Hello Guest it is July 23, 2019, 10:11:42 AM

Author Topic: burned a servo  (Read 13921 times)

0 Members and 1 Guest are viewing this topic.

burned a servo
« on: September 11, 2012, 10:26:15 PM »
i goofed... burned a z axis servo. moved machine and left gibs tight from when i lifted it, and started to re-tram Z from move. Axis moved just fine... but little servo got real hot until I realised what I did.

it's a industrial hobbies (RF45 style) mill. It has Gecko 320 drivers,Mach3, and servos.

After i realized what I did, shut off machine to allow servo to cool (it was still working fine) when I restarted it Z no longer worked.

I replaced servo, and new one faults when limit on Gecko is anywhere over 30%. Gain and damp have no effect at all.

I swapped driver from a working axis... and Z acts bad still.

I replaced encoder, still doesn't work. Did I burn out a prarallel cable or parallel card? I'm stumped and need to get this running again, any suggestions greatly appreciated!

Mach3's DRO does show movement, but no movement from servo
« Last Edit: September 11, 2012, 10:33:57 PM by jonny quest »

Offline Hood

*
  •  25,849 25,849
  • Carnoustie, Scotland
    • View Profile
Re: burned a servo
« Reply #1 on: September 12, 2012, 03:02:21 AM »
When you say it faults could that just be indicating that your axis motor is too small and with you tightening the gibs it just cant keep on track without exceeding the following error? Have you tried with the motor disconnected from the axis? Is the axis properly lubed (screw and slides)
Hood
Re: burned a servo
« Reply #2 on: September 12, 2012, 09:24:02 AM »
Encoder is attached to ballscrew on this machine.

What I did do last night is take a battery charger... 12v 10a unplugged servo from system and hooked charger directly to servo... it barely lifted z, and easily dropped z. So servo is working correctly. It a brushed dc servo.

Problem is in machines power supply to z servo I think.
Re: burned a servo
« Reply #3 on: September 12, 2012, 01:02:05 PM »
Can you burn out a parallel port card or cable when a servo gets overheated?

What's the trick to measuring the parallel port to see if my z pins are sending out a signal?

Offline Hood

*
  •  25,849 25,849
  • Carnoustie, Scotland
    • View Profile
Re: burned a servo
« Reply #4 on: September 12, 2012, 01:27:05 PM »
Would think that almost impossible as the servo is connected to the drive and then the drive to the breakout (if you have one) then finally the breakout to the port so it would be the breakout that damaged the port if it is but cant see how an overheat could  cause that to happen.

You can test the Dir pin with a volt meter, if you connect the meter between the Dir pin and a Gnd pin you can jog one way and the other and you will see the voltage change, the Step pin can also be checked to a certain extent with a volt meter. You connect between the step pin and Gnd and depending on the active state you will either see maybe a few hundred mV register when you jog or see the 5v drop a few hundred mV. The only real way to check though is with a scope.

Have you tried using different pins on the breakout if you have any spare, even swapping around an axis on the breakout, say X for Z and vice versa.
Hood
Re: burned a servo
« Reply #5 on: September 12, 2012, 01:36:32 PM »
I did swap drives all around. It is definitely just a z axis issue, with gecko driver known to be good, and servo known to be good.

When I check voltage on just the z axis servo... at rest I get same power as known good axis. As soon as I jog the bad axis voltage drops to zero for both directions.

The z definitely isn't getting power when jogged

Offline Hood

*
  •  25,849 25,849
  • Carnoustie, Scotland
    • View Profile
Re: burned a servo
« Reply #6 on: September 12, 2012, 01:50:25 PM »
I was really meaning to try different pins on the BOB, its not uncommon for CNC4PC bobs to blow their optos, dont know if thats what make you have but if it is then it could well be the problem.
Hood
Re: burned a servo
« Reply #7 on: September 12, 2012, 06:05:29 PM »
I'm a doofus with the electrical stuff. This was a turnkey mill, I didnt build it.

coming into control cabinet, I switched parallel cable wires 4/5 (which is the Y axis) with 6/7 (which is troublesome Z axis). Y still works fine, but Z still does the same thing.

So that will rule out the parallel cables, computer, and parallel port.... I think?

Re: burned a servo
« Reply #8 on: September 13, 2012, 05:22:08 PM »
I'm a doofus with the electrical stuff. This was a turnkey mill, I didnt build it.

coming into control cabinet, I switched parallel cable wires 4/5 (which is the Y axis) with 6/7 (which is troublesome Z axis). Y still works fine, but Z still does the same thing.

So that will rule out the parallel cables, computer, and parallel port.... I think?

Pretty good troubleshooting for a doofous. Can you measure volts between terminals coming from the bob Z axis when you do a jog move? You can compare to the working axis values. Maybe you did this? Your getting warm pun intended. Not sure if you covered the bob yet in your process of elimination. Your running out of things to check!


Re: burned a servo
« Reply #9 on: September 14, 2012, 02:51:39 AM »
I don't know what a "bob" is?

Apparently there is no breakout board.... so I'm told. I'll snap a picture tomorrow and post cabinet electronics.

Couple more tests I did... verified the 4 encoder wires aren't shorted.

I then disconnect my two Z axis servo wires from Z gecko... piggybacked them to my working Y... and jogged Y. Z moved fine. That verified Z servo Is working correctly (it used Y's power and encoder)

I think there is only two possibilities left, bad encoder... or power going to gecko.

I did check voltage variance on working drives to bad drives.. they do seem similar.

Could a bad encoder head cause gecko to not allow me to turn up limit past 30% without faulting?
« Last Edit: September 14, 2012, 02:58:55 AM by jonny quest »