Backlash Aid is an experimental tool for measuring the backlash of Crayford / Rack & Pinion focusers. It implements and interesting idea given by my friend George Novtekov.
Here is the algorithm workflow:
- Get current focuser position and measure the length of the visible focuser tube
- Move the focuser with round 1/3 of the tube length
- Go to new position and measure the length of the visible focuser tube
- Calculate how many millimeters/inches correspond to one focuser position
- Make a good number of focuser moves in both directions in order to make the backlash easier to be measured
- Measure the length of the visible focuser tube
- Calculate the backlash value and direction
Backlash aid makes the algorithm easy for execution. Follow these steps:
1. Position the focuser in 1/3 of the focuser tube length using
Gear tab and click on Position 1 Get button to save the position
2. Carefully measure the visible part of the focuser tube and enter it in Position 1 section
3. Move the focuser with 1/3 of the focuser tube length using
Gear tab and click on Position 2 Get button to save the position
4. Carefully measure the visible part of the focuser tube and enter it in Position 2 section
5. Click on Calculate to get the millimeters/inches correspond to one focuser position
6. Enter the number of steps and the number of iterations to make in order to generate backlash and click on Start to begin the moving sequence
7. Carefully measure the visible part of the focuser tube and enter it in the Current Length field
8. Click on Calculate to get the backlash value and direction.
Notes: For measuring the tube length use gauge, micrometer or fine ruler. Make the measurement without applying any force on the focuser. More precise the measurement are, more precise the backlash calculation will be. There is no need to use large number of the steps for the backlash creation, use a value that gives visible move of the focuser. Use good number of iterations - 50 or even 100 in order to generate easier to measure influence of the backlash.
Make sure that the scope/focuser is not horizontal. Also make sure that it is loaded with the usual load - camera, filter wheel and etc.
The calculated backlash can be positive (inwards) or negative (outwards), however when you use the value in the
Scope & Focuser settings tab, enter the value without sign. For example if calculated value is -1 you have to enter 1 in the outwards field.
 Position 1
Click on Get to save the current focuser position as first reference point. Measure and enter the length of the visible focuser tube.
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 Position 2
Click on Get to save the current focuser position as second reference point. Measure and enter the length of the visible focuser tube.
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 Calculate
Calculates the mm/in per one position change
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 mm/in per position
Shows the calculated mm/in per one position change.
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 Creation params
Defines how many steps to make in both inward and outward direction in order to create backlash. These moves will be repeated for the defined number of iterations.
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 Start
Starts the moving sequence.
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 Status
Shows how many iterations are executed.
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 Current Length
Measure and enter the visible tube length after the moving sequence.
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 Calculate backlash
Calculates the backlash value.
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 Backlash value
Shows the calculated backlash value.
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 Reset button
Resets all values in the Aid.
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