Servo's are herky-jerky/slow/odd acting w/ mach3

Before I explain the problem, here is what i'm using.

Leadshine DCS303 DC Servo Drive http://www.leadshine.com/UploadFile/...2592891415.pdf
Pittman 9234 Brushed 24V DC Servo
US Digital HEDS-9100 512cpr Optical Encoder

Using the software that came with the drives the servo's work great, i can jog them all over and have no issues, they are fast and very quiet.
With mach3 i hardly get them to work at all. The Drive has PUL/DIR inputs, i have them hooked up to the para port and the pins are setup correctly in Mach. Using unmodified tuning values in mach, When i try to manually jog in mach the servo spins but it looks like its pulsing back and fourth while spinning, and almost sounds like a stepper motor, and it only turns in one direction, its just alot slower in one direction than the other.

If i go into the motor tuning window, and put 250 in the "Counts per" and 500 in the field right next to it (can't think of what it is right now, no mach on this computer) i can get it to jog smoothly and its quiet, but it goes faster one way than the other, and if i try to run a program its right back to vibrating and jerking around. If i set the feed rate just right and its on a long straight part of the program, it will turn smooth, but thats the only time..

If i set the "Counts per" or the one next to it to anything +- 20 or so then it will go back to running bad, the more i stray from these numbers the worse it gets.

If anyone has any ideas at all as to what could be the problem here i'd really like to hear them, i've been trying to get it working for days now and i'm about to blow my top.

You can't just try random numbers in the motor tuning. The steps per unit needs to be the correct number, and you need to properly set the accel and velocity. You might want to increase the pulse widths and see if that helps out. Are you using a breakout board? If not, you may need one.

thanks for the response :)

But having the "steps per" set wrong shouldn't make the servo go completely wacko. I've tried so many numbers, and they all have the same result, a servo going wacko.. i tried 20,000 wich i *think* should be somewhere near were i need to be and it was still messed up. Having the "steps per" set wrong wouldn't make the motor spin the same direction weather you press left or right would it?? i can't see how.. it almost seems to me that the signalling mach3 is sending to the drive isn't working with the drive well, its just going stupid.

I also did the thing where it will calculate the correct steps per rev. by telling it to move so far, then putting in how far it actually moved, that number did not work..

i worked out the steps per several times, and even tried mixing things up to get a different number and it still would not work right. Half the time the motor spins the same direction when you try to jog either direction..

I downloaded linux emc2, and it worked right after installed. I did some tuning with the electronic gear ratio on the driver and now its even working inch for inch. With the current setup i've obtained 2.2inch/second (132in/min) feed rate and it is very smooth and almost silent.

I'm still not sure what configuration was wrong in mach, i've tried about everything i could think of to make it work and it just wouldn't work.

All i did with emc2 was load the configuration program, it had a list of different pre-configured setups, just for the heck of it i chose shereline and then corrected the pin out to match what i had wired up, and it worked fine, just very slow. So i used my drive tuning software to change the electronic gear ratio to 25:1 and i guess just out of luck i told it to move the X axis -10 inches, and it moved it -10 inches. I don't know how it was that easy but it just worked. I'm not preaching saying emc2 is better but in my case it just worked.

Just for the sake of it could anyone here interpret the emc2 config file i'm using, and see if they can't figure out what settings need to be put in place in mach for it to work properly? This may help others in the future using the same setup that i am.

I plan to go ahead and use emc2 since it has all the functionality i need and it was easier to work with (not to mention its free, and runs on a free operating system, and i do happen to be a linux fan).

It sounds as though you may have the motors wired incorrectly. I have a motor that had two wires reversed and it made the motor jump around erratically back and forth jump all over the place. once I reversed the two wires, the motor ran perfectly fine. Make one hundred percent certain you wired the motors correctly before going on.

Be aware the the Step signal polarity in MACH (Ports& Pins/Motor Outputs) has to be right for your drives. It all depends on if you supply the drives with common +5 or common PCGND. I assume the drives have opto isolated inputs so the common determines the step polarity. Step signals are short duration so if you pick the wrong polarity for the drive it will move but unreliable. Also Sherline mode uses mach wider pulse widths because their drive would not handle narrow pulses. It's about 10 times wider that a normal pulse. If it won't work in EMC with a normal profile either the drives have poor input response or the signaling is wrong.

The motors are wired right or they would run off and fault and they would not work at lower speeds.

TOM Caudle
www.CandCNC.com
Totally Modualr CNC Electronics.