RE: GeckoDrive 201 and Bridgeport Stepper Motors -was- Re: [CAD_C AM_EDM_DRO] Hello!

> Howdy All! This is one of the few places where this does not make you
> the "Lone Ranger". <G> But alas, mine only weighed 3000+
> pounds, a mere
> 1 1/2 tons. Hard to imagine this is a "lightweight" mill. Now the
> obligatory [CAD_CAM_EDM_DRO] content. I got some GeckoDrives #201 to
> drive the 3 stack NEMA 42 motors (known as Big Mutha' or BM) on my
> Bridgeport Series I CNC, and have some observations after running a
> drive on my workbench. For those of you considering these
> modules, here
> are a few things I discovered. The test routine is a simple basic
> program which outputs step and direction to the parallel port
> (PP) on a
> 66MHz 486.

Does anyone know if this is the same motor values that are on the series 2
machines? I was considering trying a set of Mariss's stepper drivers on my
machine, but it the motors are the same it sounds as if they just don't have
enough voltage capacity.

> 1. Mariss is GREAT to deal with. After someone in the Post Office
> purloined the the 1st set of GeckoDrives he sent, he very graciously
> sent a second set at no charge. I may be biased as a result,
> but that's
> life.

I will second the comment on Mariss being a great guy to deal with. I am
adding him to my list of tremendous vendors that go beyond the call of duty
which so far has only included Dan at Camtronics and Fred at IMService.

> 1a. He also really knows some stuff! And he told me before I
> bought the
> drives about the ins and outs of these units. So any problems or
> difficulties arise from my own ignorance or silliness.

I certainly vouch for that> I have spoken to him a few times and his wealth
of knowledge is impressive.

> 2. The modules are very easy to setup and run. (My electronics
> background is fairly limited, basic AC/DC, soldering etc.) 2 wires for
> the power, 3 wires for the step/dir/+5, 4 wires for the stepper coils.
> He has 2 terminals so you can set current limiting, but I
> didn't bother
> with that. Physically they about 2 1/2" square and 3/4" high.
> The screw
> terminals won't allow any wire larger than 14AWG, which is no problem
> for the step/dir but might be a concern when running the
> drive at 80vdc
> and 7 amps. (I always over-engineer everything I build, so may just be
> my mania for "more".)

Checking the chart I have 14 ga is over engineered. The chart is listing 14
ga as up to 25 amps!!

> 3. These are micro-stepping drives. Period. They take 2000 step pulses
> from the PP to get 1 rev from a 200 step motor. This is not a
> problem if
> you can work with that. I don't know if CNC Pro or the other
> front-ends
> will allow me to scale the output to take care of this.

Mariss will be releasing a new version called the G210 that will have a
pulse multiplying circuit. It will allow you to send full steps from the
computer and the drive will handle converting this to the 10 micro steps. It
will be selectable to allow multiplication values from 10X (as above) to 1X
(no multiplication just as described for the G201).

> 3a. The printed instructions point out that the module supply is
> 24-80vdc and the supply should be in the range of 4 to 10 times the
> nominal stepper voltage to get good micro-stepping. The BMs
> operate at a
> nominal 56 volts which doesn't leave much headroom for the
> microstepping
> to happen. I ran the drive at 74vdc and found the performance on this
> Big Mutha' less than stellar. The actual test showed that the stepper
> was energized and would vaguely run. It didn't seem to have any real
> "sense of commitment to the effort".

Hummmm, Makes me wonder if I will just be better off finding some good size
servos motors and just using the Gecko step and direction servo driver for
my series 2??

> 4. I have run several smaller steppers on this drive and have been
> amazed with how well it worked. The best one was a Matshusita NEMA 34
> 5.5v 4.4ohm/coil running off 24vdc. Good solid feel, nice micro step,
> some "hunting" when it settled on one spot. I expect the
> hunting will be
> eliminated when there is a mechanical load on the stepper.

Mariss has mentioned something about a variant of the G201 that is optimized
for NEMA 43 sized motors if I remember correctly. Is this the units you
have? I don't remember Mariss saying what the difference is.

> Next Steps
>
> 1. Swap both motor and drive module to determine where the problem
> really lays. I will post more later on what I find.
>
> 2. I'm going to look at the output pulses of one of my Geckos and will
> consider using the output to drive some 200v 10amp MOSFETs.

You will now have the problem of no current limiting to the motors. If you
use 10X over voltage without a chopper circuit limiting the current you will
likely let the magic smoke out of the motors.

> 3. If that isn't the answer, I'll use them to CAM my lathe. <G>

Not a bad use at all!

Tim
[Denver, CO]