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Hello all
I will be putting together a cnc controller using an AXBB-e controller and JMC 180 w servo motors. For the Z axis I have a motor with an intergrated brake. The question I have is how is the brake wired up in the system? It needs 24 volts to release the brake. Does the servo motor hold it's position when the system is energized and the brake released ? I wouldn't want the spindle dropping and breaking cutters. A wiring diagram would help me. Thanks in advance.
Cheers
Andrew

Personally I think that a 180W servo is not optimal for Z. It is a pretty weak servo, with only 0.6Nm holding torque. This is considerably less than any decent stepper motor with the same footprint but smaller in size have.





As you can see above, the stepper is about half the size of the servo. This may not matter, but I think it's important to consider that the holding torque of that stepper is three times the servo torque. Of course, the servo has other advantages, like higher maximum speed, and that the torque is constant, as well as that is is not losing step to a limit, where it throws an error and stops, while the stepper torque is declining as it speeds up, but it does not drop immediately. So in my opinion, a 180W servo is too weak, especially if you have a decently heavy Z. It may be able to hold, but it may also cause a problem because of the low holding torque. Of course, the holding torque is increased if you have some gearing down, like I have 3:1 in that picture above, but a 3:1 gear requires quite a large gear, increasing the size. I don't know if you intend to drive the shaft directly or through a belt, but it does make a difference. Also note that I assume you plan for driving the servo with 50VDC, or something very near. Normally, the Chinese recommend 36VDC, in which case you lose performance. I drive mine with 48VDC 9A, and that is really necessary due to the fact that the servo can suddenly increase the current consumption, so you need the margin. On the other hand, for that stepper above a 48VDC 4.5A is enough to get the maximum performance.

I know not everyone will agree with me, but personally I would NOT use this servo for Z. The minimum I'd use is a 400W servo, but while that is even larger, requires an even higher current and voltage, it is still weaker (in terms of holding torque) compared to that stepper above. However, if speed is the main goal then the servo beats the stepper hands down. Speed is in my opinion more important on X and Y than on Z, due to the fact that the Z is very short, so fast moves without cutting will be very short also. In my opinion, holding torque is however very important for Z.

Hello
Thank you for your input. Deffinitely food for thought. I will try the servo to see how it works. I have seen plenty of you tube videos showing the power of these small servos. I do have closed loop steppers at hand if required. This is a long term project for me.

Regards
Andrew

This is what I mean:



Watch how easy it is to rock the chuck. That slight touch would NEVER rock any half-decent stepper. Of course, it may not matter in your case, so I don't know. Anyway, it is good that you have steppers also, in case it is a problem it is easy to swap if they are also NEMA23 or NEMA24 steppers.

BTW, I hope your servos are version 6 or later. They may be better than my version 5.52, at least that's what the manufacturer told me.

Hi
Yes they are version 6.04 from what I can gather a lot of the motors performance depends on the tuning of the motors although I have noticed that you have tried that. I'll see how it goes. Learning by doing !!!
Cheers
Andrew