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# The question for How can calculate Motor[x].Servo.NominalGain

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Hi,

My system environment is not suitable for executing Position loop Auto-tune of PowerPMAC IDE.

So, I'd rather to know equation of calculating Motor[x].Servo.NominalGain value but it is not mentioned anywhere.

(PowerPMAC Users manual, Software reference manual, PowerPMAC forum threads)

It is mentioned as "the value for Motor[x].Servo.NominalGain can be determined analytically" at PowerPMAC Software reference manual 521page(Motor[x].Servo.NominalGain part).

Could Somebody let me know the equation?

Thank you.

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Analytically, it is best to think of this in terms of the detailed block diagram transfer functions, evaluating the gains of each step.

For example, if you have a +/-10V analog output to a current mode amplifier that commands +/-30A over the full command range, driving a motor with a torque constant of 0.5 N-m/A, with an effective total inertia of 5 kg-m^2, with 360 motor units defined per revolution, you would have the following gains:

Kdac = 10V / 32768 LSBs

Kamp = 3A / V

Kt = 0.5 N-m / A = 0.5 [kg-m^2/s^2] / A

Kmech = 1/J = 0.2 (1 / [kg-m^2])

Kenc = 360 motor units / (2*Pi)

The total gain is just the product of all of these individual gain terms.

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Hi,

My system environment is not suitable for executing Position loop Auto-tune of PowerPMAC IDE.

So, I'd rather to know equation of calculating Motor[x].Servo.NominalGain value but it is not mentioned anywhere.

(PowerPMAC Users manual, Software reference manual, PowerPMAC forum threads)

It is mentioned as "the value for Motor[x].Servo.NominalGain can be determined analytically" at PowerPMAC Software reference manual 521page(Motor[x].Servo.NominalGain part).

Could Somebody let me know the equation?

Thank you.

The units are Acceleration in motor units per single bit of dac.

10 Volts/32768 * Amplifier tranconductance in Amp/Volt * Motor Force/Amp *1/Stage Mass

A = F/M

Gearing and ballscrew efficiency tend to muddy things a bit. I typically write a plc to output some small dac voltage per a time unit, capturing the velocity at the end of the time. A=V/T and scale this down to a single bit of DAC. repetition and averaging improve the results.

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Dear, curtwilson and JeffLowe,

With your help, I can solve the question probably.

Thank you for your kind explanation.

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