"This is my design for a highly adaptable gantry crane for use in my home garage/shop. I wanted to use some parts already in my possession rather than buying new parts, and those parts were the 2x2 square tubes and the 2x3 rectangular tube. All I needed to purchase was some flat plate for the reinforcement of the legs and for the mounting parts for the main beam and trolley. Since most gantry cranes are designed around an I-Beam and mine is not, I had to design the trolley for the 2x3 rectangular tube beam. I designed the trolley to fit directly to a Harbor Freight AC motor hoist."
My first version which is in the first photo rendering below used a rocking gripper atop each upright. The idea was to rock it back and slide the cross bar through to create different length options. It failed due to instability. There was no way to lock them in place perpendicular to the uprights. Other images show the solution I developed for version 2. The photo of it in my shop shows the working model. To date I have lifted up to 700lbs (318Kg). My FEA analysis indicates it will lift a ton+.
Notice, though the concept enables the swivel bar to lock onto the cross bar, the the upright is still free to pivot which makes them prone to fall over. Version 2 makes the upright fixed to the locking supports.
There is an inner tubing and an outer tubing with cams on the levers to lock the inner tube section to the crass bar.
During use I have determined the locking levers for the cam hold downs need a ratcheting mechanism to lock them in place. They are too close together as well. If I decide to put them into production, I will redesign the new upright holders wider from the current 9" to 12".