Servo Drivers

[billy_vandori]

Hey Guys,

I'm really new to this stuff so please excuse my ignorance. I currently built a hobby 3 axis machine with Nema 23 Steppers and now am looking to replace with Servo or Servo Hybrids. All the articles I've read state that servo's come with the encoder and driver built in, but when I look for servo's on Ali Express I see they have servo's, most of them with a driver box. Would these "servo's" that have a driver box not be considered real servo's then? For example:

https://www.aliexpress.com/item/3298...archweb201603_

Package Listing:

1 PCS Servo Motor
1 PCS Drive <--- thought these were "built-in" with servos?
1 PCS 3M Encoder Cable
1 PCS 3M Power Cable
1PCS 25Pins Cable

Thanks Alot,

Billi.

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[joeavaerage]

Hi,
most modern AC servos have a motor and a servo drive control box. If you look closely you will see that like most servos they have two cables,
one, a low power cable, is for the encoder and the other carries the three power wires for the servo motor.

There ar a lot of really cheap Chinese made servos on AliExpress but the manufacturers are little known and the quality and backup on their servos
is questionable. Two brands, Delta (Taiwanese manufactured in China) and DMM ( Canadian manufactured in China) are good quality with good support
and won't break the bank, but they are more than the Chinese bargain basement units but still much cheaper than Yaskawa, Seimens and Fanuc.

There are some servos that have the control electronics built into the motor. Clearpath's are the most common example. They are made by Technics
and are good quality but they are expensive for what they are. You could buy a Delta servo, drive and cables for less and be twice or three times more
powerful. Clearpath advertise that their servos are a drop in replacement for steppers, and they do fill that role well.

There are lots of closed loop steppers available, cheaper than servos and to listen to the bulls****t that the manufacturers spout you swear they were
as good as servos.....THEY AREN'T.

ALL steppers lose torque the faster they go, having a closed loop driver does not change that. If a closed loop stepper is marginally overloaded and loses
a step the drive will insert an extra step to catch up.....but guess what...the extra step suffers the same fate as the ones gone before it...it gets missed
because the stepper doesn't have the POWER to catch up.

Closed loop steppers do have a few advantages but if you want genuine closed loop performance and decent overload tolerance get AC servos,
don't muck around with 'Mr. In Between'

Craig

[Jim Dawson]

What Joeavarage said above ^^^^^^^^^^ Up until just the last few years, the electronics in the drives were so large they could not be attached to the motor. But like everything else, drive electronics are getting smaller.

I have never used Delta products but have heard good things about them. I have used both DMM and ClearPath systems and have been happy with the performance. Both have their place, but in most applications the DMM systems are a better fit and are less expensive.

Hybrid stepper systems are still stepper motors, and subject to the limitations of stepper motors. A little better than an open loop stepper system, but they do not have the performance of an AC servo motor system.

A servo is not a type of motor or motor/driver combination. A servo is any system that has a feedback loop, your home heating system for instance. You (the controller) set the thermostat to a comfortable level, the heater turns on, and when the room temperature reaches the set temperature the heater turns off. The feedback in this case is the air temperature acting on the thermostat.

Another example of a very complex servo system is an automobile and driver. You as the driver receive feedback from everything going on around you and the controller (your brain) processes all of that data and causes your muscles to feed the correct outputs to the various systems in the automobile, stearing, throttle, and braking.

[joeavaerage]

Hi,

Another example of a very complex servo system is an automobile and driver. You as the driver receive feedback from everything going on around you and the controller (your brain) processes all of that data and causes your muscles to feed the correct outputs to the various systems in the automobile, stearing, throttle, and braking.

Yep, and that servo control system even has a PID loop (Pissed In Drivers seat)!!

Craig