Here is another great example of a large multi-purpose attachment used in FIRST LEGO League competitions. This one is specifically for the 2017-2018 Hydrodynamics competitions and is doing a number of missions. (01) Pipe removal, (06) Water Treatment and (08) Manhole cover.
The attachment consists of two parts. The first part is placed on the robot while the second part is in front of the robot and the robot pushes it. While working on the field the robot leaves the second part on the Water Treatment plant and when returning back collects it back and returns to base.
The goal of the attachment is for you to build it and experiment with it with the existing field. Use Box Robot 2 as a robot base on which to add the attachments.