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Author Topic: Unable to move accurately on X axis.  (Read 877 times)

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tjd

• 4
Unable to move accurately on X axis.
« on: October 16, 2020, 02:03:10 PM »
In short, if I enter a value for 'counts per unit', I can get it move 1 inch accurately
but not for longer distances (9") and V.S.

Initial X motor settings:

counts per unit:  25850.3034  <- generated using Mach StepsPerUnitCalculator to calculate steps per 1 inch distance
velocity (units/minute): 200
acceleration (units/(sec^2)): 24.18

for 1 inch distance. result is 1" +/- .001" - repeatable
for 9 inch distance, result is ~9.25" <- ** BAD ** - repeatable

changed counts per unit to:  25108.1258  <- generated using Mach StepsPerUnitCalculator to calculate steps per 9 inch distance

for 9 inch distance, result is 9" to 9 & 1/64"  - repeatable
for 1 inch distance. result is 0.96" <- ** BAD ** - repeatable

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This is only a problem for X axis.

Y motor settings:

counts per unit:  25121.7720   <- generated using Mach StepsPerUnitCalculator to calculate steps per 1 inch distance
velocity (units/minute): 200
acceleration (units/(sec^2)): 24.18

For distance in y axis, result is accurate for 1" (+/- .001") inch and 4" (w/in 1/64") inches - is repeatable.

Z motor settings:

counts per unit:  25075.2508   <- generated using Mach StepsPerUnitCalculator to calculate steps per 1 inch distance
velocity (units/minute): 200
acceleration (units/(sec^2)): 25

For distance in z axis, result is accurate for 1" (+/- .001") inch and 6" (w/in 1/64") inches - is repeatable.

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Based on videos:

- Mach support:  Mach4's Steps Per Unit Calculator Wizard  -  https://www.youtube.com/watch?v=d-xCWDR0Uvg

- Mach4 Motor Calibration - Counts Per Unit  -  https://www.youtube.com/watch?v=jzYG5VOztFY

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Used a dial indicator for 1" distance and pointer pointing at a ruler for longer measurements.

Used simple commands like:

G20
G91
G00 X1

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The setup:

- software: Mach 4.

- A LittleMachineShop.com  HiTorque Mini Mill 3990
https://littlemachineshop.com/products/product_view.php?ProductID=3990&category=1387807683

- Thomson C7 ball screws. .625" X .2" pitch.
https://www.heavymetalcnc.com/x2/

- motors:
https://www.automationtechnologiesinc.com/products-page/stepper-nema23-3-axis-kits/cnc-stepper-motor-3-axis-kit-3/

- pokeys57cnc board

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Tried:

- initially all the motors were set to 16 micro steps. Figured some steps were being ?skipped?. Changed to 4 micro steps for X motor controller.

X settings:
counts per unit:  52221.3064  <- generated using Mach StepsPerUnitCalculator to calculate steps per 1 inch distance
velocity (units/minute): 200
acceleration (units/(sec^2)): 24

for 1 inch distance. is 1" +/- .005" - repeatable
for 9 inch distance, is ~9.3125" (20/64") - repeatable  (worse than 16 micro steps)

- Changed to 32 micro steps for X. Got similar results as 4 micro steps.

- changed velocity for x motor to 100 and acceleration to 5 - made no difference.

- Played with 'rapid rate' at different percentages like ~30%  - made no difference.

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Any ideas, suggestions?

tjd

• 4
Re: Unable to move accurately on X axis.
« Reply #1 on: October 16, 2020, 05:11:35 PM »
Your math is the same as mine. Don't know where the disconnect is. '16000' is way too small of a number.

The motor is connected via a "Zero backlash helical coupling" to the screw. Like:
https://openbuildspartstore.com/1-4-x-8mm-flexible-coupling/

What I dont get is why this is happening to 1 axis. The other 2 work fine.

Bill_O

• 533
Re: Unable to move accurately on X axis.
« Reply #2 on: October 19, 2020, 12:49:39 PM »
it sounds like you might be loosing steps.
slow down the velocity and accel by 1/2 and try again

tjd

• 4
Re: Unable to move accurately on X axis.
« Reply #3 on: October 22, 2020, 01:23:02 AM »
> it sounds like you might be loosing steps.

I think you are right.

> slow down the velocity and accel by 1/2 and try again

basically have tried that. Just ordered new motors with greater holding torque.

tjd

• 4
Re: Unable to move accurately on X axis.
« Reply #4 on: October 22, 2020, 01:29:16 AM »
I just figured out something. I come from a programming background. Universal programming truth:  '1' =s true, '0' =s false.

Just noticed the table on the motor controller says '0'=on, '1'=off.  F***!