# 7kw dc brushless help



## Reeyah (Mar 30, 2010)

Hi! I stumbled upon this forum researching EV's and hybrids because I am toying with the idea of building a hybrid from scratch. My question revolves around this motor: http://www.unitedhobbies.com/UNITEDHOBBIES/store/uh_viewItem.asp?idProduct=5139 This is a brushless outrunner that is used in RC aircraft and I was thinking that this may be a good candidate for my hybrid. The motor that I used will be run through a cvt system similar to that on the Urba electric. I am hoping to achieve a cruising speed of 65 with a max of 70-75. I was wondering what some experienced EV designers/builders/gurus initial thoughts about this motor were. Also brushless outrunners for rc aircraft tend to heat up rapidly and I was trying to think of methods of cooling. My ideas were: attach a heat sink to the motor case (which spins), cooling with external air, and/or having 2 motors that can be toggled between to allow one to cool. Also attached is a messy sketch of my design. Feel free to suggest/criticize anything about it.


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## maxvtol (Nov 11, 2009)

Hey Reeyah,
I'm buy no means an expert on motors, but I do know a little about RC motors from using them on RC planes. That motor is probably sensorless, which means the controller doesn't know exactly where the motor position is so it tries to figure it out based on feedback (voltage or current?), so starting under a load may cause some jerking as it tries to figure out if it's going backwards or forwards. (I only know this from researching using an RC motor for my ebike, so I don't know from experience, or even if my explaination of the above is 100% correct. Maybe someone who knows could chime in before you spend any money). If you're using a CVT and keeping the centrifugal clutch (or however it engages) it may not be an issue, though you would probably want it to engage at as low rpm as possible.

I found that if you keep these RC motors at about 1/3 max rating they're not too hard to keep cool, and don't forget the controller needs cooling as well. I would also make your mounting plate a heat sink since the wires are on the armature(?), which doesn't move, and is where the heat is generated. The controller would need a heat sink as well (I really have no clue if the ESC you normally use on these would work, or if you would have to go with something like this from Kelly.) Maybe some small aluminum fan blades on outer casing to blow on the stationary heat sinks, or use a separate fan. 

I think a CVT would work good for a low power electric motor. I thought about using a snowmobile CVT for my application, but have decided to use gears and a clutch just because that's what it has now.


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