Re: [CAD_CAM_EDM_DRO] 4wire vs 6wire step mtrs also Taig mill S&D conversion

At 01:53 04/02/2002 -0500, you wrote:

>I recently bought a "preowned" Taig CNC mill and I've
>already decided I want to convert it to Step & Direction
>for a number of reasons (which I won't go into here).
>I would really appreciate some advice/comment from
>those of you out there who have experience in stepper
>drive systems. I know how to use them, and basically
>how they work, but some of the electrical requirements
>and connection considerations I'm a bit weak on.

>Q1: Have any of you other Taig CNC mill owners out there
>converted your system from the LAMDA phase controller to
>Step & Direction and what was your approach. Did you
>use any part of the LAMDA controller (ex: the power
>supply, case and connectors) or did you just set it
>aside and put in a new front end?

I have one of the Taig phase controllers and have considered converting it
to S&D - there's a PIC-based solution to this that can be found on:

http://www.dakeng.com/u2.html

For $10 to convert two inputs it would be worth a try.

What software are you planning to use to drive it? If your existing Taig
setup is fairly standard, you will probably have the "lite" version of
Supercam; this is limited to Taig phase drive only, so if you want to
change to S&D, you will need to upgrade to the full version of Supercam, or
go for different controller s/w altogether (for example Turbo CNC, Master
5, CNC Pro...etc.)

>Q2: I am looking at Stepperworld's FET-3 product which
>looks great for what I want to do (I think).
>
>http://209.41.165.153/stepper/fet3.htm
>
>has anyone else used this board with the Taig motors
>which are 6 wire steppers from Shinana Kenshi Co. Ltd. (SKC)
>model # SST57D5101 / 1.8 deg/step / 9.2v / 1.0A / 200 oz/in
>holding torque with the following wiring which I assume
>makes them unipolar:
>
>Phase 1 ------+
> |
> +------Common---(13)
> |
>Phase 3 ------+
>
>Phase 2 ------+
> |
> +------Common---(24)
> |
>Phase 4 ------+
>
>Noting that they are 6 wire motors and assuming they are
>unipolar is an integral part of my befuddlement and the
>questions that follow.
>
>(about here is where the waters begin to close over my head :-)

You're right that the standard Taig setup (using the Shinana Kenshi 200
oz/in motors) is unipolar. Stepperworld's controllers are also unipolar,
so it should be possible to make these work with your motors. Its not clear
from the Stepperworld site whether it is a simple L-R drive or a chopper,
but I would assume the former, in which case you will need to wire 2
suitable power resistors in series with the "common" connections to your
motor coils in order to limit the current, restistor values dependent upon
your choice of supply voltage. For example, if you were using a 36 volt
supply, you would need a series resistance of 3 times the phase resistance
- i.e., 27 ohms, and this would need to be capable of dissipating 30 watts.

Seems to me that converting the existing controller to S&D is a far simpler
option than this though.

>Q3: Can I use my PacSci 6410 drivers?
>
>Another way I can go in doing the conversion to S&D is to
>use a bank of (4) Pacific Scientific 6410 drivers I have all
>powered up/wired up/ and ready to go (this has the advantage
>of letting me add a rotary "A" axis later and keep everything
>the same). I am using the 6410's to drive steppers which I am
>installing on my Taig lathe (these are 4 wire motors and work
>just fine). My question is can I treat the Taig motors
>as (4) wire motors by just tying both commons together back
>at the 6410. If you want to look at the 6410 reference the
>.pdf is part way down the page here:
>
>http://www.pacsci.com/support/downloads.html#6400
>
>In the .pdf manual for the 6410 they describe driving 4 wire motors
>and 8 wire motors but not 6 wire motors. Is this a problem? The
>voltage supplied to the 6410's is 24v and I believe the LAMDA
>phase controller which comes with the Taig also is 24v. The
>thing that gives me some pause is that the cable from the Taig
>motors back to the LAMDA box have the two commons on separate
>pins ... I gotta believe that's for a reason otherwise I would
>have tied them together and plugged um into the 6410 already
>(being basically the "plug it in and scrap the melted plastic
>up later sort of guy that I am")

You can certainly drive 6 wire motors from a bipolar driver, and yes, the
two common connections are rightly kept separate. There are two options
for driving 6-wire motors:

1) ignore two of the phases altogether, and use the two centre taps & two
of the ends (one from each centre tapped coil - e.g., phase 1 & common,
plus phase 2 & common in the diagram above) as your 4 wire
connections. This is known as "half-coil" operation. The current setting
would be as per the unipolar spec - i.e., 1 amp per phase.

2) ignore the common connections altogether, and use the remaining 4 wires
as your motor connections ("full coil" operation). The current setting
would be 1/2 that of the unipolar drive, i.e., .5 amps/phase.

Of these two configurations, the half-coil is often preferred, as the
inductance of the coil is 1/4 that of the full coil, leading to much more
rapid current rise time and therefore giving better high speed performance.

Neither of these is ideal with the PacSci drivers, as the low current
settings are 1.25 and 0.625 amps, so you would be exceeding the motor's
spec, potentially resulting in overheating etc.

Others have been more adventurous, and dismantled their 6-wire motors &
converted them to 8-wire, thereby allowing them to wire two coils in
parallel. This is not to be recommended; it could prove to be an easy way
to trash the motors, either by mechanical damage, or by trashing the
windings themselves, or (some will say) by ruining the motor's permanent
magnets.

Regards,
Tony