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Author Topic: control position dc motor  (Read 1785 times)

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Offline rabochidTopic starter

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control position dc motor
« on: September 21, 2010, 10:20:11 AM »
is the LM628/9 the best way to control a position of a dc motor ?

Offline Soeren

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Re: control position dc motor
« Reply #1 on: September 21, 2010, 08:14:35 PM »
Hi,

is the LM628/9 the best way to control a position of a dc motor ?
Short answer: No.

Slightly longer answer: Not two applications are quite the same. In some apps it might be (one of) the best, in other apps, it might be (one of) the worst, it all depends on a range of criteria.
The BestTM will always be a compromise of several things - like the parameters of the motor, the work that you want it to do, how precise position control you need and your skill level being some of the most prominent factors.

Your question is as open as: "Is a drill the best tool for making a hole".

IOW: Tell us the specs of the motor, what exactly you want it to do (with tolerances), your experience level and such and we'll tell you whether a drill, a shovel or a caterpillar would be better :)
Regards,
Søren

A rather fast and fairly heavy robot with quite large wheels needs what? A lot of power?
Please remember...
Engineering is based on numbers - not adjectives

Offline rabochidTopic starter

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Re: control position dc motor
« Reply #2 on: September 22, 2010, 03:29:00 AM »
hi
well,i work with my team for build a robot it's not the first time ,in  the last time we worked with servomotors  but the robot can't walk in the right line, i want to use LM628/9 to control a dc motor for the wheels
and about the skills  of my team we control a dc motor with pic16f877 and h-bridge (L293) a servomotor with pic16f877 and a stepper motor a ultrasonic sensor and the direction of the robot always with the same pic  16f877  ;D and we have a genius of  mechanic in our groupe ,me i'm  just  a begginer
the best tool for making a hole?
you can ask women ,they know more than me about  holes  ;)

Offline Soeren

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Re: control position dc motor
« Reply #3 on: September 24, 2010, 06:39:07 PM »
hi
well,i work with my team for build a robot it's not the first time ,in  the last time we worked with servomotors  but the robot can't walk in the right line, i want to use LM628/9 to control a dc motor for the wheels
and about the skills  of my team we control a dc motor with pic16f877 and h-bridge (L293) a servomotor with pic16f877 and a stepper motor a ultrasonic sensor and the direction of the robot always with the same pic  16f877  ;D and we have a genius of  mechanic in our groupe ,me i'm  just  a begginer
the best tool for making a hole?
you can ask women ,they know more than me about  holes  ;)
I'll repeat... Tell us the specs of the motor, what exactly you want it to do (with tolerances). Engineering isn't a game of guessing.
Regards,
Søren

A rather fast and fairly heavy robot with quite large wheels needs what? A lot of power?
Please remember...
Engineering is based on numbers - not adjectives

Offline rabochidTopic starter

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Re: control position dc motor
« Reply #4 on: September 25, 2010, 03:24:00 AM »
hi soeren
if you talk about the motor ,i don't have it so i can't give you the specs of the motor ,
i need to control the position of the wheels with minimum of error so i thought i can use LM629 with dc motor

Offline Soeren

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Re: control position dc motor
« Reply #5 on: September 25, 2010, 03:49:25 AM »
Hi,

if you talk about the motor ,i don't have it so i can't give you the specs of the motor ,
Then you are kind of jumping the gun, when it comes to controlling it.


i need to control the position of the wheels with minimum of error so i thought i can use LM629 with dc motor
"[A] minimum of error" is not an engineering term. We need hard facts on precision and resolution.
Please note, that it's a common mistake for beginners to opt for unneeded hysterical precision. Be realistic in what you need (not what you want, but what is really needed to accomplish whatever task is at hand).
Also note, that precision and resolution is different beasts.

When you have an encoder that suits you, the controller gets this input and control the motor accordingly (via a suitable motor driver which don't need any fancy bells and whistles).


Regards,
Søren

A rather fast and fairly heavy robot with quite large wheels needs what? A lot of power?
Please remember...
Engineering is based on numbers - not adjectives

Offline rabochidTopic starter

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Re: control position dc motor
« Reply #6 on: September 25, 2010, 06:02:17 AM »
 I know I am a beginner but what I have to do, buy a motor and a LM629 and do some practical experience without knowing if this component is right for me or not

Offline Soeren

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Re: control position dc motor
« Reply #7 on: September 26, 2010, 11:23:34 AM »
Hi,

I know I am a beginner but what I have to do, buy a motor and a LM629 and do some practical experience without knowing if this component is right for me or not
Obviously, you don't read my answers, so I won't trouble you no further by suggesting simpler ways.
Regards,
Søren

A rather fast and fairly heavy robot with quite large wheels needs what? A lot of power?
Please remember...
Engineering is based on numbers - not adjectives

Offline rabochidTopic starter

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Re: control position dc motor
« Reply #8 on: September 28, 2010, 06:44:05 AM »
hi thank you soeren for your help ,I read your answers but I didn't understand your point  well,
i think i  have no choice

Offline knossos

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Re: control position dc motor
« Reply #9 on: September 28, 2010, 08:28:15 AM »
hi thank you soeren for your help ,I read your answers but I didn't understand your point  well,
i think i  have no choice

What Soeren is saying is that you need to do more research about what you are trying to do before we can help.  For example, we need to know specifically

 
..the parameters of the motor, the work that you want it to do, how precise position control you need and your skill level.."

First of all, have you selected a motor yet, or at least know what kind of specs your motor will need?  If you haven't, then you shouldn't really be looking at encoders just yet.

What kind of application is the motor for?  In other words, what will the motor do? (e.g. a two motor differential drive for a robot weighing approximately 2 pounds total weight with a 7.2v NiMH battery)

How precise does the position have to be?  If the motor is for the $50 robot, then you probably don't need precise control.  If instead you are working on something like a maze solving robot, then you will probably need some control, but how much do you need? (e.g. an error of +/-1" for every foot of travel)

What is your skill level?  For example if you have never touched a soldering iron before, you probably don't want to be designing your own complex circuit board.  Likewise, if you have never programmed before, you probably don't want complex logic and algorithms.  If you are an electrical engineer and have 15+ years of experience designing circuits but are new to robotics, you might be ready for something more ambitious.  We can't make suggestions without knowing what your capabilities are.

For example, if I were to use my current robot as an example and were to ask this question in the forums it would be something more like this:

Quote
I am trying to decide what kind of encoder to choose for my robot.  I am experienced with electronics repair and maintenance, but have almost no experience in electrical engineering.  I do have a good background in electronics though and am an experienced programmer.  I likewise have no mechanical engineering experience, but am mechanically inclined.  This will be my first robot and price is a concern so I would like to do this as economically as possible.

  I am using an Axon II microcontroller, and will be using two Futaba S3003 servos for a differential drive robot.  I am not certain of what would be a reasonable amount of precision but I would like to design and traverse simplistic mazes that are about 10' x 10' square with 8" pathways.  My robot is about 4 inches wide.  This gives me about 2" between my robot and the walls on either side.  So to drive the full distance of the field without hitting a wall I would need no more than + or - 1.5" for every 10' of travel.
"Never regret thy fall,
O Icarus of the fearless flight
For the greatest tragedy of them all
Is never to feel the burning light."
 
— Oscar Wilde

 


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