Running servos in position mode instead of analog

blazini36 wrote:

Do you have or can you get a measurement of the "lag" of the encoder output of whatever you have laying around?

yes, i can do it. i can couple a ABZ encoder directly to a motor and plot positions i get from the encoder and the drive. give me a few days to make a rig and i'll report back

the Sihong kb kr ka servo drives are similar " I bet all these drives share 90% of the firmware and board design. Anyway, in the Sihong drives p00.06 is the " command integration time" and this effect the response time of the servo drive to velocity commands.

www.dmm-tech.com/Files/DYN4MS-ZM7-A10A.pdf

top of page 38 is accel rate
Acceleration / Deceleration Soft Start
In Speed Servo Mode, the Max Acceleration parameter in the servo drive can be used to soft start/stop the
servo motor. If the analog speed command is sent as a step reference, it is often desirable to ramp up/
down this command to smooth motor motion. Without soft start, the servo motor can accelerate/decelerate
instantaneously. Soft start creates a smooth s-curve motion with conistent acceleration/deceleration.
The relation to physical acceleration / deceleration time is measured as the rise time from 10% of the target speed to 90% of the target speed.
Rise from 10% to 90% time = 59.98/(Max Acceleration)
2 seconds
Physical acceleration time = 1.2 * 59.98/(Max Acceleration)2 seconds

page 43

integration gain
max accel
max speed

if I am a betting main, the integration gain is the 5ms delay you are experiencing. try lowering it, and see what happens, the Sihong servos have a defualt of 50, which is 5msec.

No, there's an actual issue with DMM drives and the response to the analog input. This thread incorrectly attributed the delay to the encoder output, which I called out. However I did my own bench tests with my DMM drive and found there is absolutely a 5ms delay between the time the analog command is sent and the motor starts spinning. I made a post about it but nobody replied so it's probably hard to find......
forum.linuxcnc.org/27-driver-boards/5067...m-dyn4-test-findings Those tests were done with parameters given by DMM.

I went back and forth a bit with DMM about this and basically they showed me scope tests of only 1ms delay but couldn't deny my tests were accurate. That drive was probably purchased in 2021 but I only use it for bench testing something else I make, I never tried analog with it. They sent me a new drive and I went to test it and in analog mode it will not stop spinning. Using the same setup I used to test the first drive, the 2nd drive should not be spinning. DMM gave me some canned answer about setting the deadzone, however when you use the drive's own power supplies for the analog input there should be no need to adjust the deadzone.

I went through the manual a bit and came up with a test scenario and made a schematic for it. I sent it to DMM to see if they had any issue with that setup and they never responded. When I get a chance I'm going to wire up the drive and test it just as I mentioned to DMM and I'll post those results in that thread. Now the drive they sent me did not have the default parameters in it so I know they at least tested it. I have purchased quite a few DYN4 drives and I know what the stock params are.

I don't want to jump to conclusions but I saw some odd things on the drive they sent me so I'm a bit weary that they may have modified the drive because they know I'll be testing and posting about it. I have a bunch of DYN4 logic boards laying around so I'll be able to compare the hardware if something was messed with.

did you adjust the integration time or not ?

smc.collins wrote:

did you adjust the integration time or not ?
 

Hmm, yeah nobody in this entire thread thought to change the integration gain.....for like 2 years now. image missing /media/kunena/emoticons/silly.png

The integration gain factoring into acceleration is not going to account for 5ms delay on a single encode pulse worth of movement. In case you missed it I said this:

Those tests were done with parameters given by DMM.

And to elaborate the email said this:

Set the drive to exact same parameters as below, make sure you press Save All, then power cycle the drive. 
 

Do you have some good reason for telling me I should set the integration gain to something other than what DMM told me to set it to knowing the test I was doing?