Centroid Community CNC Support Forum

For those that don't know, DMM technologies makes an inexpensive closed loop AC servo system that will take step and direction which works well with the Acorn board.
The same drive can take an 0-10v analog signal from Acorn and drive a servo motor as if it were a straight AC motor and a VFD. Basically tell it how fast to turn, and it goes until you tell it to stop. It has an input connection for reversing and one for enable. The drive also has an encoder output that has line drive ABZ quadrature encoder signal. This goes to the Acorn encoder input so you can close loop the spindle for rigid tapping and threading as Centroid intended.

Their motors range from .05kW to 1.8kW. That's almost 2.5HP!

Since the drive can do both step and direction and analog RPM, I wondered if I could use a single motor to drive the spindle, and also function as a "C" axis?
The answer from DMM was initially "NO" because the modes have to be switched via a USB cable and a program on a PC. However, after several email exchanges and phone calls, we determined that they could modify the drive firmware to switch modes with an input pin. I agreed to beta test and they said they would not charge me for the modification if I agreed to document my progress here and through some videos.

I have ordered my drives; I should have everything by January 2nd!

If this goes well this will be a much less complicated way to have a "C" axis on a lathe. One motor, one set of mechanics, no VFD, no extra encoder. If this works it could be also be used for milling boring cycles where you want the tip in a certain retract position, or for ATC rotation, or any other spindle position application, etc...
If it doesn't go well I will have gained some really valuable experience, and have a slightly expensive VFD, motor, and encoder.

I'll keep you posted!

Clay

Clay's gonna make that C8 into freekin' machining center eh? I love it!

That sounds incredibly cool! I’ve been busy and focused on my setup issues so still haven’t placed my DMM order. Is this a modification that needs to be done by them or can you do it yourself with a firmware download/update?

ScotY wrote: ↑Sat Dec 02, 2017 3:14 pm That sounds incredibly cool! I’ve been busy and focused on my setup issues so still haven’t placed my DMM order. Is this a modification that needs to be done by them or can you do it yourself with a firmware download/update?

They agreed they would do it. If it works, they will implement it going forward.

What I was wondering about was if I should hold off on my order until you/they determine it works. If it's user upgradable, I can order my motor now (or soon) and update it later. If they need to do something at the factory, I should wait.

Question: If you'll be using the motor encoder for spindle location, as well as speed, does that mean you'll have to belt the motor 1:1 to the spindle?

If so, how well will that work at low speeds? I know a DC servo has a great deal of torque even at low speeds, but how about an AC servo? There's a huge amount of torque multiplication in the typical lathe reduction belt-drive. Admittedly, with a good CNC setup, you might not necessarily need a particularly low spindle speed- I usually never drop under 500 RPM or so unless I'm threading- but I can still see some good low speed grunt being necessary for things like rigid tapping.

Doc.

DocsMachine wrote: ↑Sat Dec 02, 2017 10:37 pm Question: If you'll be using the motor encoder for spindle location, as well as speed, does that mean you'll have to belt the motor 1:1 to the spindle?

If so, how well will that work at low speeds? I know a DC servo has a great deal of torque even at low speeds, but how about an AC servo? There's a huge amount of torque multiplication in the typical lathe reduction belt-drive. Admittedly, with a good CNC setup, you might not necessarily need a particularly low spindle speed- I usually never drop under 500 RPM or so unless I'm threading- but I can still see some good low speed grunt being necessary for things like rigid tapping.

Doc.

Yup, he has to belt to the spindle at 1:1 or get a separate encoder on the spindle.
Going to be interesting to see how it works out for sure....
Holy Frijoli!

martyscncgarage wrote: ↑Sat Dec 02, 2017 11:59 pm

DocsMachine wrote: ↑Sat Dec 02, 2017 10:37 pm Question: If you'll be using the motor encoder for spindle location, as well as speed, does that mean you'll have to belt the motor 1:1 to the spindle?

If so, how well will that work at low speeds? I know a DC servo has a great deal of torque even at low speeds, but how about an AC servo? There's a huge amount of torque multiplication in the typical lathe reduction belt-drive. Admittedly, with a good CNC setup, you might not necessarily need a particularly low spindle speed- I usually never drop under 500 RPM or so unless I'm threading- but I can still see some good low speed grunt being necessary for things like rigid tapping.

Doc.

Yup, he has to belt to the spindle at 1:1 or get a separate encoder on the spindle.
Going to be interesting to see how it works out for sure....
Holy Frijoli!

LOL, Like I said, worst case I have a pricey VFD!

DocsMachine wrote: ↑Sat Dec 02, 2017 10:37 pm Question: If you'll be using the motor encoder for spindle location, as well as speed, does that mean you'll have to belt the motor 1:1 to the spindle?

If so, how well will that work at low speeds? I know a DC servo has a great deal of torque even at low speeds, but how about an AC servo? There's a huge amount of torque multiplication in the typical lathe reduction belt-drive. Admittedly, with a good CNC setup, you might not necessarily need a particularly low spindle speed- I usually never drop under 500 RPM or so unless I'm threading- but I can still see some good low speed grunt being necessary for things like rigid tapping.

Doc.

I agree about the typical torque multiplication. However since my lathe was 1/2hp, and the new motor will be 1 HP things "should" be okay. I don't plan on hogging steel, and the AC servo has full torque at stall.
What's the worst that could happen right?

Clay

frijoli wrote: ↑Sun Dec 03, 2017 12:23 am

DocsMachine wrote: ↑Sat Dec 02, 2017 10:37 pm Question: If you'll be using the motor encoder for spindle location, as well as speed, does that mean you'll have to belt the motor 1:1 to the spindle?

If so, how well will that work at low speeds? I know a DC servo has a great deal of torque even at low speeds, but how about an AC servo? There's a huge amount of torque multiplication in the typical lathe reduction belt-drive. Admittedly, with a good CNC setup, you might not necessarily need a particularly low spindle speed- I usually never drop under 500 RPM or so unless I'm threading- but I can still see some good low speed grunt being necessary for things like rigid tapping.

Doc.

I agree about the typical torque multiplication. However since my lathe was 1/2hp, and the new motor will be 1 HP things "should" be okay. I don't plan on hogging steel, and the AC servo has full torque at stall.
What's the worst that could happen right?

Clay

Keep us posted and do post pictures!