5 ms·

It has the wrong kind of motors to be interesting. Servos are a dead end, imo. The interesting robot projects now are the ones embracing brushless motors with

by Torkel 6y ago

It has the wrong kind of motors to be interesting. Servos are a dead end, imo. The interesting robot projects now are the ones embracing brushless motors with encoders and dynamic walking gaits. It’s the same components that are used in drones.

outworlder 6y ago
Why are they a dead end?
- modeless 6y ago
  Too slow, too weak, too inefficient, too much backlash, not backdrivable, no energy regeneration, no built in force sensing.
  - accurrent 6y ago
    Add sloppy controls to the list.
  - numpad0 6y ago
    They aren’t sexy, isn’t that it — you want a sexy robot and RC servos don’t cut it
    - Torkel 6y ago
      It's not that rc-servos are not sexy. It't that they suck. For a number of specific reasons well listed in other posts here. RC-servos are very cheap and very easy to use, so there are many projects using them. But there is no way to make a good robot out of them. It's a local maximum.
      - craftinator 6y ago
        All true. But they are cheap, available, and have well understood limitations. Which means you can design and build your project quickly and cheaply, then upgrade to brushless motors with encoders or whatever when you have the time and funds. I think from that aspect they are a great way to get a project started without flinging cash at it.
- taneq 6y ago
  IMO the only inherent issues with hobby-style servos are lack of feedback (force and position) and lack of direct torque control. The rest of the complaints are features of all cheap positioning elements and aren't unique to hobby servos.
fake-name 6y ago
A brushless motor with an encoder and a feedback loop is a servo. It's just not a crappy integrated RC model servo motor assembly. The (ab)use of the term "servo" is a major pet-peeve of mine.
- Torkel 6y ago
  Sure. I should have written "rc-servo". But in this context it was not ambiguous and the point stands - anything that uses rc-servos is a dead end. Personally I'm also skeptical of series elastic actuators - it seems like a half-assed solution where the proper solution is to embrace full direct-drive digital control of electrical <-> force conversion.
  - michaelt 6y ago
    The "problem" I've seen with a lot of walking robot projects is, where an RC car needs 2 motors and a quadcopter 4, most "interesting" walking robots need 12 - which means they instantly have to start making compromises due to cost and weight. This robot ain't exactly large - but it's already needed $450 worth of Dynaixel AX-12A servos.
    - fho 6y ago
      We have a hexapod (18 Dynapixels) at work ... apart from giving demos to visitors it's not used at all. Gait patterns and (inverse) kinematics are a solved problem ... dynamic gaits are becoming more mainstream now, but those require motors that are reasonably backdrivable. Maybe the Dynapixels can be configured to do that, but I think the high gear ratio will prevent that.
colordrops 6y ago
Could you provide some examples of these projects?
- modeless 6y ago
  Stanford Doggo: https://nathankau.com/Research https://nathankau.com/Research https://github.com/Nate711/StanfordDoggoProject https://github.com/Nate711/StanfordDoggoProject
- Torkel 6y ago
  Here are two: MIT Cheetah: https://biomimetics.mit.edu/ https://biomimetics.mit.edu/ Unitree/laikago: http://www.unitree.cc/ http://www.unitree.cc/
- mandor 6y ago
  Here is an open-source, 3D-printable quadruped with (almost) direct-drive actuation: https://open-dynamic-robot-initiative.github.io https://open-dynamic-robot-initiative.github.io Paper: https://arxiv.org/pdf/1910.00093.pdf https://arxiv.org/pdf/1910.00093.pdf Videos: https://www.youtube.com/watch?v=MkXU-5Oupg4 https://www.youtube.com/watch?v=MkXU-5Oupg4
fh973 6y ago
Can you do without an encoder for legs? Maybe attach an IMU like you do for gimbals? Or measure current?
- Torkel 6y ago
  No. For these motors to do their job at these low speeds you need to know where the windings are relative to the magnets so you can apply a controlled force instantaneously. Btw, this is true for gimbals too, and good gimbals use sensors.
wlll 6y ago
I'm interested in Robotics (I made a simple ping-pong ball collector a while back https://sendcat.com/dl/D9DI15MAOjhKMFJYLJLADj64ywyU2qGWaKMSlskgRpJzKnJ7pqcWPFW https://sendcat.com/dl/D9DI15MAOjhKMFJYLJLADj64ywyU2qGWaKMSl...). Are there places I should go or things I should read to find out more about the latest developments in robotics in general, or the use of brushless motors with encoders/dynamic walking gaits specifically?
- Torkel 6y ago
  Nice build :) Have you checked out EasyEDA + jlcpcb? It can improve the electronics aspects of robot projects. I searched a bit now to see if any new projects have shown up. Came across this one: https://hackaday.io/project/167845-mjbots-quad https://hackaday.io/project/167845-mjbots-quad Could maybe be interesting, but I haven't looked into it. Here is a chinese motor manufacturer that makes more sane motors: http://www.gyems.cn/product.html http://www.gyems.cn/product.html Getting a drone or gimbal working properly from scratch is a lot of work. And these dynamic walking systems are more complex endeavors because there is less info out there. So I would recommend to find some project with people who seems talented and has a nice atmosphere and then get building :) edit: Ratholed on this, here is a nice blog with inspiration (scroll for lots of awesome) https://build-its-inprogress.blogspot.com/ https://build-its-inprogress.blogspot.com/
  - wlll 6y ago
    > Nice build :) Have you checked out EasyEDA + jlcpcb? It can improve the electronics aspects of robot projects. Thanks! Yeah, the electronics is a bit gross. This build was probably 6 years ago perhaps? I got it to the point that it worked and then it was kinda "done" and all that was left was polish, but it was really a toy so there wasn't much point and I left it. Planning on building something for slug and snail control (NW UK, they can be a problem), and cat/badger/squirrel scaring in my garden (they dig up things). Will likely make use of PCBs with this so will check out the links. > Here is a chinese motor manufacturer that makes more sane motors: http://www.gyems.cn/product.html http://www.gyems.cn/product.html So I did some digging and found this guy: https://www.youtube.com/user/SkyentificTube/videos https://www.youtube.com/user/SkyentificTube/videos He does a some testing of some Turnigy motors (a bit like this: https://hobbyking.com/en_us/turnigy-aerodrive-sk3-6374-149kv-brushless-outrunner-motor.html?queryID=&objectID=17314&indexName=hbk_live_magento_en_us_products https://hobbyking.com/en_us/turnigy-aerodrive-sk3-6374-149kv..., there's a whole range) which looked cool, and he was using an odrive controller https://odriverobotics.com/ https://odriverobotics.com/ which also looked pretty handy, so there's some stuff to check out there, but he also did some tests with some gyems motors and they looked great: https://www.youtube.com/watch?v=smQJeg87ff8 https://www.youtube.com/watch?v=smQJeg87ff8 > dynamic walking systems are more complex Given the speed of slugs and snails I am going to probably go for a less dynamic movement style. Less force, smaller motors, longer battery life. Though I like the idea of trying to program dynamic movement. The physical build for my more static movement style shouldn't be too hard to do. > https://build-its-inprogress.blogspot.com/ https://build-its-inprogress.blogspot.com/ Thanks, this is great!
lootsauce 6y ago
Just going to share a YouTube channel (Skyentific) that I have learned a ton from when it comes to the considerations of sizing and power consumption when selecting motors for robotics. https://www.youtube.com/channel/UCcgqJ1blFKqbC2bWGY4Opmg https://www.youtube.com/channel/UCcgqJ1blFKqbC2bWGY4Opmg
craftinator 6y ago
Servos (hobbyist level) are a dead end in this application, but even marginal quality BLDCs are quite a bit more expensive. These servos can be swapped out for BLDCs in a retrofit, so I think this is a good starting point that can be expanded on.

by Torkel 6y ago

outworlder 6y ago

Why are they a dead end?

modeless 6y ago
Too slow, too weak, too inefficient, too much backlash, not backdrivable, no energy regeneration, no built in force sensing.
- accurrent 6y ago
  Add sloppy controls to the list.
- numpad0 6y ago
  They aren’t sexy, isn’t that it — you want a sexy robot and RC servos don’t cut it
  - Torkel 6y ago
    It's not that rc-servos are not sexy. It't that they suck. For a number of specific reasons well listed in other posts here. RC-servos are very cheap and very easy to use, so there are many projects using them. But there is no way to make a good robot out of them. It's a local maximum.
    - craftinator 6y ago
      All true. But they are cheap, available, and have well understood limitations. Which means you can design and build your project quickly and cheaply, then upgrade to brushless motors with encoders or whatever when you have the time and funds. I think from that aspect they are a great way to get a project started without flinging cash at it.
taneq 6y ago
IMO the only inherent issues with hobby-style servos are lack of feedback (force and position) and lack of direct torque control. The rest of the complaints are features of all cheap positioning elements and aren't unique to hobby servos.

fake-name 6y ago

A brushless motor with an encoder and a feedback loop is a servo. It's just not a crappy integrated RC model servo motor assembly. The (ab)use of the term "servo" is a major pet-peeve of mine.

Torkel 6y ago
Sure. I should have written "rc-servo". But in this context it was not ambiguous and the point stands - anything that uses rc-servos is a dead end. Personally I'm also skeptical of series elastic actuators - it seems like a half-assed solution where the proper solution is to embrace full direct-drive digital control of electrical <-> force conversion.
- michaelt 6y ago
  The "problem" I've seen with a lot of walking robot projects is, where an RC car needs 2 motors and a quadcopter 4, most "interesting" walking robots need 12 - which means they instantly have to start making compromises due to cost and weight. This robot ain't exactly large - but it's already needed $450 worth of Dynaixel AX-12A servos.
  - fho 6y ago
    We have a hexapod (18 Dynapixels) at work ... apart from giving demos to visitors it's not used at all. Gait patterns and (inverse) kinematics are a solved problem ... dynamic gaits are becoming more mainstream now, but those require motors that are reasonably backdrivable. Maybe the Dynapixels can be configured to do that, but I think the high gear ratio will prevent that.

colordrops 6y ago

Could you provide some examples of these projects?

modeless 6y ago
Stanford Doggo: https://nathankau.com/Research https://nathankau.com/Research https://github.com/Nate711/StanfordDoggoProject https://github.com/Nate711/StanfordDoggoProject
Torkel 6y ago
Here are two: MIT Cheetah: https://biomimetics.mit.edu/ https://biomimetics.mit.edu/ Unitree/laikago: http://www.unitree.cc/ http://www.unitree.cc/
mandor 6y ago
Here is an open-source, 3D-printable quadruped with (almost) direct-drive actuation: https://open-dynamic-robot-initiative.github.io https://open-dynamic-robot-initiative.github.io Paper: https://arxiv.org/pdf/1910.00093.pdf https://arxiv.org/pdf/1910.00093.pdf Videos: https://www.youtube.com/watch?v=MkXU-5Oupg4 https://www.youtube.com/watch?v=MkXU-5Oupg4

fh973 6y ago

Can you do without an encoder for legs? Maybe attach an IMU like you do for gimbals? Or measure current?

Torkel 6y ago
No. For these motors to do their job at these low speeds you need to know where the windings are relative to the magnets so you can apply a controlled force instantaneously. Btw, this is true for gimbals too, and good gimbals use sensors.

wlll 6y ago

I'm interested in Robotics (I made a simple ping-pong ball collector a while back https://sendcat.com/dl/D9DI15MAOjhKMFJYLJLADj64ywyU2qGWaKMSlskgRpJzKnJ7pqcWPFW https://sendcat.com/dl/D9DI15MAOjhKMFJYLJLADj64ywyU2qGWaKMSl...). Are there places I should go or things I should read to find out more about the latest developments in robotics in general, or the use of brushless motors with encoders/dynamic walking gaits specifically?

Torkel 6y ago
Nice build :) Have you checked out EasyEDA + jlcpcb? It can improve the electronics aspects of robot projects. I searched a bit now to see if any new projects have shown up. Came across this one: https://hackaday.io/project/167845-mjbots-quad https://hackaday.io/project/167845-mjbots-quad Could maybe be interesting, but I haven't looked into it. Here is a chinese motor manufacturer that makes more sane motors: http://www.gyems.cn/product.html http://www.gyems.cn/product.html Getting a drone or gimbal working properly from scratch is a lot of work. And these dynamic walking systems are more complex endeavors because there is less info out there. So I would recommend to find some project with people who seems talented and has a nice atmosphere and then get building :) edit: Ratholed on this, here is a nice blog with inspiration (scroll for lots of awesome) https://build-its-inprogress.blogspot.com/ https://build-its-inprogress.blogspot.com/
- wlll 6y ago
  > Nice build :) Have you checked out EasyEDA + jlcpcb? It can improve the electronics aspects of robot projects. Thanks! Yeah, the electronics is a bit gross. This build was probably 6 years ago perhaps? I got it to the point that it worked and then it was kinda "done" and all that was left was polish, but it was really a toy so there wasn't much point and I left it. Planning on building something for slug and snail control (NW UK, they can be a problem), and cat/badger/squirrel scaring in my garden (they dig up things). Will likely make use of PCBs with this so will check out the links. > Here is a chinese motor manufacturer that makes more sane motors: http://www.gyems.cn/product.html http://www.gyems.cn/product.html So I did some digging and found this guy: https://www.youtube.com/user/SkyentificTube/videos https://www.youtube.com/user/SkyentificTube/videos He does a some testing of some Turnigy motors (a bit like this: https://hobbyking.com/en_us/turnigy-aerodrive-sk3-6374-149kv-brushless-outrunner-motor.html?queryID=&objectID=17314&indexName=hbk_live_magento_en_us_products https://hobbyking.com/en_us/turnigy-aerodrive-sk3-6374-149kv..., there's a whole range) which looked cool, and he was using an odrive controller https://odriverobotics.com/ https://odriverobotics.com/ which also looked pretty handy, so there's some stuff to check out there, but he also did some tests with some gyems motors and they looked great: https://www.youtube.com/watch?v=smQJeg87ff8 https://www.youtube.com/watch?v=smQJeg87ff8 > dynamic walking systems are more complex Given the speed of slugs and snails I am going to probably go for a less dynamic movement style. Less force, smaller motors, longer battery life. Though I like the idea of trying to program dynamic movement. The physical build for my more static movement style shouldn't be too hard to do. > https://build-its-inprogress.blogspot.com/ https://build-its-inprogress.blogspot.com/ Thanks, this is great!

lootsauce 6y ago

Just going to share a YouTube channel (Skyentific) that I have learned a ton from when it comes to the considerations of sizing and power consumption when selecting motors for robotics. https://www.youtube.com/channel/UCcgqJ1blFKqbC2bWGY4Opmg https://www.youtube.com/channel/UCcgqJ1blFKqbC2bWGY4Opmg

craftinator 6y ago

Servos (hobbyist level) are a dead end in this application, but even marginal quality BLDCs are quite a bit more expensive. These servos can be swapped out for BLDCs in a retrofit, so I think this is a good starting point that can be expanded on.