Trouble with Z-step amount

Hi, I've got all my axes working except for the z axis. After finding that using 3200/1.25 in my config H did not cause the z-axis to move the required amount, I plugged my numbers into a calculator (http://calculator.josefprusa.cz/), and got 6720.

When I tried to move the z-axis down 10mm again, I measured that it only moved 6.78mm, so I tried multiplying the previous amount by 10/6.78, making it roughly 9912.

At this setting the z-axis now won't allow me to move it by increments of 10mm(making a squeaky noise as I try to do so), but only in increments of 1mm. Even moving it 1mm at a time, moving it 10 times still didn't actually move it 10mm. Am I changing the number in the wrong place, or is there something I'm not taking into account?

I am running pronterface and sprinter software with a Ramps 1.4 board.

Any help would be appreciated.

What sort of machine do you have, e..g. Prusa or Mendel and what type of threaded rod?

Most motors are 200 step and ramps is at most 16x microstepping so you have 3200 steps per rev. M8 rod has a pitch of 1.25, hence 3200/1.25 = 2560. To get nearly 10000 you would need a very fine pitch screw, even with 400 step motors.

I suspect you were skipping steps before so by increasing steps per mm the motor is being stepped even faster and stalls. Try reducing the speed.

Edited 2 time(s). Last edit at 01/04/2012 11:55AM by nophead.

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[www.hydraraptor.blogspot.com]

I just got my Prusa setup with RAMPS 1.3 AND Marlin and Pront. and Im having similar issues...X and Y are moving fine but the Z sounds just like windcatcher's. I uncouple the rods(M8 1.25) an they make sounds when trying to move in 10+ increments. Seems fine when moving +/- 1mm incs.
Any help will be appreciated.

Edited 1 time(s). Last edit at 01/04/2012 03:08PM by Damian.

Hi Nophead,

The machine type is Mendal.
The pully on the z motor is 8 tooth and the one on the belt is 21 tooth.
My belt is 5mm and I am using the standard 8mm rod with 1.25 pitch.

I checked to make sure that all three jumpers were on the Ramps 1.4 board and they are.
I purchaced the board fully populated from Mixshop so I don't think it is a cold solder issue either.

I will try that later today when I get home and let you know how it turns out.

What is a good speed for the Z axis?

For Mendel it should be 200 * 16 / (1.25 * 8 / 21) = 6720.

My guess is you were trying to move too fast and losing steps.

I run my Z at 5 mm/s.

Edited 2 time(s). Last edit at 01/04/2012 07:53PM by nophead.

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[www.hydraraptor.blogspot.com]

Source: wiki

Calibration will ensure your motors are moving the correct distance each time they are told to move.

Calibrating your Z initially involves determining three values and plugging them into a formula. The result of the formula is then used in your firmware. The following takes you step-by-step on how to do this. You will likely need to look up some motor and stepper driver data sheets via google to do this (don't trust your seller's ads/info about capabilities - verify with the manufac data).

===
For your Z axis and the value you use in your firmware (e.g., "#define z_steps_per_mm") the following formula applies:



Steps = Number of motor steps per one revolution (200 for 1.8 degree, 400 for 0.9 degree motor, etc.)
Microstepping = Microstepping ratio of controller (1/8 for Gen6, 1/16 for Pololu, etc.)
Zd = Distance in millimeters between threads of Z rods (1.25mm for M8)
===

1st: determine your "steps" value by looking at the data sheet for your Z motors (if 1.8 degree use 200, if .9 degree use 400, etc.).

2nd: determine your "microstepping" ratio value by looking at the data sheet for your stepper drivers and check that your controller (e.g., Ramps 1.4, etc.) is compatible with your motor driver's best microstepping ratio (e.g., Pololu A4988 Stepper Driver data sheets says "Five selectable step modes: full, 1/2, 1/4, 1/8, and 1/16"). You can only use 1/16 if both your controller and your motor drivers support it.

3rd: determine your distance in millimeters between threads of Z rods. This is easy because the wiki tells you this value for your M8 rods is 1.25mm.

Plug the numbers into the formula and you should be set.

I agree with Nophead. The squeaking sound is probably your motors skipping due to high speeds or acceleration. I had to turn down my acceleration/speed in firmware on my Mendel's Z axis due to the same issue. Also, be sure your Z belt routing is straight and check for binding on the threaded Z rods.

I am using Marlin and I had to turn down my Z jerkiness and my Z acceleration.

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Message if there is anything you need...I have more than what is listed on my site.
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Hi Guys,

I've done everything I can as far as trying the formulas that you suggest.
As most others do not seem to have this weird Z axis problem I think I need to look elswhere.

I noticed that the top Z end stop does not light up and I think this may be causing my problem somehow.
When I unplug the Z top endstop the Z will only move one direction.

I also noticed that my extruder heats up as soon as turn on the power and seems difficult to control so I will start with the end stop and begin to check wires until I find the culprit.

Thanks for you help so far.

I will post again once I learn more.

Windcatcher

Hang in there

The following is a pretty good calibration video although it sounds like you may something more fundamental to fix before calibrating

Still Extruding: Calibrating XY&Z Step/MM
[www.youtube.com]

Edited 1 time(s). Last edit at 01/05/2012 02:59PM by thewaterengine.

@windcatcher: If you only have the MIN endstop attached and the axis only moves in one direction then you MUST:

• Invert the endstop, or
• Rewire the endstop, or
• Replace the endstop.

In any case, in 99% of the causes movement in only one direction is caused by an endstop problem.

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Bob Morrison
Wörth am Rhein, Germany
"Luke, use the source!"
BLOG - PHOTOS - Thingiverse

Hi Guys,

So after some troubleshooting I found that the upper opto endstop v2.1 on the Z axis is not working. (See attached photo)

I plugged the endstop in place of one that is working and it doesn't light up.
I thought I may have made a mistake and soldered the light in backwards or it may be a bad led so I pulled the old one off and soldered on a new light with the long leg closest to the switch but this failed to fix it. I also resoldered all of the joints in case I had a cold solder joint but no luck there either. I have some old electronics I can steal bits from so I hope if its the switch itself I can find a replacement.

Aside from the opto vertyhing else is as it should be.
I can turn the Z axis up and down easily with my fingers so I know its not a mechanical binding problem.
My Ramps 1.4 supports 1/16th stepping.
My gear ratio is 8:21
My rod is the standard 8mm with a 1.25 thread pitch
My speed is set to 6720 in the Sprinter config.h file

I will have to fix the endstop tonight and hope that this is the reason my Z axis is only moving up 6 mm when I tell it to move 10mm.

If that doesn't do it I may need a sledge hammer.

Windcatcher

@windcatcher nice machine!
I've got my XY and Z moving in the right direction...I added the jumpers to all drivers for 1/16 step like the instructions said to do , which I overlooked(duh).
Now its time to calibrate. Thanks, everyone, for the input.

Wow,

I finally reached reached my wits end.
I removed all of the Max endstops and changed my config.h file in Sprinter so it would work without them enabled to eliminate the problem with the faulty one. (I will order another later)
.
It turns out that the only way I can make my machine work is to double the 6720 that works fine for everyone else in the world except me.

My machine finally works but I am running my Z axis at 13440 and my Z motor has a maximum speed of 50.

The only thing that makes any sense is that the 3 jumpers under the Z pololu drive carrier chip on my Ramps 1.4 board are having no effect and the motor is running at 1/2 the rate it should be.

My motors are all Zapp Automation / SY42STH47-1684B
200 steps per revolution (1.8 deg/step)
Rated current: 1.68 A
Phase resistance: 1.65 ohm
Phase inductance: 2.8 mH
Holding torque: 4400 g-cm [0.43 N-m]
Shaft diameter: 5 mm
Shaft length: 22 mm
Motor depth: 47 mm

I hope this helps someone else so they don't have to go through all this trouble.

Thanks to all who provided advice.

Cheers

Quote

The only thing that makes any sense is that the 3 jumpers under the Z pololu drive carrier chip on my Ramps 1.4 board are having no effect and the motor is running at 1/2 the rate it should be.

The chips do a maximum of x16 but you are using twice as many steps, i.e. x32. The only explanation I can think of is that your motor is actually 400 stop, i.e. 0.9 degree, or your threaded is not metric M8.

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[www.hydraraptor.blogspot.com]