Foxprints and others:
I feel I should at least offer a little imput here. I'm afraid you may be a little disappointed with what I have to offer, however.
Foxprints has really given a very detailed report here. Thank you for this.
I seldom go to the trouble getting the tuning as precise as you did. I do rather quick tests on drive /motor combinations and in my test environment do not normally bother to get it just right.
I always recommend that users just begin to tune slightly, say do a quick tune with kp first, then kd, spending only minutes doing this. Then try different servo loop times, and doing both step and run profile tests select the servo loop time that seems to work best, trying each one out. For small light motors, try fast servo loop times. For larger motors, try longer times like 1 ms.
Then I go about tuning the pid.
As far as the current limit is concerned, I only want to give you the limits that I have found work for me. I would not try higher than a setting of 35 on the R2010 drives. Some are getting away with higher settings and it is hard for me to know what circumstances this works ok with. In general terms, I consider this kind of an average current over a brief period of time. It is not the peak current that the drive can put out instantaneously, and it is not the average current over all. If you run the cutting tool into a wall and let it just keep struggling to push the wall out of the way, the current will rise to the current trip point, and after two seconds it will fall back to the current fall back setting, which I usually set to 10. It allows just enough power to move the tool back off the "wall." I think with lower voltages, the current trip can be set a little higher.
On the R2020 drives, I have blown drives doing the above test at 95 vdc, and with the current trip setting to 75. I think it should be able to do better than this, but the heat sinking capacity of the anodized aluminum plate that the drive is mounted to cannot sink the current fast enough. If you put your finger on the back of the plate and hold it there while you crash the cutting tool into the wall, the mosfets will heat up the plate so hot before two seconds ever get there that the drive will blow with a setting of 75 and a VM of around 100 vdc. Vladimir is working on an improvement to this on the next production run of the R2020 drives. For the R2020's I limit my current trip settings to 60 with around 95 volts VM. Again, I set the fall backs to a setting of 10.
I am not trying to defend the specs. of the drive. I am only reporting my findings at this point. I am hoping that Vladimir's changes will help the drives to survive better in the current trip test.
They still drive large motors well, and in my humble opinion, still give the most bang for the buck.
By the way, I always leave all the faults disabled until I am almost through with my tuning. In the real world, with acceleration and deceleration provided for in the cnc control, the machine should never see these instantaneous stresses, and it is a pain in the neck trying to tune with faults going off all the time. Get your tuning done, then turn on the fault limit parameters. The step response has no accel or decel in it. It is a raw command to move a preset distance. I never change the settings for the step response test. I leave them the way Vladimir has set them up.
I do change the run profile parameters. Increase them gradually and observe the affects. Then you can know how to make longer and faster run profile tests.
I hope this helps a little. I know it is very general. Thanks again, foxprints for your detailed contributions. I would prefer to let Vladimir get more technical than this if he chooses. I will forward these posts to him.
Tom Eldredge
Rutex LLC
(Note: The opinions expressed in this post are my own and are not necessarily those of CNCzone and its management)