Problem of a NEMA 17 1.7A Motor in an Arduino CNC

Thread Starter

Roberto Rmz

Joined Mar 21, 2018
10
Good evening, I just finished assembling a homemade CNC. But when testing the Z axis, when pressing the Z + or Z- buttons of the GCode (version 1.0.9), the axis moves upwards and other times downwards, Noce whatever the reason for that happens, I hope and someone can help me understand this problem.

First of all use a CNC Shield applying a voltage of 19.5 V using A4988 drivers mounted on an Arduino Uno. These Drivers calibrate them in the following way to be used on NEMA 1.7 A motors:

Vref = Imax (8 * Rs)
Vref = 1.7 (8 * 0.1)
Vref = 1.36

Multiplying by 70% which is 0.7
Vref = 1.36 * 0.7
Vref = 0.952 V

After calibrating the drivers. Connect coils 1A and 2A, 1B and 2B in the driver. The configuration of parameters in the Universal Gcode Sender is as follows:

$0=10 (step pulse, usec)
$1=25 (step idle delay, msec)
$2=0 (step port invert mask:00000000)
$3=0 (dir port invert mask:00000000)
$4=0 (step enable invert, bool)
$5=0 (limit pins invert, bool)
$6=0 (probe pin invert, bool)
$10=3 (status report mask:00000011)
$11=0.010 (junction deviation, mm)
$12=0.002 (arc tolerance, mm)
$13=1 (report inches, bool)
$20=0 (soft limits, bool)
$21=0 (hard limits, bool)
$22=0 (homing cycle, bool)
$23=0 (homing dir invert mask:00000000)
$24=350.000 (homing feed, mm/min)
$25=500.000 (homing seek, mm/min)
$26=250 (homing debounce, msec)
$27=1.000 (homing pull-off, mm)
$100=25.000 (x, step/mm)
$101=25.000 (y, step/mm)
$102=25.000 (z, step/mm)
$110=1000.000 (x max rate, mm/min)
$111=1000.000 (y max rate, mm/min)
$112=1000.000 (z max rate, mm/min)
$120=500.000 (x accel, mm/sec^2)
$121=500.000 (y accel, mm/sec^2)
$122=500.000 (z accel, mm/sec^2)
$130=500.000 (x max travel, mm)
$131=500.000 (y max travel, mm)
$132=500.000 (z max travel, mm)

At $ 100, $ 101 and $ 102 I use 25 steps / mm because the NEMA 17 motor takes 200 steps to make a turn but I divide it by 8 because I use a 4 thread ACME thread, then 200/8 = 25 steps / mm.

Next I present a photo of the CNC and video on how the motor behaves every time that pulse Z +, it is observed as it moves towards both sides or sometimes as it does not move.

Noce why this problem happens and apart from the engine vibrates, I hope and someone can help me with a suggestion to this problem or if someone has already happened this.

 

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AlbertHall

Joined Jun 4, 2014
12,345
First guess: Try slowing it down (both acceleration and step speed) - start at very slow, if it works slowly properly then you can speed it up to see how fast is OK.
 

Ian Rogers

Joined Dec 12, 2012
1,136
It looks like you bought a kit off "Flebay" That looks to me like one of the interconnecting wires has been over crimped..

I bought a similar setup and made a PCB routing mill... But one of the motor drivers was gerfunckt!! If there are four drivers swap out the one that isn't being used, and check continuity over the connectors...
 
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