[Chris Fultz]

Some tips for managing weight:

Before you start anything, weight the parts that will absolutely be on your robot -

the controller, spikes, radio, etc.
Include some extra weight for wiring. Include the back-up battery.
Then add transmissions, drive motors and some drive gears and some chain.
Then add wheels or treads.
Add the pneumatic pump and mandatory controls (regulator, switch, etc.
At this ponit, you have the required basics covered.

Subtract all this from 120 pounds and this is the weight you really have to work with.

Assign maximum allowable weights to each remaining subsystem based on past history.

For example:

Frame 8 pounds -
Ball lifting mechanism with motors 12 pounds
Shooter mechanism with 2 motors 15 pounds
etc.
Make sure the estimates are realistic for your capabilities and materials.

It is important to know that you really don't have 120 pounds to work with.
A big percentage of that weight is already allocated to the mandatory robot materials.