I hope this one will help
https://en.m.wikipedia.org/wiki/File:Di ... Aguado.jpg
Regarding this monstrous support, I have tried one support in same principle as this, based on ground and clamps lower side of guitar, but differ on supporting position. The one I tried is monstrous support with supporting pole placed on space between player's thighs, as opposed to Aguado's (pole on right side of player's right leg).
Unfortunately, disadvantages are their size makes difficulties for carrying, take more time to adjust, and they don't allow guitar position changes for temporary time while player is currently playing.