Guys - all the talk of insanity level hot rodding is off topic. While I am very interested and very happy to weigh in on the topic I don't think this is the best venue. It dilutes the core theme - definitive testing. Supposition and anecdotes have their place elsewhere.
Thanks Ohbse, and John earlier, for trying to keep things on tract. ES is an open forum, but the purpose of this particular topic is to stay on a certain theme for the benefit of anyone following for concrete info, and I appreciate those who've kept the contributions on the subject of the actual thermal test results and related input, ever difficult a battle that seems to be.
Earlier I had posted this:
On that front, lots and lots of new test data with the MXUS motors on the way, this here is what is spinning in the wind tunnel right now.
What I wanted to experiment with here was using stationary
scoops to help direct airflow through the large open holes in the motor to encourage lateral airflow in and out of the hub. I've mentioned again
and again on this thread that the speed of air moving past the hub motor as a result of the bike moving forwards is MUCH faster than any relative rotational speeds from the hub spinning.
In the above example I folded some simple 'scoops' from aluminum sheet and had one zip-tied to the fork of the test stand, and another attached to the axle bolt. These are both things that could be attached with relative ease to an existing front or rear hub motor, and they allow for a much larger input 'capture' area than you can get with scoops that are bolted on the motor cover itself, but they're also potentially more delicate.
For a reasons of happenstance the motor core under testing here was now potted, so I wanted to repeat all the testing I had done previously with this motor core with one modification at a time. That meant running the motor under the following possible scenarios:
a) drilled holes on 2 side covers
b) with the drilled holes and scoops
c) drilled holes and scoops and Statorade
d) drilled holes and Statorade but no scoops
e) Only Statorade (holes taped up)
The plain numeric test results for thermal resistances, running the hub at ~160 watts with the shell IR temperature taken just from the steel ring and not the side covers, is as follows
Plotted graphically, things are a bit easier to see. If we start with the stock unmodified hub motor, and then add the large vent holes around the perimeter, the thermal resistance drops in half on average, reaching a 116% improvement at 40kph speeds. Adding the scoops improves things by another 23% (40kph resistance dropping from .177 to .144 deg/watt). When we then add the 5mL or Statorade Ferrofluid, the thermal resistance improves another 31% still, dropping down to .110 deg/watt.
When we compare that to the the original unmodified motor at 40kph, the net resistance drops from 0.384 to 0.110, a 3.5 TIMES
improvement in thermal conductivity with the compounding effects of passive ventilation with scoops and Statorade. That is a massive total increase in heat shedding capability from the motor core, and it corresponds to almost a 90% increase in the continuous
current and torque capability of the motor. So yes, for those who had been wondering there is still benefit to the ferrofluid even with a motor that is already open and air cooled. I can't speak to the overall wisdom of having the FF in an open motor as far as long term contamination etc. but I can say that not a single drop spilled out from the motor during testing with the large holes and scoops for encouraging sideways air flow.
Now, approaching this result from the other direction of first adding the Statorade, then drilling the holes, and then adding the scoops, it's a similar progression
The Statorade by itself improves things by a factor of 2, the addition of large vent holes leads to another 40-50% improvement, and scoops on top of this lead to another 20% gain.
Here it is with all the plots super imposed. Make of it what you like
If there is to be a rough conclusion from all this, it's that the addition of 5mL of ferrofluids is more or less equivalent to drilling large vent holes on both side covers of your hub motor, with both approaches roughly doubling the core to ambient conductivity, though the FF working a bit better at low speeds and Vent Holes having an edge at high speeds. The vent hole performance can be improved somewhat (~20%) with the addition of scoops to help direct air-flow through the hub, but a greater (30%) effect is had by adding FF, and the combination of all these techniques leads to a compounding benefit that is 3.5 times better than the stock hub.