Initial and Sensorless Homing Parameter Selection - AlistairSymonds/SympleAstroFocus GitHub Wiki

In addition to the standard reverse, set zero and set max commands commonly seen in astronomy focussers, the SympleAstroFocus also has a number of parameters that can be tuned to allow it work more optimally or with a wider range of motors, focussers and imaging trains.

saf_config

Standard Controls

(Red)

  • Set current position as zero: Resets the current position to be zero

  • Reverse direction: changes which direction of the motor will count up or down. Will also flip the movements to match.

  • Halt: stop the current motor move

  • Move: Trigger the motor to move to the value in set position

  • Update Max: use value next to button as new maximum step count

Generally these should be set such that 0 is with the focusser fully retracted, with larger numbers corresponding to a more extended imagining train and therefore path length to sensor.

Config options

(Green)

Moving Current: (1 - 32)

This controls the scaling of the motor current when performing moves. 32 corresponds to the full current as determined by your combination of sense resistors and vref, whilst 1 is 1/32 of that full current.

  • Lower this value to reduce movement power consumption and thermal load on motor
  • Raise if the motor is not moving smoothly when doing a move

Holding Current: (1 - 32)

This controls the scaling of the motor current when stopped. 32 corresponds to the full current as determined by your combination of sense resistors and vref, whilst 1 is 1/32 of that full current.

  • Lower this value to reduce standby power consumption and thermal load on motor
  • Raise if the motor is slipping when not moving

Motor Speed: (1x - 4x)

Controls the speed at which step pulses are issued for all moves. Speed of 1x rate chosen arbitrarily due to the variation in steppers/gears/focussers that could be connected to output.

  • Lower if concerned about impact of imaging train crash at speed or gears in system not rated for higher speeds
  • Raise if impatient for your autofocus runs to complete 🙂

Autohoming setup

(Blue)

After setting the motor parameters, the next step is tuning autohoming if desired. If the above parameters are changed you will likely have to update the stall threshold as well.

  1. Perform a decent move that covers at least 25% of the full range of motion in the focusser. Take note of the rough range of SG_RESULT values under debug info, this value can be thought of as the amount of spare capacity the driver has - as it drops its closer to a stall. Note on geared systems the values of SG_RESULT might be quite varied due to the difficulty of the motor in reading the load. In these cases you may be unable to use sensorless homing

  2. Select the homing directions you want to be enabled - it will respect the "reversed" setting same as regular moves.

  3. Press trigger homing, and hopefully watch your focusser smoothly move through its range of travel and find the ends as demo'd here: https://www.youtube.com/watch?v=gBrDgyxgXSc

  4. Generally for repeatability its best to only "Home towards zero" now the max step value has been accurately determined. This is because the process of finding the stall at max may not be perfectly repeatable based on your stall detection settings. With that home one more time and enjoy your repeatable positioning.