Advice on buying servos.

[Boyan Silyavski]

Thanks, sorry for being so dim about this - it's begging to make sense. Also many thanks for the links.

BTW. Apart from power, is there any difference between servo motors used for positioning ie x,y,z axis motors and servos used for spindles?

Yes and No. Any servo motor rightly belted could serve for spindle. But then comes the RPM. The servos that are meant for spindles could spin at higher RPM and have slightly different curve. We are talking about typical motor that will be connected to BT30, etc spindle via belt. As Yes, you could gear up any servo motor but then you need bigger more expensive motor.

these are the servo spindle motors. they gto up to 15k rpm https://www.aliexpress.com/store/pro...809932059.html

[Agathon]

Yes and No. Any servo motor rightly belted could serve for spindle. But then comes the RPM. The servos that are meant for spindles could spin at higher RPM and have slightly different curve. We are talking about typical motor that will be connected to BT30, etc spindle via belt. As Yes, you could gear up any servo motor but then you need bigger more expensive motor.

these are the servo spindle motors. they gto up to 15k rpm https://www.aliexpress.com/store/pro...809932059.html

Thanks again. Not cheap then.

While I'm here. Am I right in thinking that the advantage of an absolute encoder over incremental is that the motor position is known after power-down?

[Gary]

Yes, but there are different types of absolute. you have single turn and multi-turn, the name is self-explanatory.
Also, Absolute encoders have a much higher resolution than incremental.

Thanks again. Not cheap then.

While I'm here. Am I right in thinking that the advantage of an absolute encoder over incremental is that the motor position is known after power-down?

[Agathon]

Yes, but there are different types of absolute. you have single turn and multi-turn, the name is self-explanatory.
Also, Absolute encoders have a much higher resolution than incremental.

Thanks. I notice that you have both DC brushless and AC servos on your website - what are the advantages and disadvantages?

[Gary]

Thanks. I notice that you have both DC brushless and AC servos on your website - what are the advantages and disadvantages?

One take DC and the other takes AC, so the AC servo driver has a power supply built in that is rated to the nominal and peak rated current of the driver.
Also Just because it's a DC servo does not mean its brushed, a DC servo can be brushed or brushless.

[Agathon]

One take DC and the other takes AC, so the AC servo driver has a power supply built in that is rated to the nominal and peak rated current of the driver.
Also Just because it's a DC servo does not mean its brushed, a DC servo can be brushed or brushless.

OK, that's a very concise reply, but why buy a DC over and AC and vice versa?

[Gary]

There are a few reasons, but this one normally gives you an indication.
Ok, lets say you have a machine with 8 axis and each axis needs a servo, that is not too large.
you can get 8 AC servo motors and driver and you will be paying more because each driver has its own power supply.
with the DC option, you will have 8 DC servo drivers and a large power supply.
Also DC servo motors are typically low voltage DC, so the current is higher, so typically the motors dont go too big (under a KW)
Personally, i would not even consider a DC servo system, unless you know why you need it. AN ac servo system is typically a better option.

OK, that's a very concise reply, but why buy a DC over and AC and vice versa?

[Boyan Silyavski]

Thanks again. Not cheap then.

Servo controller for me is a must for a metal working machine, a heavy gantry router or a high precision machine for miniature machining, industrial production machine that needs to be fast as possible For all else a stepper will do just fine job.

[Agathon]

Servo controller for me is a must for a metal working machine, a heavy gantry router or a high precision machine for miniature machining, industrial production machine that needs to be fast as possible For all else a stepper will do just fine job.

What I really meant was that servos for spindles weren't cheap. I'm a great believer in "getting what you pay for". I can live without a servo spindle, but I think I need to invest in servos for the x and y axes of my mill.