Robots wont move on the floor

Discussion in 'The Projects Forum' started by auto21555, May 19, 2015.

  1. auto21555

    Thread Starter New Member

    May 19, 2015
    2
    0
    I have made a robots that can move, If I raise it in the air the wheel turn fine, but when I put it in the ground nothing happend, does anyone have any suggestions?

    For me I think the problems in the output of PIC Microcontroler, even if I have supplied the PIC with 5v but the output gives only 3V, knowing that in the code I haven't use "PWM" instruction for motors, I used only 1/0 logics for exemple:
    Code (Text):
    1. )if(PORTA.RA1==1)
    2.               PORTC.RC1=1;
    3.  
    and I have linked the RC1 with an optocouplers (to increase the courant) and then to motors.
     
  2. DickCappels

    Moderator

    Aug 21, 2008
    2,647
    632
    It is unlikely that an optocoupler can supply enough current directly for your application. (Using the coupler is a good way to protect the PIC, but the way.)

    If you tell us what kind of optocoupler(s) you are using and how much current you want the motor to be able to draw there is a good chance that somebody can make a helpful suggestion. If you can post a schematic that would also be very helpful.
     
  3. djsfantasi

    AAC Fanatic!

    Apr 11, 2010
    2,796
    831
    Agreeing with Dick, here. There is a minimal load on the motors when they are "in the air". Hence, they operate with less current than when they are on the floor, supporting the weight of the 'bot and working against the friction of the floor. If there is insufficient current available to overcome this additional load, the motors will stall.
     
  4. DerStrom8

    Well-Known Member

    Feb 20, 2011
    2,428
    1,328
    Definitely not enough current being supplied to the motors. What kind of motors are you using, and what is your power source?
     
  5. auto21555

    Thread Starter New Member

    May 19, 2015
    2
    0
    upload_2015-5-19_16-7-29.png

    that's the ciruit of motors, I'm using 4n25 as optocoupler, and I have 2 kind of motors both at direct current 5V and 12V and I have a battery of 9V as supplier, I have used tension regulator to make the supplier to 5V ( so my PIC wont be hurt), would you tell me which motor I use ( 5V or 12V)? and what I can do to increase the courant.
    Thanks.
     
  6. MaxHeadRoom

    Expert

    Jul 18, 2013
    10,509
    2,369
    Measure the voltage across the motor and then supply when it is placed on the floor.
    Max.
     
  7. Alec_t

    AAC Fanatic!

    Sep 17, 2013
    5,775
    1,103
    At least 1.2V is being dropped by the H-bridge transistors. That doesn't help the situation :(.
     
  8. crutschow

    Expert

    Mar 14, 2008
    12,991
    3,227
    Yes. For lower drop you can connect the PNP's to the plus supply and the NPN's to common. Of course, you need to reverse the input logic when you do that.

    You could also use MOSFETs instead of BJTs in the bridge which can be easily driven directly from opto couplers.
     
  9. panic mode

    Senior Member

    Oct 10, 2011
    1,318
    304
    those optos are poor for this application... they have terrible CTR. if you drive them with 10mA, output current is only 1mA. 1mA into base of switching transistor means some 10mA output - way too little. you want to saturate them and get 100mA for example. the entire circuit is just a mess. you don't want common collector motor drivers, you want common emitter. also no current limiting anywhere (well in this case circuit does not work even without them). I suggest redesign...
     
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