16" Motor Tear-down & Individual Component Weigh-in

[Jason McNeil]

There's some debate about much weight savings potential there is in 16" eWheel. I took apart the motor on the IPS132 & weighed each element to try to understand where these reductions might come from. 

Component	Weight	%
Rotor & Rim	2185g	24.69%
Tire & Inner	965g	10.90%
Stator	2845g	32.15%
Arm & screws	505g	5.71%
Covers	1150g	12.99%
Pedals	1200g	13.56%
Total	8850g

Tire & inner tube weigh just under 1kg, by sourcing a lighter tire, it's probably possible to get this down to around 500gm

Rotor, rim, tire & inner tube (I deducted the last two from the net weight). Here the permanent magnets are placed side-by-side without any gap between them; according to a hub motor specialist, this produces a sub-optimal flux field & also uses more materials for a given diameter Wheel, than with a calculated spacing. 

Stator & armature: the armature is composed of steel, without utter destroying the motor, unable to say how much this contributes to weight vs using aluminum. 

Close-up of the stator: quality of the laminated iron core looks reasonably good, so too are the copper windings.

The two motor plates (one's underneath), is surprising heavy at 1.15kg. Equivalent strength carbon-fiber covers could be made weighing a fraction of this. 

Pedals & support pins: aluminum, 1.2kg exactly! Again, with a redesign/rethink, these could probably be made to weigh half this & still be just as strong. 

Support arm columns & screws, aluminum, 505gm. A couple hundred gm savings at most.   

32 cell IPS132 battery pack with wires, connectors, & casing, but not BMS, which is part of the control-board. 1,520gm

400Wh Li-Po pack, as used on the F400/111, 2,170gm. 

Conclusion: it should be possible to shave around 3kg from a 16" eWheel, without any dramatic redesign to the fundamental structure. Cost of replacing certain parts with carbon fiber might add another $100 USD to the construction, but there are grounds to believe there is a large section of the market who will pay for a corresponding 3kg reduction in weight; alternatively high-grade ABS/PVC plastics could be used instead.

It will be interesting to see where IPS saved so much weight in the Zero, a Wheel with a 800W motor (sustained?) & 32 cells for 9.3kg is quite an accomplishment, if it lives up to the hype.

[Daan]

It will be interesting to see where IPS saved so much weight in the Zero, a Wheel with a 800W motor (sustained?) & 32 cells for 9.3kg is quite an accomplishment, if it lives up to the hype.

I am interested too -- can't wait to see the first reviews and take-downs

Great post -- I am very interested to see how to make a more light wheel; currently, the direct-drive BLDC motor has many advantages (silent, smooth, regenerative braking, no maintenance, super robust) but the weight is a real problem :-( 

From you figure, almost all weight, 6.180g is in just the motor part... I would like to see a sub 8kg wheel that is still robust; Clearly, the covers don't need to be at all 1150g!  Plastic would just be fine and perhaps 300g?  But otherwise it'll be hard to save weight on the motor ...

What I don't understand is that the Rockwheel has a smaller geared BLDC motor but it is still quite heavy. My feeling is that it should be possible to design a geared BLDC motor from scratch that can be made much more light weight -- perhaps even just 1.5kg for a 500W motor; that would bring down your example 8.8kg down to 4.1kg   Rockwheel are you listening!!