hey, i try to starting a 5V RC engine.
the digital pin get only 'HIGH'.
when i connect directly to the GND and 5V its work but its shortens the circuit.
what is the problem ?
You can’t power your “ engine” using the Arduino to supply the power . you need a seperate power source for it .
i saw this on youtube :
link
L298n tutorial There are other newer types available. Many YT videos.
What type transistor? Which of the three leads is Emitter? Base? Collector? How much current does the motor require? What voltage? How do you power the motor? Where is your free wheeling diode? Just asking. 
What is "RC motor"? DC? Brushed? Brushless? A link to the one you're using would help.
Steve
Don't start two Threads about the same project. I have suggested to the Moderator to merge them.
In both Threads you have been very reluctant to give useful information.
If you describe the project you are trying to create people will find it much easier to give useful advice.
...R
slipstick:
What is "RC motor"? DC? Brushed? Brushless? A link to the one you're using would help.Steve
outsider:
What type transistor? Which of the three leads is Emitter? Base? Collector? How much current does the motor require? What voltage? How do you power the motor? Where is your free wheeling diode? Just asking.
I did just as described ther.
So that's not the same motor and the video never says what sort of transistor he's using. So how do you know that you're using the same thing? Motors and transistors aren't interchangeable...you can't just use any old one in place of any other.
So what type of transistor are you using? Are you certain that the pins are in the same place as the one in the video? Instead of a useless Fritzing diagram can you please post a clear photograph of YOUR actual circuit with details of the components.
Steve
Just because it’s on you tube ...
- it’s not good practice to supply any significant load from the Arduino regulator .
- motors generate a lot of electrical noise , another reason not power via the Arduino .