by TheOther10

The 'Art Book' for the film has a couple of good photos of the actual prop made for the film. It's even 3D printed (and you can tell..)
So I thought I'll whip one up because I can. Very much a work still in progress - as I type this the UP Box is whirring away making the first set of parts. Only got half of it out so far but everything fits together as planned.
No time yet to do the interior parts, but you don't see that stuff in the film, so it can wait.
It's big of course, so you may want/need to do it half scale, both to fit it in your machine and on your shelf when done.

Print Settings

Printer Brand:                          

Up

Printer:                          

Up Plus

Rafts:                          

Yes

Supports:                          

Yes

Resolution:                          

as fine as possible for the rollers and roller bases

Infill:                          

15%

Filament:                                            3D Fillies ABS                                        silver; red                                        

Notes:

The "Shell" parts print well standing up on one of the flat edges

Post-Printing

I was pleased to see this all stays together without glue, as long as you don't swing it around too vigorously.

Only five different parts. You'll need 6 each of the rollers and roller bases; 8 shell  segments; 24 finger-hole surrounds; and 24 pegs.

Join two shell parts together with the little brick-shaped pegs; then another two (orientation of the finger-holes is random, not symmetrical). Then push the two pairs together either side of one of the roller base rings. Repeat this so that you have two half balls; then insert the remaining four roller base rings into one of the halves and join the two halves around them with eight more of the pegs. Finally snap the six rollers onto their ring bases; and push the finger hole bezels into all the holes in the shells..
Easy.

How I Designed This

Photo of the actual prop, from the book "Alita Battle Angel: The Art and Making of the Movie". Lots of stuff inside to do next time I have a long weekend..

According to the book, as in the manga, the motorball is 30cm in diameter. I've assumed that means the red bit is 30cm (but perhaps it's 30cm from tip to tip of  the silver roller-balls?) Next I'm guessing the six rollers in their holes are about 10cm and the red shell looks to be around an inch thick (metric inch). I think maybe I've made the finger-holes a bit big, but wanted my thumb to be an easy fit. I may yet make some sleeves to narrow them a little, and perhaps thicken up the bezels around them. And of course it's designed to allow addition of the internal detail in the future that never comes.

Solidworks again