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Why do we still use stepper motors?
(sopuli.xyz)
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this post was submitted on 10 Jan 2024
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Just trying to understand this. Then how come all CNC precision machines use a servo instead of a stepper? I mean there are some ridiculously accurate machines that can position itself over and over varying under a micron (<.001mm) but the manufacturers choose servo over stepper. Is it for the sake of holding torque that servos have to be used over steppers?
All the DIY CNC machines I've seen use larger stepper motors. The commercial CNC machines I've seen can cost $10,000 to hundreds of thousands.
It seems like the argument is that at the lower price bracket, stepper motors offer higher performance than what a equivalently priced servo+encoder+controller combo can perform.
I felt like what I was reading in this thread wasn't matching up with that I see out in industry... concerns about 'price' didn't come up until your post.
Diamond turning machines are inherently low torque, low speed, AND nanoscale operations which uses servos for driving its respective axis. See precitech -youtube and in stark comparison Roeder's 5axis optical mold machining. Wire EDM's were all driven by servo motors until linear motors became popular. Even those famous JingDiao test samples are made on machines driven by servos.
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That's actually exactly my point, steppers are objectively inferior to servos when it comes to dynamic positioning (which is what 3D printing is), but servos are too expensive compared to performance gains for hobbyists.
I don't think the sentence you have is entirely accurate.
High cost servo systems (motor, encoder, and driver) are superior to high cost strippers for dynamic positioning. Even that can be tenuous for low torque low speed applications, or nanoscale applications, etc... Certainly for 3 axis table/gantry CNC systems (router, laser, 3d print) for commercial/industrial grade applications servos are superior.
If you're aiming for a hobbyist price point steppers have better dynamic positioning performance than servos. You can build a $300-$1000 3d printer with servos, but especially at the low end, it's not going to be good.
But that just highlights the statement/question in my OP, it's just cost prohibitive to use servos as a hobbyist. You will as a hobbyist get a better system with (proper) servos, but not for a reasonable price point.
Do you want to have a conversation, or do you want people to agree with you?
Your post is phrased like a question, but your comments feel like the opposite.
If you are buying industrial grade 1000+ dollar servos you are no longer "hobbyist" in the price range that hobby level 3D printers exist steppers are more precise than servos.
Yes that's exactly what I'm saying...it's the cost that's in the way of the switch, not that steppers are the best solution. They're only the best solution within the price constraints we have as hobbyists.
But how do you define "best?" Servos may be functionally better, but if you can't sell your product to consumers because it's so expensive, is it really the best product out there and who exactly is it the best for?
It's like saying Kobe beef makes the best burgers, but if you're trying to feed 10,000 people then wouldn't your typical 80/20 ground beef from Walmart be the best option? I don't think hungry patrons would appreciate paying $100 for a kobe burger over $1 for your standard burger. They just want to eat.
You will not get a better system when using servos no matter the price point at the moment. People have tried and failed just because the software support isn't there yet for 3d printing.
The biggest issue I'm aware of is matching the timing between the extruder stepper and the servos that do the XY motion.
Which isn't apparent at lower speeds but at higher speeds you can notice they're no longer in sync which leads to all sorts of issues and artifacts.
I'm currently waiting on some 3 phase steppers and drivers to test to hopefully get something with less speed deviation than a normal 2 phase stepper and more reverse torque but don't cost too much and are still easily driven by connecting a driver to your boards step/dir output.
I don't know why you're getting down voted. You're correct, steppers are used due to cost.
Which makes them superior, which is why they are used. Cost can't be ignored any more than the torque or speed, speccing parts that are considerably more expensive that achieve equivalent results is bad engineering unless you have a very specific application that requires it.
If it was 'objectively inferior' we wouldn't use them. You build to your requirements, not by playing top trumps with competing technologies while ignoring the cost.