Calibration Problem With A Axis >HELP Please<

Hi Community!

I have a confusing problem with the calibration of my A Axis.
My setup:

1080oz Stepper and 1:5 gear ration realized with a chain (very strong and backlash free)
I found out that the Error has a system, but i can't realize the fault in the Setup.
So I hope that there is someone who can find it out or can give me tips.
I think it could be a software problem but I'm not sure.
I'm sure that i don't lost stepps on the motor.

To show the problem.:

G0 A360 --> turns 359° --> -1° offset
G0 A720--> turns 719° --> -1° offset
G0 A1080--> turns 1079,3° --> -0,7° offset
G0 A1440--> turns 1439,3° --> -0,7° offset
Now I turn back:
G0 A1080--> turns 1080 --> 0° offset
G0 A720 --> turns 720 --> 0° offset
G0 A360--> turns 360 --> 0° offset
G0 A0--> turns 0--> 0° offset

Next symptom:

At the Stepper config wizzard in the test panel for the A Axis:
I let the Axis run for about 1minute for each setting.
If i coose +180° the stepper is very accurate.
If i coose +-180° i got a offset.
It seems that the error is systematic but i can't figure out the cause or root.

So please, if there is someone who can dont hesitate.

THANK YOU!

this is more to do with gear ratio than anything else, and stepper steps , in some cases not adding up to a divideable number
/360
Andy may have an idea

Hi Sarah!

Thank you for your reply.
What do you mean with : stepper steps , in some cases not adding up to a divideable number
/360?
Should i post my setting and hardware to solve the problem?

can you change the ratio ?
you need one that divides equally into 360

if you think that a 1:5 , if used as a straight line will give you 15.7in in one turn ,for example

Hi Sarah!

Yes i can change. I need to buy another gearwheel.
I made all by myself, so i can change.
I think I made a mistake in my description:
The ratio is 5:1. Five turns of my stepper = one turn on the A axis.
360/5=72° per turn.
I can't undestand the problem? Sorry I have not the best english skills.
pi x 5 = 15,7?

Hi again!

i was now on the machine to find out a little more about the Problem.
I made some tests with the "test axis window" and made this:

+20° no error
-20° error
+20° no error...
move to another Position:
+20° error
-20° no error
+20° error...

+-20° error if the rotation came form +
no error if the rotation came from -

It seems that the error happens with the change in the move direction, but not with the direction itself.
I played around with the timing setup but nothing changed my Problem.
I have rechecked the chain system, but i cant find anything wrong.
Any idea?
And please can you explain the point with "ratio should devide by 360"


Thank You!

Have you tried lower velocity and or lower acceleration?
I assume you are not using Backlash compensation.

Rick G

Rick wrote:

Have you tried lower velocity and or lower acceleration?
I assume you are not using Backlash compensation.

Rick G

Hi Rick!

I have tried out lower velocity and lower acceleration, but both changed nothing.
I don't use backlash compensation, becaus i thought that I should not have a backlash.
I tried to move the A axis under "1/2 holding torque" but there is no possibility to move the axis.
I use a motorbike chain Gear. Maybe there is a backlash I don't recognise, but if there is one I can't work accurate with the system because the error is not equal. (Between 1°-0,2°).
I need to research into this topic.
What do you think?.

it's ok Sergio,
dont worry over language .

remember a stepper moves only in 1.8degree steps , and cannot stop inbetween , microstepping can help but is not the real answer , if the stepper moves to a position but the ratio of the pully is not totally divisable by 360 , you will get a remainder of the value , over a large number of steps this can become so large that it is noticed ( as is what you you are seeing )

so you need to find a ratio that will divide the number of steps , equally into 360 degrees , with no remainder .
if you look up information on rotary tables this is well noted .

also if your using a microstepping drive , you will find it better to use the full or half step settings .
as this gives you more torque for holding a position ,
this is more of a mechanical problem & mathmatics than software or electronics unfortunately .

what steps setting are you using ?

Hi Sarah!

At the moment i use 1600 on my driver and on the Software.
Also full step setting
72°/rotation without or instead of the option of gear reduction.

By now i communicate with my gear supplier and he told me that i should have a little backlash with the chain and i should use a belt drive to reduce this error. So maybe i have two problems wich result in one error.

I think i'm to confused for that issue.
I can see that i need 22,2steps for one degree and I think this is just theoretical, so i can just reach 0,99° or 1,03°. And my error in ressolution should be 0,04°.
Can you please calculate a example for me?