Re: [CAD_CAM_EDM_DRO] Re: Question for Mariss - Servo Motor Current

Hi Mariss & Jon,

Many thanks for your comments and insights. To clarify, I did look at
my motor's no load RPM and then calculate the pulley/belt reductions.
That's partly why I was happy with 65V DC rather than upping the
voltage any further. Also, now I run out of steps from my Flashcut
(with Lightning chip) controller before I run out of motor speed on
rapids. I also selected my encoders to take into account my maximum
step rate of around 35K steps per second. I'll be quite happy with
around 1500-2000mm per minute rapids once I address my peak current demands.

During rapids (steady speed), the pulsing current (drawn by all three
motors) peaks around 5-7 amps. It is only during stops and starts that
the current was peaking to around the 35 amp level. After an hour of
exercises, the motors are only very slightly warm to the touch.

I have ordered a big cap (18,000uF) which will come in tomorrow and
which I will put in parallel with my existing big cap, but in the mean
time, I fitted a 1000uF/100V cap across each Gecko power input. Now, I
can observe the peak current coming out of the central 15,000uF cap has
dropped to around 25-27 amps and the supply voltage only drops by about
5-6 volts. I'm measuring the current coming out of the central cap and
obviously some of the peak current now flows out of each 1000uF cap
straight into the Gecko. FYI, my big cap is only about 6" from the
Gecko's.

Jon, you're right about the inductance of the resistor being a potential
unknown (not to say it couldn't be measured) but at 0.1 ohm it should be
"pretty" low. In any event, the exercise is still very helpful in
understanding the peak current demands of the motors and observing
voltage & current changes based on component changes..

I'll report back after I fit the additional big cap.

Thanks, guys,

Cheers, Peter


mariss92705 wrote:

>Peter,
>
>I assume 20A is the stall or locked rotor current. Keep in mind your
>motor is delivering no power at that point (lots of torque but zero
>speed)...
>