Motor encoder scaling

H Tommy,

I think the wiring is ok.

I have had some success this morning since my last post.
Here is what I did
I changed these figures in the ini file.

Z MKD041 encoder scale 21000 (PncConf had these at 600 800 and 1600)
Y MKD041 encoder scale 21000
X MKD071 encoder scale 32000

Now when I enable the servos I get a small amount of drift until I toggle F2 then they stop and I am able to jog each axis around. The direction is correct but the DRO does not match the machine movement now (which I expected)

I have done what you said and rotated the y axis one turn, 8000 was the count.

You can't change the scale to tune the axes.
You must set the scale so the DRO and movement are in agreement.
Then you tune the PID

When I did that the motors went nuts. 3 tonnes of machine jumping around aint pretty. I don't know where to start in PID when they are doing that.

So after checking the raw encoder count of 8000 (as Tommy instructed) how do I utilize that in the axis scaling? I'm obviously missing something.

This is the last setup I tried and would continue on PID tuning but the DRO/Machine scaling is way out.
Z MKD041 encoder scale 24000
Y MKD041 encoder scale 24000
X MKD071 encoder scale 32000

Peter

See my last message
Axis scaling is what linuxcnc uses to know how much to move to get to a requested position. It must be correct and there is only one correct setting.

PID tuning is what linuxcnc uses to correct the requested command based on the current feedback position (ie smooth accurate movement)

Untuned position loop can be very violent.

I suggest googling linuxcnc PID tuning.
Unfortunately it's a little black magic and the best information is spread around in wikis and forum posts
eg:
wiki.linuxcnc.org/cgi-bin/wiki.pl?PWM_Servo_Amplifiers

Chris

Does the raw encoder (8000/rev) count have anything to do with how I scale the axis.
Peter.

yes. scale means counts per unit of travel ie 20000 counts per inch

This 'counts' includes any encoder counts, gearing, lead screw pitch and or electronic dividing of the encoder counts.

ie A motor with a 2000 counts per revolution encoder tied directly to a 10 revolution per inch lead screw(10 tpi) = 20000 scale

2000 X 10 = 20000 counts per inch

same thing but wiih a 2:1 gear ratio added between the motor and lead screw:

2000 (encoder counts) X 10 (10 TPI) X 2 (gear ratio) = 40000 counts per inch

Chris

I understand what your saying but I cant get to work in Pncconf.

Peter

So I'd need more information about the machine to guide you.
I find it confusing too as you said you had the DRO correct at one time.

Lets start a bit back -
Are you using the drive in analog mode (+-10 volt input)?
if in analog mode, does the drive analog input control torque or speed (speed is usual)

What Mesa cards are you using?
pick an axis:
-What is the thread TPI or lead of the lead screw?
-is there any gearing/belt drive, if so what is the ratio?

Anything else you think may be pertinent to set the scaling of one axis.

Chris

Hi Chris thanks for being patient and I appreciate your help.

I'm using Mesa 5i25/7i77 Pack and go the the 2.8 buster preemmpt iso.

The servo drives are +-10v analogue. The model I have are DKC11.1-040-7-FW

If you don't mind have a look in the attached PDF section 4-25.

I have X3. wire 1 and 2 connected to 7i77 AOUT and GND.

The Z and Y are the easiest to work with and I uncoupled them from the lead screws.

The Z axis is direct drive 5mm lead screw pitch

The Y axis is 24-60 teeth belt drive, motor to lead screw. The lead screw is a four start thread 25mm pitch

The x axis is rack and pinion. Rack 30 teeth in 200mm. Pinion 20 teeth. The motor drives this through a planetary gear (I will see if I can work out the reduction now). Edited 10:1 ratio

Note: this manual also cover the model with the stepper module.


Peter