The design is good for higher latitudes. It will track the sun when it is low in the sky. Also when it rises and sets during cold season.
That looks like a counterweight at the back. Good idea. You can make that part out of steel of course.
Questions:
* Is the base supposed to be fastened to a roof? Does it allow access for you to clear away water, leaves, debris, wasp nests, etc.
* Is the center hold-down sturdy enough so the assembly will not tip over in high winds? For similar reasons is the assembly as short as possible?
* Are the wheels large enough that they can easily roll over leaf stems, twigs, etc.?
* Do you intend for the tracker to locate the sun automatically at sunrise (east horizon)?
* Do the curved rails permit sufficient travel of the assembly, so it can turn directly toward the east and west?
* Do the motors spin slowly enough to make tiny movements as the sun moves slowly across the sky?
* Can wiring be positioned to be clear of moving parts, yet without repeated sharp bending and causing wires to break?
* Will this design be able to follow the sun as it transitions through all 4 quadrants of the sky near zenith (as it can do if you are located within 23.5 degrees of the equator).
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The up-down-left-right motion is an economical way to obtain alt-azimuth movement.
However the sun can be tracked over the entire day with just one motor. The axis of turning is around the polar axis.
Such a design would require a completely revised rack to support the solar panel.
The other motor will only need to turn on briefly every few weeks as the seasons change. It will tilt the panel higher or lower in the sky as the sun tracks a higher or lower arc in the sky.
Or the second motor can be omitted entirely, and the panel can be tilted manually at the change of seasons, four times a year (maybe as little as twice a year).