I’ve been looking high and low for something thats like a servo saver, but is used between a motor shaft and a wheel. I’m trying to make a “throwable” recon robot (at least dropable). upon impact, the wheels will be jarred, potentially stripping motor gears. I figured something spring loaded like a servo saver would absorb some of the energy instead of damaging the motor. Any thoughts and/or links on this?
I’m thinking a pair of disks with a spline for the servo that squeeze the wheel. A compression spring would “load” the “sandwich”.
Alan KM6VV
Would your design lend itself to a different approach? If I understood your first post correctly, you are concerned only about protecting your motors from jarring when your wheels first contact the ground after your bot is thrown or dropped - some kind of clutch or torsion absorbtion mechanism at each wheel.
Thinking a little differently, could you use some kind of sacrificial, discardable cage that would prevent wheel contact when the bot first strikes the ground. The cage could be discarded (ejected?) after the bot comes to rest. This might mean only one mechanism instead of one at each wheel, and the weight would fall off the bot instead of having to be carried for evermore long after the clutches have served their purpose. I’m thinking of the soft landing devices NASA sometimes uses.
Unless you have an extraordinary pitching arm, you should be able to retrieve and reuse the discarded cage. 
Good luck however you decide to go. I’d like to see pictures.
Ted
Options might be to make the wheels out of soft springy material, or make a section of axel shaft connecting to the wheel out of a spring that will flex under load.
Thanks everyone for the ideas. I kinda like the idea of using a spring as part of the shaft, that may be the simple solution. I post pictures when i get a little further along.