[sm3]

Hello Everyone,
I am building a CNC machine. It is not usual/well known machine and I need in it 2 spindles running with exactly the same speed and other parameters but in opposite direction to each other.
Is it possible in any way to run 2 motors fed from one VFD but in opposite direction to each other?
With steppers it quit easy - just connect 2 motors to the same controller and reverse wires of one the motors.
It is my understanding it would not be possible with 3 phase motors. or is it?
I would very much appreciate any suggestion to solve it.

Thank you very much in advance.

[Algirdas]

It is possible to connect motors the way you want. Not spindles however. Because the load on spindles will not be equal enough.
I think, you use two VFD's or better - servo's, and synchronize them.

[machinehop5]

Hello Everyone,
I am building a CNC machine. It is not usual/well known machine and I need in it 2 spindles running with exactly the same speed and other parameters but in opposite direction to each other.
Is it possible in any way to run 2 motors fed from one VFD but in opposite direction to each other?
With steppers it quit easy - just connect 2 motors to the same controller and reverse wires of one the motors.
It is my understanding it would not be possible with 3 phase motors. or is it?
I would very much appreciate any suggestion to solve it.

Thank you very much in advance.

...if, you only need high speed why use a VFD?

[CitizenOfDreams]

In general, there is nothing wrong with connecting several motors to one VFD. Some woodworking machines by respectable manufacturers (such as SCM) are built that way.

I have not seen a configuration with two motors mechanically connected to each other, but I believe that would work fine as well.

[Al_The_Man]

I have used a single VFD to control two spindle motors, but this was a double ended lathe, where the chuck held each end of the work piece. (Railway wheel axle).
Where the load varies on each motor, you are probably going to run into a problem.

[sm3]

Hi Algirdas,
Thank you for replying. What is the difference between spindle and motor?
I am thinking to equalize the axial load. Almost eliminate it by using cross-roller bearings at front of spindle (motor).
If you know how to connect to motors to the same VFD but have one of the motors running in reverse direction - could you please share how to do it?


Thank you!

[sm3]

Hi All_The_Man!
Thank you for replying.
Can you share, please, how to implement it? I need both motors be connected to one VFD, but have one the motors running in reverse - like you said - Railway wheel axle.
I am thinking to equalize/almost eliminate axial load by using cross-roller bearing at the front of each motor.
What I need is to run both motors with the same exactly speed and torque, but in opposite direction to each other. Another words - one motor clockwise, and motor two counterclockwise.
If you know how it can be done - please share your knowledge.

Thank you.

[sm3]

Hi machinehop5,
I need to motors running with speed about 2000 RPM (maybe higher in the future - I don't know yet. Have to try it first) and I need motors to keep torque value.
I used steppers first. They are pretty easy to control, but they are loosing torque dramatically with increased speed. So, I am thinking to move to brushless 3 phase motors and so will need VFD to run them.
So, what I need it 2 motors running with relatively high speed and be able to keep torque with this speed. Each motor has to run in opposite direction to each other - one clockwise and another counterclockwise.
Would you suggest any other type of motor for this?

Thank you!

[dazp1976]

Hi machinehop5,
I need to motors running with speed about 2000 RPM (maybe higher in the future - I don't know yet. Have to try it first) and I need motors to keep torque value.
I used steppers first. They are pretty easy to control, but they are loosing torque dramatically with increased speed. So, I am thinking to move to brushless 3 phase motors and so will need VFD to run them.
So, what I need it 2 motors running with relatively high speed and be able to keep torque with this speed. Each motor has to run in opposite direction to each other - one clockwise and another counterclockwise.
Would you suggest any other type of motor for this?

Thank you!

1. When you tried the steppers. Did you use a driver with a current output that was double the steppers phase value?.
2. What voltage did you use & what stepper size?.
For instance: 2 motors with 4a per phase use an 8a driver.
Nema 23/24 fly on 60vdc

[sm3]

Hi dazp1976,
steppers run on DC, so I don't think such a thing as "stepper phase" exists.
I used nema 23 motors (I actually tried other sizes, increasing them and the largest I used lastly was nema 23). I ran them by DQ860MA driver by wantai motors, providing up to 80V. motors are of the same brand.

Correct me if I am wrong, but it is my understanding that with RPM increased, steppers are loosing torque value. and torque is important to me - it has to be kept pretty much the same (ideally exactly the same).
Once set, speed will stay the same. In my machine this unit will always run with the same speed.

[Algirdas]

difference between spindle and motor is out of the scope of this discussion. My idea is that basically there is no problem to connect several motors to a single VFD. Two separate spindles would suffer different loads as normally. Unless they will be connected mechanically - holding the same workpiece.
At that case the only problem remains the difference of dynamic (electrical) parameters of the spindle motors.
Electrical parameters will differ and may differ significantly when loaded. It will not be simple serial and parallel combination. It's much better to synchronize two VFD's with constant torque set.

[sm3]

does not answer my question, but thank you.

[dazp1976]

Don't spindle (router) type motors suffer torque loss as speed increases?. Also have a minimum rpm?.
For 2000rpm and permanent torque you need AC servo's & drives synchronised tbf.

[Al_The_Man]

Hi machinehop5,
I need to motors running with speed about 2000 RPM (maybe higher in the future - I don't know yet. Have to try it first) and I need motors to keep torque value.
I used steppers first. They are pretty easy to control, but they are loosing torque dramatically with increased speed. So, I am thinking to move to brushless 3 phase motors and so will need VFD to run them.
So, what I need it 2 motors running with relatively high speed and be able to keep torque with this speed. Each motor has to run in opposite direction to each other - one clockwise and another counterclockwise.
Would you suggest any other type of motor for this?

Thank you!

The ones I used were the original/old induction motors, all you need to do is reverse the leads on one motor to have them revolving in the opposite direction.
BLDC are no good with a VFD, I have tried it. I worked with the VFD manuf engineering dept to get the recommendations

[sm3]

right. that was pretty much I have said. I tried at the beginning 2 stepper motors, but at the higher speed they are loosing torque and so I started thinking of AC motors.
My question is: is it possible to connect 2 AC motors to the same controller/drive/VFD, but have motor #1 running clockwise and motor #2 running counterclockwise?

If it is possible, can someone, please explain to me how to do it?

Thank you.

[Al_The_Man]

As already posted just hook the motors up in parallel on the output of the VFD, reverse two leads on one motor if you want the reverse.

[sm3]

Thank you Al_The_Man!