Clearing 5 Steps of backlash on AM5

enaiman

Isn't the irony obvious? On mounts which are advertised as "backlash free" (and they are) the ASIAIR guiding calibration routine is effectively clearing 5 steps of backlash between WE and NS calbration.
The mount is obviously moving in the new direction (you see it visually) and yet the ASIAIR is spitting those messages "Clearing Backlash 1" then "Clearing Backlash 2" ... then finally North Step 1 is at 17 distance from the starting point because the backlash was cleared for 13 when it didn't need to.
It is all clear in the log and it is happening over and over - not only on AM5 but on HEM27 (another harmonic mount) and seen it happening on my CEM40 - the AA was clearnig backlash when the mount was visibly moving.

Guys - this issue really needs to be addressed because it is screwing the calibration.

Thank you

Calibration Begins at 2022-09-13 19:39:39
Equipment Profile =
Camera = ZWO ASI174MM Mini
Exposure = 3000 ms
Pixel scale = 1.66 arc-sec/px, Binning = 2, Focal length = 1460 mm
Mount = ZWO AM5, Calibration Step = 800 ms, Assume orthogonal axes = no
Dec = -16.1 deg, Hour angle = -2.54 hr, Pier side = West, Rotator pos = N/A
Lock position = 852.609, 175.603, Star position = 851.423, 175.497, HFD = 3.24 px
Direction,Step,dx,dy,x,y,Dist
West,0,0.000,0.000,850.130,176.000,0.000
West,1,1.110,2.542,849.020,173.458,2.774
West,2,2.193,6.154,847.937,169.846,6.533
West,3,3.463,9.820,846.667,166.180,10.413
West,4,5.192,13.189,844.938,162.812,14.174
West,5,6.231,16.437,843.899,159.563,17.579
West,6,7.712,20.070,842.417,155.930,21.501
West,7,9.002,23.270,841.128,152.731,24.950
West,8,10.226,26.888,839.904,149.112,28.767
West calibration complete. Angle = 69.2 deg, Rate = 4.495 px/sec, Parity = N/A
East,4,10.226,26.888,839.904,149.112,28.767
East,3,11.317,25.108,838.813,150.892,27.541
East,2,11.807,15.188,838.323,160.812,19.238
East,1,12.519,7.619,837.611,168.382,14.655
East,0,13.199,2.321,836.931,173.679,13.401
Backlash,0,0.000,0.000,836.931,173.679,0.000
Backlash,1,1.578,-1.053,835.353,174.732,1.897
Backlash,2,5.002,-0.689,831.929,174.368,5.049
Backlash,3,9.027,-0.792,827.904,174.471,9.062
Backlash,4,13.358,-0.896,823.573,174.576,13.388
North,0,0.000,0.000,827.904,174.471,0.000
North,1,4.331,-0.104,823.573,174.576,4.332
North,2,8.507,-0.302,819.397,174.774,8.513
North,3,12.864,-0.397,815.040,174.868,12.870
North,4,17.373,-0.302,810.531,174.773,17.376
North,5,22.226,-0.511,805.678,174.982,22.231
North,6,26.481,-0.899,801.423,175.371,26.496
North calibration complete. Angle = 178.1 deg, Rate = 5.520 px/sec, Parity = N/A
South,2,26.481,-0.899,801.423,175.371,26.496
South,1,20.356,-1.398,807.548,175.869,20.404
South,0,17.679,-1.461,810.225,175.932,17.739
Calibration complete, mount = ZWO AM5.

w7ay

enaiman Direction,Step,dx,dy,x,y,Dist
West,0,0.000,0.000,850.130,176.000,0.000
West,1,1.110,2.542,849.020,173.458,2.774
West,2,2.193,6.154,847.937,169.846,6.533
West,3,3.463,9.820,846.667,166.180,10.413
West,4,5.192,13.189,844.938,162.812,14.174
West,5,6.231,16.437,843.899,159.563,17.579
West,6,7.712,20.070,842.417,155.930,21.501
West,7,9.002,23.270,841.128,152.731,24.950
West,8,10.226,26.888,839.904,149.112,28.767
West calibration complete. Angle = 69.2 deg, Rate = 4.495 px/sec, Parity = N/A
East,4,10.226,26.888,839.904,149.112,28.767
East,3,11.317,25.108,838.813,150.892,27.541
East,2,11.807,15.188,838.323,160.812,19.238
East,1,12.519,7.619,837.611,168.382,14.655
East,0,13.199,2.321,836.931,173.679,13.401

This is the truly weird part...

For my mount (RainbowAstro RST-135), ASIAIR's calibration would go West 0, West 1,, ... West N-1, West N, like yours.

However, when stepping east, it will start at N-1, then N-2, ... until 0.

It looks like you are missing East 7, East 6, East 5 completely.

Similar disparity of behavior for North and south.

The other thing is that my dx eventually settles down after the east steps to where it began in the first west step. Notice that your East steps continue to move away from where it started! Only dy settled back to where it began.

Is there any way you can check if the mount's tracking has been turned off? With a mount that has a real hand controller, we can simply watch the tracking on the hand controller. Is there a way you can check if tracking was turned off durinng calibration? (That would be a disaster.)

Chen

enaiman

Hi Chen,
I know what the weird part is (missing steps) and I do have a separate thread about it but nobody "important" answered it so I decided to split the issues (weird calibration and unneeded backlash) so for this post sake let's forget about anything but the backlash.
Please forget about anything else because I have the same behaviour even when the calibration process is normal.
I will post soon a part of another log showing the same backlash clearing with a normal calibration session.

enaiman

I haven't used again the AM5 yet but this is a part of the last PHD2 log from last night - you can see the West calibration ends at 1.298 distance from starting point and yet there are 4 Backlash steps for 11.392 before calibration starts on the next axis.
There are no missing steps (because I have not used the OAG this time) but the backlash problem is still the same.

Equipment Profile =
Camera = ZWO ASI120MM Mini
Exposure = 2000 ms
Pixel scale = 3.87 arc-sec/px, Binning = 1, Focal length = 200 mm
Mount = iOptron CEM40/GEM45 HC-FW 210101+, Calibration Step = 2000 ms, Assume orthogonal axes = no
Dec = -24.2 deg, Hour angle = 2.95 hr, Pier side = East, Rotator pos = N/A
Lock position = 1127.096, 392.295, Star position = 1126.959, 391.061, HFD = 4.49 px
Direction,Step,dx,dy,x,y,Dist
West,0,0.000,0.000,1126.888,391.437,0.000
West,1,0.697,3.354,1126.191,388.084,3.425
West,2,1.350,6.929,1125.538,384.508,7.060
West,3,2.113,10.578,1124.776,380.860,10.787
West,4,2.603,14.135,1124.285,377.303,14.372
West,5,3.235,17.652,1123.653,373.785,17.946
West,6,4.056,21.381,1122.832,370.057,21.762
West,7,4.695,25.125,1122.193,366.312,25.560
West calibration complete. Angle = 79.4 deg, Rate = 1.826 px/sec, Parity = Even
East,7,4.695,25.125,1122.193,366.312,25.560
East,6,4.145,21.551,1122.743,369.886,21.946
East,5,3.584,17.951,1123.304,373.487,18.305
East,4,2.734,14.107,1124.154,377.331,14.369
East,3,2.018,10.385,1124.870,381.052,10.579
East,2,1.486,6.713,1125.402,384.725,6.875
East,1,0.506,2.607,1126.382,388.831,2.655
East,0,-0.126,-1.292,1127.015,392.729,1.298
Backlash,0,0.000,0.000,1127.015,392.729,0.000
Backlash,1,-3.020,0.832,1130.035,391.897,3.133
Backlash,2,-6.890,0.945,1133.905,391.784,6.955
Backlash,3,-11.240,1.853,1138.255,390.876,11.392
North,0,0.000,0.000,1133.905,391.784,0.000
North,1,-4.350,0.909,1138.255,390.876,4.444
North,2,-8.120,1.391,1142.025,390.393,8.238
North,3,-11.913,2.107,1145.818,389.677,12.098
North,4,-15.782,2.866,1149.687,388.918,16.041
North,5,-19.424,3.494,1153.329,388.290,19.736
North,6,-23.496,4.335,1157.401,387.449,23.892
North,7,-27.166,5.066,1161.071,386.718,27.634
North calibration complete. Angle = -10.6 deg, Rate = 1.974 px/sec, Parity = Odd
South,7,-27.166,5.066,1161.071,386.718,27.634
South,6,-24.413,4.612,1158.318,387.172,24.845
South,5,-20.658,4.038,1154.563,387.747,21.049
South,4,-16.860,3.156,1150.765,388.629,17.153
South,3,-13.281,2.782,1147.186,389.002,13.570
South,2,-9.405,2.011,1143.310,389.773,9.618
South,1,-5.812,1.535,1139.717,390.249,6.011
South,0,-1.966,0.627,1135.871,391.158,2.063
Calibration complete, mount = iOptron CEM40/GEM45 HC-FW 210101+.

Walf@ZWO

In guiding，RA has no backlash，because RA only turns in one direction.the backlash of DEC is very small，we will check what you said