Hey Doc,
I'm just happy we're back on the same page. In that pic, what is that gray ring on the hubbie cover between the ring of holes and the brake disc? I don't remember seeing that before.
I've been spending some time today running numbers, and using some conservative but I think reasonable estimates of stator surface areas and convective heat transfer coefficients, and limiting stator temps to 200°C, it looks like our 200mm motors are going to be limited to somewhere around 2500W in heat rejection. Hopefully my estimates were overly conservative. Your X54 will be somewhat more capable due to a lot more exposed copper surface, but definitely do your stress testing incrementally if you're able to run a continuous load at those levels. Also Zombiess' idea that he's going to be anywhere near peak efficiency at such high power isn't realistic at all, since peak power will be more in the mid 70's in efficiency.
On another note, I was running numbers on oil cooling, and it's simply not the answer, not for maximizing continuous power from our hubmotors. The reason is because the magnets have such a low thermal limits and the outer shell can't be allowed to exceed that limit. Since the external surface area is unchanged and the heat is dissipated to the environment the same, then the continuous power limit is virtually the same as from the factory with only air sealed inside. We don't typically operate continuous, so oil cooling will provide some benefit, but I certainly don't see it being better than air cooling, which I've proven to double the continuous power handling of my motors. I get on the highway running at high speed, and I have to climb mountains, so I have to build for continuous operation, and I have no interest in running motors past stator saturation.
John