Hybrid Stepper motors or Closed loop?

Hi everyone,

I'm designing a 2'x4' cnc router with a 3 kw air-cooled spindle and 15mm ballscrews, but i'm running into an issue. Servos are well out of my price range, so I was looking at close loop steppers like this one: NEMA 23 Closed Loop Stepper Motor System-Hybrid Servo Kit, 32 bit DSP Based | Automation Technology Inc. My only concern is that the stepper is only has 282 oz-in. of torque and i'm not sure if that's enough for this table size. The open loop stepper I was looking at was 570 oz-in. or torque.

Any suggestions?
-Patrick Youssef
CAD Student on FRC team 1671

There was a thread about closed loop steppers a few months ago with lots of discussion.

From my perspective it is of limited use. The closed loop may give you signal that you lost steps but if you overload the stepper(e.g. too much acceleration of other forces) then it will just stall, closed loop or not. Unlike servos the closed loop driver will not increase torque to make good for it (as far as I know) it will just try to repeat the missed steps. But my knowledge may be outdated here.

And, as you mention, 282 in-oz may be a little on the low side for your heavy spindle and the mid-size machine. At least if you want to run it at reasonable speed.

The 282 might actually be stronger at high speed than the 570 motor, depending on the specs of the motor. It's impossible to say without comparing the torque curves for the two motors.

This is the link for the open loop stepper motor. It would be paired with a keling digital driver. NEMA23 570oz/in 5A 3/8? Dual Shaft Stepper Motor (KL23H2100-50-4B) | Automation Technology Inc

They don't list a torque curve for that motor, so you really have no idea how it will perform.
I've never seen anyone using them, either, so there's just nothing to go by.

I have seen a few posts that make it seem like the 570 oz motors do not perform well at higher speeds.

What's the pitch of your ballscrews? If they are 5mm, then I would guess that those motors might be OK, as smaller motors can spin a lot faster. If they are 10mm or higher pitch, then I would guess that these may be underpowered.

But these are just guesses, as I haven't seen any data to go by.

I am using 5mm pitch ballscrews for all 3 axes, and I saw a link for the toque curve at the bottom of the automation technology page. Also, opinion on these linear rails? AGW20CB1TxxxxZ1H, Combo, 20mm T Rail, 4 Bolt Flange Block, Specify Length, Hiwin AG 20 Combos - automation products from Automation 4 Less

There's no torque curve for the closed loop stepper, though.

Those are decent bearings at a very good price. I'll be using the heavier duty version on my new router. Note that that package only contains one bearing, and you'll want/need two per rail. You can get more here. automation products from Automation Overstock: AGW20CAZ1H, 20mm Bearing Block, 4 Bolt Flange, Hiwin AG 20 Blocks

Also be aware that it can be difficult to mount those rails from the bottom, depending on your machine design.

I was able to find the torque curve for 48v in the Manuals and Download, it's the first link. And i'm still trying to figure out a way to mount that rails, although you cant beat the price. Thanks for all the help!

OK, the nice thing about that torque curve is that it **should** be fairly accurate, as you'll be using the exact same drive the curve was generated with. With open loop steppers, there's no guarantee the curve will be anywhere even close to a published curve, as you'll most likely use different drives and settings.

Looking at the curve, it looks like you'll have about 150oz-in of torque at 900 rpm. You'll need to determine if this is enough torque for your application. If you need to go even faster, is the available torque at that rpm sufficient.

Alright, so you recommend using these over stand open loop? Also, is it necessary to have dual ballscrews for a 3 foot wide gantry. We may even move up to a 4 foot wide.

Uh, I didn't recommend anything. I haven't used either one, and don't know what you need them to do, or if they'll be able to do what you want.

I would recommend the dual screws, though.

Hello,
What do you all think about this product NEMA34 1128 oz-in closed-loop stepper Motors 4 Axis CNC Kit (110VAC/220VAC) - See more at: NEMA34 1128 oz-in closed-loop stepper Motors 4 Axis CNC Kit (110VAC/220VAC) | Automation Technology Inc ? Is there any issue on controller? Is this system working OK?

Thanks.

ypatrick

Almost the same cost as getting/using ac servos
DMM | AC SERVO DRIVE | AC SERVO MOTOR | ROTARY ENCODER