Trying to optimize base period, etc.

Tom,
The Y and Z axis are just 3/8-16 threaded rod. These are limited to about 30ips. The X axis is a ball screw with a 5mm lead (5.08 rev/in). The X axis moves at 96ips with a little lower resolution but adequate for my needs. In each case above ~3200Hz the motors stop turning and emit a louder vibration/tone.

You wrote:
"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."

Are you saying these drives/motors are limited to 3200Hz and increasing the voltage will not change this? Stepconf says the max step rate is 32258Hz but it also says the minimum base period id 31000ns even though it sets it to 100000. As you suggested even with a 100000ns base period the system should be capable of ~10000Hz.

I am also looking at rebuilding the machine. Now that I have used it awhile I see many opportunities for improvement. Replacing the threaded rod with better lead screws with more lead is certainly one improvement. I always figured I would use this machine to build the next one. I'm just trying to better understand my driver/motor capabilities so I keep any future mechanical changes within their limits.

Thanks.

John

In each case above ~3200Hz the motors stop turning and emit a louder vibration/tone.

In this case it is probably not the 3200Hz that is stalling the motors but the motors are unable to provide the torque to move at that speed.
Keep in mine with stepper motors after a certain rpm their torque drops off very quickly, as noted previously in this thread higher voltage may help. But it does have it's limits.
For example...
www.automationtechnologiesinc.com/wp-con...4/11/Torquecurve.pdf
Balls screws are more efficient and available in ratios that may work better for you.

Rick G

A quick follow-up...

I changed to a 48V power supply and now each axis is able to move at >4000Hz. About a 25% improvement is great for such a simple change. As part of a general mechanical rebuilding of the machine I purchased a 250mm C-Beam actuator bundle from Openbuilds during their cyber Monday sale. It uses a 8mm leadscrew with a 8mm lead. The reduced friction of the leadscrew vs. 3/8-16 threaded rod allows much faster travel. Changing to 1/4 stepping I get about 120 IPS at around 5000Hz. It will probably go faster but my Y axis isn't stiff enough to handle the forces generated by these speeds.

Y-axis upgrades are next...

Thanks for the help.

FYI - The C-Beam internal wheels allow too much deflection. If you are interested in the Openbuilds stuff go with a wider plate and external wheels.

John

I'm new to linuxCNC and I haven't quite grasped the limits and relationships between things. I'm currently running the nema42 stepper motors w/ no load and am getting some errors. If I run @ 200 s/r or 400 s/r (2 micros) I have no errors. But if I go to 4 or more microsteps I either get the realtime error OR if I manually increase the base period in the BOB.ini file from 62,000 to something greater I get "following errors" in running the axis test file.

Is there a theoretical (empirical) limit to the number of micro-steps an parport can do? I've never seen my jitter higher than 5.1us. Setting higher jitter doesn't seem to solve the "unexpected realtime delay on task 1". It also doesn't seem to matter w/ the step timings (for example 2500/2500/5000/5000). Not really sure what the MA2722M should be but I'm probably in the ball park.

Just trying to understand the best practices. Thanks!

nerdsite wrote: if I manually increase the base period in the BOB.ini file from 62,000 to something greater I get "following errors" in running the axis test file.

With a stepper system the "following error" means that the system simply hasn't been able to make enough steps to move the motor far enough.

If the base period is 50uS then is can only make 20,000 steps per second. If the base period is longer then it can make less.

What's the PC? 5.1uS isn't particularly good latency. Have you tried any optimisation?

I thought 5100ns was pretty good jitter (just according to what I read on this site). I've only used isocpus=1 for a dual-core G620 cpu. I've done nothing else other than using an external graphics card. If I get that down to, say 3000, will that make a big difference? Thanks.