Re: What makes a motor a servo? calculating power

--- In CAD_CAM_EDM_DRO@yahoogroups.com, "Polaraligned"
<polaraligned@o...> wrote:

> --- In CAD_CAM_EDM_DRO@yahoogroups.com, Jon Elson <elson@p...> wrote:
> > Polaraligned wrote:
> >
> > >So let's see what is going on here:
> > >At 300 RPM when the stepper is producing full power of 133W

making the

> > >deep cut, the servo is making the same cut, at 3000 RPM, and using
> > >the same 133W.
> > >
> > Well, no, the servo would be delivering 1330 W due to the 10 x

greater

> > speed.
> >
> > Jon
>
>
> Well, no Jon. The servo is delivering 60 oz-in and 3000 RPM.
> This product divided by 1351 puts 133W at the motor shaft.
>
> I chose 3000 RPM for the servo speed to compare it to the power
> put out by the stepper at it's peak. So the servo is putting
> out the exact same power as the stepper for that same feedrate
> at the table. Hmmmm.....yet there is 10x more power available
> at the leadscrew due to the reduction?
> I believe Mariss was talking about power at the motor shaft in his
> post otherwise his chart for the servo is off by a factor of 10.
> That said, would this not make the servos performance 10x more
> impressive seeing as though there is 10x more power available
> at the leadscrew than in the chart he posted? Isn't power at the
> leadscrew what is going to get the work done?
>
>
> Scott

This has me stumped as I'm sure it does others who only learn enough
to get by...


I have this nice servo. 1/8 hp, 1,700 rpm, 90 volts.

run it at ??? speed

For the plasma table, it needs higher torque to start to move the axis
than to keep the axis in constant motion.

Just because it's geared for a maximum rapid of 600 ipm does not mean
that it will live there. it will live in the higher power bands at
low speed, and even at cutting speed on long straight cuts it does not
need much power.

I figured the 1-1/2hp treadmill motors would be so far overkill as to
not need calculation.

As for the stepper.
800 oz-in, NEMA42.

The calculations that have been posted include the power, but from
what I have seen of the charts, the rated power is often at 100 or 150
rpm, and not at 1,000 rpm.

I know you're not talking motor electrical watts, but delivered power
watts. The motor is 250 oz-in at 150 RPM and 150 oz-in at 300 rpm
or constant power but torque dependant on speed. The data sheets
don't show really high speed operation, and unfortunately, Camtronics
and HobbyCNC don't offer links to motor spec sheets. (I didn't look
at others but went straight to where I knew there were data sheets at
AutomationDirect)

as one increases speed of shafts, the required forces to rotate the
shaft (in a non-contact cutting use) follow a curve similar to the
stepper with higher forces at breakaway, and then level out. One has
to select motor power that has enough of a safety margin as to never
approach the required machine force curve with the motor output curve.

A contact cutting machine has a second level of required power. this
would be the normal cutting forces for the hardest material and the
biggest cutter (highest anticipated force) and as most people have
pointed out, that is also in the lower motor speeds (higher stepper
torque ranges) so the stepper motor fit starts to look good. And
since one does not cut at the higher speeds, the forces needed for
higher speeds are much lower.

OK, so my question is about power in the calculation. at what point
do you select power for either type of motor ?

Is my NEMA42 800oz in motor just as good as a NEM34 800oz-in motor? I
thought there were reasons the NEMA42 were not as good.

Also, since I have never seen an inductance listed for the older
motors we often get, how can we do many of the calculations ?

As for servo's. how do you calculate for a 230 volt motor that is
rated for 1-1/2 hp and 5,600 rpm when you are going to use a Gecko on
it with a 66 volt power supply ?

I'm glad the experts are kicking this around as us novices are
starting to gleam some of the data from the posts.

Dave