curious about motor speed vs travel speed

[Angie Orfanedes]

I have Nema 23 steppers on my CNC router with rack and pinion drives, which provide about a 3:1 step-down in speed; see
http://www.cncrouterparts.com/rack-a...a-23-p-50.html

My machine can travel about 1000 ipm, but I find that a bit scarey so I usually keep it below 200 ipm. The motors are driven by this controller, which is a popular one for home hobbyist CNC machines as well as some commercial ones:

http://www.geckodrive.com/geckodrive...ives/g540.html

Look at the bottom of this page for the documentation.

Angie

[Neal Schlee]

I have Nema 23 steppers on my CNC router with rack and pinion drives, which provide about a 3:1 step-down in speed; see
http://www.cncrouterparts.com/rack-a...a-23-p-50.html

My machine can travel about 1000 ipm, but I find that a bit scarey so I usually keep it below 200 ipm. The motors are driven by this controller, which is a popular one for home hobbyist CNC machines as well as some commercial ones:

http://www.geckodrive.com/geckodrive...ives/g540.html

Look at the bottom of this page for the documentation.

Angie

I've rebuilt Multicam R&P transmissions more than a few times. The CNC Router Parts tranny looks to be a very nice and simple solution for R&P stepper systems, reasonably priced to. Just needs a dust cover.
And of course Gecko stuff is good too.

Neal

[Michael Weber]

Thanks Angie. I looked at the specs and noticed a much higher pulse input frequency than I am using. I did manage to speed up the motor rpms above the preiviouis high of 375 by ramping the frequency slowly per John's post. I was just curioius how the cnc machines achieved the high ipm speeds. I read a bit this morning about stepper motor theory but mostly just gave myself a headache. If and when I persue this interest it will certainly be with an available kit.
thanks to all

[George Carlson]

Stepper motors are current driven devices. Because the windings have quite a bit of inductance, it can be difficult to bring the current uip quick enough to get decent torque at high speed (dI/dT). To get around this, drivers use higher voltages with circuits that limit the current. If you see a voltage rating on a stepper motor, it is the voltage required across the winding to get the proper current at stady state. Most small steppers are run using 24V supplies. Supplies up to 48V are common for high proformace systems.
Using microstepping can really help improve torque. With the proper drive/power supply you should be able to run at 3000RPM without any problems.

[John McClanahan]

I have built 2 stepper driven router tables, and I would say that your speed is correct for your setup, and nothing is wrong. Your drivers are set for half stepping, hence the 400 steps per turn. To get more travel speed you need far fewer TPI on the lead screw. Some setups use as few as 2 turns per inch of travel. That would be a 10 TPI, 5 start screw.

Unlike regular motors, steppers produce maximum torque at slow RPMs. As the motors speed up they will loose power, to the point they simply stall and squeal, even with no load. I don't mean to argue, but unlike servos, steppers don't run in the thousands of RPMs. A few hundred is more like it.

Stepper motors have a bad habit of producing a lot of vibration at medium speed. Fractional stepping, or micro stepping helps to reduce this. Micro stepping increases resolution, improving machine accuracy when a low TPI lead screw is used, or with a rack and pinion drive. Micro stepping also requires higher pulse streams from the controller. For older, slower PCs, this can sometimes be a problem, and limit maximum speed.

A good source for information is at geckodrive.com. They have a FAQ section that explains things well. Also check out cnczone.com.

John

[Michael Weber]

Thanks John, good info.