My main problem is the width of the shafts. Since the inner one is about 2mm(thinnest brushless motor shaft) then the outer one would be about 9mm (the bearings for 2mm shaft are 1/4 inch + almost 2mm at least shaft width) Now the shaft is getting pretty thick. Now the second motor tube would have to be 16mm (14 mm bearings) THat's kinda thick. I don't if that might bea problem. THe stators for the 2nd motor would have to be drilled out, and I don't know if that will fit. But the most serious problem would be making the shaft. It would probably have to be custom made unless I can find a ready-made , and custom making it would really cost a lot, and since you want it to be stainless steel, it would be pretty hard to machine it at home. Any of you guys know where to find a 1/4 inch ID Stainless Steel Shaft? (The OD isn't as important, but it shouldn't be too large) Another Idea for the shaft was using Carbon fiber. Would that work?
Also, I don't think there should be too much trouble with having the two shafts having bearings directly between each other. The only problem I can see is that the bearings have to be able to withstand 2x the rpm, but with a 15,000 system (the max I'm estimating for this, it should be lower), this shouldn't be a problem. If there is one I can't see, please point it out.
Thanks
Mitek