I followed circus to find out which pins control motor, servo and receive signal from RF. I see pin 1,2 go to Diot to couple mosfets to big mosfet with heatsink.
What I would do then is this: Find the closest solder point away from each pin, and solder a wire to it (label everything, too); then between that solder point and the pin on the IC, use an x-acto knife or something to cut the trace - so that the IC pin is no longer connected to the rest of the circuit.
Then, hook the wire to a digital output pin on the Arduino in series with a resistor - start with about 1 K, then gradually work your way down (no lower than 330 ohm); remember to hook the ground wire to the Arduino's ground. At some value you should get a response from those pins.
Now - that relay is, like I said, likely for direction control - so one of those pins (pin 1 or pin 2) will control that relay, and the big MOSFET is likely controlled by the other pin - for now, you can just switch it on or off, but later, when you find which pin controls which part, you will want to use a PWM pin to control the MOSFET (while the relay control can happen with any digital pin).
Be sure to switch the relay direction ONLY when the PWM pin is LOW (0% PWM) - otherwise magic smoke might get let out.
my servo has 6 wires.Green is GND. Blue and Yellow is left or right controlled by pin 13, 14.
Again - do the same as above (any digital pin, with the resistor) to those pins (and cutting the trace as noted).
Red, Orange, and Brown seem like serve break. when server spin to left or right , brown and red or brown and orange are connected.
Find which pins these are connected to; or connect brown to ground, and red and orange to digital input pins and activate the internal pull-up resistor on those pins. Then - you can use those pins so that when you see a LOW level in your code, you know the limit has been reached by the motor, and can shut it off to prevent the motor from stripping its gears, or burning the motor out, etc.
can i connect pin 1,2,13,14 as forward; backward; left; right to arduino board? if not, can you advice me some things can run mortor? and use servo that comes with arduino kits.
I don't know what kit you have, or what the servo is - but if it is a standard sized servo, you could use it in place of the (apparently?) non-servo steering mechanism (what you describe sounds like a "bang-bang" steering system - common in these cheap R/C toys); with a servo you could get more proportional control over the steering, potentially. It would, however, take some mechanical know-how and modding to fit the servo in (providing, again, that the servo is large enough to act as a steering servo).
Or - you could mount a distance sensor of some sort (some kind of Sharp IR or an ultrasonic distance sensor), and "pan" it with the servo to get a 2D representation of what is in front and to the sides of the car.
RS-550 Motor - 12V
Operating v : 6v - 14.4v
Nominal v : 12v
No Load RPM : 19300
No Load A : 1.2A
Stall Torque : 70.55 oz-in 498.2 mN-m
Stall Current : 85A
Kt : 0.83 oz-in/A 5.9 mN-m/A
Kv : 1608 rpm/V
Efficiency : 70%
RPM - Peak Eff : 17250
Current - Peak Eff : 10A
Weight : 7.7 oz (218g)
Length - for motor : 2.24 in (57mm)
Diameter (with flux ring) : 1.52 in (38.5mm)
Diameter (no flux ring) : 1.41 in (35.8mm)
ShaftDiameter : 0.12 in (3.2mm)
Shaft Length : 0.3 in (7.6mm)
Mounting Screws (2) M3
If that's really the motor in the car, they really undersized the relay for it's stall current (then again, where are you going to find a 75A small PCB mounted relay, anyhow?). The MOSFET might be sized OK for it, though (I can only guess, because there isn't a known number for the MOSFET).
You'll want to find and use the proper battery for the RC car to power the PCB and motors; ideally, you only want to provide power to the motors and support circuitry - not to the rest of the PCB (because you aren't using those parts - and thus it only wastes energy to power them); but for the time being, just getting it to work will be enough (cutting away the traces to isolate the driver parts can be very difficult, but not impossible to do).
Also note that it is very easy to blow the drivers on the board - even with the precautions I gave above using a resistor and such, because you don't know what the output voltage from the pins of the CPU on that PCB actually were (vs the 5V TTL digital voltages from the Arduino); if you wanted to be really careful, you could probe around first using a voltage divider to drop the voltage from the control pin on the Arduino to 3.3V before plugging it in; if it works, leave it.
Again - this is all experimental - you very well could blow the driver, the Arduino, or both. Good luck!