setting up servo drives

[planeflier]

I just finished upgrading my router from a Hobbycnc stepper drive system to a servo drive system. I am CandCnc mino io supercombo for my breakout board. I am using Gecko 320's driving my servo motors.

my computer is a 2.5 ghz w/1gig ram running mach 3. I am having problems with the axis not moving smoothly and missing steps. I am running 42 volts dc to my servo motors. I have adjusted my max speed in mach to 200ip and sill I am getting missed steps. I have tried 25khz 35 khz, and 45 khz in mach and this seems to not help the problem.

looking for suggestions on how to insure that I have set my Geckos up correctly as I don't have a oscope. This servo thing is all new to me I had my machine working with steppers but was looking for more speed and no more lost steps by going to servos.

Any help would be greatly appreciated.

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[miljnor]

you don't really need a scope for setup.

what software are you using for control?

Did you follow your instructions with the gecko setup and tune?

servos don't really miss steps, they have a following error but not missed steps.

if there is an actuall missed step and the gecko isn't picking it up then maybe your encoder signal is getting interferance of some sort. You need shielded encoder cable and if your not using quadrature encoders you should save your self some heart ache and get a converter for quadrature output.

[planeflier]

I am using Mach 3 for my control software. I followed the directions that came with the gecko drives. I purchased the encoder cables from us digital. they are quadrature encoders.

If I hold the key to rapid the axis it will run for a short while then stop without me taking my hand off the key. I think I am going to try and do a clean install of windows xp on the computer.

any other suggestions?

[ger21]

Noise on your encoder lines??

[HillBilly]

You need shielded encoder cable and if your not using quadrature encoders you should save your self some heart ache and get a converter for quadrature output.

I believe what you mean to say is differential output. Quadrature can be in the form of single ended or differential. To take full advantage of this you would have to have a reciever also because the Gecko only has provision for single ended encoder input.

Darek

[planeflier]

I am using motors from home cnc they are 360 oz motors with us digital 250 cpr encoders. the motors are geared 2:1 spinning nook 5/8 x .200 ball screws.

[miljnor]

I believe what you mean to say is differential output. Quadrature can be in the form of single ended or differential. To take full advantage of this you would have to have a reciever also because the Gecko only has provision for single ended encoder input.

thank you

I am using rutex and they use ttl or differential. The differential will save you alot of heartache, unless of course the drive doesn't use it.

[planeflier]

I have narrowed it down to the y axis only having problems. I have reformatted my cnc computer so I know that I have a clean install and nothing extra running in the background. Do the Geckos prefer to be driven high or low to engage a step? Anyone else have any suggestions?

[jeffery71]

Leave Mach3 set to the default 25khz for now.

The geckos will fault if the motor falls behind. This can be cause by not having large enough motors, miss tuned motors, not correct gearing, binding in the axis, .. Also if Mach3 is set to accelerate the motors faster than you motors are capable of.

You say you are having trouble with your Y axis. Is the X axis identical as far as motors gearing and so on?

Jeff T.

[planeflier]

Booth the x axis and the y axis are both driven by the same make motors and are both reduced 2:1. the x axis has more weight and larger as this is providing the movement for the gantry that the y axis is mounted on. It appears as if the motors are missing steps as when I was using stepper motors and was trying to drive them to fast. I will take the y axis apart tonight and see if anything is binding in the system.

[jeffery71]

Well if they are the same setup and the Y axis acutally has less load then I would point back to what Gerry said. Noise in the encoder lines.. How long are your cables between the encoders and the G320? longer lines are not good.

Jeff T.

[planeflier]

both of the encoder cables are 6' long and purchased from us digital.

[ger21]

Have you tried increasing the pulse width?

[Mariss Freimanis]

1) Use a breakout board from Bob Campbell Designs, PMDX or CNC4PC. These boards convert the 3.3V logic from your parallel port to 5V logic the G320 needs.

2) Set Mach3 ports and pins to 'active low' on all outputs. Set Mach3 motor tuning 'step pulse width' to '3uS'.

3) Run a wire from your motor case to terminal 1 (GND) of the G320. Have this wire in the same cable with the 2 motor armature wires.

4) Use twisted pair cable for long encoder cable runs (> 10 ft or 3 m). Put CH_A and GND on one pair, CH_B and +5VDC on another pair. Never put CH_A and CH_B on the same twisted pair.

5) Do not bundle the motor cable with the encoder cable unless both cables are shielded. Ground the shield at one end only, usually at the control box end.

Mariss

[planeflier]

I seperated the motor and the signal wires and this seems to have cleared up the problem.

Thanks for the help guys.

[routerman]

Isolate the heatsink, since you may have a ground loop problem.
You will waste a lot of time before you realize that Geckoservos are just toys. They look good but work poorly.

If all else fails, Take a big hammer and give them a good wack!

[Bloy2004]

gee.... I thought they looked liked a lizard, but worked really well!
I've got seven 320's working just dandy running my router and lathe/mill.

Routerman....I guess you just have to know how to use them...

[mcpltd]

Is it the shielded cable
CA-3935-6FT? are you grounding the shield at one end?

both of the encoder cables are 6' long and purchased from us digital.