The following pictures are my 2 versions of a homemade mallard machine. .

This trolling motor fit perfect inside a piece of 3 inch pvc pipe.

The folding arms were made from 12 inch cut lengths of an old army cot legs. Holes drilled and bolted to the piece of pvc pipe, run bolts from the inside out...

As you can see on this one, the legs fold up nicely for storage.
I cut the trolling motor shaft off about an inch and a half, then I wired about 100 foot electrical cord to the 2 wires for high speed only.
I then pushed the wires inside the inch and a half shaft and filled full of silicone caulk.
I use 3 regular decoys on this version, tied about 4 inches above each end.
The most difficult part of making this version was finding the right size pipe to fit your trolling motor,
since they come in all shapes and sizes.....good luck and good hunting.

The next page is the 2nd version of my homemade mallard machine.