how to find motor ratings

[chrischristian]

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

[RobD]

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.       

[chrischristian]

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 ?

[RobD]

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. 

[chrischristian]

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


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  )

[RobD]

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     

[chrischristian]

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 

[dunk]

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.

[chrischristian]

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.