Re: Are Chinese servos a gamble? Servos vs Leadshine closed loop
Quote:
Originally Posted by
ger21
There is really no comparison between closed loop steppers and servos. Look at a torque curve for a closed loop stepper. At 1000 rpm, it will have lost at least half of it's rated torque. A servo will have full torque up to 3000rpm, with 3x peak torque still in reserve.
When used properly, an open loop stepper should give nearly identical performance to a closed loop stepper. They are both steppers, after all, with the same amount of power.
I have leadshine easy servos. they don't "stall" and fault when you drift past your allowed error. beyond that, they are just steppers, with all of the performance benefits and drawbacks. id call them safety steppers, cause they are not at all like your typical ac servos.
I was hoping someone in this thread would have some first hand info on these Chinese servos. I have a couple of brother tapping centres, and they take an unusual motor size - 86mm metric. the stock sanyo motors also pack a very big punch for a little motor. my drives are dead in one of the machines (previous owner was not too bright with his electricity knowledge) and new sanyo stuff makes yaskawa look like discount bin on prices. were talking 3k+ per axis for new motors and drives. oddly though, one of these Chinese brands makes a servo the exact right size and torque. its only lacking on speed, limited to 3000rpm. at $350-$400cdn per axis from a (seemingly) reputable seller, I'm kinda thinking they could be a good short term solution to get the machine running with linuxcnc. delta also makes a kits in the right size, but less torque, and $1000 per axis - id just go with sanyo when we get into that price range. of course, the delta and sanyo (and yaskawa etc) have very advanced dynamic auto tuning, 3khz bandwidth, 24 bit encoders, and all the most modern fluffy features you could ask. I expect little of the Chinese motors and drives other than to move where its been asked.
on power - this may be where paying for good hardware is worth while sometimes. a good servo drive, like my now dead sanyo for example said to take in "200v" can often take anything from 190v single phase to 245v 3 phase and still run. a properly built industrial class machine (like my brother) also has a biasing transformer, which allows it to take in all sorts of voltage in 5% increments and spit out the desired level (220v in this machine). my power is stable 600v, plus or minus maybe 5% on a bad day. if you have very bad stability, you really need to have that taken care of, as it can damage things. the idiot who last tried to hook up my machine tried to convert it from 380v in, to 220v in, but did not wire the internal transformers correctly an poof. all drives dead on power up.
anyhow, who has actually used those Chinese servo kits in a machine?
Re: Are Chinese servos a gamble? Servos vs Leadshine closed loop
Quote:
Originally Posted by
ihavenofish
I have leadshine easy servos. they don't "stall" and fault when you drift past your allowed error. beyond that, they are just steppers, with all of the performance benefits and drawbacks. id call them safety steppers, cause they are not at all like your typical ac servos.
I was hoping someone in this thread would have some first hand info on these Chinese servos. I have a couple of brother tapping centres, and they take an unusual motor size - 86mm metric. the stock sanyo motors also pack a very big punch for a little motor. my drives are dead in one of the machines (previous owner was not too bright with his electricity knowledge) and new sanyo stuff makes yaskawa look like discount bin on prices. were talking 3k+ per axis for new motors and drives. oddly though, one of these Chinese brands makes a servo the exact right size and torque. its only lacking on speed, limited to 3000rpm. at $350-$400cdn per axis from a (seemingly) reputable seller, I'm kinda thinking they could be a good short term solution to get the machine running with linuxcnc. delta also makes a kits in the right size, but less torque, and $1000 per axis - id just go with sanyo when we get into that price range. of course, the delta and sanyo (and yaskawa etc) have very advanced dynamic auto tuning, 3khz bandwidth, 24 bit encoders, and all the most modern fluffy features you could ask. I expect little of the Chinese motors and drives other than to move where its been asked.
on power - this may be where paying for good hardware is worth while sometimes. a good servo drive, like my now dead sanyo for example said to take in "200v" can often take anything from 190v single phase to 245v 3 phase and still run. a properly built industrial class machine (like my brother) also has a biasing transformer, which allows it to take in all sorts of voltage in 5% increments and spit out the desired level (220v in this machine). my power is stable 600v, plus or minus maybe 5% on a bad day. if you have very bad stability, you really need to have that taken care of, as it can damage things. the idiot who last tried to hook up my machine tried to convert it from 380v in, to 220v in, but did not wire the internal transformers correctly an poof. all drives dead on power up.
anyhow, who has actually used those Chinese servo kits in a machine?
Only feedback I have received is from this guy, who said "[COLOR=var(--ytd-comment-text-color)]Thanks, those you sent me link, are KRS. Those work fine. I would suggest you to go 750W because this servos dont have auto tunning option, and there is no pc software for them to have scope. So they can be a bit more tricky to tune. So you wouldnt want to push them, as you will have quite a bit of follow error. I can give you contact of my forwarder, and he will give you 750W set of motor, drive and cables for 250USD." See the youtube comments in this vid:[/COLOR]
https://www.youtube.com/watch?v=_ztj...13526415759229
So there are chinese price servos with 20 bit encoders, they're a bit more expensive though. Is this a big deal? You might want to look at them
https://www.aliexpress.com/item/750W...ceBeautifyAB=0
If you could elaborate on why 2500ppr is inadequate for a home gamer like me and I need 20 bit I'd appreciate it. Seems like a fair bit. Also if someone could explain why he basically says "Go big on the servos" above. Kind of worrying.
Can I ask you a question? For $1000, I can grab 3 of these servos, with their 2500ppr encoders. Would you do that over spending $300 less on leadshine hybrid steppers for a home cnc? I almost think for a home game like me I could get more accuracy out of the steppers, which is my primary concern. But microstepping and blah blah stuff I don't totally understand, which servos don't suffer from. I don't like the idea of poor 'strength' between steps when microstepping.
Re: Are Chinese servos a gamble? Servos vs Leadshine closed loop
Quote:
Originally Posted by
j3dprints
Only feedback I have received is from this guy, who said "[COLOR=var(--ytd-comment-text-color)]Thanks, those you sent me link, are KRS. Those work fine. I would suggest you to go 750W because this servos dont have auto tunning option, and there is no pc software for them to have scope. So they can be a bit more tricky to tune. So you wouldnt want to push them, as you will have quite a bit of follow error. I can give you contact of my forwarder, and he will give you 750W set of motor, drive and cables for 250USD." See the youtube comments in this vid:[/COLOR]
https://www.youtube.com/watch?v=_ztj...13526415759229
So there are chinese price servos with 20 bit encoders, they're a bit more expensive though. Is this a big deal? You might want to look at them
https://www.aliexpress.com/item/750W...ceBeautifyAB=0
If you could elaborate on why 2500ppr is inadequate for a home gamer like me and I need 20 bit I'd appreciate it. Seems like a fair bit. Also if someone could explain why he basically says "Go big on the servos" above. Kind of worrying.
Can I ask you a question? For $1000, I can grab 3 of these servos, with their 2500ppr encoders. Would you do that over spending $300 less on leadshine hybrid steppers for a home cnc? I almost think for a home game like me I could get more accuracy out of the steppers, which is my primary concern. But microstepping and blah blah stuff I don't totally understand, which servos don't suffer from. I don't like the idea of poor 'strength' between steps when microstepping.
my sanyo servos are 2500 line and 1024 line. under the brother control, both are/were perfectly fine. under linuxcnc I am having issues tuning the 1024 line ones at its original 787ipm, 0.25g acceleration, but I do not know if that is in any way related to the encoders. as a reference, the 2500 line motors on the other machine run 1420ipm, 0.5g acceleration under the stock brother control. ive not tried them under Linux of course as the drives are dead.
high resolution encoders are generally not that important unless your machine is of a very high performance. 2000ipm, 2g acceleration, high servo loop rates, etc. something you don't encounter much in the sub $100000 machine market. on the flip side, the extra encoder counts can help the drive run the motor more smoothly at very low speeds - imagine milling a line from x0y0 to x0.0001 y10 at 2ipm. lots of encoder counts help that x move to create an actual line, not a stair step. its hard to say how critical this is though if your mechanicals are not also super precision. even 0.0002" of backlash could erase many of the benefits.
you also need to know what you get with each encoder in terms of precision. most of these 2500line types are glass. they are very precise, if not high resolution. encoders like the dmm ones, and similar types are magnetic, and not very precise in comparison, but have a lot of resolution. so, between the 2, the "precision" of your machine likely is the same. the higher resolution one might just run a little smoother, a little quieter, and track a little better going fast. 24 bit encoders like on new high end drives are a different matter. they are both precise and stupid high res, but also cost more for one encoder than a set of 3 Chinese drives and motors. example: siemens ~750w servo with "low precision" resolver $699. same motor with 24 bit endat multi turn absolute encoder $1999. eep!
of course, then you go and run step and direction out of mach3 at 50khz and you may as well flush it all down the toilet :)
I don't really have a suggestion for stepper vs servo for your performance target. its kinda right on the cusp where both have benefits and drawbacks.