New mill, which motors?

[Robin Hewitt]

I am a bit out of touch, what is good in stepping motors these days? Have they improved?

Robin

29263

[Voicecoil]

Closed loop types seem to be much more affordable now, and would be my route of choice, less chance of losing steps when going hard.

[pippin88]

Budget? Consider servos: Delta AC servos are excellent.

[Robin Hewitt]

I was thinking more along the lines of £100 per axis.

I saw closed loop on Bang Good for £46 per axis, is that the ones?

I'd like 5um per half step so I'm thinking 2:1 down on to a 4mm screw. I ordered 3 screws and 8 nuts with custom end machining from Wendy Wu. The FedEx costs more than the parts :thumsup:

[Muzzer]

How do you plan to drive the Z axis? On a Bridgeport head you have access to the quill via the feed stop but on your rather nice machine I don't see anything like that. Some sort of collar on the base of the quill?

[Robin Hewitt]

Absolutely right, it has to be the quill for the Z axis but I haven't figured out how to do a quick release for drilling. Needs thinking about.

[Muzzer]

I originally planned that on my Bridgeport conversion but after using my CNC-only Shizuoka for a while (it never had any handwheels), I decided that for me there's no point retaining manual controls when you have a wireless MPG. This achieves the same effect (handwheel controlling quill and table movement) yet can be used almost anywhere. You also get consistent and deadly accurate operation with DRO readout and the moment of inertia of the X&Y handwheels wasn't improving the servo responses on my system. I often do manual operations using the MPG such as squaring up stock, slotting, drilling holes etc.

I'm starting to have similar thoughts about my lathe conversion, having started out planning to retain all manual controls. Instead I think I'll keep the manual parts in case I sell the machine and go fully CNC.

[JAZZCNC]

What Nema Size you wanting Robin 23/24 or 34's.?

I've got some Lichuan Nema 24 5.5Nm 2 phase closed loop with 70V AC or 100Vdc drives with 3Mtr cables which I'm offering to Forum members. £125.00 plus postage.

https://www.aliexpress.com/item/1005001370469790.html?spm=2114.12010612.8148356.11 .568f4df8dMSFFL


Also got some Closed loop 10Nm 3 phase Nema 34's using Mains voltage drives but those might be a little too large and expensive.
These are great for large machines where high speed isn't required and simplicity is prefered to more complicated servo's. The motors are nice and smooth being 3 phase and with being mains drives they still spin at resonable rate with good torque at higher rpm's. The closed loop makes them nice and reliable in position terms.

If you don't require what Servo's offer then they are good option and pretty much plug n play with no messing around tuning etc.


https://www.aliexpress.com/item/32799243070.html?spm=2114.12010612.8148356.1.42906 f37My63lC

[Robin Hewitt]

Good question, no good answer, I don't know what I want...

High speed may be preferable to high power?
Cool running is nice.
A sexy power against speed graph that doesn't fall of a cliff could get my juices flowing.
Something that doesn't come in sets of 3 is handy because X and Z can be very different.
I do know it will drive a 4mm ball screw using timing pulleys, I have a thing about XL pulleys :joyous:

[JAZZCNC]

Good question, no good answer, I don't know what I want...

High speed may be preferable to high power?
Cool running is nice.
A sexy power against speed graph that doesn't fall of a cliff could get my juices flowing.
Something that doesn't come in sets of 3 is handy because X and Z can be very different.
I do know it will drive a 4mm ball screw using timing pulleys, I have a thing about XL pulleys :joyous:

Robin modern Digital drives are completely different animals to old Analog drives, they are light years better and run motors much cooler with much much smoother operation.
The minute the motor spins you'll understand what I mean because they sound very different as well, much quieter. And with the newer closed-loop, esp the 3 phase motors, they have taken another, if slightly smaller leap forward.

You'll find with the new breed of steppers/drives you get higher rpm's and they carry the torque higher up the curve. Also. with most of the drives allowing AC connections, you don't have to mess around building DC PSU, just hook them up to a transformer, and away you go.

[Robin Hewitt]

I see what you mean...

This doesn't look half bad for £72, UK stock, it has the closed loop but not the 3 phase.

29279

Slightly naughty testing at 48V when they suggest 36V typical but good enough.

0.8Nm falling to 0.5Nm at 25 rps, I could get anywhere in the machine envelope in just 12 seconds. Maybe faster, they say it can do twice that before it clacks out.

Next question, three 36V 5A PSU's or one 15A? :whistle:

[Voicecoil]

I would guess they suggest 36V to allow for back EMF from the motor and variations in mains voltage when using an unregulated supply, which could momentarily bump it up by 10 volts or so. If you were running at 48V nominal with a 50V drive then that would make 58V which would quite possibly fry the drive, though you can add a clamp circuit to prevent this.

[Muzzer]

The best solution for these low voltage drives would be a regulated (switched mode) power supply combined with a clamp circuit. That way you could safely operate a 48V drive at around 45V or so, to exploit the higher speed capability to the full. I haven't seen a clamp circuit available or in use (haven't been looking, mind) - is there something readily available on the market?

It tends to be periods of rapid deceleration that result in overvoltage due to regeneration of the kinetic energy back into the DC bus. One simpler option might be to limit the deceleration setting (or acceleration if not controlled independently). That way you could run fast rapids as long as your e-stop didn't try to force a quicker stop.

[Robin Hewitt]

Good point. I just ordered 3 of the next size up and a 36V15A power supply
29280
The extra Amp to compensate for the lower voltage
The hasty purchase because we may be entering interesting times... :encouragement:

[Robin Hewitt]

Muzzer you jumped in while I was in mid-reply...
I shall start at 36V and if that's not enough then 48V and clamps it is.
When you say clamp is this the infamous crowbar circuit with a fat DIAC hard across the PSU to blow the fuse?
Cool! :beer:

[Muzzer]

No, I'm thinking of the "chopping / braking resistor" concept. Acts like a giant zener diode. Usually they have a switching transistor and a low value resistor. Once the voltage exceeds a threshold, the PWM duty cycles increases over a 5-10V band. That's the mechanism used within VFDs and servo drives but they are also available as standalone "braking units".
https://inverterdrive.com/group/Universal-Brake-Chopper/WEG-DBW03-Braking-Module/

CNCdrive do one, although I had to repair the one I bought after it broke down across one of the insulators. A lot of the compts we use on our systems are little more than hobby grade - along with the low price you have to expect questionable quality or design and manufacture.
http://www.shop.cncdrive.com/index.php?productID=260

A big f*** off zener diode would do the trick but it's not very sophisticated and choice is rather limited.

[Voicecoil]

I couldn't find one so made my own - like you say a big fat switching transistor and a big (100W IIRC) wirewound resistor - I'll PM you the circuit if you want.

[Muzzer]

You can even use a hysteretic controller where the switch turns on above a high threshold and stays on until it falls to a low threshold. Can be implemented with just one comparator. As long as the switch is turned on and off cleanly, it doesn't care - and as long as the resistor value is low enough it will control the transients when they occur.

I suspect for most of our machines, the resistor would barely get warm. An LED would be a useful indicator to give some idea if it actually does anything. I might try that on mine some day - it needn't be much more than a resistor and LED across the braking resistor.

[Doddy]

Genuine interest... why not a TVS/MOV device? (I can guess at tolerance/variance at the switching voltage - but that is just a guess).

[Muzzer]

Yes, usually the combination of the limited number of nominal voltages and the tolerance. They aren't too bad actually but you may struggle to find a voltage that is much above 36V but safely below the max allowable voltage for the drive. I'd be more confident in MOV than a TVS but that probably won't make much difference here. They are both deadly fast, so speed isn't an issue.

[Robin Hewitt]

Gosh I am out of date. Mind you, the power feed I am rewiring uses a DIAC for the speed control so I am not completely passed it :wink:

[Muzzer]

Yes, I remember them. Presumably used in the gate of a triac or scr, then. That dates the controller, as that threshold function has been built into triacs for many years now. I'd guess 1980s, most likely.

[Robin Hewitt]

1980's? Warco sold it as new :pirate:

[Muzzer]

Perhaps an SCR drive then, as SCRs don't have a 30V threshold on them. But even so, the market for diacs is very limited these days.

What's it driving? Is it a triac or an SCR?

[Robin Hewitt]

SCR that's the beastie, my ageing brain has obviously succumbed to the barrage of transient ischaemic attacks.

Fortunately, I can still understand how the circuit works even if I can no longer name the individual components :smug:

[Robin Hewitt]

Motors and PSU have arrived, I wasn't actually expecting them before 10/1/21 :smug:

Look great, comfortably heavy.

I read the manual and just when I thought it must be reaching the bit about the USB connection it suddenly stopped, repeated itself in German and ended.

Guess you aren't supposed to use that part :topsy_turvy:

[hanermo2]

Good luck mate.

Upto about 100$ some steppers are ok for better stuff.
After that, ac brushless servos are the right choice - about 5-7x better by every possible measure.
About the same money, all-in.

Lets see how it works out for you.

[Robin Hewitt]

A bit late now, I am already compensating for my poor choice by printing lightweight handles :beer:
29283

[Muzzer]

I had large cast iron wheels like that on my Bridgeport. I couldn't get a decent response from the DMM servos until I removed them. Their moment of inertia was much bigger than the ballscrew itself and the reflected inertia of the table and vise, particularly on the X axis which had 2 of the buggers. As I have an MPG, turns out I never use the handwheels anyway but your solution would be a pragmatic middle way.

[Robin Hewitt]

Oh yes, don't give up on your handles, I am fighting to keep the dials. What is MPG? Miles per gallon doesn't seem to fit the context :topsy_turvy:

Not fighting to keep these ghastly, spring-loaded, press in before you can turn it handles though.

New handles need paint - wondered if aluminium coloured paint existed - had forgotten about alloy car wheels - spoilt for choice :eagerness:

29287

[Neale]

MPG - manual pulse generator. Handheld controller, pendant, or somesuch. My router doesn't have handwheels and I don't bother on my mill either. Wireless mpg or MDI on controller does the job. It's easier than folding out the handles on the handwheels and quicker as well - I can't wind by hand that fast!

[michaelmo]

What Nema Size you wanting Robin 23/24 or 34's.?

I've got some Lichuan Nema 24 5.5Nm 2 phase closed loop with 70V AC or 100Vdc drives with 3Mtr cables which I'm offering to Forum members. £125.00 plus postage.

https://www.aliexpress.com/item/1005001370469790.html?spm=2114.12010612.8148356.11 .568f4df8dMSFFL


Also got some Closed loop 10Nm 3 phase Nema 34's using Mains voltage drives but those might be a little too large and expensive.
These are great for large machines where high speed isn't required and simplicity is prefered to more complicated servo's. The motors are nice and smooth being 3 phase and with being mains drives they still spin at resonable rate with good torque at higher rpm's. The closed loop makes them nice and reliable in position terms.

If you don't require what Servo's offer then they are good option and pretty much plug n play with no messing around tuning etc.


https://www.aliexpress.com/item/32799243070.html?spm=2114.12010612.8148356.1.42906 f37My63lC

Hi @JAZZCNC,

Might be an odd question, but with the 220V drives do you find it necessary to step the incoming voltage down to suit? Interested in trying out some 34's in the 10-12 range and just looking to see how others have done it - assuming 30A supply single phase?

Thanks.

[michaelmo]

What Nema Size you wanting Robin 23/24 or 34's.?

I've got some Lichuan Nema 24 5.5Nm 2 phase closed loop with 70V AC or 100Vdc drives with 3Mtr cables which I'm offering to Forum members. £125.00 plus postage.

https://www.aliexpress.com/item/1005001370469790.html?spm=2114.12010612.8148356.11 .568f4df8dMSFFL


Also got some Closed loop 10Nm 3 phase Nema 34's using Mains voltage drives but those might be a little too large and expensive.
These are great for large machines where high speed isn't required and simplicity is prefered to more complicated servo's. The motors are nice and smooth being 3 phase and with being mains drives they still spin at resonable rate with good torque at higher rpm's. The closed loop makes them nice and reliable in position terms.

If you don't require what Servo's offer then they are good option and pretty much plug n play with no messing around tuning etc.


https://www.aliexpress.com/item/32799243070.html?spm=2114.12010612.8148356.1.42906 f37My63lC

Apologies for the hijack, just wondering if it's necessary to step down the mains voltage for the 220V drivers?