Confused about how to drive a rc car using arduino

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hi folks, I am trying to build an autonomous car by attaching my arduino uno r3  to my rc car. Please pardon me if there are certain stuff I don't understand as my electronics knowledge has long vaporised since my education days and im starting from zero again.

In particular, i'm using this guide http://www.instructables.com/id/Autonomous-Control-of-RC-Car-Using-Arduino/?ALLSTEPS as my RC car is also using a RX-2B chip.

So I've followed the steps.. but made a mistake. 1. Instead of attaching a seperate battery to power the uno, I connected Vin to Vcc of the RX-2B, while still using the same ground.

Now, to test the circuit before commiting, I let the UNO output a HIGH signal on pin 2 and use a jumper wire to probe the pins from the control chip. For the left and right signals, they work well - touch the correct pins, bam! the wheels turn.

However, for the forward and backward pins, when I probe them, the motor only register a very very small movement. Initially, the impression is insufficient current. However, when I do the same with the 5V pin from arduino, the motor runs perfectly.

So, my questions are:

1. Reading the uno datasheet, the 5v pin and digital pins both outputs the same voltage and current. Why the latter works and former don't?

 

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I will agree that it doesn’t make much sense.

The toy is being driven by the same logic levels that your UNO can output. I can only guess that the RX2 chip has similar limitations related to current.

Worst case scenario, you have to add a couple transistors with their associated resistors to drive the vehicle forward/reverse.