How Servo Motors Work | Hacker News Reader

How Servo Motors Work

jameco.com

113 pointskaycebasques26 comments

> Understanding the technical aspects of a servo motor and how it works

I don't feel like the article explains that at all. They explain the control signal and what the servo does as a result. The "how" in between is completely missing though. How is that pulse translated? How does the feedback work? What are the safety mechanisms involved?

That’s because the control circuit is hidden in a monolithic IC. If you’re really curious, here’s a datasheet for an old fashioned design with a block diagram and theory of operation described that should give you some hints. https://www.meditronik.com.pl/doc/plus/zn409.pdf

If that sort of thing interests you, there’s a whole field of control theory to study.

https://lastminuteengineers.com/servo-motor-arduino-tutorial...

Interactive diagrams + code

I think this is a pretty good overview of how motors work and how you can write algorithms to control how much torque they generate by varying the PWM:

https://www.actronic-solutions.de/files/actronic/FTPROOT/Fie...

Yeah, it's more "How and Why/When to work with Servo Motors"

It's about how radio control toy servos from the 1970s work. Annoyingly, those pre-computer dumb devices with no feedback output still dominate the low end of mechanical output devices.

Makes me wonder if the generic servos of the described kind are really close enough to the performance a cheap-class servo can have, or if modern advances in monolithic power stage ICs could allow a servo free of sliding movement (no brushes, no wiper potentiometer (maybe a capacitively coupled differential sensing of angle, or the tricks of the cheap digital calipers with their iirc nonius-like scale read through several parallel tracks of non-touching capacitive electrodes?), instead just a clever chip digitally controlling a brushless electric machine using the feedback sensing available to it).

Being able to run an even just very simple digital controller allows things like severely dropping negative feedback gain at a resonance frequency of the larger system. And so much more.

The nice thing about using a potentiometer for position sensing is that you don't have to home the thing.

There are lots of alternative sensors, but most are bigger, heavier, or more expensive. If 1% precision is good enough, pots are fine. The next step up is Dynamixel servos, which have a nice daisy-chain digital interface, encoders, about the same form factor as toy-type servos, at about 10x the price.[1]

[1] https://www.robotis.us/dynamixel/

Yeah, but they're cheap and basically trivial to use. Cheap enough and trivial enough that they can replace solenoids in a lot of use cases.

One of my most amusing applications was the client who put an R/C servo on the choke cable of a carbureted generator motor instead of spending more money to buy the fuel-injected version. Servo cost about $5 and we were already measuring air temperature and had a PWM output available.

I’ve noticed that distributors (Jameco, Mouser, etc) have a surprising number of introductory education articles. I’ve seen this pattern on websites for car dealerships and HVAC installers, so I assumed it was for SEO purposes. But electronic parts distribution seems like a much more niche audience; why bother with SEO?

I think it's just a tradition in the electronics world to write and publish hobby and educational articles. It dates back to well before the the Internet. People enjoy this interaction, and the distributors give them space for it.

People like HVAC installers -- I've seen most of that on YouTube, where there's a chance of monetizing the content. I've repaired nearly every appliance in my house, thanks to blogs and videos posted by strangers.

Indeed. Vancouver Carpenter got me through a minor drywall repair job.

He's fantastic. I still suck at drywall work, but I suck way less after watching a bunch of his videos.

It brings you to their site as well as advertises a specific component or range of components from a manufacturer.

The Digikey articles I've come across are well written. This article however is artificially inflated using SEO style writing. I mean after they supposedly explained servo motors you'll find this ugly sentence further down: "Still, how does a servo motor work?" I mean holy shit man, do you even care about your writing or the subject? Likely not. And really, the article is so light on details its barely technical and only talks about the RC servo. This is pretty much junk.

Electronics distributors have published educational material for decades. Knowing how something works and how to choose the best option reduces their support burden and itself a form of marketing.

Omega Engineering used to (still does?) publish a set of absolutely massive hardcover catalogs on sensors and industrial controls that contained detailed tutorials and theory of operation. In some cases, they published entire books devoted to teaching you how stuff worked. Their Temperature Sensors Handbook always had a place on my bookshelf for many years.

If I recall correctly these pages are useful for teachers and students, and Jameco has relatively high-touch education sales (for example, their kitting program: https://www.jameco.com/Jameco/workshop/education-center/educ...).

I want to say that I remember seeing this page in high school in the late 00s, although the Internet Archive only seems to go back to 2012 for this exact URL.

This reminds me that Monoprice used to have a "knowledge base" for many of their products. I don't remember if they were just written directly on an item's page, or if there was a link to the relevant article, but it was very informative.

Is it this? I didn't know about it until your post.

https://help.matterhackers.com

Some may be application notes from the manufacturers.

Jameco also supplies mid level engineering firms, so similar to application notes. Think automation integration company buying xyz specialty robotics controller.

I think of mouser as more like digikey, so I don't really know why they would have similar educational information above the level of PCB board component. But, they may also have business in the low-quantity higher margin business.

Tldr: not seo. Customers actually need to know about the product

Exactly, as one of their target audience I'm not searching for them, I know who they are. I go to their website regularly and articles like these are how I find out about new stuff and how to use it.

I just want to put this hack here which enables the toy servos with a very high accuracy and repeatability

https://youtu.be/ECLrLupFW10?si=dQPSq-hjMTaVGuQS

I tried using a hobby servo but it was very loud with a high pitched annoying sound. What servos are better?

How does it hold its position? Does that take energy?

I don't think servos normally do this, but it's possible to have self-locking worm drives.

Only if there's some force pushing it away from the goal position.

hmm. this looks suspiciously AI generated to me.

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