This model plugs into a 110v wall outlet, so there are no batteries to mess with (and no corrosive byproducts that seem to come with old battery powered toys).
The right knob turns the motor on and off, while the left lever is the clutch to engage and disengage the rubber-tired drive wheel.
The thread spool makes this thing look tiny.
It still sews great. It makes a chain stitch, so it can easily be pulled out in case of a boo boo.
This is a shot of where the motor and rubber drive wheel reside.
The back comes off with two screws so the internal workings can be lubricated. Notice the timing belt in the left part of the photo.
Such a deal, I couldn't pass it up. They even gave me a 15% off senior discount.
Here is a photo of the 50D next to my Singer 404.