Re: [CAD_CAM_EDM_DRO] Geckodrive

thanks, mariss. brilliant!
that's a focus on the true control point all right.


--- Mariss Freimanis <mariss92705@...> wrote:

> Sorry for the cross posting but it's been a stellar
> day here. This
> has to do with the "Unstallable Step Motor Project"
> that may be of
> interest to some:
> -----------------------------
> Hi,
>
> The very crux of the G100 project is to have PID
> servoed step motors
> that cannot be stalled under load. The G100 hardware
> was designed with
> this goal in mind; that is why it has 6 encoder
> input channels, one
> for
> each axis. I have recently made/found the time to
> work towards this
> goal.
>
> Before anyone asks "When will it be done?", don't.
> It will be done
> when
> it's done. A lot of steps, work and time stands
> between what has been
> recently accomplished and a finished product.
>
> The goal: Imagine you are doing 3-D contouring
> (X,Y,Z) when someone
> decides to sit on your gantry. An ordinary open-loop
> stepper or servo
> motor would stall/fault-out and that would be that.
>
> Now imagine the overloaded X-axis servo-stepper
> would just slow down
> under this load. The other axis (Y,Z) would slow
> down as well, keeping
> their speed ratios with the overburdened X-axis. The
> 3-D contouring
> path would be strictly maintained albeit at a much
> reduced speed. Once
> your friend got off of the gantry, speed would pick
> up to where it was
> before. Your work would not be ruined.
>
> How would this be done? Your step motors would be
> mounted with
> encoders. The G100 would sense 1 or more motors are
> about to stall
> (develop a phase lag of 1.8 degrees). The G100 would
> slow them down
> and
> back up the speed-torque curve to where more "grunt"
> (torque) was
> available.
>
> Steppers have the unique characteristic of having a
> speed-torque curve
> where the slower you go, the more torque that is
> available. Can't do
> that with a regular servomotor.
>
> OK. That's the goal; that's the picture in my mind.
> Here's what has
> been done by today:
>
> I have a G100 driving a G201 running a step motor at
> 3,000 RPM (NEMA
> 23, 3A/phase, 24VDC). Open-loop, you so much as look
> at it and it will
> stall. A flea landing on the shaft would stall it
> open-loop. I take a
> pair of pliers and clamp down on a wet paper towel
> folded over the
> motor shaft and all I get is steam. The motor will
> not stall. It slows
> down under load but it delivers 50W to the paper
> towel/pliers combo to
> make said steam. It goes all the way down to zero
> RPM without losing
> position.
>
> I ease up on the pliers and the motor is back up to
> 3,000 RPM
> lickedly-
> split, gives a chance for the boiling-hot paper
> towel to cool off. Not
> a step has been lost; you just can't kill the motor
> (stall it).
>
> This is just the first step (though a very important
> one) to integrate
> the unstallable feature into a working CNC firmware.
> There are many
> problems this feature presents.
>
> Just right now, having it do what it does, has me
> totally stoked. It,s
> so cool, jerk down on the pliers, motor slows down.
> Instruments say
> it's delivering 95%+ of all it has to give at all
> speeds. Let up and
> bing-boom-bam, 3,000 RPM again. Just can't kill it
> no matter what I
> do;
> very fine Friday nite indeed.
>
> Before you ask #2: Yes, it will traslate into all
> step motors of all
> sizes at all supply voltages at all speeds.
>
> Mariss
>
>
>
>
>
>
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