How to set up a oscilloscope to tune Gecko 320's not X's

[whiteriver]

I have a small 5'x5'x16" router I built. Has all THK slides. Ball screws on the X and Z axis. dual belt drive on the Y axis.
Motors are 850 oz/in Nema 34 servos from Home Shop CNC. All drives are Gecko 320's from 2005. I put building this off for a while. I am using a Candcnc PSC 1500 power supply with his differential encoder pigtails and servo cards.
Final reduction on X and Y axis is about 4:1.
Computer is a Dell 3ghz. Mach3 running at 45hz.
I have a Tectonics 2236YA scope with 1/10x probes.

I have tuned X and Y drives by ear as good as I can get. I can get both axis running at 280 ipm back and forth with no faults. I set up a small program to run one axis and bounce it back and forth for 10 min. Acc is 0.05G's. Each one works fine. Now if I try and jog both the X and Y at the same time Both drives will fault. Every time I try it at 280 ipm both will fault. If I back it down to 150 ipm then they only fault some of the time. Is this a limitation of the power supply or lack of tuning?

Second problem. Now if I shut down and go to lunch. When I come back fire everything up. When I try and run I get faults at almost any speed mainly in the X axis. This has a 1:1 screw and a 4:1 reduction belt from the motor to the screw. It takes no effort to turn the screw let alone the large pulley on it. I have changed drives, motors, encoders and differential pigtails. I have hooked this motor to the Y axis and it still faults at all speeds. After hooking it back up to the right drive and spend a while retuning I can get it back to 280 ipm stable. But if I shut it down and turn it back on it looses tuning and faults. The Y axis will do the same thing but not as bad as the X axis.
Any suggestions. I am on my second controller from CandCNC I have gone through 3 Servos drives from Gecko and several motors. The motors and Drives were bought in 2005 the PSC 1500 was replaced new in May this year minus the Torrid. None of the electronics were used till this project.

Third problem: I hooked the Scope up to the drive via the instructions in the Gecko Manual. By the way the test points are different than the diagram. They are located in different positions. I used a meter to figure out witch one was ground. Channel 1 test point ground to ground. Channel 2 Direction pin leaving drive. Dc couple Trigger Channel 2. Norm Slope Positive. 2v on input and 1ms on horizontal. I cannot get a trace that looks anything like the diagram. All I get is a flat line that jumps every other direction change. No matter where I tune the drive. I have had 2 other people that supposedly know how to run scopes come over and they cannot get a trace that looks similar to the one in the gecko manual either. Any suggestions. This is making more grey.

Donny

[whiteriver]

Guess CNC Zone is not as active as it was 5 years ago. To bad. I am still stumped. I did make some progress by dropping Mach 3 from 45 to 35. Slowed my top end down but it will run in all axis now at the same time and more stable with motor tuning. But still way out. Would love to figure out the scope stuff.

Donny

[Bubba]

Whiteriver,
I have been following your thread hoping for an answer also. First off, I am not practiced or knowledgeable in the use of a scope so I am suggesting from a blind aspect!
I went back and looked at an older version of the manual I have for the 320 and after having read it over the years several times, I finally "think" I may have a possible answer for both of us.

From the manual:
"To see how your servo is compensated it is first necessary to induce a disturbance. The easiest way is to switch the
DIRECTION input while commanding a constant speed via the STEP input. The abrupt direction change puts just the
momentary load needed on the motor while you watch how it responds.
If you are using an oscilloscope, use channel 1 on the test point and channel 2 on the DIRECTION input. Set the trigger to“normal” , trigger source to channel 2 and trigger edge to “+”. You should see a single sweep for every clockwise changein direction.
Slowly increase STEP speed until you get a picture similar to one of the three above, and then do the following:"


From this, I think we need to have a signal generator to put on the step line to generate a constant series of pulses (constant feed rate) AND then an electronic toggle switch on the direction line. I think this will trigger the sweep needed to generate the desired trace on the scope??? This could be done with a couple of 555 timing chips if necessary!

I wish someone who is knowledgeable would jump in and confirm or set me straight!

[ksanalytical]

Whiteriver,

I was also following waiting for a solution. I'm not having any trouble, but was really curious to hear what came out of this. My first guess was power supply current. I have a set of those big motor and they need a very high "limit" setting as they pull alot of current on acceleration. You might check you acceleration rates too and try a slower speed if they tend to fail right when they start moving.

I had a similar problem with a set of stepper motors that appears to have been current related a while back and had similar symptoms. My 850oz-inchers had the same symptoms until I cranked up the limit.

Best of luck...

Ken

[whiteriver]

The limit pot on the drive is maxed. CandCnc is selling these power supplies to run 5 850 oz/in servos at the same time full tilt. How that can happen with a 1500 watt power supply is beyond me but I guess it works. I was getting 450 ipm with different axis's at 25 i/s/s acceleration one motor at a time. That was Mach 3 running at 65 or 75 hz don't remember. To get all motors to run I had to go back to 35 hz and drop my speed to 240 ipm and Acceleration to 20 i/s/s.
I think the signal from the computer is to noisy to run faster. Although the pp test shows good. I am running a separate parallel port card. Not using the computers pp.

Donny

[whiteriver]

"Gecko Drives Discuss all Gecko drives here and get direct support!"

Guess the tittle of the forum is wrong. Or everyone is enjoying this nice cool summer.

[Jackal66]

I don't have an answer, but I am interested in how to tune with an oscilloscope.

Check here:

Machsupport Forum - Index

These guys are good. They can tell you anything concerning Mach 3 and maybe someone there is running the same set-up you are.

Hope this helps,

Jackal

[Iron-Man]

It would be helpful if you could post pictures of your cnc controller box. I am building a cnc system from scratch, form the chips up. You mentioned that your electronics sat idle for a while. Take a closer look at the following items:
1. Were the conditions damp, etc. If so, you could be having problems with some of the capacitors. This could be why after the system is left on for a while that it operates differently when first turned on.
2. In addition, are your encoder cables shielded? Poorly shielded encoder cables can cause some of the problems that you describe.
3. Are any of the encoder cables running near HV sources?
4. In mach 3 have you adjusted the min step pulse?
5. In order to help with the oscilloscope issue, a picture of the circuit board and test procedure would be helpful.
a. If you can, set up your scope to a known frequency source, say 10 Khz to 100 Khz, to make sure that you are getting a stable waveform.
b. Make sure that the scope is set correctly, ie trigger, range etc.

Hope this can help,

Iron-Man

[Runner4404spd]

In order to tune with scope you need one that can record the trace. the trace shoots by the window of the scope so fast that you never see it and then its gone. most scopes as far as i know are not setup to record their traces. other than that you have it setup correctly.

the faults i'm guessing are from noise in the lines. put the scope on the encoder wires that feedback to the drives and move the machine around. see what you get. i would try and put some capacitors on the encoder wires at the encoder. that does a pretty good job in eliminating or at least minimizing noise. when i first setup my system i didn't used shield twisted pair wire for the encoders and what a mistake. at 5 volts output, the wires had about 4.8 volts of oscilating noise on them. with the shielded wire it was much better. also make sure to only ground the shield wire at one end. you want it to act like an antenna and pull the emi to ground. make sure this ground is the not the computer ground by earth ground, so connect to the chassis.