[Chris is me]

Some tips if you do try wings I learned from extremely simple and not very good prototypes:

1. With a robot roughly max width, you're just short of the max horizontal width on each side of the robot to fit in the 84 inch cylinder. So your forks would probably look like this:

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2. Strong materials and fixed joints are key to cutting weight down. Once the forks are to the sides of your robot, an in bumper way to "lock" them helps, or a way to raise them ~5 degrees then lock to help ensure sliding doesn't happen. You can make the forks fall by gravity with a servo and "snap in" to place if you want.

3. Make sure your hanging mechanism works even if you only have one robot on one side. There are ways to do this.