Thread: Rotating Ballnut - design ideas
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19-06-2011 #11
That explains a lot!
I've just estimated the moment of inertia of the rotating bits of the assembly, so pulleys shaft, ballnut and bearings. Surprisingly it comes to slightly more than the inertia of the 2085mm, 25mm diameter screw! That's annoying since one of my main reasons for doing this was because I thought this value would be much lower. I've not included the inertia of the bearings I would require to rotate the screw, and I suppose I would use pulleys with it anyway. The inertia of the ballnut and shaft is still about two thirds of that of the screw.
This is going to make a big difference to the rapid speeds I can get since the torque required to move the 50kg gantry, due to the low coefficient of friction of the bearings, is very small.
Now I'm going to try modelling it with the stepper at different ratios - not 1:1, and see what happens.
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