Which Motor to Choose When Buy CNC Router? Stepper or Servo?

When you look for this answer, many pages on google you searched out may give you lots of data, and official explanation about the definition of stepper motor, servo motor, torque, terminology such words you may not familiar at all. And you feel so uncomfortable, do I have to study these very well, then can come to know which cnc router configuration I should choose for best choice? Stepper motor or servo motor?

servo motor http://www.cnczone.com/forums/attach...391056&thumb=1
Servo Motor http://www.cnczone.com/forums/attach...391079&thumb=1


Stepper Motor

I believe there must a way which can tell user how to choose, and this way must be much easier for user to understand and considering user’s benefit. Yes, it is. I am a file mover, I also searched a lot on google and listed some points of difference for servo and stepper, hope it is easier for cnc router purchaser to understand.

I think everybody willl think of cost.
if only considering this point, stepper is winner, its cost is lower than servo motor that has same power rating. Servo motor is more expensive, especially servo motors made in Japan, Germany . Servo motor we use is made in Japan, which is rather expensive than stepper motor made in China. Well, the stepper motor company we use is also cooperated with the manufacturer from Germany.

Speed & Torque
Servos are excellent in applications requiring speeds greater than 2,000 RPM and for high torque at high speeds or requiring high dynamic response. Steppers are excellent at speeds less than 2,000 RPM and for low to medium acceleration rates and for high holding torque.

Repeat ability
Because of the way stepper motors are constructed and operate they have very good repeatability with little or no tuning required. Servo motors can have very good repeatability if setup correctly. The encoder quality can also play into repeatability. So if you requires high precision work, we suggest you servo motor and driver to purchase.

Efficiency
Servo motors are very efficient. Yielding 80-90% efficiency given light loads. Stepper motors consume a lot of power for outputting, much of that is converted to heat. Stepper motors are usually about 70% efficient. This is also a good feature help you to decide which one to choose.

Least Heat production
Because the current draw of a servo motor is proportional to the load applied, heat production is very low comparing stepper motor. Stepper motors draw excess current regardless of load. The excess power is dissipated as heat.

NOISE:
Servo motors produce very little noise. Stepper motors produce a slight hum due to the control process. However OMNI offer high quality driver, and it will decrease the noise level.


I think above features could guide you to make decision which motor you better choose. Well, debate of stepper or servo that which one is better is useless, because which one to choose depends on the customer budget and the work he gonna do by cnc router. Tell the sales engineer your budget and the work you do, let him help you get a suitable configuration cnc router.

As a rule for the home/hobiest CNC it generally comes down to cost, while a stepper motor operates economically in most instances on small gantry's, the overall superior choice is servo's for many reasons, there is practically no professional made CNC machines that use steppers, I personally have always used servo's regardless of the size of the machine.
Al.

Hi just new here….so please do not shoot me.

“the overall superior choice is servo's for many reasons, there is practically no professional made CNC machines that use steppers, I personally have always used servo's regardless of the size of the machine.
Al”

As a newbie to this field, I would like to base my CNC 3-axis on servo motors. My bed is 380x380mm, this is my starting position and I would like to buy servo motors. I make watches, so precision is important

I think I want to use the Centroid Acord controller.

My confusion is some sellers call Steppers Servos and Steppers as Hybrid, but so far I cannot find/do a search that comes up with servo motors. Price is always a consideration.

My fall back position as I am an idiot and learning is the Clear Path servos. As they call them servos and I understand they are servos. More than happy to buy Chinese/Japanese/Asian…

Can someone point me in the right direction.

Thanks for reading and sorry to waste your time

D

Quote:

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Originally Posted by foxint

Hi just new here….so please do not shoot me.

I think I want to use the Centroid Acord controller.

My confusion is some sellers call Steppers Servos and Steppers as Hybrid, but so far I cannot find/do a search that comes up with servo motors. Price is always a consideration.


Thanks for reading and sorry to waste your time

D

---

We won't shoot you today :)

Centroid Acorn is just fine.

A servo system is any closed loop system with feedback to a controller and a controller output to a device. A home heating system for instance, the thermostat is the controller and the feedback device is a thermal sensor, the controlled device is the heater.

A hybrid stepper or closed loop stepper is by definition a servo system. In other words, it is a stepper motor with an encoder hung on it that feeds position data back to a drive to close the loop. It still has the limitations of a stepper system.

Since you want servos, take a look at DMM Tech https://store.dmm-tech.com/ and Automation Direct SureServo2 units https://www.automationdirect.com/selectors/sureservo2 Both of these are compatable with Centroid Acorn.

For a machine in your size range something in the sub-500W range would be in the ballpark.

You are not wasting our time at all, good questions. :)

Sir
Thank you.

Those pages were far more helpful than anything I have seen before.

I think I will go for the - https://store.dmm-tech.com/products/...c-servo-system. It is a kit and a little more powerful (0.75kW) than the 0.400kW for less than $100 more.

Unless you think this is a bad decision, I will give them an email.

Thank you. I knew if was not so hard that is seems impossible. The next steps are probably impossible... ha-ha.

I am so pleased with friendly response - again thanks.

D

I recommend Centroid Acorn plus ClearPath servos. Very easy to wire up and a quality setup.


Sent from my iPhone using Tapatalk Pro

My pleasure. Happy to help.

750W might be a bit overkill, but no problem, you won't run out of power. And you can always dial the power back.

Hi Koenbro,

Thank you. ClearPath seem very good.

I have looked at the ClearPath, but as I am a novice, the guys there were not too willing to help, aside with a ballpark set of parts. I totally understand and this is not a criticism of them. I did not provide the right answers.

A side issue is AUD/USD. Currently my bank has screwed up my Credit Card and is “fixing.” Teknic will not accept PayPal and I have USD in PayPal…so that is clouding my judgement.

I know that reads a little strange, but if the DMM product is similar…it may be OK.

I am in rural/regional Australia...so things can become difficult

D

While the ClearPath units are easier to wire with less external hardware required, they do have some limitations in the resolution. Where the DMM units have 16 bit encoders vs. the ~12 bit encoders (with the enhanced option) on the ClearPath units. Actually quite a bit of difference.

I have used the ClearPath, DMM, and SureServo2 units on various projects, and have been happy with the performance of all of them. If the DMM units fit with your needs and you can get them shipped to you, then that is a safe bet. The Automation Direct SureServo2 units are made by Delta, you might be able to find a local vendor for them. https://www.deltaww.com/en-US/about/Global-Operations They have corporate offices in Sydney, Melbourne, and Perth.

Hi Guys – thank you.

May I ask more??

The AU guys from Delta, did not return my 3 calls. So that is typical of Australian customer support.

In the DMM kit they have DYN2 AC Servo Drive - https://dmm-store-shopify.myshopify....ac-servo-drive

(Kit - https://store.dmm-tech.com/products/...c-servo-system)

As my friend pointed out, the Servo Drive looks like it has an OLD school printer port interface rather than USB. I have no PC with this old interface…. I am waiting on an email from DMM, but in the meantime, what do you guys suggest??

D

The interface port on the DMM units is a 25 pin D-sub connector like a printer port, but it is not a printer port connection. That is just the connector style that they chose to make the external connections to the drive. The drive is not connected to a computer at all for operation. You can use a 25 pin D-sub cable to connect to the motion controller I/O.

It does have a special USB cable for computer communication with the drive for tuning and setup, and I believe that cable is included in the kit.

EDIT: It looks like they have made a change in the DYN2 drives and have changed the interface plug, it's now a screw terminal plug. The breakout board they supply does have a printer port interface. You are going to need to get an ethernet or USB breakout to be compatible with your computer if you don't have a printer port.

Something like this https://www.automationtechnologiesin...ard-for-mach-3

I quite like the Lichuan AC servos you can find on Aliexpress.
The B2 and A4 servo drives are relatively straightforward if you can understand a wiring diagram. The documentation sucks a little in terms of wiring, but most AC drives have similarities and you can figure it out.

Thanks guys.

I had a nice conversation wit the PMM guys, they were super helpful. The Delta people here in AU were expensive. Generally buying from anywhere but here is better than buying here.

I had a discussion with my local CNC friend, and he was questioning the Acorn. He seems to think there are better boards (cheaper and newer tech). He is suggesting that the Acorn is using Old tech and there is something better.

I know I am not explaining myself well, because I am not understanding the problem.

Is there an option for a novice like me?

D

Hi,
I got (last week) two Delta B2 series servo kits (servo/drive/cables), a 750W and a 400W.

The 750W was $435USD
The 400W was $390USD
Shipping was $285USD..........DHL, four days from Hong Kong to New Zealand

Clearpath are good quality but have limited IO, low resolution encoders and are just too dammed expensive for their power output. Delta kicks their arse!

Craig

Hi,
I use Mach4 ($200USD license), and have done so for seven years, with an Ethernet SmoothStepper (Victorian reseller charges $190USD).
It is broadly speaking more flexible than the Acorn.

UCCNC software ($60USD license) and a CNCDrive motion controller (approx $160USD depending on model) and breakout board/boards are another good choice. Easily a match or better than the Acorn.

LinuxCNC (free and open source) software and a Mesa board (approx $200USD depending on model) is a very capable solution provided your OK with a Linux platform.

Craig

Hi Craig – thank you.

The local AU Delta guy quoted me Servo Motor A3L Low Inertia 700W 3000rpm AUD635 for 1. The PMM seemed a lot more reasonable at about 50%

I am not good with Linx. I tried a Raspberry Pi and after a while I went back to Windows.

Dan

Hi,
an A3 series for 635AUD....thats good buying.

The B2 series is Deltas entry level, it has a 160,000 count per rev incremental ecnoder.
The A2 series has a 1,289,000 count per rev incremental encoder....and dual position sensing.
If you can get these for as sharp a price GET IN MATE!!....and let me know....I could be up for some more myself.
The A3 series has 1,280,000 count absolute encoder.
The B3 series has a multiturn absolute encoder....and is their latest and greatest.

Craig

Hi Craig

DEVAECMA3LCY0807RS1 Servo Motor A3L Low Inertia 700W 3000rpm (24 Bit 3 Absolute Encoder)

The DMM (Dynamic Motor Motion)

85M-DHT-A6MK1 86mm Frame 0.75kWm medium inertia.

Are we comparing apples with apples?

Dan

Hi,
both servos are good and would make a fine addition to any hobby CNC machine.....but two models are not the same and some of those differences are significant and
affect the price considerably.

The Delta A3 has a 24 bit (16,777,216 count per rev) absolute single turn encoder.
The DMM DHT model is fitted with a 16 bit absolute encoder. Note that DMM do offer other models that include 32bit multi turn absolute encoders, with and without battery backup,
at no doubt a price premium.

The DMM model you linked to compares very closely with the Delta B2 series, while the A3 series is two generations later, and rather puts the DMM into the shade. Not that there
is anything wrong with the DMM, I could swap them for my Delta B2's on my machine and wouldn't be able to tell the difference in performance

To be honest the multi-turn absolute encoders are out of my price range.....and with Mach4 software that I use I'm not at all sure I could take advantage of the multi turn features anyway.

As I posted earlier I use B2 series servos with 17 bit (160,000 count per rev) encoders and they are superb....with more resolution than I can use as is. What more do I need?
Truth is....not much. There is one feature that I would like, even if at the moment I can't afford the extra hardware to take advantage of it, is dual loop sensing.
Such a servo drive has its regular rotary encoder feed from the servo, and is of course essential to be able to control an AC servo, but has a secondary encoder input
from say a linear scale. This allows dual loop, and is also called 'load sensing' and is the last word in position feedback control. the A2 series has it, as does the A3 series and I'm guessing
the latest B3 series will have it also.

If the B2 series is the cheapest that Delta make, their entry level, then the A2 series is one step up, and is available at really sharp prices. If I were buying again I would go for A2's or even A3's if the
price was right. Having said that my existing B2 series are very good indeed, much better than I even imagined....being my first use of AC servos outside of one Allen Bradley servo I use as a
spindle motor.

Craig

Hi Craig,

Thanks for the explanation.

I suppose AUD3,000 vs AUD5,600 is a reasonable difference for just the motors/controller and not much else.

From what I am understanding, the DMM would be fine for my small needs. Eventually I want to make watch parts, watch cases and alike.

The guy at DMM was insistent that the Acorn was good. So I am back were I started….ha-ha.

But my local friend is suggesting - https://openbuildspartstore.com/blac...ontrol-system/ . It is far tidier.

With more knowledge brings greater confusion.

Thanks again
Dan
PS… time to feed the dogs and will probably feed myself at the same time.