Using DMM 750W servo as spindle motor

[Richards]

Marty.

I just checked the speed with a digital tachometer. It matches the RPM that Centroid displays. Then, I changed the gear number. That got me as close as I will probably get. With the gear number set at 3,100 instead of the default 4096, I get 490 RPM with S500, 1,007 RPM with S1000, 1,525 with S1500, and 2,797 with S3000. With the gear number set to 3,300, I get 2,980 with S3000 and 1,072 with S1000. I think I'll leave it at 3,300 until I put a load on the motor. Now that I know what to change, I'll play with the gear number when I mount the motor to a machine.

Thanks for your help.

[martyscncgarage]

Marty.

I just checked the speed with a digital tachometer. It matches the RPM that Centroid displays. Then, I changed the gear number. That got me as close as I will probably get. With the gear number set at 3,100 instead of the default 4096, I get 490 RPM with S500, 1,007 RPM with S1000, 1,525 with S1500, and 2,797 with S3000. With the gear number set to 3,300, I get 2,980 with S3000 and 1,072 with S1000. I think I'll leave it at 3,300 until I put a load on the motor. Now that I know what to change, I'll play with the gear number when I mount the motor to a machine.

Thanks for your help.

Old memory is hard to Jog. Please keep us posted as to how you make out.

[Richards]

The DYN4 750W motor is running fine on the test bench. I tweaked a few settings in the DMM software to slow down the acceleration just a little and to more closely match the actual RPM to the requested RPM. If I were going to use the motor for threading, I would probably tweak the Gear Number setting in DMM so that the RPM shown by Centroidcnc matched the S (speed) setting at the speed that I use for threading. (I assume that the encoder, either built-in or an auxiliary encoder, would handle any diviations, but, since changing the Gear Number setting can get an exact match at any one speed, why not use it?)

I used a DB25M breakout board on the DYN4 driver to make wiring easy. I also used two DB9M breakout boards, one on the Acorn and one on the DYN4 driver to connect the DYN4's encoder to the Acorn's encoder inputs. I had them on-hand and they make wiring easy.

One other setting that I changed was to set the DMM Line Number to 2048. The manual states that values between 500 and 4096 can be used. 2,048 is 2^11 power. 500 is about 2^9 power. I imagine that 512, 1024 or 2048 could be used as long as 4X that number was entered into the spindle setting in the Wizard. 500 works, but I chose to use 2^ to a power rather than trusting decimal math on a microcontroller.

I'll attach a DMM screen shot with the values that I'm using, a Wizard spindle settings screen shot and a Wizard output settings screen shot. Note that in the output screen photo that I have Output #1 configured at spindle forward. That is NOT necessary. The DYN4 driver automatically spins the motor CW unless pin 10 is pulled low, which is handled by Acorn's output #2. The motor does NOT have a brake. Output #4 is used to enable/disable the motor. In the DMM setup, I selected the Enable LOW check box. Centroidcnc automatically turns on output #4 before the motor spins. Without disabling the motor, the DMM motor constantly turns very slowly even when the speed is set to zero.

I only have 120VAC on the test bench which means that the 750W motor will spin up to 3,000 RPM. It will spin up to 5,000 RPM if 240VAC is used.

Anyway, it works on the test bench. It may be awhile before I build/buy a mounting plate for the Taig Mill and toothed pulleys and belt.

[BounceCycles]

Hi Mike,

Did you resolve the motor spinning slowly, I'm using a 750w DMM DYN4 motor as a spindle. Switched onposrange to 111 and max speed to 13 as suggested by DMM but this only stopped the motor creeping when in rs232, as soon as I switch to analogue it starts again. Wondered if you found a solution?

[frijoli]

Hi Mike,

Did you resolve the motor spinning slowly, I'm using a 750w DMM DYN4 motor as a spindle. Switched onposrange to 111 and max speed to 13 as suggested by DMM but this only stopped the motor creeping when in rs232, as soon as I switch to analogue it starts again. Wondered if you found a solution?

DMM says you can set the deadband in the controller to a minimum voltage slightly higher than Acorn has at the analog terminals when "at zero". Recalling from memory as I have been working on other projects.

[Richards]

I've taken a different approach to the "creeping" problem. I've wired the DMM enable to Output 1 on the Acorn and Spindle Reverse to Output 1 on the Acorn. Here's a some G-code that I that shows how it works, but first, when Output 1 is HIGH, the DMM is enabled and when Output 1 is LOW, the DMM motor is disabled.

(MDI G-code commands to run spindle CW)
G1
S250 M3 ; set spindle speed and turn spindle CW
M61 ; Enable spindle
(insert G-code to make cut)
M81 ; Disable spindle
M5 ; turn spindle OFF

(MDI G-code commands to run spindle CCW)
G1
S250 M4 ; set spindle speed and turn spindle CCW
M61 ; Enable spindle
(insert G-code to make cut)
M81 ; Disable spindle
M5 ; turn spindle OFF

(If I remember correctly, M6x turns ON an Acorn output with x = 1 to 8, i.e., M61 turns on Output 1 and M68 turns on Output 8. M8x turns OFF an Acorn output, i.e., M81 turns OFF Output 1 and M88 turns OFF Output 8.)

[ElsetDesai]

Hello...i have a small query. If I was to use a constant torque VFD with this motor, then it could be considered equivalent to a 2.41 n.m servo motor?
So if I looked for a servo motor which delivered a bit more than this I'd be in the same ball park, and I can focus on frame and shaft size?

quick turn pcb assembly in usa

[Richards]

I asked DMM about using a VFD with the 750W servo. They discouraged the idea. I've never tried it due to lack of motor name plate data to properly configure the VFD.

[Richards]

I got tired of messing around with custom code to control the DMM DYN4 750W spindle motor that I'm running on the test bench. What I wanted to do is to have the DMM servo spin forward when the Acorn turns on the Spin Forward output and to spin in reverse when the Acorn turns on the Spin Reverse output. Also, I didn't want the DMM servo to "creep" when no signal was being sent by the Acorn. I installed a CLICK PLC to handle the simple logic required. The DMM servo defaults to turning forward when the Enable line is NOT at GND level, so when the Acorn gives the Spin Forward command, the CLICK simply lets the Enable line float HIGH. When the Acorn gives the Spin Reverse command, the CLICK pulls the DIR- line on the DYN4 to LOW and lets the Enable line float HIGH.

There are cheaper ways to do this, but I had an idle CLICK PLC C0-10DRE-D CPU, so I used it to solve the problem. Now the DMM servo acts as if it were a VFD controlled motor that is controlled by the Acorn.

Attached is the ladder logic for the CLICK.

[martyscncgarage]

Curious to know those that are trying to use DYN4 and Servo as spindle motor, how its working out.
Did you get it configured properly?
Is the spindle stable? NOT Creeping?
Did you get the encoder wired to Acorn properly?
Is it displaying motor RPM correctly?
Do you have plenty of low end torque?