Spindle and encoder

There should be no significant tracking errors regardless of the RPM
as the Z motion is independent of RPM (it's "geared" to the spindle angle
from the spindle encoder)

Not aware of any tracking errors. The G96 and RPM corresponds with the encoder and the X and Z axis feed IPR okay lately, except, commanding the spindle doesn't match the RPM. The BIAS 160 and OUTPUT_MIN_LIMIT = 0 accelerating the spindle the RPM offset increases and decreases as the spindle nears maximum RPM. Set at 10v maximum motor RPM but at maximum RPM is at 9.6v. Is that part of the offset? Is the offset from frequency and or duty cycle and how is the starting offset and voltage determined? The 7i96s manual and page 12 indicates the PWM optimal range is 10000 to 20000 Hz. The firmware defaults to 20000 Hz which is the present setting.

setp hm2_7i96s.0.pwmgen.pwm_frequency 20000
setp hm2_7i96s.0.pwmgen.pdm_frequency 6000000
setp hm2_7i96s.0.watchdog.timeout_ns 5000000

I could test spindle commands, RPM and voltage, compare and calculate a ratio as the offset increases and decreases. The ratio could be made a variable with an algebraic expression for G97 either in the main program or a sub-program. However if the offset of the ratio or constant vary it could have ratio too. Unsure how operable the ratio would be with G96 and time constraints. Such variance maybe redundant to test many individual spindle, RPMs and voltage. Could the each commanded spindle, RPM and voltage be recorded at a file from a program which would indicate the offset values? How is RPM calculated if 20000 Hz and 0.016667 Hz per 1 revolution because the 20000 seems excessive? I wonder if the Hertz relative to RPM could be sent to a file and besides probe some tests.

If the offset is expected with brush motors, speed controllers and breakout boards and not fully correctable then it could get ignored. Nonetheless, I like the offset and or scaling corrected as much a possible and including the G96 calculation.

The inaccuracy is in the motor controller
(the 7I96S analog output is better than 1% accurate)

What actual problem do you have?
 

Could the 20000 be maximum Hertz generated?

The only discrepancy yet is the commanded spindle not matching the RPM and looking for a solution.

Is inaccuracy from the pot of the 7i96s or speed control unit? Is such a speed control unit that's anymore accurate?

The error is from the speed control unit.

As I said the 7I96S analog output is better than 1% accurate.

20 KHz is the suggested frequency for the 7I96S analog output
there is no advantage to changing this.

Speed controller unit pot dial adjustment to the lower spindle to rpm offset.
Earlier, I referred to the speed controller unit pot 3 dial as acceleration but it's max speed and set at about 3 o'clock CW. At 10v maximum motor RPM. Pot 2 is an acceleration dial that is preset CCW at about 8 o'clock. I turned the pot 2 dial full CCW to 5 o'clock, s1000 m3 and the start is a bit abrupt which sounds as if it's a surge or jump. Turned the pot 2 dial CW beyond 8 o'clock and started the spindle the sound was smoother but it increased the rpm offset. The acceleration dial could go as low as 7 o'clock and at s1000 m3 a smooth start but remains with the offset. I didn't move the pot 3 dial min speed because it seemed too stiff or as if it was seized but might not be necessary by now. The IR and CL dials were entirely left at their presets per motor and factory setting.