It'll allow some small amount of airflow into the casing. That may keep the rotor bell with the magnets on it cooler (assuming the common outrunner motor design inside the hubmotor).
The rotor bell itself still keeps the majority of the stator and windings from seeing much, if any, of that airflow; depends on the motor design.
Some rotor bells have holes in the side facing the clutch (usually completely open on the other side), which may allow more airflow, but the clutch and planetary gearing is usually in the way of any straightforward airflow.
Those are part of the problem with heat retention in a typical geared hubmotor to begin with, before even looking at modifications.
OTOH, all the moving/spinning parts inside may cause even more air circulation than you'd get with a DD hubmotor.
Either way, remember a geared hubmotor typically has grease inside on the gears, and holes that let enough air in to do any good will also let in dust and road debris. In a DD hub that's not typically a problem, as there's nothing for it to stick to (unless it's metallic and can stick to the magnets, like some of the bits from worn-out steel-belted tires that gets thrown up in the air by traffic), and even then the surfaces don't mesh together or contact each other anyway.
But the grease gives that stuff something to stick to, and if it is abrasive and ends up in the gear teeth meshing surfaces, it will wear them faster than normal. The clutch's working surfaces may also wear faster from abrasive dust settling on it, even if it isn't greased.
It might not be an issue, especially if you know you'll replace the clutch/gears anyway over time, as they can break and/or wear out even in a sealed motor, especially when used at high enough torques / power levels to require ventilation in the first place.
If you put filters over the air holes, you'd need active powered fans of some type to create suction to pull air thru the filters, otherwise probably not get any significant airflow. The fans may need to be a type that normally moves a lot of air to get just a little thru a filter, depending on the whole system design.
Water intrusion could be an issue as well, if the clutch is made of corrodable steel, but if the holes are large enough then water should evaporate quickly and be even less of a problem than in an unmodified hubmotor that gets water in it. (A DD hubmotor can be coated with anticorrosion/waterproofing materials internally on every surface, but the gears and clutch in the geared hubs cannot, on their working surfaces).
Not much hard data on doing this for geared hubs; most of the threads I've read over the years that have discussed it went thru the above issues and ended up using some form of oil instead, or skipped the whole thing entirely for one reason or another.
chuyskywalker said:
I've been diving through some of the posts here about air cooling by drilling holes into the side plates of direct drive motors, but I can't seem to find any info about the effects of this on geared hub motors.
Is there any info about this that I've missed? Seems like it would be super helpful given that these motors have all the same heat transfer issues that a DD drive has...and then it's wrapped in another layer of metal cage
Clutch welded for strength and regen braking as "bonus".
