I have some pretty accurate data on the slightly bigger jm1 JOBY motor (40mm wide stator) that might be worth adding to the spreadsheet,
and for that matter maby gng type "1000w" big block, colossus, revolt 120 etc.
The JOBY has a kv of around 98, phase resistance (as seen by the controller) of 9.7 m ohms,
no load Watts are 93w for 1000 rpm 286w for 5000 rpm and 565w for 9000rpm, and these include about 40 to 100w in switching losses/phase current ripple, and (somewhat incorrectly) all tested at 88v.
driven it at 33khz pwm, theres 22 poles so at max rpm its 1650hz and the laminations are now down to .12mm, split magnets and they are wrapped in kevlar with around a 1mm air gap, it totals 2.7kg.
im genuinely impressed with how well put this argument is and gave some thought as to how it applies to an off road enduro race bike .
liveforphysics said:
Somewhere we may have a conceptual issue. Let's look at what gearing does.
Picture a statically loaded cog/cog interface. Trim away all the teeth that aren't engaged right now (typically just 1 tooth at a time is carrying torque). So it looks like a pair of lever arms interfacing with each other, whatever ratio between lever arm lengths happens to be is the amount of additional rotation needed by the shorter lever, and also the amount of force increased by the leverage on the longer lever. In a gear box with a bunch of stages, it's a bunch of lever arms pushing on lever arms, so we can make a bunch bunch of input motion on the lever become a tiny amount of motion on the output lever with proportionately increased force.
All I'm advocating, is rather than getting your 'gearing' through a bunch of external series lever arm arrangements (which each add mass that isn't copper or iron and hence not helping convert electricity into what you ultimately wanted, torque at the rear wheel over a speed range), to instead just use single stage lever geometry that permits achieving the same amount of leverage you wanted, but in a single stage that has no additional moving parts (failure modes) and weight.
So we need between 300 to 400NM at the tire to match the acceleration of most smoker enduro bikes and run between 8:1 and 12.5:1 gearing depending on the track with the above motor.
the magic pie headed us in the right direction over 5 years ago with a massive 265mm diameter 56 poles and only 18mm wide stator (they can do 120NM max saturated), so a double like falarfles would be about as good as good a china hub as any, but for now even the monster 10 to 15 kg hubs require over 10kw of waste heat to not really make the torque we need, ive tried a smaller rear (moto) wheel to get closer to the same newtons at the tread on same bike design and they seem impressive on their own but get cooked after a kw/hr or so and completely hosed by the joby that also uses about a third less power to do it (less than 1/5th the battery power needed to get the same off the line acceleration), so fine for commuting on smooth roads but fall well short in both acceleration, off road ability, and wh/km (efficiency) aand means we have to leave the battery behind to keep the same bike weight, seemingly not a win here.
Using an up-diametered joby (for 12 times the torque) about the diameter of the wheel would be cool, and about max out current high end and lightweight motor designs but there are inherent scaling problems involved.
-a bit like an insect strolling on the water but an elephant not so well. :wink: For this application the hub would ideally weigh under half a kilo and the motors weight be central to the bike, so even if it could be done to anywhere near the same 2.7 kg on the wheel i have gained little and it still triples the wheels unsprung mass..
to me it seems that we have found ourselves alive NOW to design our electric weapons, NOT at some point in the future -whilst its interesting to ponder which way things might go, its very difficult to design and ride machines with parts that are yet to, and may never exist.
Not much chop waiting if we can get the performance needed already, with over 3kw/hr onboard, more power and (real not just peak) efficiency and the total weight less than most that carry about 1kw/hr, we then have a platform to head in to battle with the smokers and cover heaps of off road miles and press on in the development gaining experience, understanding and good fun along the way.
Im pretty sure (unlike the big ICE manufacturers who will have us all old and grey waiting for the big breakthrough) most folks here are not prepared to wait, and want to get their high performance ev's builds happening now.
let me know if you need more info on the motor specs.
