Monday, January 06, 2014

solar tracking motor drive explained

I created this short amateur video to help explain some aspects about the motor drive that I am using for the diy gen2 solar parabolic trough heater.

The actual motor drive in this video has been in service for five years in a Canadian climate running a tracking heater for a swimming pool.

In a different use, the same motor drive served in a series of experiments done to compare performance of a concentrating trough with a flat plate collector where it was used to track both collectors. Here is the report on those experiments.

I have refined and improved the overall design through several iterations until the version published in my book. Other than some small tweaks and techniques, the motor drive shown is what I am recommending for upcoming gen2 book as reliable, inexpensive and easy to construct and maintain. If you built what I described in the book, this is how it should work for you.

There is some rust and wear to give it authenticity - it does work well. I did replace the gear motor two years ago as well as the axle nut which holds the bearings inside the arm. The bronze thread in the axle nut wore out while out riding repeatedly on the steel 1/2" threaded rod which is actually not very smooth.

In previous service this motor drive successfully swung 13 parabolic troughs following the sun over about 100 degrees of sky. It is important that the troughs be more or less mechanically balanced for the simple push pull mechanism used to be successful. A single steel rod (I used a 1/4" stainless) coupled to the end of the motor drive arm both pushes and pulls the array into position through control arms attached to the bottom of each reflector.

It is when the arm pushes the control rod that is the problem, not when it pulls. If there is too much unbalanced weight in the array, the control arm will tend to bend when it is pushed and that bending is a problem.

You can see the action on a properly set up array on a hazy day (some wandering as the sun goes behind clouds) in this video:

If you watch carefully, you will notice the vertical post which holds the motor drive moves slightly when the arm pushes the array revealing that some force is being exerted, enough to sway the post slightly. I could have done a better job with the balance and possibly have been able to move more than 13 collectors with the one motor drive but this is the largest that I have attempted.

After making this video I did brace the motor drive support post to the main array frame to give added support.

You can also watch the control arm from the other end of the array in this video:

As always, thank you for your interest in my work.

George Plhak

Other articles I have written about the motor drive:
Reliability and repair of the solar gear motor
Sources for gear motors
Further improvements to the motor drive
Motor drive mechanical 2 (early work)
Motor drive mechanical 1 (early work)

[to the gen2 intro and reading list]


frazelle09 said...

Dear George - this is frazelle09 again. We have made some changes in our design and now the rod that connects the collector and the motor angles up and down as the motor rotates the collector. i'm suspecting that this is due to the fact that we have altered the height of the collector. i'm trying to get it right again and to understand what's going on. Should the distance from the top of the motor arm to the push rod and the distance from the point where the arm on the collector to where the push rod is connected, be the same, i.e. should they form some sort of paralelogram?
i'd also like to send you the link to our photo page in Goggle Docs, if you like.
Warmest regards, fred.

George Plhak said...

Fred, I am not sure why you are writing this as a comment rather than writing to me directly at my email (in the plan book and on the web site). I have difficulty understanding your description in words, perhaps a picture of the change you have made would help me to understand. The rotation and length of the motor drive arm should exactly match the rotation of the reflector arm around the focus and it's length from the focus. If you watch the video at the beginning of this article, I think you should find the answer you are looking for. If not, please use my email and send me a picture. OK? George