Extruder Stepper needs a lower voltage than Axis Stepper

Hey Everyone!

I've been having a really interesting time trying to get this 'Homemade' 3D Printer going. (I'm having a blast though!)

Specs:

Denford Micromill 2000 Axes assembly (24v 2A Steppers 200 step)
QU-BD Extruder (6.7v 1.2A stepper 200 step)

RAMPS 1.4 (w/ 5 Pololu Drivers)
Arduino Mega 2560
Repitier Firmware (also trying Marlin)
Repitier Host (also trying Cura)

I have finally been able to get the stepper motors on the axes to have enough torque to move by boosting the voltage to 24v input. BUT my QU-BD stepper cannot handle that high of a voltage...

Can RAMPS be programmed to control the voltage that goes to the extruder? (aka can I drop it to 12v)

Thanks in advance!

... the steper drivers controls the current, so the voltage is only interesting for higher dynamics/speeds - my mill is equipped with 2Amps@3Volts-steppers and the drivers can output 6Amps@70Volts ... with adjusting the current to around 1.8Amps my 3V-motors are happy turning without overheating or other issues

---

Viktor
--------
Aufruf zum Projekt "Müll-freie Meere" - [reprap.org] -- Deutsche Facebook-Gruppe - [www.facebook.com]

Call for the project "garbage-free seas" - [reprap.org]

VDX Wrote:
-------------------------------------------------------
> ... the steper drivers controls the current, so
> the voltage is only interesting for higher
> dynamics/speeds - my mill is equipped with
> 2Amps@3Volts-steppers and the drivers can output
> 6Amps@70Volts ... with adjusting the current to
> around 1.8Amps my 3V-motors are happy turning
> without overheating or other issues


Thanks for the quick response Viktor!

I was running the RAMPS off of 12v but it did not give the larger x, y, z steppers enough torque. So now at 24v they spin with the proper. Is it the current that is making it spin properly? Or voltage?

If you don't mind me asking, what is your input voltage to your pololu? And what is your measured voltage out on pololu drivers?

Thanks for your help

... you need at least the voltage specified for your motors - so 12V for a 24V-motor is not sufficient ... here the resistance of the coils defines the current flowing and with only 12V it's not enough to power the motors accordingly.

When you have more voltage than needed, the current sensing of the driver board will reduce the max. current to the specifeid value ... here the effective voltage for the motors will follow Ohms law ...

The max. possible voltage is defined by the driver-specs - they are mostly good for even higher voltages, but you should stay some volts below this max. settings or back-EMF from the motors can rise the voltage, so the drivers will blow ...

I'm not using Pololus -- have different comercial drivers with higher voltages for support and to the motors (35Volts, 70Volts and 325Volts), so not comparable ...

---

Viktor
--------
Aufruf zum Projekt "Müll-freie Meere" - [reprap.org] -- Deutsche Facebook-Gruppe - [www.facebook.com]

Call for the project "garbage-free seas" - [reprap.org]

So the driver automatically sends the proper voltage to the stepper motor as long as i set the amperage. OH! Current from the driver is constant and the Resistance of the motor is constant which makes the Voltage automatically set to the proper value!!!! LIGHTBULB!!! Thank you!!!!!!

Ok So now that I know the larger axis steppers are working properly based on 24v @ 1A output of the driver. (Axes stepper is rated 2A @ 24v and have a coil resistance of 3.5 ohms)

My Extruder stepper motor on the other hand is rated 1.2A @ 6v with a measured coil resistance of 5 ohms. if I put 24v into the stepper driver what would I have to adjust the driver current to? will 24v damage the stepper? or do i need to put a voltage regulator inline with the stepper to get it down to 6v?

Thanks again!

While I don't exactly understand what goes on in the background with the relationship between voltage, current, reisistance (ok Ohm's law here, but how it applies to steppers has been a mystery) I can confirm that I am running my setup successfully without a problem and without much heat.

My motors are model 42BYGHW811, which are 2.5A and 3.1 volts. I am running them at 24v; I have never measured the current, but my drivers are set between 25% and 40% (which might be high, but I am trying to push printing speeds of around 180mm/min).

To set yours up, I would simply turn the potentiometer down, and slowly increment it.

Works for me, but is a mystery why...maybe someone smarter has a simple answer

mitchese Wrote:
-------------------------------------------------------
> While I don't exactly understand what goes on in
> the background with the relationship between
> voltage, current, reisistance (ok Ohm's law here,
> but how it applies to steppers has been a mystery)
> I can confirm that I am running my setup
> successfully without a problem and without much
> heat.
>
> My motors are model 42BYGHW811, which are 2.5A and
> 3.1 volts. I am running them at 24v; I have never
> measured the current, but my drivers are set
> between 25% and 40% (which might be high, but I am
> trying to push printing speeds of around
> 180mm/min).
>
> To set yours up, I would simply turn the
> potentiometer down, and slowly increment it.
>
> Works for me, but is a mystery why...maybe someone
> smarter has a simple answer





To be honest with you Mitchese this whole project is a mystery! It's so much fun though!!! thanks for the idea!

... it's much simpler - adjust the current-trimpot for the smallest possible value (mostly CCW), then power on, try to run the motor and adjust the pot until the motor is running and then slightly more, until it's enough torque to drive the axis.

Check if the motor gets hot after some minutes on power - if not, you could rise the current slightly more if wished ... if it gets hot, then reduce the current and/or add some coolers to the motor ...

Edited 1 time(s). Last edit at 01/29/2013 02:20PM by VDX.

---

Viktor
--------
Aufruf zum Projekt "Müll-freie Meere" - [reprap.org] -- Deutsche Facebook-Gruppe - [www.facebook.com]

Call for the project "garbage-free seas" - [reprap.org]

Well that is MUCH Simpler than I thought!

Thanks Viktor!

Quote

(Axes stepper is rated 2A @ 24v and have a coil resistance of 3.5 ohms)

2A and 3.5R make a 7V motor, not 24V. Often 24V is used when showing speed torque curves assuming the motor is driven from a constant current drive.

---

[www.hydraraptor.blogspot.com]

nophead Wrote:
-------------------------------------------------------
> (Axes stepper is rated 2A @ 24v and have a coil
> resistance of 3.5 ohms)
>
> 2A and 3.5R make a 7V motor, not 24V. Often 24V is
> used when showing speed torque curves assuming the
> motor is driven from a constant current drive.


Any Chance you could translate? I'm a bit new to this and am unsure how this effects the steppers that i'm using.

Thanks

Reprap electronics use constant current drives, so the stepper motor voltage doesn't affect the current. It does affect how fast they will spin though. The higher the supply voltage is relative to the motor's rated voltage the faster the current builds up to its target value.

---

[www.hydraraptor.blogspot.com]