Technics SP-10mk2 oscillations

Attention, these are not experiments to be done!
The engine must work with the platter inserted, it is not allowed to play with the engine without the platter inserted .... it would end up being damaged.

What Best-groove said.  What you observed, rays, is normal and not a good idea in practice. The servo system needs the mass of the platter in order to operate properly.  The herky jerky motion of the rotor without any mass on it is what to expect.

Without the platter, the rotor oscillates  at high frequency and amplitude while turning at 33rpm. At 78rpm, the oscillations are much less so. With the heavy platter on, oscillations disappear. No gridding noises, etc.

@rays19 The servo 'hunts' without the flywheel effect of the platter. That's why it jerks like that- and many direct drive turntables do exactly the same thing. You got good advice above!

Some manufactures state,

"damage may occur if running with plater removed"