The bldc.c component computes the two-phase sin/cos
terms from phase angle, but I don't think it outputs them,
so a very slight modification would be necessary. The sin/cos
output values would be connected to PWM inputs in hostmot2,
which would generate the actual signals for two H-bridges to
switch the motor phases. The Mesa card generates the high
speed PWM. A 1kHz servo thread should be sufficient for
computing the sin/cos values. Here are the relevant lines in
bldc.c:
sintheta = sin(phase_angle * pi2);
costheta = cos(phase_angle * pi2);
A_value = out_abs * costheta;
B_value = out_abs * (costheta * cos120 + sintheta * sin120);
C_value = out_abs * (costheta * cos120 - sintheta * sin120);
The sintheta and costheta are appropriate for two-phase steppers,
and the A, B, and C_values are for three-phase bldc motors.
The sintheta and costheta values could be multiplied by the output
of a PID loop to adjust the amplitude based on torque or velocity
requirements. Bldc connects to an encoder counter to track rotor angle.
-- Ralph
________________________________________
From: Chris Albertson [albertson.ch...@gmail.com]
Sent: Wednesday, January 12, 2022 5:41 PM
To: Enhanced Machine Controller (EMC)
Subject: Re: [Emc-users] Field Oriented Control (FOC) algorithm for BLDC and
Stepper motors.
CAUTION: This email originated from outside the Walla Walla University email
system.
So how would I connect the four wire stepper motor to my PC to allow for
software commutation and continuous rotation of a stepper?
If this works, it could save people money by eliminating the need for a VFD
spindle drive and also
People are paying quite a lot for these self-contained "closed-loop
steppers" If this can already be done in software how?
But I have serious doubts a Linuc PC has good enough timing even with an RT
kernel. But in theory, how to connect the stepper?
On Wed, Jan 12, 2022 at 1:26 AM andy pugh <bodge...@gmail.com> wrote:
> On Wed, 12 Jan 2022 at 01:28, Chris Albertson <albertson.ch...@gmail.com>
> wrote:
>
> > This library would allow the stepper to be commanded
> > as if it were a serial interfaced servo motor.
>
> In principle so does LinuxCNC HAL and the "bldc" HAL component.
>
> --
> atp
> "A motorcycle is a bicycle with a pandemonium attachment and is
> designed for the especial use of mechanical geniuses, daredevils and
> lunatics."
> — George Fitch, Atlanta Constitution Newspaper, 1912
>
>
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--
Chris Albertson
Redondo Beach, California
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