Initial Tuning DC Servos Fadal + Glentek + Kanalog

[DiligentCNC]

Hello All,

Tom has been more than helpful and generous. I bought the Kanalog setup inspired by Mark's Fadal retrofit. I have the same or very similar machine and hope to get it back to life. My machine has the old Glen Tek drives and they worked before trying to retrofit. The control had other issues.

I am working my way through and am a bit confused. I tuned a small frame size (4th axis indexer) glentek DC motor to this drive to get my bearings straight and I had it servoing. Saved the channel and am now trying to get similar results from the larger frame size that drive the other axis. I think all my DC motors are okay too... but. When I power up and Kanalog DACs are 0.000 Volts sometimes the motor creeps. So I put a few lines into the Console.
1 DAC1=00
2 DAC1=10
3 DAC1=-10
The 10 value sets DACS to .049 Volts +/- depending on sign. The negative value will usually stop motion. The positive is a relatively high RPM starts creep but speeds up then stabilizes. My understanding is my drives are acceleration or torque type.

Further weirdness... Whenever I check the Encoder Enable box inside the Axis dialog. The motor takes off, runaway style.
Could be a drive. I might swap them around, but I just had this drive running a small motor without any issue. I ran 2 of the big motors I have with the same runaway/creep results.

I feel really dumb, challenged, not smart here. Hopefully I haven't bitten off more than I can chew.
Maybe the pots on my drive board need tweaking? I am hopeful that someone can help

[TomKerekes]

Hi,

Creeping is normal for analog drives due to any offset. See here.

A common cause of runaway when the servo is enabled is positive feedback instead of negative feedback. See FAQ here. If you enable the Axis by pushing "Move" on the Step Response Screen the plot should help understand what is going on.

Hang in there I'm sure you will get through this. You communicate well.

[TomKerekes]

Also in a Kanalog system there isn't any Supply Voltage information. So on the Step Response Screen Plot Command, Position, and Output to see the DAC Output.

[DiligentCNC]

Thanks for the response Tom. We swapped the pos/neg wires on the drive for the main DC and then things began to behave better.
I swapped them back to original position now and changed the gain to neg 1 and that has the same result as swapping motor leads. Thanks for the direction on how to do that.

My next big concern is when I power on the motor spins slowly and then accelerates. Until I enter the -.049 voltage command through the console. Will this need to be tuned out before actually connecting the motor to hardware. It may need to be tuned out of the "pots" on the drive, maybe?

Many thanks
Greg

[TomKerekes]

Its difficult/impossible to adjust analog servos to command exactly zero and remain still. There will always be some offset and noise with analog drives. If you try something might change next month. Especially with torque Drives as any amount of torque will continue to accelerate. I'm not sure why it moves slowly then accelerates. Possibly for a while friction balances the torque but as soon as it finds a spot with less friction it then accelerates to higher speed. This is of no consequence once the axis is enabled as the Servo will output whatever is necessary to hold position correcting for noise or offset. Its only a problem with the servo disabled. The best solution is to interface an enable signal to the Drives to keep them turned off until you are ready to enable the servo. Then enable the Drives and the Axis. You can have a background C Program to do this automatically. Whenever the axis is disabled it disables the Drives and vice versa. See the example watchenable.c

HTH

[DiligentCNC]

10-4, Tom.
Much appreciated. Gonna try to continue progress today. The ice has the roads shut down. Great day for electronics.
Super excited to get things moving.
Thank you, Thank you!