OK...

I have gone back and looked closely at Andre's reconstruction. It seems that we are closer to being on the same page than I thought at first, and my initial reaction was too hasty and too harsh.

Andre's reconstruction is consistent with my current understanding of these objects. I have looked carefully at the videos; freezing them to examine the mechanism. The mechanism only serves to secure the shield, and then release it on impact.

I was initially disappointed that the shield did not fly into the air, but I now believe that the balsa tipped lance is not supplying enough energy to make that happen. If it were struck with a solid lance, I imagine that it really would go up into the air. The mechanism is essentially well reconstructed, and working reasonable within the limits of the constraints imposed by the armor and the lance.

If you are out there, Andre, please accept my apologies.

Mac

Edward,

Do you mean the big forked arm that sits beneath the lower wheels?

Unless I miss my guess, that's the trigger. The wheels are able to travel a short distance in slots. If they are pressed in by the impact of the lance on the shield, they press on the ends of that bar, and that trips the mechanism.

Half way up that bar is a screw, I believe it is sensitivity adjustment.

Mac

Robert,

Just to make sure we are comparing apples to apples I'm primarily speaking about the first image in the post.

A few inches above the screw you mentioned is a hinge that allows the entire assembly to swing up. Centered between the brass wheels is an eye bolt with the top section cut out. I think that this and the two eye bolts at the top of the breastplate are the attachment points for the shield. I suspect that the shield was attached with wooden dowels designed to fail on impact at the top attachment points and something more durable at the bottom point. The bottom eye bolt with the cutout would act like a hook on a trebuchet and not release the shield until it a certian point. The wheels are there to reduce friction and help the shield fly off at the right point. The image quality isn't fantastic but I don't see any evidence of a catch holding the arm down and if I'm right about the wooden dowels then they could act as a trigger for any mechanism designed to pop the arm out.

The order of operations that I envision is
1. Lance strikes shield
2. Wooden dowels break releasing mechanism
3. Arm swings out
4. Shield reaches release point and flies into the air

On a good strike the rider's torso would thrown back violently causing that arm to swing out rapidly and impart a great deal of upward momentum to the shield.

-Edward

Edit - Just watched the video... I missed it the first time reading through this thread. Sigh, all that speculative reverse engineering gone to waste. Though I do believe that the physics behind how I pictured this functioning would work.