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what motor to use?? Answered

I'm a novice with motors, so would appreciate some help and advice.

I envision a project with two blocks of wood side by side.   Just a couple of 12 inch wood squares, for example.   I want to rotate each individually, though to different degrees and at different increments.  The first block should rotate 90 degrees at 15 second intervals.  The second block should rotate 180 degrees at 30 second intervals.

How would you recommend i accomplish this?  what motor would you recommend? must i use a microcontroller and a step motor?  I have some experience with arduino, but wondering whether there is a simple circuit or a simpler mechanism of some kind

Thanks very much in advance.

Tags:motor

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Honus

7 years ago

So do the wood blocks end up rotating 360 degrees continuously or does one rotate 90 degrees in one direction and then reverse 90 degrees 15 seconds later?

If they continuously rotate I'd be inclined to use stepper motors. You call out step and direction and then specify your time interval. Adafruit makes a small stepper driver arduino shield here- http://www.adafruit.com/products/81

If the wood blocks rotate to one position and then reverse direction servo motors would be another option- in other words the servos never travel more than 180 degrees. Then you just have to call out the servo position and the time interval. This is really easy to do using the arduino servo library.

If you need more help just let me know!

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pfred2Honus

Reply 7 years ago

I don't know enough about the application to make any kind of a sound recommendation but I would like to point one thing out.

Dinky toy radio control servos have a limited range of motion by design but servo motors are rotary motors.

Learn more here:

http://en.wikipedia.org/wiki/Servomechanism

If you scroll down that page some you'll find out why you think RC servos are "limited" to 180 degrees. They are but it is only because of some junk slapped onto them. Other than that they're just motors.

I still think a servo motor is not a good choice for the application, but not because of any artificial rotation limit. I've heard tale told that people have hacked RC servos to fully rotate too. But I still think they are a poor choice.

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Honuspfred2

Reply 7 years ago

I do not think RC servos are limited to 180 degree movement- he stated that he wanted it to rotate 180 degrees so they would provide a simple solution given that specification. I've hacked multiple servo motors over the years to remove the rotation limitation and have also used external potentiometers (both ten turn rotary pots and linear "soft pots") to control positioning. It is also possible to build your own servo motors using external control boards.

There are a huge variety of servo motors available- not just dinky toy radio servos. Many of them rotate more than 180 degrees stock and you can buy RC servo motors that are rated over 1000 oz/in. Servo motors would work quite well for his application given the information provided. There are linear motors available but they don't make sense in this application.

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pfred2Honus

Reply 7 years ago

Whether something can work does not mean it is the best choice. There are other factors to consider. So until they start giving servos out for free, and vastly simplify their use they remain a difficult choice to make.

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Honuspfred2

Reply 7 years ago

I'm not quite sure I understand your comments. Could you please explain in greater detail why you think servo motors are a poor choice?

The author did not ask for a "best" choice- he asked for recommendations. It would be foolish to say one is "best" with less than all of the information necessary to make such a decision- that is why I asked for additional information in my first post.

Hobby servo motors are extremely easy to use- even for a complete novice. For very little money you get a motor, gearbox and control circuitry in a nice little package that is very simple to control using a microcontroller with just a few lines of code. They are an excellent choice when you want to control rotational position when your application does not require continuous rotation.

Continuous rotation applications with positioning control are better served by stepper motors or closed loop motor systems- a DC motor with shaft encoder would work just fine but it is a more complex control system for the novice to integrate.

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steveastroukHonus

Reply 7 years ago

A closed loop motor system IS a servo.

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pfred2steveastrouk

Reply 7 years ago

You can even run a stepper in a closed loop system. It isn't done all the time, but that doesn't discount it from being done.

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steveastroukpfred2

Reply 7 years ago

Yes. Only amateur class machines use stepper motors for machine tools though. The big guys ALL use either AC or DC servomotors.

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pfred2steveastrouk

Reply 7 years ago

I guess when Bridgeport built the CNC-1 they were amateurs then.

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steveastroukpfred2

Reply 7 years ago

The CNC-1 is so old it illustrates perfectly the problem of early adoption - name me a serious industrial machine that uses steppers.

I think your phrasing is perfect, they were amateurs then. My 25 year old Hurco uses DC servo drives.

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Honuspfred2

Reply 7 years ago

I've heard of this only recently- have you done it and if so was it difficult to implement? I've had many conversations with a machinist friend about open vs. closed loop control for CNC machines...

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Honussteveastrouk

Reply 7 years ago

Correct you are! And technically speaking, I shouldn't call hobby servos "hobby servo motors" as servo motors are used in servos. :)

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pfred2Honus

Reply 7 years ago

You're right I'm wrong you win. Actually I could care less but you are wrong now it'd be pointless for me to point it all out to you. I tried several times and I could write a book on the topic. This isn't the forum for such. Good day.

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Honuspfred2

Reply 7 years ago

Ummm- OK? I'm just trying to understand why you say a RC servo is a poor choice (given the limited information we have to go on- non continuous rotation in this instance) and would greatly appreciate any additional information you could provide.

I also really shouldn't use the terms "servo", "servo motor" and "hobby servo motor" interchangeably. Obviously a servo motor by itself won't accomplish much...

So just for clarification, we have RC servos (hobby servos) and servos (any closed loop motor system.) I differentiate between the two for the sake of simplification as there are obviously many different types of servo systems. Given that clarification, I recommended a RC servo for non continuous rotation (with position control) vs. a servo based on ease of use, relative cost and the author's familiarity with the Arduino microcontroller.