12 ms·
Servo vs. steppers: Speed, Torque and Accuracy [video]
- brcmthrowaway 2y agoIs there something like an sg90 toy servo but rotates 360 and gives me position with similar speed?
- HeyLaughingBoy 2y agoI think this might be what you're looking for: https://www.pololu.com/product/3432 https://www.pololu.com/product/3432
- ge96 2y ago$30? That's steep edit: granted it pulls 35oz
- TechSquidTV 2y agoI was googling exactly this just two days ago. Great timing.
- riiii 2y agoPublished 1h ago and already on HN. Not surprised, Matthias Wandel is always worth a watch!
- fotta 2y agoHis breadth of knowledge constantly amazes me
- LeifCarrotson 2y agoEh, as a controls engineer, I get a bit of Gell-Mann amnesia watching his content on drives and motors. There's a complete lack of tuning described in the video, it seems a lot of his performance complaints are due to conservative out-of-the box defaults. The stuff he builds very cheaply with little more than some wood, Python, and Raspberry Pis is impressive, and he deserves all the kudos for building cool shit and putting it on the Internet (I'm just a consumer and critic, not a creator in comparison). But serial control from an interpreted script instead of CAN/Ethercat messaging from a motion controller or PLC is not the way these products are typically used in industry, and most people don't run the defaults. There's definitely a niche for hobbyist-grade, student-grade, or lab-grade motion products that name brands like Beckhoff, Omron, Fanuc, Rockwell, and Siemens largely ignore. You could get 4 axes from DMM for the price of 1 from most of those vendors. And while simple serial commands can make interesting things happen with the DMM unit, you'd have to scale a daunting cliff of a learning curve just to get a motion axis initialized in their massive, standardized, proprietary, legacy ecosystems. Again, no disrespect intended: I've invested thousands of hours into building custom, multi-million-dollar machine tools at my day job and instead of challenging myself, going to the workshop and turning on a camera when I get home, I've vegetated on the couch, entertained, and sometimes educated by his content building a milling machine or lathe out of wood. But this "servos vs. steppers" debate really only applies to low-cost, simple, hobbyist-grade equipment, and isn't such a big topic in the industrial space.
- HeyLaughingBoy 2y agoYeah. The first (and only, so far) time I came up against a servo controller from AMC (https://www.a-m-c.com/ https://www.a-m-c.com/) my initial thought was "why the hell is this so difficult?" Sure, the product manual has everything you need to know about how to program the device. But that manual is also practically unreadable unless you already know how to program the device Contrast with Teknic where I could get the servo drive up and running in a few hours because of an actually readable product manual and plenty of sample code and a Windows DLL to make everything easy. There's definitely opportunity at the lower end of the market.
- bluGill 2y ago> I've invested thousands of hours into building custom, multi-million-dollar machine tools at my day job One key is find a hobby that is enough different from your day job you are not burned out of doing it. I can write code at home and sometimes I do - but most of the time I'm burned out after doing that for my day job. However I can still bend the sides of a ukulele, use CAD to design a new switch housing for some manual machine, practice trumpet, or other such tasks that are not related to my day job. I personally am not interested in editing a video (which takes a lot of time to do well) so you won't see me on youtube, that too is something I could do if I was interested in it. Though with kids often all I have time for is cooking a meal before getting them to bed and then I'm off to bed myself. I wouldn't trade it for the world, but there is limited time and so there are a lot of things I want to do that I don't have time to do.
- gaze 2y agoYeah Matthias is fun to watch because he does a lot of hack stuff with plywood that works better than you'd expect. He does a lot of stuff with a lot of confidence, a lot of it dangerous. He's a smart guy for sure, so for what the setups are, the data is interesting. However, the problem is that people extrapolate beyond the setup. It's rare that the way he does something is a _good_ way to do something. He doesn't demonstrate himself to be an expert in much beyond software and hacking stuff together with wood, and I don't think he claims much beyond that.
- 2y ago
- on_the_train 2y agoThe guy who fell for the most basic boomer Phishing mail - two times in quick succession
- mikey_p 2y agoYeah, clearly tech people never get their Youtube hacked: https://www.theverge.com/2023/3/24/23654996/linus-tech-tips-channel-hack-session-token-elon-musk-crypto-scam https://www.theverge.com/2023/3/24/23654996/linus-tech-tips-...
- on_the_train 2y agoLinus isn't really a tech guy, at least not software.
- YZF 2y agoBrushless servo motors and steppers are very similar, it's just that steppers have many more poles.
- zwieback 2y agoIn my mind the main difference is steppers always taking full current, that's why we tend to switch to traditional servos past a certain size or use hybrid steppers like the MDrive
- SequoiaHope 2y agoI used to think this but you can actually drive steppers with FOC (if they have appropriate feedback) and modulate the current based on required torque. It’s open-loop steppers that don’t do this.
- mitthrowaway2 2y agoYou can do this but it's very difficult; the high pole count means it requires extremely precise and high-speed feedback to get good torque control on a stepper motor.
- SequoiaHope 2y agoYeah ain’t that the truth. This is a problem I’ve been fighting at work lately with a trinamic based system. Trinamic should be good but I see it’s touchy to properly phase align a stepper.
- YZF 2y agoIf you're micro-stepping a stepper then you're applying different currents to the coils. You can also microstep/openloop a BLDC just like a stepper and you can run a stepper with a closed loop controller just like it's bigger BLDC cousin. Steppers had a niche in situations where you want to take discrete/accurate steps with very little control circuitry, e.g. printers, disk drivers etc. they're much simpler to work with vs. a closed loop bldc system, require no tuning, less software, etc.
- 01HNNWZ0MV43FF 2y agoNice that the servo tells you the position. The only time I used a servo it was a cheap 3-wire one, and it didn't tell me the position. So even though it was "closed-loop" internally, it was open-loop from the perspective of my code. Still mad about that...
- HeyLaughingBoy 2y agoR/C servo? If so that's not surprising: they're designed for use in radio-controlled vehicles where the main feedback to the operator is the vehicle's motion.
- hydrogen7800 2y agoWhen I was about 13 I took apart a broken servo from a hobby RC car I had. What a revelation to me. The circuit board was pretty mysterious to me, but I noticed the encoder (didn't know what it was called then) on the output shaft, and immediately realized its purpose. It looked to me a bit like a volume knob. I wondered why the servo motor didn't keep turning, but I realized this thing must be telling the motor "a little more" or "a little less", and it would have to keep making small oscillations back and forth to compensate for external forces, etc, which explained all the twitching noises it made. It was a great discovery at that age.
- HeyLaughingBoy 2y agoIt's amazing how many parts they fit into such a tiny space, isn't it? Those things are little marvels. It's a potentiometer most of the time, BTW. Encoders are on the spendy "digital servos"
- hydrogen7800 2y agoYeah, it was a potentiometer. Is an encoder not simply any device that provides a signal proportional to its position or displacement? It had wiper arms (brushes?) that dragged along a conducting surface on a PCB below the rotor.
- ge96 2y agoI'm gonna experiment with adding hall effect sensors to a standard servo to make a cheap feedback mechanism since those are pretty cheap nowadays seems like. Steppers still have a place but for hobby stuff with basic "what pos is it" this could be something I use a lot.
- Animats 2y agoA "standard servo" of R/C toy type does have feedback. It just doesn't come out the standard 3-wire interface. Robotics hobbyists have been fighting this for decades.[1] There are "digital servos" for R/C, but they have the same 3-wire interface. They just have better motor drive circuitry. Dynamixel [2] has been selling R/C type servos with a digital interface for years, but they are somewhat overpriced. It's a tiny product niche. Rod Brooks' original insect robots used R/C servos where someone had wired in an extra wire to extract the analog error signal. This provided force feedback. So that's quite possible. The general problem with servomotors for hobbyist use is price. Note that the OP was given those motors as an influencer. Industrial motors with encoders are expensive, and controllers are worse. Some years ago I was talking to a Maxon rep at a trade show. They'd just introduced their own controllers. He told me that the motor and the controller cost about the same to make, but the controller people were getting 90% of the profit because controllers had become cheap to make. So they built a controller to improve their margins. [1] https://github.com/SUSF-Robotics-and-Software/OpenServo https://github.com/SUSF-Robotics-and-Software/OpenServo [2] https://www.robotis.us/dynamixel/ https://www.robotis.us/dynamixel/
- ge96 2y agoI have tried that one time to tap into the potentiometer (not sure if that's what you're talking about with hobby servos). Eventually you do want to fork out money for more expensive servos as those cheap 9g blue ones don't cut it, start to get hot/melt when used in a more serious robot application. Granted at that time I was using one cell so maybe that was more current. At any rate when I switched from $2 to $10 servos (especially metal gear) it was noticeable. The price matters when your robot has 12 or 18 of these servos on it. Thanks for the links, as my robotic projects get more serious I do want positional feedback, term I picked up from a fun book "proprioception"
- Animats 2y agoThat's a unusual servo. Servos usually have a small optical encoder that emits quadrature pulses as it rotates. That's immune to magnetic interference but can potentially miss counts. This servo seems to have an magnetic analog position sensor. Something like this.[1] Can't miss counts but has less noise immunity. [1] https://www.analog.com/en/products/adaf1080.html https://www.analog.com/en/products/adaf1080.html
- zwieback 2y agoOur nomenclature for servos in machine controls is a little different, for example a traditional 3phase servo with a 3phase hall sensor is still called "servo" even if it doesn't have an optical encoder. With this setup you can commutate the motor and get smooth motion and variable speed control but not precise position control. We then add on a optical shaft encoder or a optical linear encoder for position control. In the video he has what looks like a magnetic absolute encoder, I have honestly never seen that in industrial applications although I have seen "absolute" optical encoders that have a backup battery to store the home point, kind of weird imo. I was surprised when I first encountered servos with just magnetic hall effect sensors but there are actually lots of applications where you want speed control but not accurate position control.
- GabeIsko 2y agoAbsolute encoders can be really good for position critical applications that you don't want to re-home all the time. Linear stages, winches - if you don't want to re home it and it needs accurate position control you start looking at an absolute encoder. Even for speed control, hall effect sensors are kind of a poor way to track position. What is nice about hall effect sensors is that you can use them as a signal to perform brushless commutation in your motor controller, and then also use them as a poor-man's encoder. Very useful if you don't need that much accuracy in your application, but you do need brushless motors for some reason. But one of the first things I would go to as a application engineer was recommend customers get an encoder mounted.
- aidenn0 2y ago
- btbuildem 2y agoThat's an impressive servo! I've been messing around in this space lately, though on a smaller budget. The cheap NEMA-x motors he mentions are still quite decent, and you can do a lot of the position keeping etc in software. Accel/decel curves are a _whole thing_, there's definitely a lot to learn and explore here. I'm making a set of roller blinds, and it's a pretty fun/challenging project that incorporates 3d design and printing, circuit design, and "microprogramming" (using a pico w board). It's really neat seeing physical manifestations of running code!
- kuon 2y agoIf you want high quality affordable servo motor, I highly recommend the clearpath from teknic.
- HeyLaughingBoy 2y agoSeconded. Add "incredibly simple to use" to the list of qualifications.
- jcims 2y agoCheck out his video on turning one into a catapult: https://www.youtube.com/watch?v=IF78MpQqejI https://www.youtube.com/watch?v=IF78MpQqejI
- nimish 2y ago"Servo" is a control method. You can control steppers using servo methods and it's pretty good actually. There are chinese encoder boards that'll do everything for like $10
- stavros 2y agoThe ones with the magnet? Those are really cool indeed, such a great idea.
- thatcat 2y agointeresting observation. i found a reference project detailing how this works below https://calischs.pages.cba.mit.edu/step/servo-stepper/ https://calischs.pages.cba.mit.edu/step/servo-stepper/
- YZF 2y agoTechnically the motor is also called "brushless servo motor". AI says: "A servo is a control system that converts a small mechanical motion into a larger one. It can also be used as a noun to describe a part of a machine that controls a larger machine." which sounds reasonable. Stepper motors can be controlled with closed loop controllers and an encoder. As I said in some other comment way down the only difference between a stepper motor and a brushless servo is that steppers have more poles. A by the way is you can also "step" a BLDC (i.e. run it in open loop just like a stepper motor).
- analog31 2y agoThis is good to point out, and is a typical problem with terminology, which is that a term picks up popular definitions that differ from the technical ones. I've seen the term "servo motor" applied to little DC motors that have no feedback sensor.
- bsder 2y agoThat's one of the motors that the video covers. And it shows that there are limitations to steppers with servos.
- arghwhat 2y agoClosed loop is the control method, "servo" describes an assembly of a servo motor and its controls. Good closed loop stepper controllers are a huge step up (heh) from open loop control, but there's a big difference in characteristics of a stepper motor - which is a very special motor configuration making huge trade-offs specifically to allow repeatable open-loop operation - and the more standard servo motor choices. Because steppers are special you also tend to specifically say "closed loop stepper" rather than considering it a servo. Be a bit careful with random closed loop controllers though. Cheap ones can be finicky, and poor tuning and broken failure modes is no fun when used in machinery that could injure you, which tends to be where such steppers are installed. Aggressive and erratic movement or randomly entering fault and powering down is quite a lot different from simply losing steps.
- globalnode 2y agoreally liked his software's ascii display of the rpm in big letters when he was running the fan. also hope he had an e-stop nearby, that looked a little unsafe!
- alkonaut 2y agoNow I understand why these 10-15Nm race sim wheels are really expensive.
- numpad0 2y agoWhy aren't everyone buying power steering column units for simracing purposes? They're cheap and plenty powerful. Only problems are that they're heavier and brushed DC types are deliberately imprecise for simplicity.
- oinx 2y agoServo
- benbojangles 2y agostick a planetary gearbox on any motor and you have a much more powerful motor
- MisterTea 2y agoNot more power but more torque with a sacrifice in velocity.