Moment of inertia calculations - think again, fat boy

Despite the fact that the inertia of the Blidgeport table and load masses, expressed as moments of inertia at the servo motor are pretty small relative to the MoI of the X and Y servo motors themselves, the best response I could get out of them wasn't exactly lightening fast. These motors are rated at 400W continuous, with something like 2-3 times that in the short term.

Of course, I made an early decision to retain the handwheels so that I could retain a lot of the manual features of the machine. And the handwheels on this particular model are pretty large in terms of MoI, when compared against the simple "ball" handles often seen on Bridgeports.

When you look at the contribution that the handwheels make to the total MoI of the combined system referred to the servo motor (through the 2.5:1 reduction stage), it is dominated by the MoIs of the handwheels. There is only 1 on the Y axis but there are 2 on the X axis.

I reran the calculations with and without the handwheels. The "inertia ratio" is the ratio of the final MoI to the MoI of the servo motor alone. Without the handwheels, the motor MoIs dominate. With the handwheels, the MoI is almost an order of magnitude greater than the motor. The servos are basically expending most of their effort twiddling the handwheels. 

As you can see, the net MoIs can be reduced by more than an order of magnitude and the effect on the P, I & D terms is significant. So I should be able to improve the response significantly by removing them.