Were a rookie team this year team 1511 and i am wondering how many teams are reducing the weight of their drivetrain/ gearbox. Any help would be awsome.
Couple of examples shown here:
http://www.chiefdelphi.com/forums/showthread.php?t=33481
We already took a lot of weight out of our gears. Any other ideas?
sawsall and giant holesaws 
take the main channels/tubes of the robot and put a bunch of holes in them with a holesaw… the result–> swiss cheese… just make sure you dont completely compromise the integrity of the robot… 
It would help to know what your robot looks like before offering ideas about it. Perhaps show a picture?
You can try lightening metal, welding instead of bolts, using thinner skins (or no skins), or drilling out holes. 
One of my jobs with FIRST in the past few Years has been inspector at many events. I have seen many machines that look like moths have attacked it, with holes everywhere. You know a team is in trouble when you see several students attacking their machine with hole saws on Thursday. The holes are not to create less wind resistance.
What really needs to be done is “Weight Management”. Drilling holes is only a partial answer and only if you are drilling steel. There is very little weight savings with lighter materials.
Look at each sub-system in detail. What supports and brackets are vital and necessary for strength and durability, which can be eliminated? Do you really need a gear made of steel, when a lighter material would work as it is not going to see massive stress?
Do you have extra wire? Cooper is very heavy. Are you using the correct wire gage?
Finally, call a meeting of the leaders of each sub system and give them a target weight they can have or a amount they must loose. Making the final weight is important.
Also consider pulling functionality off your robot. Generally (discounting the drive train) consider doing only 1 or 2 things within the game… usually n tasks, n - 2 for time and then from that subtract 1 for weight. For example, this year you could be grabbing a tetra off the stand and putting it on a goal. If you’ve been following the good advice of the people here and lighting up your gearbox… you got to take the weight off elsewhere. The “stock” FIRST transmission they gave use needs serious machine time to make it “reasonable” to install.
nahh minis are quite light relative to the 80% SUV population around here.
if you are using solid rubber tires, thats also another place you could choose to drill into. but dont make the holes too big or too close or you will have a ‘flat’ solid (with holes in it) rubber tire
and if your axles are longer than they need to be cut them off. but remember to leave enough for the collars if that is how you secure them. those 1/2 in axles are quite heavy. and drilling your gears/sprockets will definitly help
also think about rebuilding certain parts with a lighter material… consider 1/16 inch wall aluminum box or angle instead of 1/8 inch. If you have alot of PVC, consider small walls, or switching to some aluminum of smaller size that can get you the same strength but less weight.
Many teams use [1/4"] steel bolts to connect parts when a [quarter-inch] aluminum dowel with pins on the end can do the same job. Last year, our robot, when hanging, was supported by a 2" long dowel. The little bits of weight you save do add up.
if you only need to get rid of a few lbs cheese holing everything can help, turn your gears into patterns like car rims, but remember to keep at least 3 supports for each section that you take chunks out of.
Length of chain and chain pitch used in drive mechanisms can also reduce weight. If you can shorten the chains by relocating the drive/transmission closer to the mechanism it will add up fast. Also if you use No. 35 chain every where look at the actual loading that you see at different locations. My team was shocked last year when I showed them that No. 25 chain could take the load for a 2 motor drivetrain. We had typically used No. 35 and it hadn’t been questioned. I just want to stress though make sure you do the stress calculations before making this change.
Pete