[BoronNitride]

Hi i have a GE Fanuc alpha C6 spindle motor (A06B-0844-B200#3000) has anyone had any experience using these types of motor? Im looking for an amplifier to run this motor, there are quite a few different types offered by fanuc however i have no experience using these, the requirements of this motor are to be used as a CNC lathe spindle motor for a project i am working on, i require the functionality of rigid tapping and C-axis interpolation, machine controller is likely to be something along the lines of the GSK980TDc controller, does the fanuc drive have functionality for closed loop at the drive for a spindle motor such as this? Or is it not necessary only requiring the use of an external encoder on the spindle via a belt for synchronization with the Z-axis servo for screwcutting and rigid tapping not sure about c-axis movements though? Any help would be greatly appreciated.

Edit:- also does this have to even be a fanuc drive? Or can i use a different manufacturer drive e.g. delta or allen bradley etc. that allows encoder feedback for closed loop at the drive if this is even necessary?

[Jim Dawson]

I have a similar (slightly older) motor in my lathe and am getting ready to replace it with a servo motor. The original Fanuc drive had to be connected to a Fanuc controller to generate the proper signals for the motor. I replaced the entire Fanuc system with my own and am currently running the spindle motor on a sensorless vector VFD. I am able to rigid tap but not index. But rigid tapping took some software gymnastics to make it work. The spindle is driving an external encoder that is connected to my controller. I have an encoder module for the VFD, but I haven't installed it yet. That is going to be the last try to get the spindle to index, I'll know in a week or so when I get time to work on it. If this fails, I will be replacing the motor with a 7.5KW servo.

I recommend looking for a servo motor that will meet your needs.

[BoronNitride]

I have a similar (slightly older) motor in my lathe and am getting ready to replace it with a servo motor. The original Fanuc drive had to be connected to a Fanuc controller to generate the proper signals for the motor. I replaced the entire Fanuc system with my own and am currently running the spindle motor on a sensorless vector VFD. I am able to rigid tap but not index. But rigid tapping took some software gymnastics to make it work. The spindle is driving an external encoder that is connected to my controller. I have an encoder module for the VFD, but I haven't installed it yet. That is going to be the last try to get the spindle to index, I'll know in a week or so when I get time to work on it. If this fails, I will be replacing the motor with a 7.5KW servo.

I recommend looking for a servo motor that will meet your needs.

Was originally looking at a servo however settled on this due to the cost of quality servos that have enough power for what i want, was looking at the allen bradley powerflex 525 series drives and noticed that they have an option for an encoder card that would allow closed loop control at the drive, as this motor is an induction motor any vfd should run it? does anyone have any experience with the powerflex 525 series drives?

[Jim Dawson]

Yes, any properly rated VFD will run it. I'm using a Automation Direct GS3 to run mine. VFDs with the encoder option and external encoder for feedback will give you fantastic speed control, you should be in great shape from that perspective. I can control my spindle speed down to about 2 RPM with good speed holding, even without the encoder option connected. I have live tooling so my goal is to be able to index the spindle and I'm not sure the VFD is up to that task. I can run it at very low RPM, but thus far I haven't been able to get it to stop where I want. It wants to drift around the target point. I'm hoping that closing the loop at the drive with the encoder board will resolve this. But in reality VFDs are not designed to do this.

I found a 7.5 KW servo (one of my customers has it) for US$3500, so a pretty good deal. So that makes it a viable option for me. It has a max speed of 4500 RPM, so I'll lose a bit of spindle speed, but I rarely need more than that anyway.

Sorry, I have no experience with the powerflex 525. I have installed many Allen Bradley VFDs and servo drives. They make good equipment, but they are expensive.

[BoronNitride]

Yes, any properly rated VFD will run it. I'm using a Automation Direct GS3 to run mine. VFDs with the encoder option and external encoder for feedback will give you fantastic speed control, you should be in great shape from that perspective. I can control my spindle speed down to about 2 RPM with good speed holding, even without the encoder option connected. I have live tooling so my goal is to be able to index the spindle and I'm not sure the VFD is up to that task. I can run it at very low RPM, but thus far I haven't been able to get it to stop where I want. It wants to drift around the target point. I'm hoping that closing the loop at the drive with the encoder board will resolve this. But in reality VFDs are not designed to do this.

I found a 7.5 KW servo (one of my customers has it) for US$3500, so a pretty good deal. So that makes it a viable option for me. It has a max speed of 4500 RPM, so I'll lose a bit of spindle speed, but I rarely need more than that anyway.

Sorry, I have no experience with the powerflex 525. I have installed many Allen Bradley VFDs and servo drives. They make good equipment, but they are expensive.

I too have live tooling and would like to use this motor for indexing and C-axis movements, had a look at some of the allen bradley VFDs they seem to require expansion cards for the encoder, spotted a couple of Emerson Control Techniques Unidrive SP series VFDs fairly cheap still almost a grand but i guess you get what you pay for, they seem to have an encoder input built in also if this motor is going to be run from a 415v 3 ph supply and the motor output is 240v 3ph would it be wise to buy a drive roughly double the KW rating due to increase in current from lower voltage?

[Jim Dawson]

also if this motor is going to be run from a 415v 3 ph supply and the motor output is 240v 3ph would it be wise to buy a drive roughly double the KW rating due to increase in current from lower voltage?

I would use a 415/240 transformer in front of the VFD. Should be less money than buying a VFD that has twice the output amps.