Re: Running a BOSS on single phase

My SuperMax cnc mill has the original Nema42 triple stack 1100 oz*in
Superior Electric motors, driven by Gecko G201s with my 72VDC supply. I
used to get 2ips (120 ipm) with the P100 cpu running TurboCNC, but now
I've upgraded the cpu to a whopping P300 so now I've got it set at
3ips (180 ipm) which is 30,000 steps/second in X & Y. Since Z has
far less mass (maybe 30 lbs instead of maybe 500-600 lbs) it is set
at 5 ips (300 inch/min) which is 50,000 steps/second. This faster Z
really comes into play on full-withdrawl pecking cycles, which I seem
to do a lot of.

I love it. Compared to the original Bandit control (40 Volts unipolar,
2 inch/sec and 0.000 50 steps), this setup is 50% faster (3 ips) and
5 times the resolution ( 0.000 10 inch steps). And this with one of
the very earliest Gecko G201's without the special Nema42 tweak.

The real upside with steppers is the massive amount of torque
(ie table force) down at low (ie cutting) speeds.

The downside is that the Pentium 300/TurboCNC combo cant do simultaneous
arbitrary 2 axis & 3 axis rapids without occasionally missing steps, (so
I manually program single axis rapids). Slower simultaneous axis moves,
such as cutting circular G02/G03, works fine since the combo step rate
is probably under 20,000/second.

I seem to be the only keener here on steppers for big equipment. Here
is my suggestion:
- if the original equipment came with steppers and the steppers are
still working fine, and you are a beginner or hesitant with
electronics, stay with the steppers....
- if you have to replace the ballscrews or do any major retrofitting
and you are comfortable with electronics, then go with servos.

If I had to retrofit right now, it would be hard to say which way I'd
go, but I'd lean toward staying with steppers... however I'd replace
the Nema42's with the equivalent power yet smaller and faster turning
Nema34's, such as the $125 1076 oz*in or $168 1282 oz*in motors from
http://www.clickautomation.com/products/index.php?func=list&cid=159

and the reason I'd do that is to minimize the complexity of gear/belt
reducing the servo (the SuperMax has cogged belt drives, but at a 1:1
ratio, so thats not really a huge issue, probably a 2:1 would be easy).

Regarding the single phase, the Gecko power supply is of course single
phase already. The 3 HP spindle is 3 phase, so I built a 3 HP 3500 rpm
rotary phase converter which works great, although I might up that to a
5 HP 3500 rpm phase converter (to make my 3 HP lathe happier).

Hope that helps. Don't be afraid of going servo!

cheers
Doug



Les wrote:

>I was getting 60IPM from mine but I was always plagued with occasional
>lost steps, even if I reduced the speed and acceleration. In the end I
>came to the conclusion the lost steps problem was more a Mach2 issue
>than the motors/drives. Because there is so much inertia, the pulse
>train needs to be extremely smooth. Mach2's pulse train can be a little
>rough at times.
>
>Once I bit the bullet and changed to servos all my problems went away
>and I now get up to 200IPM if I want it. Normally I have it throttled
>back to around 100IPM.
>
>To be honest 60IPM is easily fast enough unless you are doing a lot of
>production work where every second counts.
>
>Les

Polaraligned wrote:

>>It is really tempting to keep and use the steppers that are already
>>set up. I just can't get a straight up answer from the archives
>>as to how well it may perform. A bunch of people were only able
>>to get 60 or maybe 80 ipm rapids before reliability went down the
>>toilet. I wonder how well a modern NEMA 42 stepper would work
>>in comparison to the original 25+ year old steppers. The technology
>>put into them must have changed sifnificantly since then. If I buy
>>stepper drivers
>>to use with the factory motors, then I am comitted to steppers.
>>What does a modern NEMA 42 go for these days? and are they better
>>than the original ones? These are questions I need to figure out
>>before comitting to steppers.
>>
>> Maybe servos are the safest bet. Many frown on them because they
>>think they cost more, but there are servos available on e-bay that are
>>pretty inexpensive ($250 or less per axis with encoders)
>>
>>
>>Scott
>>