Robots wont move on the floor

Thread Starter

auto21555

Joined May 19, 2015
2
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:
)if(PORTA.RA1==1)
              PORTC.RC1=1;
and I have linked the RC1 with an optocouplers (to increase the courant) and then to motors.
 

DickCappels

Joined Aug 21, 2008
10,153
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.
 

djsfantasi

Joined Apr 11, 2010
9,156
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.
 

DerStrom8

Joined Feb 20, 2011
2,390
Definitely not enough current being supplied to the motors. What kind of motors are you using, and what is your power source?
 

Thread Starter

auto21555

Joined May 19, 2015
2
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.
 

crutschow

Joined Mar 14, 2008
34,281
At least 1.2V is being dropped by the H-bridge transistors. That doesn't help the situation :(.
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.
 

panic mode

Joined Oct 10, 2011
2,715
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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