On 10/25/2012 11:41 AM, andy pugh wrote:
> If the drives are using the encoders for commutation after an auto
> sense then the locked-rotor situation might be caused by the encoder
> and motor having a different idea of clockwise.
> I would certainly try swapping two motor power leads to reverse the
> motor relative to the encoder.
My thoughts exactly. That was the last thing I tried. I bought an LCR
meter so I could measure the armature inductance. It was 3X my "best
guess" value I had been using. I plugged in the correct value and the
auto tuning failed as before. Then I swapped two of the motor leads at
the servo drive. It did behave a bit differently. It moved a little bit
(still jerky) and then generated an E39 error - Self-sensing Commutation
Startup Error. I had seen that before, when I first connected the motor
and tried to move it before doing the commutation diagnostics. That
suggested to me that the servo drive probably did know the correct
> The drives are going to need to know the encoder counts per rev and
> motor pole count, I guess you have configured these? (I assume that it
> is _possible_ to configure these)
There is a place in the motor configuration database for the motor
poles, which I've correctly configured.
There's a place in Ultraware for the encoder counts. This may be the
crux of the biscuit. I'm not that sure of the encoder counts per
revolution. I've been so focused on the motor that I forgot about that
gross assumption. This is the top of my list of things to do tonight.
Put the motor leads back the way they were so the E39 error goes away,
and take a long hard look at the encoder. It's mounted on the motor so
I assume it's turning in a 1:1 ratio with the motor, but I'm not that
sure of my facts, including the 2000 line encoder count. At the very
least, it won't take long to try different encoder counts and see if the
auto tuning changes. Of course, what I failed to do in my Mountain Dew
addled sleep deprivation was put a mark on the motor pulley, manually
rotate the motor one complete turn, and see how much the encoder count
changes in Ultraware. That's DUH obvious now in the light of day.
> It is possible to run Hall-pattern translation inside the LinuxCNC
> software. The "bldc" component can do this, but it would not be the
> optimum solution.
That's another great suggestion that I hadn't considered. The Ultra3000
servo drive wants to be first in line to the encoders (doesn't
everyone?) and they offer the option of buffering the encoder signals
before sending them to the CNC controller. Currently, I'm running the
Ultra3000 and the MESA 7i77 connected to LinuxCNC in parallel on the
unbuffered encoder signals. I did measure to make sure that the
combination of the Ultra3000 and 7i77 didn't load the encoder signal too
much when I originally wired it. But I never considered using the very
versatile 7i77 as the voltage translation device, buffering the signal
for the Ultra3000. BTW - Todd gets credit for this suggestion because
he answered off list, 30 minutes before Andy. :-)
On 10/25/2012 02:14 PM, John figie wrote:
> Voltage translation of the 24V hall sensor outputs to 5V would be
> straight forward. Inside the Ultra the hall sensor inputs are pulled
> up to 5V by 1K and also the input goes through 1K to the input of a
> 74HCT14. There are clamp diodes at the 74HCT and a small cap.
I had already looked ahead that far, so I wasn't too concerned about the
15V encoder signals into the Ultra3000. I hadn't looked into the 7i77
encoder inputs yet, and was thinking that in the worst case, I might
need to use the Ultra3000 to buffer the encoder signals to the 7i77.
Mostly, I wasn't happy about soldering a new high density D-sub
connector cable to get the Hall Effect sensor data into the three
Ultra3000 servo drives. There was also the ugliness of using a zener
diode to make 15V from 24V that I was hoping to avoid if it wasn't
All of these are viable suggestions. My prioritized To Do list:
1) Verify the encoder counts per revolution.
2) Verify that the Ultra3000 is configured for the proper encoder
3) See if the Hall Effect sensors will operate from 5V.
4) If not, run the Hall Effect sensors from 15V.
5) Sell the antique Siemens servo motors on eBay for outrageous prices
to some desperate souls who need to keep their ancient CNC machines
running, buy shiny new plug-n-play Allen Bradley servo motors, and let
Joe the brilliant maintenance guy figure out how to mount them to The
Big thanks to everyone for taking the time to reply to my desperate cry
for help. Your replies were very helpful, and are much appreciated.