Go Down

Topic: is nema 17 very weak? (Read 3008 times) previous topic - next topic

fatecasino

I just bought a nema 17 step motor:
https://www.ebay.com/itm/3D-Printer-CNC-Mill-Router-300mm-TR8x8-Lead-Screw-NEMA-17-Stepper-Motor-Prusa-ZQ/182415736146?ssPageName=STRK%3AMEBIDX%3AIT&_trksid=p2057872.m2749.l2649

I use the a4988 driver with Vmot = 12V@2A.
I just realised that I can easily stop it by almost touching it with my fingers!
How many grams can it lift vertically more or less?
Code: [Select]

int stp = 4;  //connect pin 13 to step
int dir = 2;  // connect pin 12 to dir
int a = 0;     //  gen counter
int delayTime = 10;

void setup()
{
  pinMode(stp, OUTPUT);
  pinMode(dir, OUTPUT);
}


void loop()
{
  if (a <  2000)  //sweep 200 step in dir 1
  {
    a++;
    digitalWrite(stp, HIGH);

    delay(delayTime);
    digitalWrite(stp, LOW);
    delay(delayTime);
  }
  else
  {
    digitalWrite(dir, HIGH);
    a++;
    digitalWrite(stp, HIGH);
    delay(delayTime);
    digitalWrite(stp, LOW);
    delay(delayTime);

    if (a > 4000)  //sweep 200 in dir 2
    {
      a = 0;
      digitalWrite(dir, LOW);
    }
  }
}




Is there an alternative more powerful step motor?

groundFungus

The motor is rated for 1.5A.  Have you adjusted the Vref as described on this page to provide the rated current to the motor?

jremington

#2
Nov 25, 2017, 02:29 am Last Edit: Nov 25, 2017, 02:40 am by jremington
NEMA 17 specifies the size of the motor mounting plate, nothing else.

It is absolutely essential to adjust the current limit on the driver, but the A4988 can supply only about 1.2A/winding continuously without extra cooling. You are better off with the DRV8825 driver, which can supply 1.5A/winding, without extra cooling.

SMallea

 if your motor have this big screw as it shows in your picture it make sense
because the torque of the motor at greater distance is weaker, but if your motor is without that and you can stop it with your finger u should follow the advices of adjusting the current limiter, becouse this motor can be even use in printers and some small CNC.

jremington

Quote
the torque of the motor at greater distance is weaker
No, the torque is everywhere the same in a rotating shaft (or lead screw, in this case).

Daenerys

Impressive combo motor/leadscrew thing.
Like a stepper motor f*'d a leadscrew and that is the offspring.


It should have some oomph to it.  Maybe you did not set current properly on the driver?

That is my guess, and also everyone else's.  :-)





Robin2

Two or three hours spent thinking and reading documentation solves most programming problems.

MarkT

I think you have midband-resonance, probably not helped by the undamped mechanical load of the leadscrew.
Use x8 or x16 microstepping and see if it cures it.

Undamped stepper motors are really easy to stall.  Belt-drive is great for providing damping, and leadscrews
much less so (unless a really tight fit on the nut).
[ I will NOT respond to personal messages, I WILL delete them, use the forum please ]

fatecasino

Hi people,
really thanks for your quick responses.
Well, it my first stepper application and I was not sure what's going on.
I tried all possible power configuration of the driver and I didn't get any extra power. Even at 100% of the pot, with 12V/2A power supply the power of the motor was very low. Perhaps 1.5A is not enough for this leadscrew.
Then a friend who has created an arduino CNC came over, and brought some other driver.
We connected the TB6560 (3A) instead of a4988 driver and .....voila! The stepper motor was turning strongly and quickly,  I had to apply much power  to stop it with my fingers.
I don't really know what was wrong with a4988, it could be that I didn't manage to configure it properly. Perhaps it was a faulty part. The heat sink would never get warm or something.
I wanted to ask, its tiny trimpot, how many rounds does it make? Because of the heatsink I can only turn it only ~340 degrees, almost a full circle.
I have also ordered a DRV8825 driver to see if it goes any better.
I will post back with the testing results

jremington

#9
Dec 15, 2017, 02:43 am Last Edit: Dec 15, 2017, 02:44 am by jremington
If you buy modules like motor drivers, sensors or MCUs cheap on eBay, expect failures.

MarkT

You may have blown the driver - its very important to never hot-plug the motor to a driver, securely
connect motor windings before applying power, as the motor is a very inductive load and loose connections
lead to arcing and damage.   But it could have been a knock-off - not uncommon for fake chips or production
line rejects to appear on eBay, a real curse in fact.
The A4988 is also not powerful enough for 1.5A.  The DRV8825 is just about able to handle that.
[ I will NOT respond to personal messages, I WILL delete them, use the forum please ]

MorganS

Even at 100% of the pot,
You can't adjust the pot by percent. The maximum rotation position is not the maximum current that the driver can provide. You must use the technique shown by the manufacturer, where you measure the voltage while turning the pot.

And yes, never plug or unplug any of the stepper motor wires while the driver has power. That will destroy it instantly.
"The problem is in the code you didn't post."

rpt007

You can find some information about how to adjust the current of an A4988 or DRV8825 here.
Before you ask:
Did you really read and understand How to use this forum ?
AND:
Do you have already some solution or is a part of the problem sitting in front of the screen?  :)

Go Up