large deviation range in probing

Hi veryone,
I am using marlin 1.04 with kossel mini. But I can't finish the G30 A auto calbiration because the deviation range of the probe is very large. I used z probe before, now I am using FSR sensor, but the problem is more serious than before.
It has troubled me for a month. Anyone can help
Thanks

FSR's are very fickle, we spent a long time getting ours working even remotely decent on our printers. It took 2 months on our XL and 3 months on the smaller printers before we had a system of bed mounting/fsr mounting that we liked and worked.

Usually when there is an issue with something, you hear lots of complaints, but for some reason, that doesn't seem to happen much with RepRap printers. Maybe everyone builds theirs and assumes it was something they did wrong, but lots of people have trouble with probes and FSR's they just aren't talking about it much. In person, it comes up in discussion though. Magnetic rod ends and fishing line drive are the same, lots of people showing off good results, but few talking about the bad results.


Best way to find the issue is to put your bed on, and test each section of the bed with your finger, checking activation. This is easy with a Trinket setup as you can see the lights, but if you are running straight to the controller using Johann's code, you will need to keep re-running m119. You will need to keep checking and adjusting the bed until they work similar.

FSR's have a lip around the outer edge, so they need something on them, on our prototypes we used double sided tape, electrical tape, fiber washers, metal washers... I recommend some tape cut to fit inside, sometimes you need more than one layer to get the sensitivity right. You want them about as sensitive as you can, WITH the bed in place. They will work fine with your finger, but it only matters how they work with the bed.

Thank you for your reply sheepdog43.
I just stick 2 wound tapes above the sensor. Now I have changed to Johann's version. Fortunately I got good result in printing.
The following was my G29 result:
Bed x: -22.50 y: -67.50 z: -23.72 FSR: 718
Bed x: 0.00 y: -67.50 z: -23.63 FSR: 753
Bed x: 22.50 y: -67.50 z: -23.65 FSR: 686
Bed x: 45.00 y: -45.00 z: -23.67 FSR: 702
Bed x: 22.50 y: -45.00 z: -23.59 FSR: 706
Bed x: 0.00 y: -45.00 z: -23.60 FSR: 725
Bed x: -22.50 y: -45.00 z: -23.62 FSR: 730
Bed x: -45.00 y: -45.00 z: -23.64 FSR: 764
Bed x: -67.50 y: -22.50 z: -23.75 FSR: 731
Bed x: -45.00 y: -22.50 z: -23.67 FSR: 762
Bed x: -22.50 y: -22.50 z: -23.69 FSR: 671
Bed x: 0.00 y: -22.50 z: -23.61 FSR: 724
Bed x: 22.50 y: -22.50 z: -23.52 FSR: 761
Bed x: 45.00 y: -22.50 z: -23.64 FSR: 695
Bed x: 67.50 y: -22.50 z: -23.76 FSR: 696
Bed x: 67.50 y: 0.00 z: -23.67 FSR: 737
Bed x: 45.00 y: 0.00 z: -23.59 FSR: 726
Bed x: 22.50 y: 0.00 z: -23.61 FSR: 706
Bed x: 0.00 y: 0.00 z: -23.53 FSR: 746
Bed x: -22.50 y: 0.00 z: -23.64 FSR: 678
Bed x: -45.00 y: 0.00 z: -23.66 FSR: 726
Bed x: -67.50 y: 0.00 z: -23.78 FSR: 680
Bed x: -67.50 y: 22.50 z: -23.74 FSR: 749
Bed x: -45.00 y: 22.50 z: -23.76 FSR: 645
Bed x: -22.50 y: 22.50 z: -23.58 FSR: 798
Bed x: 0.00 y: 22.50 z: -23.60 FSR: 714
Bed x: 22.50 y: 22.50 z: -23.61 FSR: 683
Bed x: 45.00 y: 22.50 z: -23.53 FSR: 783
Bed x: 67.50 y: 22.50 z: -23.65 FSR: 718
Bed x: 45.00 y: 45.00 z: -23.56 FSR: 759
Bed x: 22.50 y: 45.00 z: -23.58 FSR: 731
Bed x: 0.00 y: 45.00 z: -23.70 FSR: 658
Bed x: -22.50 y: 45.00 z: -23.72 FSR: 685
Bed x: -45.00 y: 45.00 z: -23.73 FSR: 707
Bed x: -22.50 y: 67.50 z: -23.75 FSR: 701
Bed x: 0.00 y: 67.50 z: -23.67 FSR: 682
Bed x: 22.50 y: 67.50 z: -23.48 FSR: 770
-23.53 -23.65 -23.83 -23.81 -23.67 -23.72 -23.70 -23.74 -23.80
-23.72 -23.59 -23.63 -23.72 -23.63 -23.65 -23.67 -23.75 -23.86
-23.78 -23.70 -23.64 -23.62 -23.60 -23.59 -23.67 -23.75 -23.92
-23.84 -23.75 -23.67 -23.69 -23.61 -23.52 -23.64 -23.76 -23.87
-23.89 -23.78 -23.66 -23.64 -23.53 -23.61 -23.59 -23.67 -23.76
-23.73 -23.74 -23.76 -23.58 -23.60 -23.61 -23.53 -23.65 -23.76
-23.77 -23.75 -23.73 -23.72 -23.70 -23.58 -23.56 -23.55 -23.70
-23.81 -23.89 -23.83 -23.75 -23.67 -23.48 -23.57 -23.52 -23.56
-24.04 -24.03 -23.93 -23.78 -23.64 -23.39 -23.27 -23.48 -23.47

I increse the home distance to prevent the hotend dragging on the bed while G29.
I think the analog signal is better than digital signal for auto levelling.