Motor Control

On 12/23/15 2:56 PM, Jessica Shaw wrote:
> I am using a single axis accelerometer to measure the tilt. Since,
> its single axis tracking. I am planning to only follow the elevation
> of the Sun not azimuth.
>
> So, I have Real Time clock on board and then I calculate the Sun's
> elevation for that particular day w.r.t time.  So, the motor starts
> from 40 degrees ( mechanical assembly mounted to face the Sun at 40
> degrees at Sun rise) and moves "x" ( elevation angle)  degrees every
> hour until it reaches -40 degrees.
>
> I can calculate the Sun elevation w.r.t to time but how can I map the
> Sun's elevation values into my code to control the motor.  I just
> turn ON and OFF the motor and monitor the tilt using accelerometer. I
> am not using PWM. I am just little confused about it
>

Elevation tracking will work if you are 'near equator' (up one side and 
down the other) as that is close to an equatorial mount there. (40 
degrees elevation sounds off for this though, and you will never find 
the sun at negative elevations, that's pointing downward). As you get 
more northern or southern, azimuth start to become more important (At 
the pole, you ONLY need azimuth tracking).

As Upsidedown said, an equatorial mount makes a good single axis 
operation. It won't correct for the seasonal north-south motion of the 
sun, but that is small enough, and slow enough that you might not need 
to automatically adjust for this. It does say that an accelerometer 
might not be the right sensor, as at higher latitudes you get less 
signal from it, a rotary encoder of some sort on the equatorial mount is 
more commonly used.

Having just a simple 'bang-bang' controller (on/off and direction), your 
control law will be fairly simple, If you are too far from the desired 
position turn on the motor in the needed direction, and when you get 
close, stop (don't wait for exactly equals, as you are going to overshoot).

One other issue with using an accelerometer for position measurement 
here is that while you are moving, that motion will affect the 
accelerometer reading, making it hard to decide when to stop.

Hi, 

You mentioned that as elevation tracking works if the tracker is near the equator but as we move more north or south azimuth becomes important. 

I am confused that my solar tracking is single axis and my solar panel is facing East with tilt -40 degrees measured with my accelerometer, the solar panel will travel to +40 degrees facing the Sun in the west. 

Since, its single axis tracking how can it follow azimuth angle at all. Because according to my understanding, I need dual axis motor to follow both azimuth ( north to south) and elevation ( east to west) to follow the Sun. 

In single axis system I can only do east to west and follow just elevation angle. How can I follow azimuth with single axis? 

On 12/23/2015 8:04 PM, Jessica Shaw wrote:
> Hi,
>
> You mentioned that as elevation tracking works if the tracker is near
> the equator but as we move more north or south azimuth becomes
> important.
>
> I am confused that my solar tracking is single axis and my solar
> panel is facing East with tilt -40 degrees measured with my
> accelerometer, the solar panel will travel to +40 degrees facing the
> Sun in the west.
>
> Since, its single axis tracking how can it follow azimuth angle at
> all. Because according to my understanding, I need dual axis motor to
> follow both azimuth ( north to south) and elevation ( east to west)
> to follow the Sun.
>
> In single axis system I can only do east to west and follow just
> elevation angle. How can I follow azimuth with single axis?

You confuse me a lot with your misunderstandings.  Azimuth is not a 
North/South measurement at all.  Azimuth is the horizontal component 
(along the horizon like a compass measurement, 0 to 360 degrees) and 
elevation is the vertical (up from the horizon, 0 to 90 degrees).

What some here have tried to explain is that you can use an equatorial 
mount where the axis of the movement is aligned along the line parallel 
to the axis of the earth.  Then the movement of your panel around this 
single axis will come fairly close to the path of the sun all through 
the year with some variation from season to season.

-- 

Rick

Ok. I appreciate that you are trying to teach me. But the thing is to point the solar panel towards the sun at 90 degrees requires dual axis motor.

My understanding is that with one axis control ( East to West) setup I can only do Elevation and not azimuth. I might be wrong. 

On 12/23/2015 8:43 PM, Jessica Shaw wrote:
>
> Ok. I appreciate that you are trying to teach me. But the thing is to point the solar panel towards the sun at 90 degrees requires dual axis motor.
>
> My understanding is that with one axis control ( East to West) setup I can only do Elevation and not azimuth. I might be wrong.

Read up on equatorial mounts.  No, a single axis won't follow the sun 
exactly, but on any given day the sun follows a straight line across the 
sky that you can track with a single axis.  This straight line changes a 
tiny amount from day to day.  So there will be some inaccuracy over the 
seasons, but you can either set the axis to a mid position which will 
minimize the average error... or you can provide for a periodic manual 
adjustment over the seasons... or you can use another motor to move the 
axis up and down a handful of degrees... or you can add a mechanism that 
will work from the first motor and each time it cycles through a day it 
takes a step in the right direction and reverses every 6 months.

Those are all my ideas.  But before you will understand this very well I 
think you need to learn about equatorial mounts.

-- 

Rick

I will read about equatorial mount. But would you please look at the following video. 

https://www.youtube.com/watch?v=Sgz-qbDu6sY

Its a single axis horizontal tracker. Can I say that this tracker can only do Azimuth tracking not elevation tracker? 

The following video shows vertical axis solar tracker. Can I say that this tracker can only do elevation tracking only? 
 
https://www.youtube.com/watch?v=SJ-DbQwTO-c

The trackers in the videos are not equatorial mounts. I am working with the tracker that is shown in the following video link, not exactly the same tracker but much smaller than this.  

https://www.youtube.com/watch?v=SJ-DbQwTO-c


This is not equatorial mount plus it can not follow azimuth but can only follow elevation. Am I right? 

On 12/23/2015 10:22 PM, Jessica Shaw wrote:
> I will read about equatorial mount. But would you please look at the following video.
>
> https://www.youtube.com/watch?v=Sgz-qbDu6sY
>
> Its a single axis horizontal tracker. Can I say that this tracker can only do Azimuth tracking not elevation tracker?

The axis of this unit is vertical.  The movement is azimuth.


> The following video shows vertical axis solar tracker. Can I say that this tracker can only do elevation tracking only?
>
> https://www.youtube.com/watch?v=SJ-DbQwTO-c

The axis of this unit is horizontal, most likely aligned north/south. 
The movement is elevation.

Near the equator an equatorial mount axis is horizontal like the 
elevation unit.  At other latitudes an equatorial mount axis raises up 
from horizontal according to the longitude.  The result is that as it 
sweeps the sky, it tracks pretty close to a direct line to the sun.  It 
will vary a bit over the course of the year which will be less than 
either the horizontal axis mount or the vertical axis mount.

-- 

Rick

My tracker looks like the tracker in the following video aligned east / west. 


 https://www.youtube.com/watch?v=SJ-DbQwTO-c 

It starts at 40 degrees facing east and then travels to -40 degrees facing west and then stops. 

So, it will follow only the elevation of the Sun. Because of horizontal axis it can only follow the elevation of the Sun. Am I correct?

Plus if I move it 15 degrees every hour then that would be enough to follow the Sun or is there any roam to do any fancy tracking algorithm stuff. 

Does 15 degrees every hour elevation following  will take care of all the seasons and months of the year? 

On 12/23/2015 11:28 PM, Jessica Shaw wrote:
> My tracker looks like the tracker in the following video aligned east
> / west.
>
>
> https://www.youtube.com/watch?v=SJ-DbQwTO-c

One thing I don't get in this video is that they show all the panels 
lying flat at the midpoint.  They would have better utilization of the 
panels if they were tilted out of the plane according to the latitude, 
at least it would be better during the middle of the day when the 
highest power is received and somewhat less in the early hours and late 
hours at some times of the year.


> It starts at 40 degrees facing east and then travels to -40 degrees
> facing west and then stops.

Why just 40 degrees each way?  Unless there are obstructions, there 
would be useful power available over a much wider range of motion.


> So, it will follow only the elevation of the Sun. Because of
> horizontal axis it can only follow the elevation of the Sun. Am I
> correct?

I'm not crazy about your terminology using the word "elevation".  If you 
have the elevation and azimuth of the sun, the elevation will not match 
the angle of elevation of your mechanism.  But I guess you are 
describing it correctly otherwise.


> Plus if I move it 15 degrees every hour then that would be enough to
> follow the Sun or is there any roam to do any fancy tracking
> algorithm stuff.

The sun moves over an arc of 180 degrees in an average of 12 hours which 
amounts to 15 degrees per hour.  Your device will only follow the sun 
for less than 6 hours.


> Does 15 degrees every hour elevation following  will take care of all
> the seasons and months of the year?

With significant error in pointing at all times.

-- 

Rick