Sun Tracking Drive

This test model is the first to used full scale sun tracking.

The first thing that was done was to build the sun tracking drive system. This rotates the mirror and receives signals from the sun tracking control system in order to point the mirror towards the sun.

You can see the video of the sun tracking drive at 40 4x2ft Test Unit Sun Tracking Drive.

Mirror

In this test there were several things that needed to be tested.

1 Is the drive system strong enough to rotate the mirror to point at the setting sun?

2 Does the mirror rotate slow enough to allow small adjustments and high accuracy?

3 Does the motor hold the system in place when turned off so it stays pointed at the sun?



The first system that was attempted used a chain that followed a 2ft diameter half circle. A car windshield wiper motor and a sprocket were used to drive the chain. It was obvious that the mirror moved too quickly and that there was not enough power to rotate the mirror at steep angles.

We then built a system that used a 4ft diameter half circle guide for the chain. 1X2 wood supports were screwed into the mirror supports and a 2 inch wide 1/4 plywood track was bent over the supports. Doubling the diameter of the guide curve doubled the torque and dropped the rotation speed to half.

Mirror

A support for the windshield wiper motor was installed under the mirror on the support frame.

4x2ft test unit suntracking motor mount

The test with this system went much better but there were still some problems.

The garage door chain is much wider than some of the bicycle sprockets used so they would jump off the chain.

4x2ft test unit suntracking motor sprocket

A tension spring was added to the chain to ensure that there was always tension on the chain to keep it seated on the sprocket.

4x2ft test unit suntracking tension spring

The mirror rotated well to the high angles. The sprocket still made some noises like it was going to jump off the chain. The mirror did rotate in about 9 second which is much too fast to be accurate. The current sun tracking control system turn the motor on and then needs to shut it off before it has rotated too far. If the motor is too fast the system will have to adjust in one direction and will overshoot and then have to adjust back. The motor has a worm gear drive which is non back drivable so the motor seems to hold the mirror in position very well when it is off.



Improvements to the system.

I would like to use a 8 tooth garage door gear. The sprocket that was used in the test was a 18 tooth bicycle sprocket. The new sprocket will be wider and fit the chain better and will also have much more torque and rotate the mirror at less than half the speed. This will make the steep angles easier to achieve and will greatly improve accuracy. Also Limit switches must be installed to stop the mirror from rotating too far in either direction (see sun tracking control). 

Two extra free spinning sprocket could be installed on both sides of the drive sprocket to help it engage the chain with more teeth. For the 18 tooth sprocket only about 3 teeth were engaged with the sprocket. The free spinning sprockets could guide the chain up on both sides so the drive sprocket would engage the chain with half it's teeth.

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