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Slewing always comes up short of target using stellarium


Ignacio Banuelos
 

When slewing to stars, Onstep always comes up short even if polar alignment is good..Both axis comes up short but RA more so.. depending on star position
Tracking is very good. Using TMC 2209_VQUIET.. motors do not slip and are very silent with excellent torque. using 12V at aprox 60% max amp for each motor.

Using Stellarium for slewing with ASCOM Driver via Home Wifi and using sync when aligning various stars but never gets stars on target.. I am guessing because of slewing not getting to destination.

Any Ideas why this could be happening?
Thanks

---- Config.h settings:----
RA: 189 tooth Byers gear and worm and 20T Stepper pulley with 65T at worm, 400 step motor Nema 32
DEC 180 toot gear with 16T Stepper pulley and 60T at worm, 400 step motor Nema 17

// AXIS1 RA/AZM
// see https://onstep.groups.io/g/main/wiki/6-Configuration#AXIS1
#define AXIS1_STEPS_PER_DEGREE    43680.0 //  12800, n. Number of steps per degree:  26880                                        <-Req'd
                                          //         n = (stepper_steps * micro_steps * overall_gear_reduction)/360.0
#define AXIS1_STEPS_PER_WORMROT   83200 //  12800, n. Number of steps per worm rotation (PEC Eq mode only:)                <-Req'd
                                          //         n = (AXIS1_STEPS_PER_DEGREE*360)/reduction_final_stage

#define AXIS1_DRIVER_MODEL            TMC2209_VQUIET //    OFF, (See above.) Stepper driver model.                                      <-Often
#define AXIS1_DRIVER_MICROSTEPS       64 //    OFF, n. Microstep mode when tracking.    32                                    <-Often
#define AXIS1_DRIVER_MICROSTEPS_GOTO  OFF // OFF, n. Microstep mode used during gotos.   16                                 Option
#define AXIS1_DRIVER_IHOLD            OFF //    OFF, n, (mA.) Current during standstill. OFF uses IRUN/2.0                    Option
#define AXIS1_DRIVER_IRUN             OFF //    OFF, n, (mA.) Current during tracking, appropriate for stepper/driver/etc.    Option
#define AXIS1_DRIVER_IGOTO            OFF //    OFF, n, (mA.) Current during slews. OFF uses same as IRUN.                    Option
#define AXIS1_DRIVER_REVERSE          OFF //    OFF, ON Reverses movement direction, or reverse wiring instead to correct.   <-Often
#define AXIS1_DRIVER_STATUS           OFF //    OFF, TMC_SPI, HIGH, or LOW.  Polling for driver status info/fault detection.  Option

#define AXIS1_LIMIT_UNDER_POLE        180 //    180, n. Where n=150..180 (degrees.) Max HA hour angle + or - for Eq modes.    Infreq
#define AXIS1_LIMIT_MAXAZM            360 //    360, n. Where n=180..360 (degrees.) Max Azimuth + or - for AltAzm mode only.  Infreq

// AXIS2 DEC/ALT
// see https://onstep.groups.io/g/main/wiki/6-Configuration#AXIS2
#define AXIS2_STEPS_PER_DEGREE    48000 //  12800, n. Number of steps per degree:                                          <-Req'd
                                        //         n = (stepper_steps * micro_steps * overall_gear_reduction)/360.0

#define AXIS2_DRIVER_MODEL            TMC2209_VQUIET //    OFF, (See above.) Stepper driver model.                                      <-Often
#define AXIS2_DRIVER_MICROSTEPS       64 //    OFF, n. Microstep mode when tracking.                                        <-Often
#define AXIS2_DRIVER_MICROSTEPS_GOTO  OFF //    OFF, n. Microstep mode used during gotos.                                     Option


Khalid Baheyeldin
 

On Sat, Oct 17, 2020 at 09:19 PM, Ignacio Banuelos wrote:
When slewing to stars, Onstep always comes up short even if polar alignment is good..Both axis comes up short but RA more so.. depending on star position
Tracking is very good.
How much short? A degree? Half a degree? Five degrees?

One thing that comes to mind is backlash. Do you have a lot of backlash, but did not enter it in OnStep so it compensates for it?
That may explain being short in Gotos, but tracking being good (eventually).


Ignacio Banuelos
 

I would estimate around 1 degree.. aprox. two full moon lengths or a bit less at first slew. It improves when syncing on stars but never gets accurate goto.
I do not feel  to much backlash on the worm-gear.. but for testing purposes were can I adjust it in OnStep?
I see a default 25 on TRACK_BACKLASH_RATE but have not changed it because tracking is OK.. unless there are other settings or adjustments.


Khalid Baheyeldin
 

On Sat, Oct 17, 2020 at 10:36 PM, Ignacio Banuelos wrote:
I would estimate around 1 degree.. aprox. two full moon lengths or a bit less at first slew. It improves when syncing on stars but never gets accurate goto.
What if you do a 3 star align? Do the Gotos get fairly accurate?

I do not feel  to much backlash on the worm-gear..
Not only the worm gears. There are motors too, and whatever connects the motor to the worm gear.
Pulleys will have less backlash than if GR1 are spur gears.

but for testing purposes were can I adjust it in OnStep?
I see a default 25 on TRACK_BACKLASH_RATE but have not changed it because tracking is OK.. unless there are other settings or adjustments.

Don't change that, or anything else in Config.h.

The backlash can be adjusted from the Android App or the Smart Hand Controller.

But before adjusting, run a test to see if you have a lot of backlash or not.

In daylight, enable Tracking, then stop tracking.
Slew to a far away terrestrial object (tower, chimney, street light).
Then press N to center the object. Then press S.
Do the same with E and W.
Check if there is a lag between when you press the button, and when the object actually moves.


Ignacio Banuelos
 

I'll do some testing as you mention and get back to you on results..

I appreciate your insight and prompt response..


Keep up you excellent work!
IB


Khalid Baheyeldin
 

If you are using pulleys, it is very unlikely that your backlash will be
as high as you are seeing (1 degree).

Fortunately, testing for backlash is easy, and tuning it is not hard
(just needs time).

Let us know the results of your testing.