Expanding out of size limit

Hello. I see that in the middle school chinese final 1 (https://youtu.be/XYdanzbIQEU), they expand by going forward and back. Does anyone know how they do this?

Which team are you referring too? alliance and starting position will be sufficient.

Different robots expand differently, but for the most part the trays are split into sections (one full length c-channel long). Those sections are then connected via screw joints. Rubber bands are placed between each of these sections and joints so that when a small amount of force is applied, the rubber bands pull the tray sections into place. Here is a close up video of 742A’s. It doesn’t have to be exactly that, but its the basic idea.

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I have a flipup. The team in the bottom left corner I am referring to. They go forward and back, and their rollers flip down.

It’s probably just lightly hitched on something in the tray, the rollers flip out when jiggled, and the tray is being held in by the rollers, which then flips itself out using rubber bands.

but that would interfere with it when stacking. I dont know what it could be caught on

Actually, now that I look closer, it doesn’t look like it is being held in by anything. It looks like some good rubberbanding that barely holds the rollers in, but when the bot starts to suddenly back up after going forward, the suddenly reversed motion causes it to flip out. So the tray would be below the folded in rollers, the rollers flip out, and since the folded in tray stages are free from the rollers, they too can flip out. If I wanted to do that, I would experiment a lot with rubber band quantities until I get it right.

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Alright, thanks!

These videos could be informative to study unfolding of the very long trays: