Y axis and Z axis homing the wrong way

Hi All

I have a reprappro mendel with melzi electronics

I've just finished the wiring and linked up to my computer, I have 2 issues:


1. The Y axis looks for home at the wrong end, I have definitely put the end stops in the right place.

2. The Z axis homes upward for some reason, occasionally it will look the right way but not go down far enough.


Any help would be greatly appreciated.

I have updated the firmware, I have tried to update the firmware again to correct the problem but it's not working for some reason.

Here is what it says when I connect to my printer (please excuse the emoticons, I don't know how to stop them from appearing in the post)

Connecting...
start
Printer is now online.
echo:Marlin 1.0.1 RRP
echo: Last Updated: 2013-05-16-JMG | Author: eMAKER
echo: Free Memory: 11513  PlannerBufferBytes: 1232
echotored settings retreived:
echoteps per unit:
echo:  M92 X91.429 Y91.429 Z4000.000 E707.000
echo:Maximum feedrates (mm/s):
echo:  M203 X300.000 Y300.000 Z3.000 E40.000
echo:Maximum Acceleration (mm/s2):
echo:  M201 X1000 Y1000 Z30 E1000
echo:Acceleration: S=acceleration, T=retract acceleration
echo:  M204 S1000.000 T1000.000
echo:Advanced variables: S=Min feedrate (mm/s), T=Min travel feedrate (mm/s), B=minimum segment time (ms), X=maximum xY jerk (mm/s),  Z=maximum Z jerk (mm/s), K=advance_k
echo:  M205 S0.000 T0.000 B20000 X15.000 Z0.400 E25.000
echo:  M206 X0.000 Y-8.000 Z0.000
echo:  M208 X250.000 Y210.000 Z140.000
echoID settings:
echo:   M301 P12.000 I2.200 D80.000 W125
echo:Thermistor settings: M304 Hh Bb Rr Tt, H0=Bed, H1..n=nozzle, b=thermistor beta value, r=series resistor, t=thermistor resistance as 25C
echo: M304 H0
 B3480 R4700 T10000 M304 H1
 B3960 R4700 T100000
 FPU Enabled no
transform correction not enabled
echoD init fail

In firmware invert the dir pin for those axes you want to move the other way.

Or, alternatively, at stepper driver outputs, switch the wiring on only one of the motor coils. E.g. from 4 wires, take 2 which form a coil, and switch them in place, together (to each other's place).

Thanks very much, please could explain in very simple terms how I would do this? Can I change the firmware using Gcode commands?

If you are not familiar with uploading the firmware, i assume you got everything sort of pre-installed or something like that. If you want to upload another you will need configurations like steps per mm and thermistor tables and etc, which i assume you are not very familiar with either.

Therefore its probably better to go with the hardware method and try change motor coils, thats the wires coming from the stepper drivers and going to the motors. This, and any kind of change related to motors and stepper drivers should only be done when everything is powered down, e.g. shut down. And you will need to identify the coil wiring aka pairs. And you can reverse the two wires from a coil. If direction is all the problem, it will fix it, but seems like Z axis has something more of an issue, so dunno about Z. What kind of stepper driver it is using.

It goes the right way when you give it manual instructions, it's just the homing that's at the wrong end.....

Sounds like it might be endstops. If the firmware thinks the endstop is triggered, it backs off until it stops being triggered, so it looks like it homes the wrong way. Use M119 to get endstop status.

I checked the end stop it's self, it's not pressed down and still makes a click when you press it down

M119 says

x_min:L y_min:L z_min:H

Thanks very much for helping

Just done it again, now it says x_min:L y_min:L z_min:L

The Z axis is now homing the right way, Y is still looking for it in the wrong direction

I've unplugged the Y endstop, it now says x_min:L y_min:L z_min:L

is there a list of what this means somewhere?

L means Low, H means High. You can activate the endstops yourself and see whether they're High when you trigger them or low when you trigger them. This will tell you if they need inverting in the firmware.

It says H when triggered and L when not triggered, it's still going the wrong way..... X and Z are fine with it saying L as not triggered.

How would I changed the value in the firmware?

Are you sure it is going the wrong way?

Hi bobc

I think it is going the wrong way because it bangs into the end that doesn't have the end stop but when i manually tell it to move + it moves towards the endstop (which is at the back of the machine) and when I press - it moves towards the front on the machine.

Any suggestions?

Thanks

Well, it depends on how you set up your coordinate system, but usually (0,0) is at the front left. In that case when you press + the bed should move toward the front, and - the bed should move to the back. This can be counterintuitive, but it is the position of the hotend relative to the bed that is important.

So I would suggest your manual moves are actually moving the wrong way, and swapping the motor wires will fix that, and allow homing to work.