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

Discussion in 'CNC Mills/Routers' started by Roberto Ramírez, Apr 28, 2018.

1. ### Roberto Ramírez New Builder

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Apr 28, 2018
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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)
\$4=0 (step enable invert, bool)
\$5=0 (limit pins invert, bool)
\$6=0 (probe pin invert, bool)
\$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)
\$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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