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Author Topic: how to find motor ratings  (Read 2089 times)

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Offline chrischristianTopic starter

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how to find motor ratings
« on: August 29, 2008, 10:14:47 PM »
Hi there!

             I just have finished my first line following robot circuitry and now facing one problem that I don't know  what are the ratings of the motors I have ( I have it from china made toys just like this DC MOTOR shown on http://www.societyofrobots.com/actuators.shtml )

I also tried the bulky audio cassette player motors thinking it of having better torque but it is not enough to move the robot. When I connect those toy motors everything just stops and if I connect some resistors in series with those motors they work but very slow and defiantly can not carry the load of robot. Don't know what to do ?
              I tried different values of resistors in series but nothing works fine  :(
PLEASE HELP ME !!


N.B. : I AM USING PIC 16F628A AND L293D
« Last Edit: August 29, 2008, 10:16:20 PM by chrischristian »

Offline RobD

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Re: how to find motor ratings
« Reply #1 on: August 29, 2008, 10:31:47 PM »
There is an excellent calculator here http://www.societyofrobots.com/RMF_calculator.shtml if you know the weight of your robot.

Can't help much more if you don't have the motor part numbers or at least where they came from.  Sometimes looking up the device from where they were lifted from can help finding out which motors the original manufacturer used.       

Offline chrischristianTopic starter

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Re: how to find motor ratings
« Reply #2 on: August 30, 2008, 12:31:21 AM »
O.K. got it  :'( but i think the problem is that my L293D gives just 140mA while it should be 600mA, I checked all connection , everything is right then why it is just 140mA ?

Offline RobD

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Re: how to find motor ratings
« Reply #3 on: August 30, 2008, 12:38:52 AM »
Thats about 1/4 of the output for the "l293d" chip.

draw your current connections in schematic or picture form.  I bet we can figure it out from that. 


Offline chrischristianTopic starter

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Re: how to find motor ratings
« Reply #4 on: August 30, 2008, 02:22:45 AM »
Here it is  :) I tried removing LEDs connected to MCU and also put higher value resistance in series with LED between LDRS, but it did'nt work !! Can connecting LEDs directly create problem ? ..................................Oh ! no ! now it gives just 50mA !!!!!!, don't know what happen :o


Note that the pins of MCU which are connected with LEDs ( in alternate polarity ) are input pins for L293D, and the LEDs are to indicate that at least digital part is running well, I have tried the ckt removing these LEDs but didn't work and this disaster happen ( JUST 50mA  :o )
« Last Edit: August 30, 2008, 06:12:25 AM by chrischristian »

Offline RobD

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Re: how to find motor ratings
« Reply #5 on: August 30, 2008, 09:47:21 AM »
Not generally a good practice to direct drive an LED off of an output pin without a resistor.

After looking at your schematic, my only thoughts are :

1.  Still need to know your motor rating if you can find it.  Probably not likely. 
2.  Pull up resistors on the microcontroller outputs?   
3.  Are you doing PWM?  Maybe it's your PWM cycle in code.

Sorry I can't be much more help  :-[   


Offline chrischristianTopic starter

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Re: how to find motor ratings
« Reply #6 on: August 30, 2008, 10:44:20 AM »
Thanks RobD !

No I'm not using PWM and those pots on MCU are the onl PULL DOWN resistors while the MCU interrupts become high when LDRs resistance becomes low by light.

Any way , thanks for your time  :)

Offline dunk

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Re: how to find motor ratings
« Reply #7 on: August 31, 2008, 04:33:19 PM »
Quote
When I connect those toy motors everything just stops and if I connect some resistors in series with those motors they work but very slow and defiantly can not carry the load of robot.
hope you don't mind me stating the obvious but you know one of those motors will not have enough torque without some sort of gearing right?

dunk.

Offline chrischristianTopic starter

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Re: how to find motor ratings
« Reply #8 on: September 01, 2008, 01:04:51 AM »
You are right that had happened so I switched to those bulky cassette player motor and now I strike with new problem I have started a new thread titled " MCU hanging problem " Please read that.

 


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