i goggled around and found a tones of info on MOSFET but can i switch it on by ground because my out put pins give ground to the relays the positive is direct from the battery to the relays i will show you
http://img704.imageshack.us/i/relaytomotor.png/
here when any switch is pressed in the transmitter any out put pin gets grounded and the relay is switched on and one set of motors start (reverse or forward)so my question is can i use MOSFET in this case ???????????????

plz help i am not to good at electronics you can say i am just a bigginer
till now i made the circuit from the papers given but there is no info of the relay board and the motor connection

 

U can use MOSFET's.

Question is why do you want to use MOSFETS.

Using relays is simpler

 

the problem is relay use more power so I need some things which does not need much power.
but are you shure that I can use ground to turn it on
and can you tell me which MOSFET to use and the circuit diagram.
I am using a 12v battery to run the motors

 

U can use an inverter to switch the MOSFET's.

For proper Mosfet rating I need to know the motor model no or ratings

 

i am using this motors
http://img695.imageshack.us/i/motorsh.jpg/
each is 12v 250rpm geared motor

 

i started the car with the relays today and i needed four 9v battery and a 12v battery
one 9v for the transmitter,one 9v for the receiver,two 9v for the relay board in series and one 12v for the motors and still the relay turn on and off after some time.
How to reduce the battery consumption???????????????
plz help

 

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this is the circuit diagram
http://www.vishaworld.com/product.asp?2170
her are some images
http://img153.imageshack.us/i/receiverp.jpg/
http://img143.imageshack.us/i/transmiter.jpg/
http://img405.imageshack.us/i/relayfront.jpg/
http://img811.imageshack.us/i/relayback.jpg/
http://img826.imageshack.us/i/relaytomotor.png/
now the problem is that to move the car in any direction two relays must work form the four relays
they consume about 12v means a need another 12v battery which will increase the weight and size of the car
is there any thing else which can be used instead of the relays some thing which consumes a little voltage