Im using an Uno board mounted to an RC car and using its 9v rechargeable batteries as power.
Picture or such of the car please. Is this a 9.6V NiMH battery?
I have outputs 6, 9, 10 and 11 wired to an H-bridge of 2N3904 transistors in order to turn on the small dc motors to move forward or backward.
Those are small signal NPN transistors; given that most 9.6 VDC R/C cars have a fairly hefty motor, I doubt they have anywhere near the current capability needed to drive the motor. Without at least a picture or information on the motor, it's impossible to tell though. Have you measure the current needs of the motor (running and stall)?
The problem that I am finding is that even though I've got the 9v wired into the emitters, and the collectors to ground, the base voltage isn't enough to turn on the transistors completely.
1) From your description, you have those transistors wired "upside down", based on your description - I'm surprised they aren't smoking.
2) Do you have a schematic of your circuit?
3) Base resistors?
Any suggestions as to how I can get full power to the dc motors? Thanks.
I'm wondering why you are even using an external h-bridge - was there something wrong with the h-bridge on-board the R/C receiver of the car itself?
Also - did you happen to read this "mega-thread"?:http://arduino.cc/forum/index.php/topic,86883.0.html
I dunno what kind of car or such you have - maybe the above wouldn't help you, but I've found that most toy R/C cars made in the past decade or so use that same chipset; it's become like a de-facto standard for cheap R/C toys.