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Lets talk Raptor Hubs please


#76

@Pedrodemio with the @Hummie hub simulations I assume the 2-phase value is 0.07ohm.


#77

In your comparison both motors run with matched propellers close to peak efficiency. Even then you have 4x the losses (roughly 37W against 9W). This perfectly matches Benjamin’s statement:

losses are proportional to the square of the torque produced

A hub motor will pretty much always run far off the peak efficiency region though. The efficiency curve has a steep drop which the biggest issue. Less efficiency = more heat.
The hub motor will start to feel comfortable at constant speeds of 35-40mp/h. Then wind drag gets your issue which generates heat again. Also hot copper wire has a higher resistance which ads to the losses building up.
Losses generate heat, heat generates higher resistance and higher resistance generates more heat again.
At a certain point this becomes a viscous circle. The temp rise gets non linear and drifts away.
In a drone or RC-Plane the motor sees plenty of airflow and the copper stays way cooler.

We measured the belt drive losses the other day. Roughly 2-5% if adjusted correctly. Straight cut gears will be even better. So losses in the drive train can be overlooked in any valid comparison. Compared to the losses you build up when stripping out the gears the drive train losses are negligible.

I’m not saying that hubs can’t work, don’t get me wrong! But the physics behind them are a tough hurdle to take and the system also comes with downsides like wasting battery capacity into access heat.


#78

I’ve tried to delete off topic/negative posts on this thread. Please don’t take it personally if a post of yours was deleted, it may have simply been a reasonable response to a reply that needed to be deleted.

Members, please remember that if you have an issue with a company, take it up with the company - vendor bashing posts will be deleted.


#79

@brenternet your deal wasn’t deleted by @anorak234 , means it still stays strong :muscle:


#80

Pardon me if I’m being stupid but what’s a door stopper got to do with advanced motor controller hardware?? Aren’t they just little pieces of angled plastic you shove under the door to prevent it from moving?


#81

It means he bought a lot and doesn’t have use for them :rofl:


#82

Oh shit did not see that Jeff was replying to another comment. I get it now :man_facepalming:


#83

Which is why I created a thread about 8 months ago explaining exactly that and telling china to simply create larger hub motors with larger stators and more copper and at some point, you’ll escape it. Worked for the hummie hub.


#84

Do you happen to know the stator dimensions of the hummie, Carvon and Raptor hubs? I think the cheap hubs you find on Meepo/WowGo etc are basically the stators from 6380 motors (so 5050 stator dimensions), would be curious to hear what the higher-end solutions are using.


#85

They seem very appealing to me, is there an expected price?


#86

I highly doubt meepo and wowgo hubs are running 5050 stators. By reading the stats of it they are only like 50mm wide so I doubt that’s right. I’m pretty sure they have a 50 x 25-30 stator


#87

+1 no way they have 50 long stator. Hummies are close to 5050.


#88

@12meterkuk Just ran the no load test. My hubs definitely warm up after a couple minutes spinning no load. Here is a picture below, just rode into work so the motors started a bit warm (42 C) and after about a minute or a little more they were here:

At no load you can see we are putting about 38 watts into each motor. Since no mechanical work is being done (except into friction) we can be sure all 38 of these watts go into heat. So it isn’t particularly surprising they are warming up slowly at max no load speed. Sorry I didn’t run the full 5 min pretty sure my coworkers got tired of hearing full blast hubs.


#89

assumptions: 85kv, 39v battery, 95% max duty cycle, 0.096ohm, bldc

39v * 95% duty = 37.05v effective
85 kv * 37.05v = 3149.25rpm no load rpm

the motor has some friction, so i will assume this slows the motor to 3140rpm constant with no other load:

3140rpm / 85rpm/v = 36.94117v back emf voltage produced by the spinning magnets
(37.05v effective - 36.9411v back emf) = 0.1088v “drive” voltage above back emf
0.1088v “drive” voltage / 0.096ohm = 1.13357a motor current
1.13357a motor current * 37.05v effective = 41.99908w electrical watts
1.1335a motor current * 1.1335a motor current * 0.096ohm = 0.12336w ohmic heating

^the ohmic heating is far lower than the electrical wattage… i suspect this narrows it down to either heat from friction in the bearings, or possibly eddy currents in the stator…

60 / (2 * pi * 85kv) = 0.11234Nm/A newton meters torque per motor amp
0.11234Nm/A * 1.13357a motor current= 0.12735Nm newton meters torque
(3140rpm * 2 * pi) / 60 = 328.82003rad/sec radians per second angular velocity
0.12735Nm * 328.82003rad/sec = 41.87572w mechanical watts

^the mechanical wattage produced is about 41.87572w watts mechanical (before subtracting internal losses occurring within the motor from bearing friction and eddy currents)

1.13357a motor current * 37.05v effective = 41.99908w electrical watts
41.87572w mechanical watts + 0.12336w ohmic heating = 41.99908w electrical watts

^the mechanical power production + the ohmic heating losses equals the electrical power consumption

41.87572w mechanical watts / 41.99908w electrical watts = 99.7% electrical to mechanical conversion efficiency

^ 99.7% of the electrical wattage is converted to mechanical wattage in this no load condition, before accounting for the friction and eddy current losses occuring internally within the motor


#90

Yep probably a combo of the two, small mechanical loads on the motor add up at high RPM.


#91

Ok so I know this has been asked two times before there wasn’t a clear answer :smile:
Whats the expected price for a kit? :wink:
@onloop @Deodand