Max "move" Speed on a PRS Standard

[Howley]

I typically run my new 2013 PRS Standard (4x8) at 3"/Move and 10"/jog.

So I tried bumping the move speed to 10"/sec, it worked for a little and then it lost communication for the first time ever. I continued on and it drove my v bit almost through the table, I had to reset the CNC and computer and re zero to get it to work again.

Soooo

My question is this, in your experience what is the fastest, yet totally reliable speed you can set your move speed on a PRS Standard?

Thanks in advance for any feedback!

[Brady Watson]

...what is the fastest, yet totally reliable speed you can set your move speed on a PRS Standard?


Totally depends on your COM efficiency. 6 IPS is about the limit for most machines, although 8 IPS is not unheard of. Steppers have their most torque @ rest & lose a LOT of torque as you get up into those higher speeds.

-B

[mikeb]

I normally cut 3-3.5 and jog at 6 while using .25 downcut , taking .25 per pass cutting melamine. I just upgraded my standard to a spindle , have not tried boosting the speed yet. It would be nice to know what kinds of speeds other standard users are achieving without losing steps(both move and jog).

[jerry_stanek]

I cut sintra with a .125 bit at 5ips and .25 bits at 6ips

[Brady Watson]

http://catalog.orientalmotor.com/Asset/pk296b1a-sg_stc.jpg

If you look at the bottom most pic, it shows a PK296-SG3.6 (very similar to the motors on a Standard) @ 48v. If you are running a 25T pinion gear with a Unit Value of 1833.461 (XY), that equates to 3.927" per revolution of the output shaft & requires 7200 pulses from the controller to do it.

Steppers are like diesel engines - lots of low end torque, but they fall off pretty quick. If you look at the graph, you'll see how the torque falls off @ 50 RPM and then really starts to fall off @ 100 RPM. If my math is right, this equates to about 3.4 inches per second @ 50 RPM and 6.8 IPS @ 100 RPM - so you want to take care when cutting at those higher speeds or you may stall the stepper and mess up your work.

SB3 is capable of theoretically pushing those motors up to about 25 IPS / 375 RPM - assuming 45,000 pulse rate (SB3 capable of higher than this) but there just isn't enough torque at that speed to move the gantry around. With 93% COM speed I was able to get a PRS-S to Jog @ 17 IPS, but that was with just ONE axis jogging. When you tried an XY jog, it would choke above 14IPS.

My advice would be to test speeds on your tool both single axis (like the X only) and an XY jog to see what you are capable of doing. Running a non-Alpha machine takes some prudence to make sure you don't stall the motor or break the magnetic lock by throwing more at it than it is capable of delivering. You can cheat a little by adjusting VR settings, but you still run the risk of lost steps. There's other electronic stuff going on behind the scenes too that can influence top speed, such as microstepping to full stepping morphing - but I'll spare you the details.

I've learned that customers pay for quality - not speed. Even if they want it in a hurry - I'm not putting my name on a job that looks like it was cut with a hack saw. Haste makes waste.

-B

[jTr]

Out of curiosity, what would be the result of stalling those steppers on an Alpha,
simply lose communications and error out?

[Brady Watson]

Alphas can choke and stutter if COM speed is not fast enough to feed step & dir signals to the driver fast enough. When you run SpeedTest.exe, it tells you that 70%+ will let you run full speed (12 IPS on an Alpha), but if you are unable to hit that target, the motors will either choke or sputter/stutter. You should not lose position if this occurs, but the prudent thing would be to make sure your COM hardware is tip-top and up to the task of running a robotic tool.

Alphas have a totally different set of rules because they do some exotic things behind the scenes to get high performance results. All SBs are governed to 12 IPS when cutting (M moves) and 30 IPS when Jogging. I recommend keeping Jog Speeds below 20 IPS since you really don't need to go that fast & the Alpha gearboxes are only speed rated to about 22 IPS max. The AS911 PRTAlphas were capable of 70 IPS :eek: ...but who needs that?

-B