Homing cycle is not reliable

Hi there,
I’m having a frustrating and mysterious problem when homing my TinyG machine. Basically sometimes it homes ok sometimes it crashes. Regardless of which axis.

For example:
– G28.2 x0. Homes x ok. I send G28.2 x0 again and this time it crashes (log of this behaviour below) so I have to reset the board
– G28.2 z0. Homes z ok. I send G28.2 z0 again, homes ok again. Repeat a few times, it does it ok. Now I send G28.2 x0, homes X ok. I send G28.2 z0 again and it crashes, reset board.
– I send G28.2 z0 x0 y0. It homes z first ok, x ok, then y crashes. Have to reset the board. Then I send G28.2 y0 and homes Y ok

I have added a large Zero backoff to limit X as I read that it looked like there was a firmware bug creating problems when the limit switch is pressed while still accelerating but that doesn’t seem to be the issue

The other firmware bug I’ve read about in which “TinyG starts to monitor the switches only after the homing sequence is fully started” also is not the whole problem, as sometimes I start from a pressed position and it does back off ok before coming back to hit it again

Here I was also trying to get some clues

My settings are (which by the way I don´t know how to send $$ via Universal Gcode Sender, had to send it via Chilipeppr):

$$
{“ej”:””}
[fb] firmware build 440.20
[fv] firmware version 0.97
[hp] hardware platform 1.00
[hv] hardware version 8.00
[id] TinyG ID 9U6538-TWK
[ja] junction acceleration 100000 mm
[ct] chordal tolerance 0.0100 mm
[sl] soft limit enable 0
[st] switch type 1 [0=NO,1=NC]
[mt] motor idle timeout 2.00 Sec
[ej] enable json mode 0 [0=text,1=JSON]
[jv] json verbosity 4 [0=silent,1=footer,2=messages,3=configs,4=linenum,5=verbose]
[js] json serialize style 1 [0=relaxed,1=strict]
[tv] text verbosity 1 [0=silent,1=verbose]
[qv] queue report verbosity 1 [0=off,1=single,2=triple]
[sv] status report verbosity 1 [0=off,1=filtered,2=verbose]
[si] status interval 250 ms
[ec] expand LF to CRLF on TX 0 [0=off,1=on]
[ee] enable echo 0 [0=off,1=on]
[ex] enable flow control 1 [0=off,1=XON/XOFF, 2=RTS/CTS]
[baud] USB baud rate 5 [1=9600,2=19200,3=38400,4=57600,5=115200,6=230400]
[net] network mode 0 [0=master]
[gpl] default gcode plane 0 [0=G17,1=G18,2=G19]
[gun] default gcode units mode 1 [0=G20,1=G21]
[gco] default gcode coord system 1 [1-6 (G54-G59)]
[gpa] default gcode path control 2 [0=G61,1=G61.1,2=G64]
[gdi] default gcode distance mode 0 [0=G90,1=G91]
[1ma] m1 map to axis 0 [0=X,1=Y,2=Z…]
[1sa] m1 step angle 1.800 deg
[1tr] m1 travel per revolution 8.0000 mm
[1mi] m1 microsteps 8 [1,2,4,8]
[1po] m1 polarity 0 [0=normal,1=reverse]
[1pm] m1 power management 2 [0=disabled,1=always on,2=in cycle,3=when moving]
[2ma] m2 map to axis 1 [0=X,1=Y,2=Z…]
[2sa] m2 step angle 1.800 deg
[2tr] m2 travel per revolution 8.0000 mm
[2mi] m2 microsteps 8 [1,2,4,8]
[2po] m2 polarity 0 [0=normal,1=reverse]
[2pm] m2 power management 2 [0=disabled,1=always on,2=in cycle,3=when moving]
[3ma] m3 map to axis 2 [0=X,1=Y,2=Z…]
[3sa] m3 step angle 1.800 deg
[3tr] m3 travel per revolution 8.0000 mm
[3mi] m3 microsteps 8 [1,2,4,8]
[3po] m3 polarity 0 [0=normal,1=reverse]
[3pm] m3 power management 2 [0=disabled,1=always on,2=in cycle,3=when moving]
[4ma] m4 map to axis 3 [0=X,1=Y,2=Z…]
[4sa] m4 step angle 1.800 deg
[4tr] m4 travel per revolution 360.0000 mm
[4mi] m4 microsteps 8 [1,2,4,8]
[4po] m4 polarity 0 [0=normal,1=reverse]
[4pm] m4 power management 2 [0=disabled,1=always on,2=in cycle,3=when moving]
[xam] x axis mode 1 [standard]
[xvm] x velocity maximum 800 mm/min
[xfr] x feedrate maximum 800 mm/min
[xtn] x travel minimum -75.000 mm
[xtm] x travel maximum 75.000 mm
[xjm] x jerk maximum 20 mm/min^3 * 1 million
[xjh] x jerk homing 100 mm/min^3 * 1 million
[xjd] x junction deviation 0.0500 mm (larger is faster)
[xsn] x switch min 0 [0=off,1=homing,2=limit,3=limit+homing]
[xsx] x switch max 1 [0=off,1=homing,2=limit,3=limit+homing]
[xsv] x search velocity 500 mm/min
[xlv] x latch velocity 100 mm/min
[xlb] x latch backoff 50.000 mm (just changed these 2 as per your suggestion)
[xzb] x zero backoff 10.000 mm
[yam] y axis mode 1 [standard]
[yvm] y velocity maximum 2000 mm/min
[yfr] y feedrate maximum 800 mm/min
[ytn] y travel minimum 0.000 mm
[ytm] y travel maximum 260.000 mm
[yjm] y jerk maximum 20 mm/min^3 * 1 million
[yjh] y jerk homing 40 mm/min^3 * 1 million
[yjd] y junction deviation 0.0500 mm (larger is faster)
[ysn] y switch min 0 [0=off,1=homing,2=limit,3=limit+homing]
[ysx] y switch max 1 [0=off,1=homing,2=limit,3=limit+homing]
[ysv] y search velocity 400 mm/min
[ylv] y latch velocity 100 mm/min
[ylb] y latch backoff 5.000 mm
[yzb] y zero backoff 0.000 mm
[zam] z axis mode 1 [standard]
[zvm] z velocity maximum 800 mm/min
[zfr] z feedrate maximum 800 mm/min
[ztn] z travel minimum 0.000 mm
[ztm] z travel maximum 75.000 mm
[zjm] z jerk maximum 20 mm/min^3 * 1 million
[zjh] z jerk homing 40 mm/min^3 * 1 million
[zjd] z junction deviation 0.0500 mm (larger is faster)
[zsn] z switch min 0 [0=off,1=homing,2=limit,3=limit+homing]
[zsx] z switch max 1 [0=off,1=homing,2=limit,3=limit+homing]
[zsv] z search velocity 200 mm/min
[zlv] z latch velocity 100 mm/min
[zlb] z latch backoff 5.000 mm
[zzb] z zero backoff 0.000 mm
[aam] a axis mode 3 [radius]
[avm] a velocity maximum 230400 deg/min
[afr] a feedrate maximum 230400 deg/min
[atn] a travel minimum -1.000 deg
[atm] a travel maximum -1.000 deg
[ajm] a jerk maximum 5760 deg/min^3 * 1 million
[ajh] a jerk homing 11520 deg/min^3 * 1 million
[ajd] a junction deviation 0.0500 deg (larger is faster)
[ara] a radius value 0.1989 deg
[asn] a switch min 1 [0=off,1=homing,2=limit,3=limit+homing]
[asx] a switch max 0 [0=off,1=homing,2=limit,3=limit+homing]
[asv] a search velocity 600 deg/min
[alv] a latch velocity 100 deg/min
[alb] a latch backoff 5.000 deg
[azb] a zero backoff 2.000 deg
[bam] b axis mode 0 [disabled]
[bvm] b velocity maximum 3600 deg/min
[bfr] b feedrate maximum 3600 deg/min
[btn] b travel minimum -1.000 deg
[btm] b travel maximum -1.000 deg
[bjm] b jerk maximum 20 deg/min^3 * 1 million
[bjd] b junction deviation 0.0500 deg (larger is faster)
[bra] b radius value 1.0000 deg
[cam] c axis mode 0 [disabled]
[cvm] c velocity maximum 3600 deg/min
[cfr] c feedrate maximum 3600 deg/min
[ctn] c travel minimum -1.000 deg
[ctm] c travel maximum -1.000 deg
[cjm] c jerk maximum 20 deg/min^3 * 1 million
[cjd] c junction deviation 0.0500 deg (larger is faster)
[cra] c radius value 1.0000 deg
[p1frq] pwm frequency 100 Hz
[p1csl] pwm cw speed lo 1000 RPM
[p1csh] pwm cw speed hi 2000 RPM
[p1cpl] pwm cw phase lo 0.125 [0..1]
[p1cph] pwm cw phase hi 0.200 [0..1]
[p1wsl] pwm ccw speed lo 1000 RPM
[p1wsh] pwm ccw speed hi 2000 RPM
[p1wpl] pwm ccw phase lo 0.125 [0..1]
[p1wph] pwm ccw phase hi 0.200 [0..1]
[p1pof] pwm phase off 0.100 [0..1]
[g54x] g54 x offset -0.000 mm
[g54y] g54 y offset 0.000 mm
[g54z] g54 z offset 0.000 mm
[g54a] g54 a offset 0.000 deg
[g54b] g54 b offset 0.000 deg
[g54c] g54 c offset 0.000 deg
[g55x] g55 x offset 75.000 mm
[g55y] g55 y offset 75.000 mm
[g55z] g55 z offset 0.000 mm
[g55a] g55 a offset 0.000 deg
[g55b] g55 b offset 0.000 deg
[g55c] g55 c offset 0.000 deg
[g56x] g56 x offset 0.000 mm
[g56y] g56 y offset 0.000 mm
[g56z] g56 z offset 0.000 mm
[g56a] g56 a offset 0.000 deg
[g56b] g56 b offset 0.000 deg
[g56c] g56 c offset 0.000 deg
[g57x] g57 x offset 0.000 mm
[g57y] g57 y offset 0.000 mm
[g57z] g57 z offset 0.000 mm
[g57a] g57 a offset 0.000 deg
[g57b] g57 b offset 0.000 deg
[g57c] g57 c offset 0.000 deg
[g58x] g58 x offset 0.000 mm
[g58y] g58 y offset 0.000 mm
[g58z] g58 z offset 0.000 mm
[g58a] g58 a offset 0.000 deg
[g58b] g58 b offset 0.000 deg
[g58c] g58 c offset 0.000 deg
[g59x] g59 x offset 0.000 mm
[g59y] g59 y offset 0.000 mm
[g59z] g59 z offset 0.000 mm
[g59a] g59 a offset 0.000 deg
[g59b] g59 b offset 0.000 deg
[g59c] g59 c offset 0.000 deg
[g92x] g92 x offset 0.000 mm
[g92y] g92 y offset 0.000 mm
[g92z] g92 z offset 0.000 mm
[g92a] g92 a offset 0.000 deg
[g92b] g92 b offset 0.000 deg
[g92c] g92 c offset 0.000 deg
[g28x] g28 x position 0.000 mm
[g28y] g28 y position 0.000 mm
[g28z] g28 z position 0.000 mm
[g28a] g28 a position 0.000 deg
[g28b] g28 b position 0.000 deg
[g28c] g28 c position 0.000 deg
[g30x] g30 x position 0.000 mm
[g30y] g30 y position 0.000 mm
[g30z] g30 z position 0.000 mm
[g30a] g30 a position 0.000 deg
[g30b] g30 b position 0.000 deg
[g30c] g30 c position 0.000 deg
tinyg [mm] ok>
{“Lbs”:0}
{“r”:{“ej”:1},”f”:[1,0,10,7782]}

Starting from the leftmost position (in my setup x is positive to left, negative to right), and pressing the limit switch, I send G28.2 x0 via UGS and I get:

>>> g28.2 x0
{“r”:{},”f”:[1,0,9,4402]}
{“sr”:{“stat”:9,”dist”:1,”coor”:0}}
{“sr”:{“posx”:-0.187,”mpox”:-0.200,”vel”:162.33}}
{“sr”:{“posx”:-1.555,”mpox”:-1.555,”vel”:472.61}}
{“sr”:{“posx”:-3.542,”mpox”:-3.583,”vel”:500.00}}
{“sr”:{“posx”:-5.580,”mpox”:-5.580,”vel”:491.20}}
{“sr”:{“posx”:-7.104,”mpox”:-7.122,”vel”:214.98}}
{“sr”:{“posx”:-7.417,”mpox”:-7.417,”vel”:1.11}}
{“sr”:{“posx”:-7.417,”mpox”:-7.417,”vel”:0.00}}
{“sr”:{“posx”:-6.505,”mpox”:-6.505,”vel”:495.49}}
{“sr”:{“posx”:-4.465,”mpox”:-4.465,”vel”:500.00}}
{“sr”:{“posx”:-2.701,”mpox”:-2.701,”vel”:189.91}}
{“sr”:{“posx”:-2.598,”mpox”:-2.598,”vel”:0.00}}
{“sr”:{“posx”:-2.898,”mpox”:-2.898,”vel”:100.00}}
{“sr”:{“posx”:-3.306,”mpox”:-3.306}}
{“sr”:{“posx”:-3.714,”mpox”:-3.714}}
{“sr”:{“posx”:-4.114,”mpox”:-4.114}}
{“sr”:{“posx”:-4.522,”mpox”:-4.522}}
{“sr”:{“posx”:-4.747,”mpox”:-4.747,”vel”:0.01}}
{“sr”:{“posx”:-5.700,”mpox”:-5.700,”vel”:497.46}}
{“sr”:{“posx”:-7.734,”mpox”:-7.734,”vel”:500.00}}
{“sr”:{“posx”:-9.726,”mpox”:-9.726}}
{“sr”:{“posx”:-11.761,”mpox”:-11.761}}
{“sr”:{“posx”:-13.795,”mpox”:-13.795,”vel”:498.77}}
{“sr”:{“posx”:-14.747,”mpox”:-14.747,”vel”:0.10}}
{“sr”:{“posx”:150.000,”mpox”:150.000,”vel”:0.00}}
{“sr”:{“posx”:0.000,”mpox”:0.000,”stat”:3,”dist”:0,”coor”:1}}

which homed it all right. Note it started with the switch pressed so it does back off to the right until it’s not pressed anymore, up to x -7.417. Note it reached seek speed of 500. Then it moves to the left, at speed 500, to press the switch, which it does at about X-2.5. Then it keeps moving to the right at speed 100 for the latch backoff distance, seems the switch opens again at x”:-4.747. Then it moves more for the zero backoff of 10, at speed 500, until it reaches x”:-14.747. SO FAR SO GOOD

Now let’s send the same command again..

>>> g28.2 x0
{“r”:{},”f”:[1,0,9,4402]}
{“sr”:{“stat”:9,”dist”:1,”coor”:0}}
{“sr”:{“posx”:0.200,”mpox”:0.200,”vel”:162.33}}
{“sr”:{“posx”:1.555,”mpox”:1.555,”vel”:472.61}}
{“sr”:{“posx”:3.583,”mpox”:3.583,”vel”:500.00}}
{“sr”:{“posx”:5.583,”mpox”:5.583}}
{“sr”:{“posx”:7.625,”mpox”:7.625}}
{“sr”:{“posx”:9.625,”mpox”:9.625}}
{“sr”:{“posx”:11.664,”mpox”:11.664,”vel”:492.70}}
{“sr”:{“posx”:13.211,”mpox”:13.211,”vel”:230.49}}
{“sr”:{“posx”:13.541,”mpox”:13.541,”vel”:1.60}}
{“sr”:{“posx”:13.542,”mpox”:13.542,”vel”:0.00}}
{“sr”:{“posx”:14.494,”mpox”:14.494,”vel”:497.46}}

Remember we were 10 mm away from the switch. It starts moving left (x positive direction) again, in 3.5 mm it looks it reached max seek velocity of 500. Around x10 it hits the switch as expected and starts decelerating until it stops momentarily at x13.542. The issue comes here, when it sets the speed to 500, when it should be 100, but worst of all it goes left again instead of right, colliding with the switch

very strange!

Thank you all