home made dual axis solar tracker


Author Message
Tinker

Guru

Joined: 07/11/2007
Location: Australia
Posts: 1904
Posted: 02:30pm 23 Sep 2009      

  davef said   Thanks for those pictures. An impressive job! I assume it is on a polar (?) mount so that the 2nd axis is only adjusted every few weeks or so.

I was originally just going to use a single axis polar (?) mount and adjust the 2nd axis manually. However, the panels are now going to be mounted in a more inaccessible place . . . so, back to thinking about something like yours.

Have you got a picture of the inside of the 1st axis drive

Thanks,
Dave



Thanks for the compliments guys, I appreciate it.

Here is a brief description how the device works:
In the shed, below the tracker is the modified digital timer which turns a 240V relay on for 1 minute (its shortest interval) at each time slot set. The relay connects the tracker control & motors to 12V (tapped from one battery) for one minute only, no other electronics is used.

Up in the tracker pivot box is this gear arrangement:



The motor drive relays (simple H bridge) are in the little plastic box, the timing disk:



can be seen in on the back of the gearbox. I also include part of the circuit, lets see who can figure out how it works .
BTW, this picture shows the timing disk at 11:30AM and also where it is during the night.

Timing is this way: The panels spend all night horizontal. Just before 6AM 3 timing sequences turn it facing east at 45 degrees. It remains this way until 9:30AM when it starts tracking, moving by 15 degrees after each hour. By 2:30 it faces 45 degrees to the west and remains that way until 6PM, when it turns horizontal after 3 quick timing sequences.
The lot is a fully automatic, non power hungry simple electro mechanical system. Its a compromise, I know, but better than a fixed panel. I was limited by the timer to 12 timing programs and 6 hour tracking, for 60 to 60 degrees and 8 hour tracking I would need a 16 timing program timer which I have never seen in the digital variety. 8 hour tracking is doable with this design but would be the max, for me the 7 notch timing disk was complex enough.

Now to Dave's question, I originally had planned to adjust the second axis manually but the challenge to do it automatically proved irresistible once I realized that I already had the timing available.

What happens is this: Each time the panel moves by 15 degrees the second axis spindle turns by 90 degrees. So, in 24 hours this spindle does 3 complete turns which, multiplied by the pitch of the thread (0.1") equals the required setting for the next day.
Simple really, isn't it?

I really would be surprised if anybody comes up with a simpler two axis tracker that takes as little power as mine to run. I made a motor driven cam to replace the timer for accelerated testing and ran the thing for two years worth of tracking in the shed, it still takes about 3 days do do 6 months tracking with this. The unit performed flawlessly.
But to be fair, I only installed it on the weekend and there may be some bugs when it runs on the roof. One I already found which has to do with the slight backlash of the worm gear box that drives the panel support tube. Since the timing disk is also directly connected to the gearbox output shaft it can also slightly wiggle when the wind plays on the panels. If this happens at the instant the panel moves, the hour micro switch (center one) might do a false trigger and advance the an extra 15 degrees. It happened once and my cure will be to install gas struts (like a steering damper) to the panel tube. This only turns through 90 degrees so installing the struts should do the trick.
I happen to have this gearbox on hand, waiting for a use for years . I could have made my own, backlash free, worm drive - like the second axis one - had I known about this beforehand. Edited by Tinker 2009-09-25
Klaus