bigmoose wrote:Thanks for the great data on oil cooling Burtie! I think this will become standard practice for high performance motors as we go forward. I saw how much this improved the "Power Dense" motor system developed at Bowling Green State University about 10 years ago, and strongly felt it was applicable to hub motors. Your data now proves the point.
This should now end any lamination/magnet corrosion issues, and bump power handling a bunch. I will also bet thermal soak hall failures are a thing of the past also.
Arlo1 wrote:WHat about drag at hi rpm??
itchynackers wrote:I still don't quite understand whether the oil is just delaying thermal soak (by the oil storing the heat), or if the oil is allowing the hub to dissipate more heat.
Edit: After re-reading the thread, it seems as though the oil transfers the heat quicker to the covers (making them hotter) so more heat is carried away with the same amount of windage. Is this correct?
andynogo wrote:Try a little bit less oil and drill a small (1mm) hole in the cover near the axle. Angle it so that it traverses from the central axis towards the outer circumference as you go from outside to inside. That way, when the wheel spins, any oil that happens to splash into the hole will be flung back inside the hub
andynogo wrote:I wondered about that too as the planetary gears will be spinning through the oil as well- but it didn't seem to make much difference during testing. Not that valid a test though as the windings are damaged- I'm putting a new 10 turn stator in it soon so will do thorough dry and wet tests with a set route, amps etc.
Reid Welch wrote:WHAT: running geared transmissions in light oil is a universal practice...except in these new, geared-type hub motors.
WHY: light oil cushions gear teeth, actually preventing contact of the pressure surfaces, through a phenomenon known as
hydrodynamic lubrication: the parts surf upon each other, oil as the separating agent. This form of lubrication prevents all wear
((think of your auto's automatic transmission, how quiet its helical gears run, and with no wear-out))
IS THERE LONG TERM HARM? Ans: No, not unless the oil were to somehow degrade hall sensor adhesive (unlikely, it seems)
Q: How much oil to be installed? A: Enough to fill the motor about one third full. Then, when running, centrifugal force
throws the oil at the perifery of the gear casing, bathing the soft steel ring gear and the plastic planets. Plus, oil contantly
washes all the bearings and constantly wets the lip seals of the axle. Some slight weepage at the axle "seals" is inevitable.
About heat and expansion: when the motor warms up, its contained air expands, and will push out a minute amount of oil.
Upon cooling down, the motor will slightly inhale some of this weeped oil.
Now, consider the stock (dry, not oiled) run in the rain: it will gradually ingest small amounts of water, eventually rusting internal parts to some small extent.
Oil is dielectric and has no effect on nylon gears nor synthetic rubber seals, which are DESIGNED to run in oil.
Oil, sloshing around the inside of the hub motor, is not of sufficient quantity to drown the rapidly spinning central rotor
of the motor, itself, so no fluid spray/strain/churn on the copper windings.
The oil will all be at the ring gear, surfing the planet gears, dampening noise, and fluid polishing the parts over time (perhaps)
to make, in time (thousands of running miles) a super quiet motor, with each planet gear tooth of the three planets, shoulder exactly the same amount of the load.
Benefit accrued: maximum robustness of the geared motor: it should never "peanut butter" any teeth, until some long-away day, when plastic fatique finally breaks off a tooth, which then spells instant destruction for all the remaining planet gear teeth.
hydro-one wrote:if your going though all the trouble to liquid nitrogen cool, may as well use a high temperature superconducting coil too
im rooting to discover one that works at room temp. solve all our problems.
dfar wrote:Just wanted to state that I tried the ATF cooling method and am really impressed with the results.
Before the introduction of the oil my HS3540 would get up to 90 Celsius +++ within 15min of heavy riding. With the ATF I cannot get the temp over 55 Celsius with full throttle riding. Overheating is now not the limiting factor in the performance of the bike.
I did not drill any vent wholes in the hub motor and sealed the sides with silicone. It seems a small amount of ATF leaks out through the bearings and axle and onto the sprocket. This unintended leak effectively "oils" the chain therefore I don't really have a problem with it.
The only thing I am thinking about altering is drilling and tapping a filling valve so one could top up the ATF without taking the side cover off the bike. Maybe make it into a filing/venting valve.
sounds good! what sort of power levels are you running/what size wheel? and when you say heavy riding, do you mean riding WOT lots with no pedalling?
dfar wrote:It seems a small amount of ATF leaks out through the bearings and axle and onto the sprocket.
bobale wrote:dfar wrote:It seems a small amount of ATF leaks out through the bearings and axle and onto the sprocket.
Wait a second. Bearings are usually greased with thick grease. How will introducing light oil affect their life? Will ATF wash off thick grease, and leave bearings dry if you decide not to put any more oil into the motor?
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