Are there any good small-ish hub/DD motors?

#1

Hi guys,

Could somebody please recommend a small-ish hub/DD motor that still has okay torque/heat characteristics?

I’m working on a roller-drive e-bike and want to replace the motor (currently a Turnigy SK8 6354 140KV) with something that doesn’t overheat so fast.

I managed to buy a spare Raptor 2.1 motor, but now think it’s a little bit too big/heavy to easily mount on my frame (I know, I know - there’s no substitute for copper/iron).

I’d really appreciate if someone can chime in if they know a decent motor with roughly these specs:

  • Can diameter 60-70mm, width under 80mm,

  • ideally around 900g (the Raptor motor is 1.5kg!),

  • 70-90Kv, sensored,

  • Ideally something I can buy a single motor of (instead of a whole kit).

I know good torque and heat characteristics are generally in line with stator size, but also that there are other factors such as stator/magnet/winding design and materials.

Who makes good quality smaller motors?

I’m thinking maybe e-lofty, or trying to find one of the older Hummie motors. There are also some unsealed Maytech 6374 motors that look workable. Happy to buy used if anyone has something spare.

More info on build for reference/interest:

The motor sits under the cranks and drives the tyre. It’s working well so far. This setup is only intended to be an assist to pedalling, and as such I have limited the power to 300w.

IMG_9127
IMG_9127.jpg1227×920 209 KB

Roller-Dr-2
Roller-Dr-2.JPG732×918 79.9 KB

I know heat management is a problem for slow moving hub motors, but I expected a better result due to the low 300w power level. Though the system works well at speed, when crawling up long hills at ~10km/h the amps get up and we hit the 80°C cut-off within a few minutes. .

I want to be able to climb looong hills on a hot day at 10km/h (ideally less) with 300w of assist. I Already plan to upgrade to 10s battery, which will allow me to run a lower kv motor and still keep top speed around 40km/h.

Currently running:

Flipsky VESC 4.12 in aluminium heat sink case. Set to 300w/45A max.

Turnigy SK8 6354 140kv motor

Zippy 7s lipo battery

Thanks in advance for any help guys,

#2

Bro you need to up the voltage and tune down the amps tbh

1 Like
#3

Wattage =/= heat
AMPS= heat

1 Like
#4

You can replace the motor with a 6380 motor or 6374 but won’t change thst much if you don’t increase the voltage. ebike run easily 12s and the one I assemble with my friend is a Chinese kit that uses 14s.
With the vesc you have try 10s and see how it goes.

#5

Get an esc from an ebike or something that can push out more voltage or if you really want to use vedders code hang around 3 months, theres stuff on the horizon.

#6

Also you shouldn’t be using only one 6354 motor on a board it works better because it is not as much weight. A bigger motor will help it not run as hot.

#7

Your only option is go to a larger motor, changing Kv won’t matter, increasing voltage won’t matter

I’ve been running a setup like yours, and it definitely gets hot, add to that that the VESC has a poor low speed tracking, so the torque when slow climbing in a high gear is really bad and most of the power is going to heat

A friction drive will only work well in moderate hills where you can keep a higher speed to avoid this low efficiency zone

3 Likes
#8

It’s a bicycle mate

#9

Yeah I know. But a 6354 I feel is to small for a bike as a bike has extra weight on it compared to a board and a 6374 or 6380 would run cooler as it is a bigger motor and can handle more.

1 Like
#10

at this point, why not get something like this?
$150 for a complete 1000w kit (minus battery)

These hubs have pretty good reviews too

1 Like
#11

lower kv means less amps to achieve same torque, no? Is this because resistance goes up with kv?

#12

I think he is saying that the effort is just too much for the size of the motor to be overcome by higher voltage only.
Anyhow in my experience same motor, lower Kv higher resistance. True about the more torque with less amp in case of lower Kv.

1 Like
#13

Voltage doesn’t create torque.
voltage does create heat but only eddy currents n hysteresis due to speed and switching magnetic fields. The large majority of heat produced in all our motors and especially hubs is due to resistance in windings
amazingly the torque to heat produced is pretty fixed based on motor size and changing kv doesn’t help as resistance goes up w lower kv as said

Easy way to get more torque without more heat is adding more iron behind the magnets. All these motors could have a much lower kv with the same electrical resistance doing that. Seems the motors are all designed for planes. Another 2mm of mild steel on a 200kv and bet u drop down to like 160

3 Likes
#14

but does torque allow you to have more watt for same amount of amp at the motor level? or not? That what I was trying to say

1 Like
#15

I don’t understand u really

The voltage the motor sees will only be maybe a volt higher than the back emf produced by the spinning motor. Just enough to pass the wanted current. 100v and 1 amp is 100 watts but you need to be spinning that full speed to be doing that 100 watts.
hubs are inherently handicapped in the power dept as they don’t spin fast. Could change kv to 1000 and gear it and boom will have a more powerful output. And then the voltage finally will start making a dent w heat

2 Likes
#16

I see. Thanks for the info. So why for the same motor (hub motor at the time 60Kv) when I changed to 12s from 10s with same 3p configuration 30Q cells. I felt way more torque as well? Maybe because they reach full speed faster being 60Kv and then overall was a stronger feeling?

#17

I meant that in my mind power is measured in watt so if you have higher voltage I thought for the same amp you will have a stronger output. That what I meant.

#18

With the same settings in esc but adding voltage I’ve experirnced that as well. I don’t know. But the heat produced is related to the torque output with both. Really w 12s it will be a bit more inefficient

#19

yeh I agree that the heat is the same. Never checked so deeply but if a motor gets hot at 10s then at 12s is basically the same. I am always more focus on torque and in my experience voltage adds torque as well. Of course also top speed increases.
Thanks for the insights :grin:

1 Like
#20

The breakdown of losses in our motors w hubs is like 95% copper loss and with a pulley and 3:1 I don’t know if even that would get to the ideal of 50% copper losses. I think stooge is the only one running with a higher ratio and probably the best efficiency.

With 3p doing higher voltage maybe u were getting less sag as well. But as u say that does happen…high voltage more torque regardless of same esc settings. Wondered myself.

1 Like