yes I believe there is a threaded rod within the fake piston and a motor in the armature, it sounds like it as well.
rocks and stumps are fine, sand or gravel is fine but long grass can be a pain, I add brass parts to weigh them down and then they are almost unstopable. I like this size because it allows me to make a big course in my backyard
it took me 6 months to get all the parts ๐ mostly because the motor got lost in the mail twice and it needed a ton of bolts. building is super easy, 1 hour max.