After much trial & error I discovered that the encoder selections & loop timing are as important a factor as anything else in tuning these drives.
Since I want high speed on this machine I have to compromise accuracy to get it down to a manageable pulse rate. What I did initially that set me back was to set the encoder to read in lines instead of in 4x lines. In this set-up I was able to set Kp at 30,000 (max) and still not achieve a non-settling oscillation. Also, even with everything else "cranked up" it still wasn't performing smoothly.
It dawned on me that I could set the encoder to a higher resolution (4x) and then set the pulse multiplier to 4 to achieve the same result in terms of pulse rate vs velocity. The effect is that the drive is using 4x higher feedback resolution even though my controller doesn't have to output 4x the pulse rate. This made a huge difference in tuning. I was then able to reach P only instability (which is the normal benchmark in analog tuning) at Kp 4000. Now I felt like I was getting somewhere.
The D factor with some D-Index was very effective at dampening the P, however at a certain point it starts causing growling & I discovered that got worse with a higher D-Index number. I eventually went with a 0 there since although it made the final settling perfect, it also made less than rapid speed motion rough & growly.
The I factor is an odd one, It seems to be a time/following error amplifier, in that it amplifies the output on the basis of how long it has been in error rather than how great the error is like the P factor. I was shy of this one because in some earlier attempts it introduced wild oscillations at very low numbers, but I think that with the servo loop period set correctly you can turn up this gain to great effect.
The loop time was the most curious. The loop time appears to have 2 effects. One is that the I gain seems to be amplified by a lower loop time & if the loop time is too low then the I gain causes instability, which if this is a time factor makes sense. The second & perhaps not unrelated to the first is that a higher loop time introduces a dampening effect, and it seems more natural than the dampening of the D factor, too much, however reduces accuracy. There was a point on the scale where the D factor gain ceased to improve performance, but the system clearly still needed more dampening, increasing the loop time did the job.
Lastly, I didn't tune it so much with the step response screen, I started there, but found that results that looked like the bdi file there didn't necessarily translate into smooth and accurate motion at slower than full speed moves. I ended up in the test profile screen using trapezoidal & sinusoidal moves & watching the +/- error peaks as well as listening to the motor sounds while moving. This was much more effective after the initial P & D tuning in the step response screen. I ended up higher than I expected judging by the bdi info.
Lastly though I still would like some guidance on the current limit setpoints. During the process I got frequent overcurrent trips, invariably at times when the drive was in a steady state, drawing only a fraction of an amp, why? Also the software needs a couple important updates, #1, if a fault occurs you have to reset the drive & loose all your current values to continue, this is very annoying, it should hold the present values during a reset, or the current reset could remain as is & you should be able to clear the fault by another means that doesn't wipe out your current values. #2 is the test profile data entry, it is too cryptic, you should be able to fix a distance of travel in counts, then vary the time to complete & acceleration rate &/or max velocity and accel rate. The current system is quite difficult to get the results you want.
Bridgeport type knee mill w/4:1 belt reduction on screws
R2010 brush type drive running at 82v nominal
Motor = 80V, 6A cont. 53A peak 4k rpm
Encoder= 500line in 4x mode = 2000 PPR
Loop time = 1ms (1 point interpolation also = 1ms effective loop)
Current limit = 40 (*.2=8A) ( I think this is too low but ?)
Kp = 8000
Ki = 900
Kd = 9000
Kd Index = 0
Summary, Very tight, I cannot turn the motor shaft by hand more than 2 counts of error & even that is difficult. In rapid moves I repeatably get no more than a +/- 8 count error at rapid & +/- 4-5 in slower moves with an accel of 100 (per the profile page). 1 count = .0001" on this machine. I'm not exactly sure what the actual rapid rate is because the displayed velocity on the profile page is not accurate, except maybe for the square profile which isn't a profile you can test error with. All in all it is tight & fast with a smooth motion.