The higher frequency causes the stator metal to heat more than in 'normal use'. The amount of such heating, and its effect on the achievable torque, will vary from motor to motor.
At high frequency, there's a 'skin effect' in the stator magnetization that will cause torque to drop, and a stray inductance that will cause current to decrease, in addition to the stator heating from magnetic hysteresis.
If there's a thermal overload for the motor, the worst that will happen is it will open (if the motor has a resettable thermal overload, that isn't a big problem).
All medium/large motors have a thermal protector of some sort.
That's not a bad idea, but I think the energy levels are too high to use them alone. Most of our flywheels were in the 50,000 to 60,000 rpm range so the peripheral speeds were in the 2500 to 3000 fps range. For the above ground test rig, we used two or three layers of water filled boxes, then backed that up with a bomb blanket that was custom built. Basically it strapped together to form a cube about 6 feet on each side. Anything that made it through the water would be traveling pretty slow by then and the blanket could handle it.
Compared to building a hardened concrete room or another underground spin pit, we saved about 90% of the cost.
Commercial water barriers are used to suppress explosions and are quite effective. A car with 8" thick water bags hanging on its sides will survive a bomb blast alongside that would completey demolish an unprotected car. And anti-bomb squads have disposable containment systems that are one cardboard box inside another, with 8-10" of water bags in between.
There are even transportable magazine systems that are formed of 1 meter wide hollow plastic columns that are arc shaped in cross section. They overlap to provide a solid 1 meter wall of water. You build rooms made of them, they will contain 1000 lb aircraft bombs.
Well ... while I never brought a weapon to work, I brought something considered as bad -- a camera.
The trick is getting the proper paperwork *before* you bring it in, and then make sure that the guards see the paperwork and the item covered by the paperwork. Do that, and you are fine. Short circuit it and you are in trouble.
No -- I couldn't bring in film. That was supplied, and processed on post, so the images did not leave.
I have fired firearms there, but they belonged to the lab (testing night vision sights of various styles under the actual vibration from a M16A2 and such.)
I once took a weapon out of work and brought back, a Rem 700 in .30-06. With five rounds of armor piercing obtained for me by the head of security from the county sheriff. I was testing some vehicle armor I had made. A security captain travelled with me while I conducted the test.
We had a much lower level of "security". :-) When were developing a muzzle flash detector for a helicopter (to tell if it were being fired at from the ground) I just used an old M1 while the other helper operated the breadboard. We just went out back and fired toward the woods. :-) Those were the "good old days", I guess about 1968 or so. Incidentally it worked pretty well. :-) ...lew...
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