Searching servo motor

Hello,

I’m now working a project and in my project I will use many servo motors. I can’t find the good servo motor on the Internet because what I need is somewhat complicated. I want a servo motor,

  1. controled by degree of a signal PWM (that’s to say after the servo motor turns a certain degree, it can stop itself, I don’t need to send a signal of stop)
  2. continuous rotation (at least it could turn fours circles)
  3. bidirectional (it could turn in two directions)

I have searched on the Internet for more than a week but I don’t succeed in finding it. Do you have some suggestion?

Thank you very much!!!

Hello,

I'm now working a project and in my project I will use many servo motors. I can't find the good servo motor on the Internet because what I need is somewhat complicated. I want a servo motor,

  1. controled by degree of a signal PWM (that's to say after the servo motor turns a certain degree, it can stop itself, I don't need to send a signal of stop)
  2. continuous rotation (at least it could turn fours circles)
  3. bidirectional (it could turn in two directions)

I have searched on the Internet for more than a week but I don't succeed in finding it. Do you have some suggestion?

Thank you very much!!!

Do you mean a hobby servo? Servomotors are altogether a more serious proposition!
Hobby servos are small servomechanisms operating an arm that swings 120 degrees back and
forth, typically.

Thank you MarkT.

In fact, I need a motor that can turn continuously with high precision, so 120 degrees are not enough for me…

A genuine small servomotor with encoder? How about Parallax Feedback 360° High Speed Servo - Parallax

Look for "sail winch servo". They have full positional control over anything up to 6 full rotations. E.g. https://hobbyking.com/en_us/sw4805-6pa-sailwinch-servo-6-13kg-45g-0-70.html

Steve

Please don't multi-post the same question. Already answered in your other thread.

Steve

Bravo, MarkT!!!

After watching the video, I realize that this is exactely what I need! I can't believe that this kind of motor exists already beacause I have searched it for a long time and have communicated with many manufacturers. Maybe because I didn't search with the keyword "feedback-controled".

Thank you very much!! Really and indeed!!

Sorry slipstick, I begin to use Arduino forum just this morning and I'm not really familiar with it. I didn't think that I have posted the question in the good board at the first time so I reposted the question in board "Motors, Mechanics, and Power".

I have looked at the motor proposed by you, but I don't understand how it works. The servo motor proposed by MarkT, Parallax Feedback 360°, has a feedback and we can easily turn and hold it at any angle. Anyway, thank you very much with your help !!!

Almost any fully rotational (360) servos will do the type of task you want it is just a matter of you selecting one that is big enough for the task.

A closed loop stepper motor will also do it but prices can be quite high on those.

Hello ballscrewbob, thank you for your response. In fact, many continuous servos need a signal to stop. The PWM signal controls only the speed of this kind of servo. I have already found the good one but it is too expensive.

All motors require a signal to stop.

That is down to the code you use and how you implement any counters for rotations.
In a NON closed loop system you could use a reed switch or hall effect type arrangement for complete revolutions.

If you add a segmented disc you can also use that as a more accurate partial step counter too as is used on printers today or the older type mouse with IR sensors.

Slotted discs are easy enough to find or make to build a closed loop system.

OPs requirements:

  1. controled by degree of a signal PWM (that's to say after the servo motor turns a certain degree, it can stop itself, I don't need to send a signal of stop)
  2. continuous rotation (at least it could turn fours circles)
  3. bidirectional (it could turn in two directions)

Suggested solution:

Almost any fully rotational (360) servos will do the type of task you want it is just a matter of you selecting one that is big enough for the task.

While the typical 360 servo will meet the requirements for 2 and 3, it does not meet requirement #1.
Typical continuous rotation servos have no positional awareness whatsoever. Without adding more hardware, it will not stop itself for a given PWM command.

@vinceherman

So if I set a 360 servo to do 4x360 in the code it would STOP after reaching the required 4 rotations.
I could additionally set it for more or less degrees by code with a counter in code.

The only thing I would say with servos over steppers is the torque factor with steppers almost always being better in that regards.

With a stepper a similar approach can also be used but as I have already said it may require additional hardware.
Having said that my home brew GRBL CNC machines go to where I tell them with fantastic precision and that can also be done without GRBL

Stops are the least of the issue.
It is the sketch used that determines what how when where.

ballscrewbob:
@vinceherman

So if I set a 360 servo to do 4x360 in the code it would STOP after reaching the required 4 rotations.
I could additionally set it for more or less degrees by code with a counter in code.

No, I was saying exactly the opposite. :wink:
The typical 360 servo is simply a motor driver, motor and a gearbox. You can control the direction. You can sometimes control the speed. You can make it stop. But there is no awareness of position at all.

A winch servo offers positional awareness over several rotations. That could be one solution. Or there are other servos that offer continuous rotation with a sensor for some positional awareness. But they are not the cheapy 360 servos. I think Paralax is one brand.

The only thing I would say with servos over steppers is the torque factor with steppers almost always being better in that regards.

With a stepper a similar approach can also be used but as I have already said it may require additional hardware.
Having said that my home brew GRBL CNC machines go to where I tell them with fantastic precision and that can also be done without GRBL

Stops are the least of the issue.
It is the sketch used that determines what how when where.

Stepper motors have little positional awareness. The do know how many steps they have moved. So moving then until they hit a limit switch lets you know where they are at the moment the switch closes. Then you keep track of the number of steps moved.

Servomotors can produce some pretty decent torques, most can generate pulse torques at least 3 times
the continuous rating (which is usually only a thermal limit), and at high speed too, whereas steppers
torque drops precipitously with increasing rpm.