Newbie- mill rebuild servo controller ?

[johnscnc]

hello i am working on a tri-onics apprentice mill with contraves nc400 dc servo controller with contraves motors with specs:
30 in lb
110 volts max
14.6rms amps
4500 rpm
58.3 pulse amps
kt 2.06 in lb/amp
kv .233 volt/sec /rad
tachometer volts/1000 rpm 19
main transformer 72vac output on two diffrent taps.
third tap at 24vac
the motors are good and the controllers seem ok they home and limit and run ok but any programmed moved gives a floating point error so i think the computer is done for. we are thinking of replacing controller cards with viper or rutex and using mach or emc2 .i would like to keep the power supply as it seems fine. any advice would be appreciated. would there be something better than pp step & dir such as galil or vital systems i don't they use native g-code though?

[Jason3]

Originally Posted by johnscnc the motors are good and the controllers seem ok they home and limit and run ok but any programmed moved gives a floating point error so i think the computer is done for. we are thinking of replacing controller cards with viper or rutex and using mach or emc2 .i would like to keep the power supply as it seems fine. any advice would be appreciated. would there be something better than pp step & dir such as galil or vital systems i don't they use native g-code though?

The parallel port and step/direction is usually the default, presumably because (I think) more hobby guys use that than any other interface. There's a tradeoff between speed and resolution - the higher the resolution of your system, the higher the pulse rate required. The advantage of sticking with the parallel port and Mach3 or EMC is there's huge user base that will help you out if you get stuck!

There's a few options out there (including quadrature) if you need higher resolution, more speed, or for whatever reason you can't use a parallel port. If there's no good reason not to use the PP, it does seem the easiest route...

Best regards,

Jason

[johnscnc]

thanks jason. we are leaning towards mach3 with pp trying to decice between viper or rutex controller cards though. i looked at your stuff looks pretty cool. does one board work for brushed and brushless servos and steppers? these motors seem to be in pretty good shape and i was realy hopping to leave as much of the power supply as possible wich means i need over 100 volts. i would like to have the machine move in .0001 increments there is a 2-1 pully on the motor 5 tpi ballscrew what encoder do i need?

500 cpr in quadruture? 10000*2= 20000perinch/10=
2000per motor revolution/4= 500cpr?

would this make my theoretical max speed with mach3 300 ipm? 100000/20000=5ips*60=300

[Jason3]

Yep, the one drive will handle steppers, brushed or brushless servos. With steppers, it will currently only operate in closed loop mode, so they must have an encoder. If you're interested, they are planning a higher voltage (160v) version that might suit you - how far away it is will depend on demand, I think.

It's pretty late so my maths might be off, but I think you'd be looking for a 250 line encoder, for 1000 counts per revolution to get that resolution. I'd look for at least a 500 line encoder though - generally a higher encoder resolution will allow a 'stiffer' tune.

Yes, a 500 line encoder on your setup should give you a theoretical maximum of 300 ipm.

Best regards,

Jason

[johnscnc]

thanks jason i'm pretty shure my math was off well not the math but the usage

500 cpr in quadruture? 10000*2= 20000perinch/10= 2000per motor revolution/4= 500cpr?

should be
10000/2= 5000perinch/5tpi=1000per motor revolution/4=250cpr encoder

then my theoretical max speed would be 100000/5000=20ips*60=1200ipm

but my motors would limit that to 4500/2=2250/5tpi=450ipm

what do you mean by a "stiffer"tune?

any body have any suggestions on viper vs rutex?

[H.O]

Hi,
If the math says you need a 250 line encoder to get the desired resoultion then you should aim for twice that - at least. There's an old rule of thumb saying you should aim for an encoder resolution 10 times the intended machine resolution but YMMV.

The reason is that the servo drive needs to "see" an error in order to correct it, obviously. If one encoder count is equal to your needed resolution then you're already out of position before the drive even sees it. When the motor turns it will constantly be one or more encoder counts "behind" the target (hunting and following the moving target).

A higher resolution encoder will let you tune the servo "stiffer" because there's simply more "information" for the drive to work with. The more deviation there is between the actual and wanted position the more effort the drive will put out to bring the motor back - it'll feel a bit like a spring. The "stiffer" the tune is the harder this "spring" feels, a high res. encoder makes this easier to achive.

And, even though Mach3 CAN put out 100kHz you need a very fast computer to use smoothly. You should really evalute and test your intended computer for compatibility if you need to run it that fast.

HTH
/Henrik.

[johnscnc]

thanks for explaining that h.o. I'm a little slow at abreviations what does ymmv mean? i realize that the 100000 step output is very optomistic if i use 50000 then my max speed would be 150ipm not too bad but was hopping for a little more. i suppose i could use 2x step multiplier and still have .0001 resolution on software side! with 300ipm and 500cpr on the motor with 2-1 to the leadscrew wich would give the controller 20000 per inch. witch i think should make it pretty easy to hold +/-.0005 during machining maybe not?

[123CNC]

Henrik,

Nicely written response, A+.

Its contributions like these that greatly contribute to the wealth of knowledge of the community. Everyone's contributions are of course welcome, just thought this was very well worded, clear, and concise.

johnscnc,

your mileage may vary

[johnscnc]

thanks,for explaining that 123cnc. now to open another can of worms what about step multipliers? or do they just equal lower resolution encoders. or is one step on the input side not the same as the resolution on the encoder feedback?

[H.O]

The step multiplier will let you move the motor in increments other than a single encoder count while the drive still uses all available counts for the servo-loop. Does that make sense?

A step multiplier of 10 with a 2500 line encoder will make the motor move as if it had a 250 line encoder (ie one incoming pulse will move it 0.36° rev) but the higher resolution encoder will usually make it easier to tune the servo so it's "stiff" because the drive has 10 times as many encoder counts to use to keep track of the motor compared to the lower resolution encoder.

[johnscnc]

thanks h.o.. thats what i was hoping for ,that the multiplier only applied to the input pulses from the computer and not the feedback pulses.

[johnscnc]

hi again i need to pick your brains again what should be done with the tach feedback from the motors since they will not be used should just i pull the brushes or will that mess somthing else up? and what breakout board works good with viper 200? and any particular type of encoder to get or avoid?