Trying to optimize base period, etc.

I built a JGRO inspired machine a couple years ago and I'm now trying to optimize the setup in hopes of slightly increasing travel speeds. I have Longs Motors 280Oz-in steppers with DM542A drivers and a CNC4PC C50 breakout board. The setup I have been using uses the default "Other" stepper timing of 5000, 5000, 20000, 20000 with a latency of 16000. I have since upgraded to Ubuntu 12.04 and Linuxcnc 2.7.2. I have run the latency histogram with the new configuration and found the same latency.

Looking at the ini file I see the base period set to 100000 not the 31000 the stepconf wizzard suggested. The StepTimingCalculatorPlus spreadsheet suggests a minimum base period of 22usec with this setup. Using the 2500, 2500, 10000, 8000 stepper timing from the wiki chart the spreadsheet suggests a minimum of 19.5usec. Adjusting the base-periods in the ini file and step configuration in the hal file per the spreadsheet I get an error pointing me to check dmesg with a base period of 55usec or less. I get no error with 60usec or greater.

Why does stepconf set the base period to 100usec? What am I missing that my minimum base period seems to be 3x the spreadsheet's prediction?

All of this may be academic as I seem to be limited to about 3200Hz with this stepper/ driver combination regardless of configuration.

John

What do you have the micro-stepping set for? Full or half stepping will usually give the best results for top speeds.
What voltage are you supplying your drivers with? Increasing the voltage is often the only way to increase the top speed of a stepper. (if step generation isn't your limiting factor)

All axis are set for half stepping. Full stepping is not an option with these drivers.
Nominal 36V power supply, measures 38.3V at the input to the drivers. Drivers rated for 18-50V. The stepper motor data is attached.

I don't really understand the voltage limits of the motors. If the motors can take the higher voltage it sounds like a 48V power supply might be a worthwhile upgrade.

John

I don't really understand the voltage limits of the motors. If the motors can take the higher voltage it sounds like a 48V power supply might be a worthwhile upgrade.

You dont need to worry about stepper motor voltages and amperages, the driver takes care of that.

So long as your PSU is regulated, just go to the highest voltage your drivers will take.

going to 48v , will increase your speed , and a bonus you'll get more torq to
just don't go over the rated voltage of the stepper drivers

Let's see: when you try to get max speed do the motors stall or move at a certain speed ?
if they stall you need more voltage as suggested although with chinese drives i would not push it above what you already have, or more current if your motors can handle it without overheating.
On the other hand you have the pulses and with 3200hz you mentioned divided by 400 for half step you get 8 revolutions per second or 480 rpm from the motors so no voltage or current will help there.
I am not near my machines but i am sure you should get more than that even with 100000 base period, theoretically you should get 10000hz so 1500 rpm,
What are the motors connected to ? belts? ball screws? threaded rod ?
Depending on that you would get your actual machine speed.
Regards,
Tom