Re: Geckodrive

Perhaps I don't understand it based on what you are calling it. But
as far as I know, every motor of every kind can be stalled with
enough load on it. So, is it "Unstallable" in the sense the motor
cannot be stopped?

Or is it just closing the loop?











--- In CAD_CAM_EDM_DRO@yahoogroups.com, "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
>