[moonblack]

Hi,

Recently I resumed my cnc build that was put on hold, it's a two layers 16mm MDF for each piece, based machine. I have almost all the bits figured out the only thing that bothers me is the steppers choice. Link to the machine plan : DIY CNC Router for modelers - RC Groups

The machine will be used mainly for RC planes parts, balsa, plywood, carbon fiber, delrin to +/- 3mm thickness and foam. The work area of the machine is 625x330mm and z-axis is 110mm max

I read about unipolar and bipolar types and their advantages an drawbacks, but still don't quite understand it. Are 4 leads steppers always bipolar and 6 leads can be unipolar or bipolar ?

From: UniPolar vs BiPolar wiring schemes for 2-phase Stepper Motors

Unipolar/Bipolar Connections (2-Phase Motors)

Unipolar and Bipolar Half Coil, because we're using less turns, doesn't give us great low speed torque, but because of the low inductance, holds the torque out to high speeds.

Bipolar Series uses the full coil so it gives very good low speed torque. But because of the high inductance, the torque drops off rapidly.

Bipolar Parallel also uses the full coil so it gives good low speed performance.
And its low inductance allows the torque to be held out to high speeds. But remember, we must increase current by 40% to get those advantages.


I narrowed the choice to three different kits I found on eBay.

The first one is with nema23_270oz-in 4 leads, the second one is nema23_287oz-in 6 leads (287oz-in only in bipolar mode), see pictures.

If I understand correctly wood working, you need to go "fast" but reduce spindle speed so not to overheat the material, for high speed high torque is mostly dependent of the type unipolar/bipolar phase inductance, voltage and current.

Based on this the first kit (1.8mH, 3A, 3V) would be the best choice (the second one has 18mH, or is it a typo ?), but again what do i know about this, I'm a newbie after all.

The third kit his some monster nema 23 with 425oz-in and 4 leads, but the weight (1.55kg) of those motor is a bit to much for the Z axis of my machine, so I'm not to incline to them, but if they would give me the room to have a lot better machine I will find a way to cope with the weight.

So after all this long post (sorry), could someone help with my Cornelian choice ?

Thank you.

[SteveWill]

I like the spec of the 270 , but do not know if 270 is enough power. The other two I do not think the power supply voltage is high enough, but probably that is the max the drive board can handle.
I have a home made CNC like your and use the following and am happy with the parts.

NEMA23 381oz/in 3.5A Dual Shaft Stepper Motor KL23H2100-35-4B | Automation Technology Inc
4Axis5: BOB/Pulse/Power(PC Board ONLY) massmind Also got a break out board and cables from them. These are kits and you have to build them.
I got off E bay a 40V Adjust DC 9.7A 350W Regulated Switching Power Supply
I also need 5 volt got a wall plug in to supply it.

Added 1/2 inch thread all 13 pitch

[ger21]

What is the pitch of your leadscrews?
And what drives will you be using?\

All the components should be matched together.
Power supply, drives, motors, and screws must all work together as a matched set for best performance.

[moonblack]

@Steve thanks I'll check your link.

@Gerry, II bought them on eBay, they are the same as the ones in the picture only the lengths are different to correspond to my frame.

The chart says that the lead of 1605 ballscrews is 5 (metric I suppose), lengths are 320/520/820mm

Drives will be DM542A based like these : 2-4-phase-Nema23-Stepper-motor-driver-128micsteps-4-2A-DM542A

Power supply is 30V/9.7A


btw just found this very nice thread about ballscrews, need some time to read and digest it : http://www.cnczone.com/forums/linear...-software.html



Paulo

[ger21]

Of those 3, then I'd definitely go with the first one.

[moonblack]

Thank you Gerry for that confirmation.

So nema 23 270oz-in it is.