/diy/ - Do It Yourself

Hello guys,
I guess i need a little bit help.
I have an omni wheel platform which we had to programm in uni (all done, but improvments needed). They have three 12V dc motors with encoders on them. Two of them are dead though. Now I searched through the internet, but couldnt find any replacement.
But since it seems to be a rather simple circuit I might just design one myself and fabricate it in my uni.
The only thing I am wondering is what might be the circuit i circled in the picture? Should be a mosfet or something, right? How should the pinout of that be?

PS:
if anyone is interested this is our platform
http://www.nexusrobot.com/product/3wd-48mm-omni-wheel-robot-platform-chassiswith-encoderblack-15001b.html