Replacing STEPPERS for DMM-TECH AC Servos

https://youtube.com/shorts/rcaAeJ1-hig?

Here is a short video showing the first motion test with the DMM-TECH 400watt AC Servos on my elite foreman.

The stock stepper motors have 1.2Nm peak holding torque which drops as the motors RPM increases. Their resolution is 400 points per revolution (PPR). This works out to 0.04mm or 0.00157" per point.

The DMM-TECH 57N-DHT AC Servo motors have a CONSTANT torque of 1.27Nm no matter what the RPM and peak torque 3.82Nm. These are closed loop motors with 16bit encoders, this means the resolution could be set way higher than the Masso G3 can even handle. I set the resolution to 8000 PPR (this is what dmm recommend) which works out to 2 microns per point 0.002mm or 0.000078". These motors are leaps and bounds over any brand nema23 steppers motors whether they are opened or closed loop. The Z motors also has a breaking system to prevent spindle drop.

This upgrade is not for everybody and most people will think it’s unnecessary and overkill. But when I see people putting ATC systems on a hobby machines with tiny stepper motors I shake my head. Why invest all that money if the motors are the weakest point. All the commercial cncs I have run in the last 20 years. Use Servo motors instead of steppers. So for someone like me steppers we’re not really an option in the first place.

2 Likes

Looking forward to the build update.

I opted to use high torque steppers of my own choosing when I first started my Woodworker build, and from my experience and testing, believe overall rigidity to be more of a factor when machining than the motors.

Having said that, I have been researching servos for a long time and when funds permit, may still add them as an upgrade. I had narrowed it down to either DMM (which I like as a Canadian), or Delta. Which series did you decide to purchase? Did you buy one of their multi-axis kits, or separate components?

1 Like

hey,

We spoke about this on the Masso forums a few months back, I went with DMM because I am Canadian also but not only that i currently live in BC and their located only a few KM from where I work. I have also used the NEMA 34 motors and dyn4 drives on a previous retrofit i did on a 5’x10’ commercial machine.

When i contacted dmm about the swap they suggested the DYN2 AC Servo Drives
paired with they 400 watt NEMA 23 57N-DHT 0.4kW AC Servo Motor
The Z motor has an integrated brake.

This required me to build a whole new controller and replace all the wiring as well. The cables are pre-made by dmm are shielded and designed for the application of being folded in a drag chain.

New couplers were required and adapter plates were also required as their “NEMA 23” bolt pattern is a little different. I dont think any decent company makes a true NEMA 23 servo motor, they all seem be 60mm motors that are modified so the bolts holes never truly match a proper nema 23 hole pattern.

Obviously the stock power supply cannot handle this upgrade. I bought a 63VDC 1500W Power Supply designed for Servo applications because i am adding a 5th motor and drive to run the 4 jaw rotary axis I have.

I welded a aluminum box to fit everything and use double shielded CAT8 cable for the motor connections between the masso and the new controller box. I still have so cable management to do but its almost done.

You are correct about the overall rigidity of these machines but its also not the only machine i own. I am also converting a PM-833TV Ultra Precision Milling Machine – Precision Matthews Machinery Co. to CNC with AC servos that run on ETHERCAT. This 1f machine will be fine for most of the stuff I will be using it for. I’m pretty sure you are running an expensive ATC on your setup, which is nice but im not sure if it work the investment on a machine of this caliper. None of the commercial machines I currently run have an ATC so its not like i need one. To me this was a necessary upgrade just to get the finish i am used to. I know i can get a decent enough finish in aluminum on this 1f machine if the motor resolution is high enough.
check out my video here…
https://youtu.be/ItUUSBJ2t-4

2 Likes

Thank you for the reply (and video link), and apologies for not remembering any past forum discussions.

I would like to know if you see any improvements machining aluminum with the new motors - that would be a reason for me to upgrade in the future. I am getting good results now, but I am working slowly with very conservative machining parameters - fortunately this is currently for hobby use, and I do not need to worry about high MRR or high output production.

Your enclosure looks great - I like the AnTek power supply. Is the purple cable from Igus? Also, did you add the two small capacitors on the DIN rail distribution blocks for back EMF/voltage spike protection?

I looked these up:

4 motors (1 with a brake) and 4 drives comes to $1721. How do these compare with Clearpath servos?

I have no experience with clearpath but someone made a video years ago that should answer your question.

https://youtu.be/bWmG3iLRrII?