Get Up Close and Personal
Even though you should think three times before incorporation loud shouting, music, singing, etc. into any of your judging presentations, by the same token, make sure your talking parts are loud enough for judges to hear. Typically judging rooms have high ceilings and are separated by curtains or other temporary partitions. It's hard for kids voices to overcome these, combined with the voices coming from neighboring judging sessions.
As we said in Tip #1- get as close as you can to the judges' table. Of course, if you need space to act out any part of your presentation, back up some but for your important points, get close! The judges will appreciate it. It is frustration for them to miss part of your key information because they couldn't hear/understand you. Practice projecting your voices. Put your mock judges across the room and then try to speak loud enough for them to hear you. Put on some background noise in your practice room and work on speaking over that noise. We often set our radio between stations and turn up the static. Then we rehearse speaking as loudly as we can, as expressively as we can, as convincingly as we can - without shouting!
This is especially hard for soft-spoken team members. They definitely have to go outside their comfort zone to achieve the right vocal volume but in the end, you'll be sure that the judges get to hear all the cool things about your project/robot/team.