# Difference between Backtracking limit angle and Rotations Limitations

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I would like to understand the difference between the backtracking limit angle given in the backtracking strategy and the rotation limitations values we enter for the tracker (Min phi and max phi). Because the backtracking limit angle values are giving higher than the maximum specified as shown below

My rotation limit is +/-60° and de backtracking limit angle is +/-68,8°. What does that mean? it will rotate more than allowed?

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• 2 weeks later...

The Rotation limitations are the mechanical constraints. You cannot overcome them of course.

The "Phi limits" is the value for which the backtracking begins to be operational (i.e. when the mutual shadings begin).

At any time, the Phi value will obviously be limited by the lower of these 2 limits. Now when the sun continues to go down, the backtracking angle will come back below 60°.

You can visualize this behavior as function of the sun's position, in the "Orientation" part, "Horiz. axis Unlimited trackers".

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• 4 months later...
The Backtracking phi limits are automatically populated in PVsyst based on pitch. So if my Phi limits are +/- 61.6 degrees for 60 to 60 degree range of motion, does it mean the tracker table will move only at 60 to 60 degrees but the backtracking calculation will be enabled always?
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• 2 weeks later...

If the Mechanical Phi limits are +/-60°, and the Backtracking limits are, say, +/-63°, then

- when the calculated Backtracking angle is between 60 and 63°, the trackers are clipped to 60°.

- when the sun continues to go down, the backtracking angle diminishes and the tracker will follow the "true" backtracking orientation below 60°.

You can observe this behaviour in the tool "Orientation > Unlimited trackers".

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• 4 years later...

To me, listing the "backtracking limit" is unnecessary and confusing, given that the actual range of motion will be smaller.  I suppose it might be useful to understand your shading....