Automatic Garbage Collector

I am trying to make automatic garbage collector ...similar to this video

Can someone help understand the mechanical structure of how those arms are going down?

Thanks,

Follow this link: http://www.utkuolcar.com/en_US/2013/1...

Can you imagine the chaos if this was built ‘full size’ - a half ton of fun wandering around the parking lot collecting trash...!
But it does look like a blast.

What size of robot do You think of? I have "played" (worked) with 8 ton machines and they were defenatly not "automatic" (autonomous),