acorn and dmm dyn 4 losing steps

[fozzyber]

As requested by Marty.

https://youtu.be/Zh_FNE53oa8

https://youtu.be/Zh_FNE53oa8

[fozzyber]

I ordered DMM db25 cables last night. I don't know if this will fix anything but i will try it, as I am running out of ideas.
my current mechmate/mach3 does not use shielded cables for step/dir, and runs great, but sometimes things are different so i will try them.
Are the DMM cables shielded?

jerry

[Dan M]

Dumb question but I'm going to ask anyway, are you sure you have your overall turn ratio set correctly?

[fozzyber]

yes i am sure about turn ratio. but in this case turn ratio should not matter.
as i am telling the machine to move x distance one way then to return to zero ie turn -x distance .
so send x 5 units right then send 5 units left. the MOTOR should return to the same place it started requardless of turn ratio...
it is not
I am only working with the motors right now not mechanical moment of the machine.

Dumb question but I'm going to ask anyway, are you sure you have your overall turn ratio set correctly?

[cncman172]

Fozzyber,
Can you do that same test with the number of steps for just one revolution? If so can you see just how many steps you are missing? The motor is spinning fine and I would not think you are not missing steps based on no load. Are you driving the DYNs open collector? Do they have differential inputs available? Another test would be to do the same test you are doing but instead of running G0, use G1Y50 F20 and vary the feed rare to see if the feed rates change your results at all.

Just a couple thoughts off the top of my head.

Russ

[cut2cut]

Since I'm in the process of wiring up DMM DYN4 drives with Acorn and should be firing it up in the coming days I"ll jump in here with a question that is directly related.
Because the DMM DB25 flying lead cables looked a bit short I have made my own. The cables I used are shielded and twisted pair. I am unsure how to pair the wires however. Since we have a variety of types of 5v, 24v, common, pulse and direction its tough to decide what gets paired with what! Anyone have a suggestion how to pair them , or does it not matter how they are paired ? ( in progress photo attached )

Jake

[cncman172]

Cut2Cut,
This depends on how many leads are in your cable. The preferred way which often is not available it to use one of the twisted pair for a signal and the other for a ground. In most cases that is just not possible. The key is having the shield grounded, and all shields are not created equal. Some cables have a simple foil shield and a drain wire. They are not as good as a braided shield with a drain wire. Even the braided shield comes in different coverage from as little as 20% up to 80%, meaning the mess of the shield is tighter and tighter so it is more effective and shielding EMI.

Bottom line is most configuration will probably work, if you have the shield grounded properly.

Just my two cents.

Russ

[cncman172]

cut2cut,
Nice looking cabinet. You might want to verify the spindle cable leaving your VFD is a good shielded cable, that is a huge source of issues in cabinets and making sure that cable says away for low voltage cables is really important. If that is an un-shielded cable you will most certainly experience all kinds of ghost issues on your machine. Read up on EMI it is a huge enemy for CNC controllers.

Russ

[fozzyber]

cut2cut, on your DYN4s what are you doing with the encoder feed back?
I thought the acorn could only read one encoder

jerry

[fozzyber]

russ from what I can tell the issue seems to be between the acorn and the dyn4, the DMM stuff is closed looped, and watching the motor monitor it is not losing steps in between the dyn4 and the motor.
the problem seems to be the acorn telling the dyn4 to move 6000 steps and the DYN4 moving 5945ish steps.
it is like what the acorn says the dyn4 does not get the right command for the number of steps.
and sence the acorn is sending out pulse signals (one signal per step.) it is like the acorn is sending 5000 pulses but thdyn is only fetting 4899 of them.
This is a closed loop hybird system as the dyn4 knows if the motor loses steps but the acorn does not.

understand?

jerry

Fozzyber,
Can you do that same test with the number of steps for just one revolution? If so can you see just how many steps you are missing? The motor is spinning fine and I would not think you are not missing steps based on no load. Are you driving the DYNs open collector? Do they have differential inputs available? Another test would be to do the same test you are doing but instead of running G0, use G1Y50 F20 and vary the feed rare to see if the feed rates change your results at all.

Just a couple thoughts off the top of my head.

Russ