The best video's I've seen were the ones from the Simbotics.
They have done several online seminars covering almost all basic subjects involving FRC.
Here is one for the drive train design:
https://www.youtube.com/watch?v=ADcqUWYyHgk
You can always check out the other Simbotics seminars aswell if you want more info on stategy design, the new controle system, scouting or chairmans for example.
Another good introduction set of seminars were provided by Behind the Lines. Here is one that covers all the basic knowlage that every FRC team needs:
https://www.youtube.com/watch?v=B5QilnfA_i4
They to have several seminars covering several topics.
With these to seminar sets combined you should have plenty of preperation vídeo's to get your team well informed.
Should you have any other questions, feel free to contact me and I will try to help you out the best I can.
Greetings from team 4481 - The Rembrandts