# Outrunner Brushless Motor vs DC Inrunner



## antimattercrusader (Feb 27, 2012)

I am wondering if anyone can give me some insight as to why outrunner brushless motors are not available/popular for EV conversions? 

Their increased torque and size seems like it would be useful. I know I have been impressed with the performance of these motors for R/C applications.


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## somanywelps (Jan 25, 2012)

http://www.diyelectriccar.com/forums/showthread.php/600-series-outrunner-motor-enertrac-38486.html


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## frodus (Apr 12, 2008)

Scaling doesn't always work that great when moving from mostly AIR to mostly surface applications.

For RC stuff, you typically have lots and lots of airflow with outrunners and nothing around the motor that would get in the way (like in an airplane, or heli). I don't typically see outrunners in ground vehicles.

With a car, you have to basically support the motor from one face only, so the mechanical stress on a motor is much higher. And typically in a car, there's MUCH less airflow under the hood to properly keep the motor cool. Outrunners can be difficult to cool due to the space constraints of the stator.

For ground EV's, we typically use IPM, Induction or other brushless motors that have the ability to support on each end of the motor effectively and provide cooling via liquid or forced air cooling.

Not to say you COULDN'T make an outrunner, but there are mechanical reasons that it's not on the top of the list for companies to develop.

I think the largest outrunner I've seen is the Enstroj Emrax, but it's designed more for airplane applications.
http://www.enstroj.si/Electric-products/emrax-motors.html
(although they're outrunners, it apears as though they might have a cover over the rotor).


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## major (Apr 4, 2008)

antimattercrusader said:


> I am wondering if anyone can give me some insight as to why outrunner brushless motors are not available/popular for EV conversions?
> 
> Their increased torque and size seems like it would be useful. I know I have been impressed with the performance of these motors for R/C applications.


Hi anti,

I haven't used those motors but read some specs. Impressive. But I think they are application specific which have downsides to EV propulsion. Like:

Cooling. Propeller air blast isn't so good for a car.

Load curve. Propeller load increases as the square (to cube) of RPM. In the EV you see a lot of low speed high load requirement.

Propeller mass (inertia) vs that of a car.

Outer rotor polar moment of inertia vs interior rotor.

Cost of larger magnets.

Control. Propellers don't require torque control. They also don't require rapid frequent changes in RPM.

The high power density often comes with high RPM which is difficult to couple to drive wheels mechanically.

WTH, give it a try 

major


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## somanywelps (Jan 25, 2012)

http://www.freeair.cz/freeairen/ind...n=com_virtuemart&Itemid=53&vmcchk=1&Itemid=53

http://www.youtube.com/watch?v=jEEtCykXlsI


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## frodus (Apr 12, 2008)

So how would you cool that?

How would you mount that so that the output would couple with some sort of transmission?

Look how low the torque is at low RPM, it's in the single digits.


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## somanywelps (Jan 25, 2012)

frodus said:


> So how would you cool that?
> 
> How would you mount that so that the output would couple with some sort of transmission?
> 
> Look how low the torque is at low RPM, it's in the single digits.


They did it there with a front transaxle.

Maybe there's a transaxle you can drive from both sides?


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## lutach (May 31, 2011)

TM4 (www.tm4.com) motors are Outrunners,are liquid cooled and designed for the EV Market. Here's their video on how it works: http://www.tm4.com/howitworks.aspx. More info: http://www.tm4.com/en/external_rotor_topology.aspx, http://www.tm4.com/en/interior_permanent_magnets.aspx and they have more links on other features. You can also have a motor like the pictures I posted, which also can be liquid cooled. That is a small version that is rated 29 Nm of torque and has a max. speed of 2000rpm (I don't have info on the watts rating), but a larger version with less poles is rated for 1000 Nm and has a max. speed of 2500rpm (Again, I don't know the watts).


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## somanywelps (Jan 25, 2012)

lutach said:


> TM4 (www.tm4.com) motors are Outrunners,are liquid cooled and designed for the EV Market. Here's their video on how it works: http://www.tm4.com/howitworks.aspx. More info: http://www.tm4.com/en/external_rotor_topology.aspx, http://www.tm4.com/en/interior_permanent_magnets.aspx and they have more links on other features. You can also have a motor like the pictures I posted, which also can be liquid cooled. That is a small version that is rated 29 Nm of torque and has a max. speed of 2000rpm (I don't have info on the watts rating), but a larger version with less poles is rated for 1000 Nm and has a max. speed of 2500rpm (Again, I don't know the watts).


That is some good stuff there on their site for their main motors, which are all outrunners. Could give AC Propulsion and UQM a run for their money with that 200kw motor inverter pair.


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