Few stupid questions RC car hack

[Major_Tom]

I'm hacking apart a 20$ "New Bright" remote control car.

The controls are digital, either forward or backward, full left or full right,
so it will be very easy to use, only needing 4 pins on my chip.

I'm using a Basic-X chip that I salvaged off a robot I built for a class.

I have a few questions though.

I decided to use Tip120 transistors to control the motors.

I am kinda confused though,
so I wire the base to one of outputs on the chip (is 10ma enough to trigger a Tip120?)
And, the emitter and collector are wired just like a relay, with one going to the the motor, the other going to ground or positive voltage?

I tried wiring it like this, and the transisitor got VERY hot.

Also, what is normally used if I don't make my own custom circuit board?
I bought a board from ratshack that had just a bunch of little copper pads on it, but that turned into an absolute mess.


Just to let you know a little about what my goals are,
I'd like to use a IR reciever on the robot, and a homemade remote,
to be able to change subprograms on the robot, without having to press any buttons on the robot.
I am also using IR senders and recievers in the bumpers to detect obstacles. I will also be using a IR transciever setup higher up in the bumper to detect to see if the robot could try to climb over the obstacle (its a pretty beefy truck.)


Thank you for any help

 

[crust]

Without going into too much detail, you should put a resistor between the digital output of your receiver and the bast of the transistor. Consider for a moment that the emitter is wired to ground. So VBE is about 0.7V, your digital IO is about 5V or so, so you have basically created a short between 5V and 0.7V so as much current as the digital IO can supply will flow and bake your transistor. You can select the resistor based on the amount of collector current you need.

 

[m-theory]

Flyback diodes

Along with the base resistor to limit collecor current, you may want to consider adding some diodes across your motor to protect the transistor from the large voltage spikes the motor creates when it is starting and stopping. The motor is really just an inductor, and an inductor will resist change in the flow of current. When power is applied or removed, the motor will generate voltage in the opposite direction to oppose the change in current flow. Sometimes, these spikes can be in the hundreds of volts and kill the transistor.