Herewith report on follow-up actions to the anomalous behaviour experienced.
The rather disorganised structure of the .ini file comes straight out of PNCconf utility, and it in fact inserts the MIN_VELOCITY globals. The actual 'bug' is that it defaults the fourth joint to ANGULAR (which is acceptable), but by setting minimum velocities - separately for linear and angular joints - the velocity vectors remain zero (or so I conjecture) until respective thresholds are reached. Because PCNconf by default inserts 'loadrt trivkins' and it is up to the user to change this to 'loadrt gantrykins' with necessary parameter setup (which as you know we did), LinuxCNC has quite different setups for the Y & A joints of the gantry! Having deleted MIN_VELOCITY parms and correcting the A-joint type to LINEAR, the time lag (having resulted from very different velocity vector commands to the 5i23) is eliminated. Something I wish to know (which our Mesa colleagues will I am sure answer) is the tradeoff between control loop time and number of pulse generator and stepper motor instances invoked in the 5i23. How is the stepper control loop cycle time affected by pwm/pdm frequencies (I guess only FPGA processor resource sharing between 5i23 tasks)? Has maximum step rate been graphed against number of instances? Is similar data available for other family members? Appears to me that to optimise 5i23 performance for stepper control, one should keep pwmgen frequency around 20kHz (accepting pwmgen task is trivial vs stepper control). Racking becomes worse as we increase jog speed to a step interval around 50us (and concurrent motion on all joints). All the user group support is very much appreciated in bringing us quickly to the conclusion that the supplier of the power supply has grossly underspec'ed his product. Yes, beefing up the stepper power supply this weekend (having overcome the red herring!) should confirm the racking problem is indeed 'one of those silly things'. This is strongly indicated by following the suggestion of simply tying Y & A stepper controllers together, which (either way round) resulted in bad stepper growl, and worsening racking!!! This exercise is greatly encouraging of the flexibility and quality of LinuxCNC, but considering that PNCconf is targeted largely at the novice user, it does need some revision. It would be helpful to include a switch button to invoke gantrykins when appropriate (with pull-down selection of coupled joints), to eliminate the mixed linear/angular definitions, and remove those nasty minimum velocity globals! I will be happy to progress this with the developer of PNCconf. Thanks to all, we will confirm outcome of beefier stepper PSU asap! Hugh Wylie ------------------------------------------------------------------------------ Live Security Virtual Conference Exclusive live event will cover all the ways today's security and threat landscape has changed and how IT managers can respond. Discussions will include endpoint security, mobile security and the latest in malware threats. http://www.accelacomm.com/jaw/sfrnl04242012/114/50122263/ _______________________________________________ Emc-users mailing list [email protected] https://lists.sourceforge.net/lists/listinfo/emc-users
