Delta Tau GEO BRICK LV User Manual

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Set the Ixx32 velocity feedforward term to 2048. 

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Set the Ixx33 integral gain term to 0. 

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Set the Ixx35 acceleration feedforward term to 2048. 

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Set this command output limit to 32,767. 

Commutation Cycle Size: Ixx70 & Ixx71 

Set Ixx70 to 1 and Ixx71 to 2048 to provide 2048 counts (microsteps) per electrical cycle (512 
microsteps/step). 

Commutation Phase Angle: Ixx72 

Set the Ixx72 commutation phase-angle parameter to 512 or 1536 for the usual 2-phase microstepping 
motor.  Changing between these two values changes the direction sense of positive rotation.  If you want 
to try microstepping a 3-phase motor, use 683 or 1365.  Changing between the two possible settings for a 
given number of phases reverses the direction that is “counting up” for the motor. 

Current Magnitude: Ixx77 

Set the Ixx77 “magnetization current” parameter to control the amount of current used in the phases.  This 
holds the maximum number of 16-bit DAC bits (or equivalent that will be used to command a DAC 
output (current command to the amplifier).  For instance, a value of 16,384 provides a +/-5V sinusoidal 
output on each phase.  This value can be changed at any time to change the amount of current used. 

Slip Gain: Ixx78 

Set the Ixx78 “slip gain” parameter equal to 2.0/N, where N is the number of phasing cycles per servo 
cycle, as set by E3-E6 on a Turbo PMAC, I7002 on a Turbo PMAC2, I7202 on a typical UMAC Turbo, 
or I6802 on a Turbo PMAC2 Ultralite.  The default setting of these jumpers or variables provides an N of 
4, so Ixx78 would be set to 0.5 with the default setting. 

Commutation Position Address:Ixx83 

Set the Ixx83 commutation position address parameter to the address of the previous phase position 
register for the motor.  The addresses for each motor are shown in the following table. 
Previous Phase Position Registers (Y-addresses) 

1 $0000B2 9 $0004B2 17 $0008B2 25 $000CB2 
2  $000132 10 $000532 18 $000932 26 $000D32 
3  $0001B2 11 $0005B2 19 $0009B2 27 $000DB2 
4  $000232 12 $000632 20 $000A32 28 $000E32 
5  $0002B2 13 $0006B2 21 $000AB2 29 $000EB2 
6  $000332 14 $000732 22 $000B32 30 $000F32 
7  $0003B2 15 $0007B2 23 $000BB2 31 $000FB2 
8  $000432 16 $000832 24 $000C32 32 $001032 

Once the appropriate steps in this section have been taken, the motor’s commutation and current loop 
should be operating correctly.  The motor should be turned in both directions with O-commands; positive 
O-commands should cause the motor position to count in the positive direction, and negative O-
commands should cause the motor position to count in the negative direction. 

Once this is done, the next step is to set up and tune the position/velocity loop servo, either the standard 
PID loop, the Extended Servo Algorithm, or a user-written servo algorithm.  This is done in the same 
method as for Turbo PMAC motors without digital current loop and/or Turbo PMAC commutation.  For 
purposes of tuning, a system with PMAC commutation and/or current loop looks like a “torque mode” 
drive to the position/velocity loop. 

Remember to store the I-variable values that have been set here to the non-volatile flash memory with the 
SAVE command.