Comment by ge96
5 days ago
I'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.
A "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
[2] https://www.robotis.us/dynamixel/
FWIW (having used Dynamixels for 13+ years for hobby stuff), there are cheaper alternatives with tradeoffs now, too. Though I've only played with e.g. AX-12-sized ones (specifically HiWonder HX-35HM sitting on my desk from early last year)
There's so much to do in robotics, that you won't catch me going back and modifying RC servos, ever. I'll do hard things elsewhere! (And I don't even do autonomous hobby robots...)
Ah. Now, Dynamixel-type servos with a "China price".
Order now, before tariffs go up.
those prices look good
I 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"
Also have a look at this project, he adds an optical encoder and mc to a cheap servo to enable smooth control. So there is extra feedback, but processed on the modified servo. https://github.com/adamb314/ServoProject
If you are going to add your own sensors and feedback, then isn't using a servo kinda pointless, might as well go with plain dumb motor? I thought the whole point of servo is to have sensor+feedback+motor in a integrated package
It depends on the use case, I was curious on price. It is geometrically limited too, with regard to how to mount the magnet to the servo horn (vs. taking the body apart). I just like how you can use that tech, I've seen someone make a USB joystick with a magnet/hall effect sensor to use as a 3D mouse for example. Also have seen people taking hs and using them as rotary encoders on BLDC motors.
edit: I probably should have watched this video before my initial comment, servo I thought RC servo not these big ones. Even so the bigger one would be easier to work on than a smaller hobby one.
You can also use the motor itself for feedback. It's called "sensorless bldc". With the right controller you can run a closed loop servo with no sensor.