When I got out of my dark age 1.5 years ago it was partly because of seeing 42009 at a friends' house, but also in no small part by the great tanks created by Sariel and Tommy Styrvoky (among others).
Once my collection felt large enough that I didn't mind taking some sets apart I started looking at building something of my own.
After a few failed attempts I ended up with Boris here, the first moc that I find presentable enough to post here..
It's powered by two XL motors hooked directly up to a sprocket on their respective side (I've had problems with slipping gears on earlier attempts).
Speed is decent enough and there's no lack of torque, but unfortunately the standard lego tracks don't provide much grip.
There's also one M motor to provide rotation to the turret, while another M motor drives a small LA that sticks through the turntable to control gun elevation.
As you can see from the bottom-shot I'm still horrible at building in compact spaces so the Sbrick proved to be very valuable. (both for space and LoS concerns)
I've actually finished this moc a few months ago.
My reason for posting it now is that it'll soon be scrapped to provide parts for it's successor.
Here's a sneak preview of the new prototype, Boris for scale: