Rotating Ballnut - design ideas

[richienz]

You can certainly say that of the riders!

With that size ballscrew then you do have a problem with the rotating inertia, not so much the 150kg gantry. Can you measure the ballnut - approximate it as cylinders, then we can work out the inertia of the ballnut compared to the ballscrew to see what you could gain by rotating the nut.

My PhD studies are taking up a lot of time at the moment (need to catch up after all the racing!), but I do intend to have time to finish some rotating nut assemblies soon.

What else can you plot from your system - can you plot the motor torque in addition to the speed response? If so, that's another way to work out the inertia and get better insight into how the system will behave.

I am too scared to watch the racing almost, its impressive riding nothing else is close really is it, but scary when a rider is badly hurt or killed, seems to be all too common.

I'll measure up the ball nut and screw and also try find the original part numbers and specs weights etc.

The PID loop tuning I struggle with, yes I can measure the currents I think , my Granite Devices VSD-XE servo drives have an inbuilt virtual oscilloscope that I use to measure the response with, to be honest the PID tuning I am very hit and miss with I can;t quite qork out what low pass filters I should use and why.......

I retuned the PID loops on both x and y on the weekend and its better but still I am sure there is room for significant improvement. whip of the screw is a problem too when I get over 600RPM approx. Thats a 10mm pitch per revolution screw (isthatthe correct terminology?) so thats a speed 6000mm/min , any faster and sometimes it whips and that really gives me the shits. I'm finding that small circle cuts say a 6mm end mill cutting a small 10mm dia helix has some error in the hole and I have to crank the speed back to around 1500mm/min for cutting (the timber) rather than running at higher speeds that I'd like to.

Anyway if you have time I would appreciate your guidance, keep on top of your studies thats top priority! Even if I can plagiarise your design and try build locally with some of your engineering input that would be greatly appreciated but if I can commission you to build one at the right price that works for us both then that's even better!!!

Funny I was a bit ambitious the last figures I quoted in my earlier post looked good on the scope but in real life cutting it was terrible!

Cheers
Rich