I improved my original “basic crane” by adding 2 windlasses- one to raise and lower the load and a 2nd one for the boom. In addition I installed a Lazy susan between the 2 sections of 3/4″ plywood. Now the crane can rotate (slew in crane speak) a full 360 degrees.
The windlasses don’t have automatic locks like my more complex cranes, but there is a “lock”. Turn the windlass and move the load or the boom then to lock it off, simply stick a pencil into one of the 6 holes.
I mistakenly placed the Lazy Susan towards the front of the crane- it should be farther back closer to the CG of the crane. That’s probably why the crane tipped backwards when the load was released. I tell my students that a crane is like a see saw.
Here’s the original “basic crane” and some of the formulas I use to compute the torque.
Here’s an example of a problem you could present to your students.