A "U" shaped torsion bar would have nothing to put spring tension into it, which is key to providin a lifting force. The small part of the "L" of the torsion bar locks onto the frame below and puts a twist tension in the bar when closed. A "U" shaped bar with a motor might be an idea, but if the motor ever failed 15 minutes before checkout time ...
I am a big fan of the simplicity of the TM torsion system. I still think my idea of a torsion bar that can provide even more lift advantage at the beginning is the simplest. As Bill said, more spring tension at the beginning of the lift will make it more difficult to latch down. That's why I was suggesting a latch down mechanism that would make it easier to close. This could be an assymetrical lever or perhaps a screw down system. A lever would be quicker, but perhaps more difficult. A screw down lock could be easier, but increase the setup and close down time.
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