Closed loop steppers vs servo ?

[threedee]

Hello good people.

Please educate me on servos. I know what they are, i know how they work. In theory.
I had pleasure playing with some open steppers, fairly straightforward.
When i look up servos on ebay or aliexpress i mostly get hybrid stepper servo, which in my mind is just a stepper with an encoder bolted on.
I also have a HUUUUGE 3ph ac servo (3.8kW) kicking about. It doesnt cog, has your usual UVW etc.
Are there true nema17-23 servos out there ? What to look for ?

Having a bit of trouble with my laser cutter at the moment, returning it to get a better one. With steppers, still, but entertaining the idea of servo-rising it in the future and need to understand whole "stepper servo" vs "true servo".

Is there a point to "stepper servos" when speed is concerned ?

Am i making any sense ?

[Chaz]

Not sure what the question is however I wouldnt bother with closed loop steppers. There are a multitude of cheap true servos available in any frame / size. No reason to avoid. Most will take step / direction too.

[threedee]

Question is of nomenclature, really.

There are AC servos (big honking one i have for instance), DC servos, closed loop steppers, hybrid stepper servos (prolly just same old closed steppers), etc. Difficult sor someone not in the know unpick what's what.

I most likely am interested in DC servos. How do i weed out all undesirables in searches ?
Anyone can point me to an example of true servo with a driver ? Nema17-23 sized.

[Chaz]

Question is of nomenclature, really.

There are AC servos (big honking one i have for instance), DC servos, closed loop steppers, hybrid stepper servos (prolly just same old closed steppers), etc. Difficult sor someone not in the know unpick what's what.

I most likely am interested in DC servos. How do i weed out all undesirables in searches ?
Anyone can point me to an example of true servo with a driver ? Nema17-23 sized.

Find smaller versions of these servos.

https://www.aliexpress.com/item/32356188922.html?spm=2114.10010108.1000023.10.1aab 3a47VtrQMA

[m_c]

Servos don't generally come in NEMA sizes, they come in frame sizes. They are essentially the same thing, just slightly different standards with slightly different standard sizes. IIRC NEMA is imperial based, with frame sizing being metric based (it's been a while since I've actually looked at the specs!)

Closed loop servos do have their uses, for example where the lower speed is more beneficial than using a servo that would need gearing to achieve the same speed/torque than a direct coupled stepper motor.
However with cheap servos now available, the cost benefit of using closed loop steppers doesn't really exist anymore.

Each option has pros and cons, it's a case of deciding what is more important to you.

[threedee]

I am set on servos because lasercutting usually works better with them. Mainy due to available faster speeds. Having too powerful a tube and trying to cut paper you run into problem with overdelivery of power at too low max speed.

Laser tubes of 100W+ fire at about 10% of rated power, which is way too much for some materials. This can be fixed by spreading that power thinner by using servos and running faster.

At the moment i'm still struggling diagnosing my stepper motors as is, but time will come when i will go full servo.

[Ger21]

Look for 60mm AC servos, 200w-400w. They are slightly larger than Nema 23 steppers, but not much. A 400w 60mm servo is about 10x more powerful than a Nema 23 stepper.

https://www.ebay.com/itm/263257465942

https://www.ebay.com/itm/122654877079

200W is more than enough, though.