Sorry to be simplistic, but I take it your design is a bit like this? ( see appended.
Tp fully saturate a low power transistor you need a lot of base current - I've shown 470R
which should give 10mA drive.
If you're using a much higher value you may not be driving the transistor hard enough.
To get a really hard drive you'd be better off with a logic level mosfet.
But it ought to work anyway....
Note that the regulator on an arduino can only supply a limited amount as well .
regards
Allan
irdrive.pdf (15.5 KB)