[DaveL]

In addition to the great comments already posted, you might consider a different role.
Some ideas to keep you involved but to reduce your responsibility and increase your fun:
- Be more of a resource for your teams,
- Be a senior mentor to review what the various teams are working on,
- Be a design mentor and have Skype online meetings,
- Focus on helping the team build initial prototypes and let the team take it from there.
(If you can, pick only one of these options)

A big part of FRC mentor stress can come from not wanting to feel like you are letting your team down. One way to avoid this is to be more like a consultant. You provide options with examples from your experience and then let the team decide. Now you are off the hook. The team made their decision and they have to make it work.

Mentoring on every team is different, so its hard to know how to help.
My approach is to do more in the summer and the fall, so the build session goes smoother.
Working with experienced students verses rookie students also has its differences.
For experienced students, you can be more of a consultant. For the rookies you may spend more time on safety, proper tool use and basic assembly operations. If you decide to pull back, have your experienced students help with the rookies. Or train up parents to fill in.

Whatever you decide, I recommend you clearly communicate your intent to your team, so they can step up or find others to help.

Dave