Outrunners... what's the catch?

abudabit

New Member
Local time
5:09 AM
Joined
Aug 29, 2008
Messages
18
Outrunner motors look great on paper... superb power to weight, great cost, good efficiency... what's the catch? How come they are only used for model aircraft and not ev's or light industrial equipment?
 

terrence

Member
Local time
5:09 AM
Joined
Sep 9, 2008
Messages
221
Location
Shell Lake, Wisconsin
Outrunner motors look great on paper... superb power to weight, great cost, good efficiency... what's the catch? How come they are only used for model aircraft and not ev's or light industrial equipment?

Forgive my ignorance. Im not familiar with these. Do you have a link or
a place to educate myself on these. thanks, terrence
 

abudabit

New Member
Local time
5:09 AM
Joined
Aug 29, 2008
Messages
18
Outrunners are brushless dc's, except the magnet is the core and the wiring is the perimeter.

Here is a source of outrunners
http://www.nitroplanes.com/brmo.html

Here is one, for example:
http://www.nitroplanes.com/mo1102brmo.html
It says 2kw, although that is probably when it is being air cooled by flying around. Probably more like 1kw - 1.5kw. Still, that's a lot of power for a $79 motor that weighs only 1 lb. Also it is very small, and supposedly they are very efficient even by electric motor standards. They have lower rpms but higher torque than their inrunner (standard) brushless dc cousins.

I can't help but think there must be something wrong with them though.
 

Drunkskunk

Member
Local time
5:09 AM
Joined
Feb 18, 2008
Messages
124
they are used. For an Ebike, its used as a hub motor. lace the spokes to the outside of the motor, and you have a direct drive.

The are being tested by a few companies for cars as well, but the efficancy band is smaller than a conventional geared drive. thats fine for a bike with a narrow speed range, or power tools, pump motors, forklifts, ect... but for a car, there are other, more efficent ways to make them work
 

abudabit

New Member
Local time
5:09 AM
Joined
Aug 29, 2008
Messages
18
That's the theoretical unloaded top turning speed, where RPM = kv * volts. So 12 volts into a 3500Kv (K is uppercase and v is lowercase to avoid confusion with kilovolts) motor would be 42000 RPM.

Their peak efficiency point supposedly, and perhaps someone can correct me on this because I haven't seen many performance charts for those hobby outrunners, is at 80% of Kv. So if you were putting 12 volts into that motor, 33600 RPM would be optimal efficiency.

A 3500Kv motor is probably designed for low voltage use. For 36-48v you will probably want something a lot lower. Here is an example of a beast with low Kv:

http://www.hobbycity.com/hobbycity/...80-100-B_130Kv_Brushless_Outrunner_(eq:_70-55)

At 36 volts you would have an optimal RPM of 3744. If 2400 rpm is 60 mph on a 26 inch wheel, you reduce the motor rotation in half and get 1872 or 46 mph optimal running speed which it would easily take. Sounds dangerous on a bike though, but that's just an example of how one would be used.
 
Last edited:

Drunkskunk

Member
Local time
5:09 AM
Joined
Feb 18, 2008
Messages
124
thats an oddball motor, 3600kv is inrunner teritory. Its also listed as 6-10 nicad cells, which means 12 volts max.

inrunners are better at higher RPMs, as the narrower stator design means they accelerate faster. they also run more efficently at high RPMs.
Out runners are best around 1500Kv or less. For a bike, a 150Kv motor would be great for a gear drive, and an 8 Kv would be ideal for a hub motor (Like my Clyte motor is)
 

Bigwheel

Member
Local time
3:09 AM
Joined
May 17, 2008
Messages
55
This is all very interesting. I really like the size of these motors and their corresponding weight which coupled with LiPo should yield a nice light package? So forgive my ignorance on the electronics end of things but the way I am reading it one of these motors set up with a jackshaft running to gears would work? Similar to a setup like this:http://www.ecospeed.net/emddet.html

Thanks for any feedback in advance.
 
S

skyl4rk

Guest
A outrunner coupled with a internally geared hub (perhaps with jackshaft to reduce rpms) might be the way to go. If it is "safe" to propose a system with no pedals.
 

Bigwheel

Member
Local time
3:09 AM
Joined
May 17, 2008
Messages
55
But there would be pedals when using the jackshaft, that is what the jackshaft accomplishes is the ability to utilize the front cranks, a motor and a gear system both internal and derailleur/cassette style. So independent use of both could be used or in sync. Like the Sickshifter that is becoming so popular with the HT crowd, kind of sort of without the freewheeling front crank?
 
Top