Prusa i2 mendal printer with RAMP board

hello
i'm struggling in calibirating my pruse mendal i2 printer.
Z-axis is not working as per the command.
if i test the stepper motor of z-axis individually they are working absolutely fine for example if i give the command to right motor to move 10mm through pronterface it is moving 10 mm and also the left motor is working perfectly. if i am using them individually then are responding as per the command but as soon as i connect them together and give them command they are not moving at all but instead they keep vibrating and when i press the n-stopper button then they only move a little bit only in upper direction and if i want them to move in lower direction then it is only moving for 1mm not more then that for example if i give them command to move for 10mm the they will vibrate but not move and as soon as i press the n stop button they stop vibrating but they don't move at all.
please help.
any response will be highly appreciated.

Sounds like there is insufficient current to drive the two steppers in parallel. Have you tried increasing the current output from the stepper driver ?

does anyone know how to increase the stepper current in the z-axis when motors are connected in parallel?

you need to set your current limits on your stepper drivers.

On most they have a small variable resistor you adjust, ideally you measure the voltage and apply some maths to work out what current to set.
NB do not move this variable resistor with a metal screw driver... if you have no choice, make sure it is completely off (no power, and usb is disconnected)
Many a person has killed all their electronics by shorting something they shouldn’t while attempting this while its on.

see [reprap.org]

You could also wire your steppers in series [www.instructables.com]

Edited 1 time(s). Last edit at 02/23/2017 06:54AM by Dust.

thanks for your reply
i appreciate that.
but do you know how to make the calculations to get the proper current?

have a read of the link Dust provided though I personally I dont believe there a "proper current" it always need tweaking for individuals machine but it gets you close.
just remember to power down/off before making adjustment to the drivers

Edited 2 time(s). Last edit at 02/23/2017 08:01AM by jinx.

while checking the current at stepper driver do i have to connect the printer to laptop and electricity?

depends on driver I think which is required USB or external.
i do this
power up take a reading,then turn off and adjust.

just keep a steady hand while taking the reading. all to easy to short the pins and kill a driver.

hello I've done almost all the things to make my z-axis work but still its not working properly. I've increased the stepper current to 0.6 and its still not working good. what should i do now?

1. what is the exact type of the Steppers you are using?
2. what current are they rated?
3. what type of stepper driver do you use? eg. A4988, DRV8825,...
4. Why do you want to connect them together? - Do you have dual Extrusion? - If not you could just use the 5th Stepper Driver Position & configure Firmware accordingly.
5. If you want toconnect together, you have to take double the current!

6. Z-Axis with 2 Steppers is always a bad Idea, cause they get out of sync, and so out of Level.

how to use the 5th stepper driver position and how to configure the firmware?
thanks for the reply

I do not use the 5th Position myself, so I do not know if you have to swap the Extruder to 5th and 2nd Z to 4th Position - might depend on the Firmware too. You have to intall a stepper Driver on 5th Position.

What Firmware are you using? - You have to tell it, you are using dual Z-Axis.

Have you ever done any Firmware-Config?
Was the Printer up and running before?
Do you have the Firmware files actually loaded into the Controller? - Else it's a start from scratch - hard to do if you've never done before.
Do you really have a RAMPS on the Prusa i2? - Picture would be good.

Maybe easier way to go would be to Answer questions 1-3 from my previous post.

Quote
ashu21sol
thanks for your reply
i appreciate that.
but do you know how to make the calculations to get the proper current?

You need the ramps board powered up to measure the vref. I do this with a metal screwdriver and a steady hand. Put the negative of your voltmeter to the psu DC negative, put the screwdriver on the potentiometer, then the positive lead of your voltmeter to the screwdriver. Then turn it.

The actual current depends on the driver and the controller board. But if you can aim for 70—80% of your motors rated current. This will give you good torque and the least chance of skipping steps whilst keeping motor temperature reasonable (warm - hot to touch is okay, too hot to touch is probably too hot).

More here [reprap.org]

---

Simon Khoury

Co-founder of [www.precisionpiezo.co.uk] Accurate, repeatable, versatile Z-Probes
Published:Inventions

Quote
DjDemonD
.....


You need the ramps board powered up to measure the vref. I do this with a metal screwdriver and a steady hand. Put the negative of your voltmeter to the psu DC negative, put the screwdriver on the potentiometer, then the positive lead of your voltmeter to the screwdriver. Then turn it.

The actual current depends on the driver and the controller board. But if you can aim for 70—80% of your motors rated current. This will give you good torque and the least chance of skipping steps whilst keeping motor temperature reasonable (warm - hot to touch is okay, too hot to touch is probably too hot).

More here [reprap.org]

Yeah exactly where I want him to go. - But to tell which Vref is correct we should know the rated current of the stepper, and which stepper driver :-)

I have two z steppers paralleled up onto one stepper driver, I tried moving the second stepper motor onto the spare (5th) stepper driver and un-comment the #define Z_DUAL_STEPPER_DRIVERS line in Configuration_adv.h, however I couldn't get it to work. To be fair I didn't pursue it because I have not had any issues running both z stepper motors from the one stepper driver, I just went back to paralleling the motors.

I think I must have been lucky with the motors I bought as they all run with Vref turned down to just above minimum and the drivers all run reasonably cool with forced ventilation.(8825's)

Also not (as yet) had any issues with the Z steppers getting out of step, perhaps due to the fine pitch on the z axis leadscrews although I can see the benefit of tying to two leadscrews together mechanically and employing just one motor.....hey-ho next build!!