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Oil cooled coils on a BBS02 middrive?

Posted: Nov 18 2015 5:21am
by Speady
Hi guys, as this is my first posting i'd like to say hello to everybody first of all.

Found an interesting build a few days ago: ... build.html

Most of his great work is technically too complex to be redone by myself.
But there's one detail I would be able to copy easily. He filled the motor with oil to improve heat exchange between the coils and the housing. As oil has got a higher heat capacity than air this might help to speed up heat transfer to the housing a bit.
Probably fixing some thermal issues of the BBS02 middrive that way.
I wonder if this might cause premature failure of any internal parts, especially the plastic gearing.
What do you think about it?

Btw, sorry for my bad english, I'm a german guy, living in spain, so there's three languages spinning inside my head. :shock:

Re: Oil cooled coils on a BBS02 middrive?

Posted: Nov 21 2015 3:32pm
by k-harvey
Thats amazing what that guy did , I use cyclone & havnt found any plastic in motors , might be in low w range .
For oldies like myself that craftzmans bike make is possible bar not able to lift leg over the back of bike so i'l keep to the lady's
way with battery behind front wheel as the suspensions don't ever go up that far. With good motor bike weight dosn't matter so
easy to keep to steel & repair . I'll keep the Al for boat.

Re: Oil cooled coils on a BBS02 middrive?

Posted: Nov 21 2015 7:59pm
by k-harvey
oops new i think taiwan cyclone one (on there web) that goes up to 3000w at 72v looks like nylon gears , quiter & perhaps even better than the soft steel ones.

Re: Oil cooled coils on a BBS02 middrive?

Posted: Nov 21 2015 8:20pm
by spinningmagnets
The BBS02 is an inrunner, so the hot coils are on the outer perimeter, and already have a good heat-path to the aluminum shell. Also, due to the high reduction, the rotor spins at very high RPMs, so adding oil might cause excessive friction. I would measure the "no load" watts drawn by the motor before oil is added, and then after. If the unloaded watts are very similar, then there is not much added friction.

I don't think the oil is necessary in that application. It seems to work best in a slow RPM direct drive hubmotor (which is an outrunner), because the hot coils are insulated by air between the stator and the outer shell.