Hi,
my Z axis motor at the current time has to pick up about 50kg, and will eventually be required to pick up about 100kg when I get around to an ATC
spindle and 3kW servo motor to drive it. I elected to get one servo wit a brake rather than bother with a counterweight.
As it turns out I use 32mm diameter ground ballscrews and the large diameter screws by far and away dominate the inertia equation...NOT the axis mass at all.
I know its counter intuitive but the axis mass is only about 5%-10% of the total inertia with the ballscrews themselves contributing 80% and the servo armature another 10%.
This might surprise and that's why it makes sense to do the calculations BEFORE you commit to buy. My ballscrews are 5mm pitch and even without a brake do not slump
when de-powered. They might when I build a new spindle, but as the brake cost about $100USD premium over a plain servo I got it...so I'm ready for it no matter what happens.
Craig