!rant
Four hours of work.
You think you write spaghetti code? I write spaghetti wires.
H-Bridge dual motor tester for stepper motors.
Speed is controled by pot.
H-bride are L293D.
My third board, and the first that won't go to the trash.

Question. With the baterry off the motor continues spinning with the 5v from arduino.
My question is, is the L293D suposed to do that? Or do I have a short circuit somewhere that is giving power to the motor? Meaning it can burn the arduino.
Runs a 12v stepper from a CD-Rom driver perfectly at 5v from the arduino and actually starts to act strange when I turn the 12v on. (maby the circuit it's adding 12v + 5v?)

*The Fearless Leader*

I get a call to check up on a robot that has been exceeding weight limits at certain points of its movement (Crashing). As I get to the pendant (robo-game controller thingy I like to call it) and look over the alerts and warnings I notice some oil around the main power box of the Robot.... Nothing around this has oil.. so I start looking around and it turns out that the issue wasn’t a crash at all! It was an oily shorted out wire that kept sparking mad heavy when that servo was called on.. causing a large servo failure that required a full restart of the power box. I called our fearless leader and showed him only to find out that there was a motor leaking oil from the electrical end... My fearless leader runs both the Maintenance and Robotics department. When the motor was eventually fixed we overheard the technicians say that our fearless leader knew about this a week ago and decided to leave it that way.... with oil... coming out of an electrical cable..... *sigh* well Anyway after all the wires were fixed and motors changed. He comes up to me and says that he can’t believe that I didn’t call maintenance and fill a report on negligence of technicians for failing preventative maintenance....

I lost my cool a little, firstly that’s not my job, I’m literally one of the lowest ranking here. I called my next in command to figure out what I should do. Secondly the technicians told me that you told them to leave it like that! So if this place caught on fire this would have been on you!

Later I found out that he was trying to fire a technician and wanted me to do the dirty work.. I’m not going to be the reason another man loses the means for him to feed his family. The technician is a pretty cool and fair guy too!

Our fearless leader was a forklift driver and has no experience in robotics or maintenance... I don’t know how this happens or even why but all I know is this man is running both departments to the ground and management loves him.....

What's the most efficient motor driver for a small DC motor that I want to run off a 5V source for aurdino?

I previously had a L293D and it was inefficient as fuck, it got so hot that almost burnt my finger, (ran it from a 12V supply) and it dropped a good 2 volts from power supply to motor.

Is there a good enough off the shelf driver or do I have to make a H-bridge myself using MOFSETs?

Is connecting your aurdino and motors that it'll drive (through a motor driver of course) to the same battery bad for the aurdino?
I mean those are small DC brushed motors, will the noise/fluctuatuons they generate harm the aurdino in the long run?