The basic idea is simple. You have two pieces of wood connected by a hinge, with a bolt going through a T-nut in the bottom piece of wood, the bolt head pressing on the top piece, and a camera on the top piece. The hinge points at the North Star (or the Southern Celestial Pole), and as you turn the bolt, the camera swivels to follow the stars.
My design uses a 1/4"-20 carriage bolt. If the bolt is 292mm from the hinge, one turn per minute is what one needs to follow the stars. One can then have a rotation wheel attached to the knob with second markings printed on it, and then rotate it by hand in sync with a stopwatch. Being within 5-10 seconds of what the stopwatch is showing is generally good enough at lower magnifications, and this is quite easy to do by hand--one can either rotate continuously, or once every 5-10 seconds. A technical difficulty is "tangent error": as the bolt extends, the angle that the hinge swivels per rotation of the bolt decreases. One solution is to use a design with a circularly bent bolt (usually, a threaded rod).
But there is a simple way to get error compensation by using a carriage bolt with a rounded head in the tracker. The rounded head significantly reduces error. The attached graph shows the error in seconds of arc over time: the upper line is an uncorrected straight-bolt mount and the lower line is my mount with a rounded head carriage bolt. For 60-90 second exposures the error with the rounded head is very small. For maximal correction, after a few minutes of running you will rewind the tracker.
You can also attach a carefully cut or 3D-printed corrector to all but eliminate tangent error. There is an optional step at the end for this.