Re: [CAD_CAM_EDM_DRO] Re: Question for Kim Lux

It isn't a [step generation] frequency problem !

If I generate steps faster than the motor will move under a heavy load,
it can't keep up. There is nothing wrong with the
motor/controller/software. The issue is that if a motor has significant
armature resistance then there is an IR drop across the armature that
will limit the high speed capability of the motor, when it under a
significant load. This is true for any DC (brush) motor.

On Mon, 2004-01-05 at 16:24, Bob McKnight wrote:
> To: CAD_CAM_EDM_DRO@yahoogroups.com
> Organization:
> From: Kim Lux <lux@...>
> Date sent: 05 Jan 2004 13:28:29 -0700
> Subject: Re: [CAD_CAM_EDM_DRO] Re: Question for
> Kim Lux
> Send reply to: CAD_CAM_EDM_DRO@yahoogroups.com
> Kim
>
> I suspect the problem is a freq. prob. Increase the freq. to increase
> the rpm. Just my humble opinion.
>
> Bob McKnight
> [ Double-click this line for list subscription options ]
>
> On Mon, 2004-01-05 at 12:02, Robin Szemeti wrote:
> > On Monday 05 January 2004 16:02, Kim Lux wrote:
> > > I'd like to "over voltage" the motors so that they can run at a
> > > higher speed. These motors have significant armature resistance
> > > and with a 40V power supply we run out of supply voltage long
> > > before we are anywhere near the peak current of the motors.
> >
> > wrong solution, infact you still haven't stated exactly what
> > 'problem' you are trying to address
>
> You seem to be a pretty knowledgeable individual considering you
> don't
> know what the "problem" is !
>
> I stated that I would like the motors to run faster than they do
> presently.
>
> > if at max rated voltage the motors are not providing the speed you
> > need out of your machine and are pulling well below max rated
> > current, then the answer is to lower the gearing. Over-volting your
> > motors won't 'solve' anyhting.
>
> The motors are already direct driving the screws. The issue is that
> the motors have more torque than they really need and also run slower
> than I would like.
>
> > If you are already achieving the speeds you need, but feel that the
> > max current capabilities of your motors are never being used, then
> > you have simply over-specced your motors.
>
> Or not... The Amatek motors that I am running don't have hard specs...
> Kv is 1800 RPM for 40V input = 22ishV/1000RPM Max current is
> stated
> as 10A. I suspect that the 40V was arrived at as being the max
> voltage for which it was impossible to exceed an armature current of
> 10A, ie I suspect that the armature resistance is about 4 ohms. Using
> the motor in conjunction with a current controlled voltage source (ie
> a Gecko 320) allows the motor to be operated at a higher voltage
> without inducing any damage because:
>
> a) the controller (G320) will change the pulse width to achieve the
> desired motor speed. They are rated for 1800 RPM and I'd like to see
> 2500 RPM or so.
>
> b) the controller will limit the current according to the setting on
> the current limiting pot.
>
> > When correctly geared and appropriatly loaded, you will find that
> > you can pull maximum rated current at or below the rated voltage,
> > trying to correct you miscalculation of gearing by running the
> > motors out of spec will not benefit anyone, except perhaps the motor
> > salesmen. Remember, two wrongs do not make a right.
>
> Where do you get your knowledge from ? Provided the windings don't
> fly apart, operating the motor at a higher voltage isn't going to harm
> anything.
>
> Motor speed = Varm/Kv
> = (Vterm - Iarm*Rarm)/Kv
>
> Lets say that the motor is pulling 5 amps when running at the fastest
> speed it will allow: Varm = 40V - 5A*4ohm = 20V. At this current the
> motor will run only 900 RPM.
>
> If I increase the power supply voltage to 60V, I can run a lot faster
> because Varm will be higher.
>
> I've never seen these motors get hot, or even warm. Increasing the
> supply voltage isn't going to make the motors run warmer at the
> current speeds because the controller will still be providing the same
> current/voltage to them. They *MIGHT* run warm/hot at higher loads
> (ie higher speeds), but I'll find that out when I actually run them
> fast.
--
Kim Lux <lux@...>