load on worm gear might be 1900*16=30400Kg
These are basic step involved here. Now i based on above thing how can i calculate the exact motor & motor drive here. Need some specific relation here.
Comments
Out by a factor of 1000.
power = torque x angular-velocity
(watts) (Nm) (rad/s)
If the panels were perfectly balanced with very little friction and there wasn't any wind to worry about, you could probably move the panels with very low torque motors.
I think a very large consideration in the design is how much wind are the panels likely to experience. A combination of expected wind speed and the surface area of the panels are likely to be as important as the weight of the panels.
What about using the table from the website your pdf is from?
http://www.sunflowerenergyinc.com/Trackers.html
I think the above link should give you a rough idea of what size of motors you'll need.
The primary difference between a simple set of direct drive gears and worm gears is that the 90 degree change in direction produces more wasted energy due to friction and thrust of the gear. if you don't require a 90 degree turn, you can get more power transfered from your motor to your lever arm.
This a a mechanical engineering problem, certainly related to robotics - but not exactly electronics. So, your primary resources are mechanical engineering sites. Somebody might know a little bit here, but machinist and mechanical engineers have more experience with these things.
In order to determine how big a motor you require you either have to estimate the force required to move the solar panel from the actual plans. Or if you have already built the solar panel, then one can use a spring scale to measure the actual force requires to move it. Personally, I would prefer the use of a spring scale as you get the actual force required, not a preliminary estimate. There is less chance that you will waste money buying the wrong parts -- either too powerful or not powerful enough.
Once you have that number, you can look at your motor capacity and size a worm gear. Without such a number, we are all in the dark. Your solar panel might weight 0.5 kilogram or 500 kilograms. Obviously the size determines mass, leverage, and so on. The bigger the mass, the more though should be give to include quality bearings to reduce friction. You will have to overcome friction everytime the solar panel moves a bit.
And don't forget that wind might become a serious problem in larger panels. Either you have to shut down, or have extra power to move the panel in wind. Again, you either test under actual wind conditions, or you make an estimate from the plans. Mechanical engineers usually do both and keep revising their knowledge to perfect a design.
Doing design estimates is an acquired skill. You might start out with a textbook example, but when you actually go shopping the availability of parts, new products, and using recycled parts may all come into play.
How can make ensure i chosen right wormgear box. Since these worm gear cost more I wanted to do basic idea over it
Worm gears are very inefficient due to the high friction of the worm screw sliding across the gear teeth. This generates local heating that makes the lubricant break down much faster than standard gear boxes. This is also why ball screw worm gears are used where high reliability and efficiency are used.
They are a good choice for your application since the travel distance and speed is so small. In general I would suggest selecting a worm gear that is rated for at least 50% greater torque than that required to start the panels moving and then choosing a motor based on the worm gear input torque requirement for that.
Determine the actual force requried to move the solar panel. Everything starts with that. If that is unknown, you need to find it out. The actual match between motor and gear is never going to be perfect.
If a worm gear is too expensive -- try a direct gear drive, maybe bicycle chain drive. If new is too expensive, try used. If everything is too expensive, seek more money.
You could get a nice pair of gears and a chain salvaged from a ten speed bicycle at a junk yard. You save money by fabrication of a chain drive. If you need stronger gears and chains, there are suppliers.
In general, I simply avoid 90 degree turns in power drive. They add a big cost and waste a lot of power.
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If you really want to buy from Sunflower Energy, have their sales people check your design.
In general, I agree but I think this is one application where a worm gear is a good idea. One big advantage to worm gears is their resistance to being back driven. With a worm gear, very little power will be needed to hold the panels in place. Power should only be required when moving the panels.
In this application, a worm gear mechanism may use less power than a conventional gearbox.
Not only is it a worm-gear --- to prevent being back-driven -- it has 11 teeth engaged at all times to assure that teeth do not get stripped. And the configuration is such that the whole weight of the unit sits atop it. The unit is designed well for bad weather and easy assembly.
These guys obviously put much thought and a lot of trial and error into making an all-weather unit that was very compact and duriable. Of course, the dilemma with that is their trial and error actually represents their investment. They are not going to tell you every bit of how they engineered this. They want you to buy their package, at their price -- because they think is worth it.
So we are not going to get a simple transparent engineering school explanation from the vendor. One either has to work by relying on their reputation and recommendations, or engineer something else.
The reality is that specialized quality gearboxes are expensive.. just look at the number of machining steps, castings, casings, and forgings that goes into this.
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Granger has the roller chain sprokets that might be an alternative. Ebay may have even cheaper roller chain sprockets.
http://www.grainger.com/category/ecatalog/N-1z0drsi
https://www.applied.com/static/catalog/pdfs/allsprockets_e132_e174.pdf
But if the end-user desires to go for a ratio 1:1000, there is going to be a huge amount of torque to consider, and any backlash from a gust of wind on a large solar panel may destroy the gearing unless it is well designed for such.
It is an interesting project, but really mechanical engineering. And it is best to buy all gears from one source so they match or can be returned if they don't.