Heat Sink for Geared Motors?

[Rifle]

Has anyone contemplated or tried making it a heat sink for a geared motor so it would dissappate heat like a larger direct drive motor? Given how quiet Amped Bikes new geared motor is, the inferior cooling is the only negative I can see between direct drive and geared. Well and the maintenance, but that seems totally worth all the benefits.

 

[John in CR]

More surface area on the outside will help, but it's need even more on the inside.

FWIW, I'm just about finished with ventilation of one of my Fusin geared hubs. Included is greatly increased size of phase wires, and I'm looking at bringing the max power up to 2-3kw. I'm sure the plastic gears will be the next failure point, and I've already started looking for a steel gear like has been done with the Bafangs. This motor will be used outside the wheel, so I'll make a housing to prevent dirt and rocks from getting into the motor while still permitting fresh air flow.

Depending how this goes, I may use a ventilation strategy on my other Fusin geared hub that allows the motor to be used in the wheel. With that fast spinning motor inside of the motor housing creating a lot of spinning air flow, and the fact that you can cut into the perimeter of the housing between the spokes, I think ventilating them could work very well for those who don't ride in bad weather.

John

 

[fechter]

Right, putting more fins on the outside will help, but not that much. What's needed is better heat transfer from the windings to the outside case. Even with all the fins in the world on the outside, the inside could still overheat.

Other possible approaches are drilling out the side cover to vent the housing (dirt/water could get in) or it might help to put small 'fins' on the magnet rotor to get some air flow inside the hub which would help transfer heat to the outside case.

Normally, there's pretty good air flow over the outside housing when the bike is ridden, so heat dissipates well when you're moving.

 

[dogman dan]

The hot spot is the axle itself, but I doubt finning the axle would do as much good as ventilating. But then you have dirty air going through sticky gear grease potentially. I'd like to see a real workhorse gearmotor. Not really a fast one, but a big one. This would combine the mechanical advantage of a 5304's large diameter and mass stator with a planetary gear setup. It wouldn't cool better so much as take longer to heat up. And be able to haul just about anything up 20%. Fins on dd hubmotors seem like such a good idea, to cool the magnets around the rim, I wonder why nobody is doing it. I'm talking about on the motor body, not the covers.

 

[The Mighty Volt]

Maybe carrying a small carbon-dioxide fire extinguisher and blasting the exterior of the hub would force heat to move from a place of high temp to a much colder part of the hub.

 

[John in CR]

Yes, the axle of a gear hub motor has a much lower flow resistance in the heat circuit from the stator. The distance the heat must travel from the windings is much shorter, and the relative thickness of that metal-to-metal heat pathway is greater, compared to a direct drive hubmotor, which results in a hotter axle on the geared variety.


Because those axles do get fairly hot, an idea might me to dissipate heat faster there. I'm thinking something like those plastic axle end protectors, but threaded and made out of aluminum with a larger and/or multiple disks to act as heat sink fins. I don't know how much effect it would have, but every little bit helps.

 

[dogman dan]

Yep, do it all is the thing in hot climates. Since it's so dry where I am, I found the fastest most effective method to be stopping awhile, and putting a wet rag over the hub, and periodically pouring more water over the rag. I do this at a water fountain 3/4 of the way home at the base of the big hill. Then I can climb the hill by starting cooler. Nothing cools the motor as fast as stopping for a bit. Having a thermometer on the motor helps a lot with learning what works and what doesn't. Below 90F, slowing down for a mile cools the motor, above 90F, only stopping cools the motor.

 

[The Mighty Volt]

Yep, do it all is the thing in hot climates. Since it's so dry where I am, I found the fastest most effective method to be stopping awhile, and putting a wet rag over the hub, and periodically pouring more water over the rag. I do this at a water fountain 3/4 of the way home at the base of the big hill. Then I can climb the hill by starting cooler. Nothing cools the motor as fast as stopping for a bit. Having a thermometer on the motor helps a lot with learning what works and what doesn't. Below 90F, slowing down for a mile cools the motor, above 90F, only stopping cools the motor.

Which is why I think CO2 cartridges might be a good idea...hell, even a tin of deodorant could double as an emergency coolant, just by blasting it onto the hub. Or a small bottle of meths, or rubbing alcohol. The meths would be evaporated by the heat as fast as you can spray it on, and is sure to to cool the metal some.

 

[davespicer]

I'm thinking something like those plastic axle end protectors...

And on the side where the wires exit, it could help protect 'em in the event of a spill.

Instead of a thread-on thingie with fins, what about a larger piece of stock which ran up alongside the forks? More mass, more surface area, more airflow across it... and imagine the styling possibilities. Me, I'm thinking Buck Rogers

 

[John in CR]

I'm thinking something like those plastic axle end protectors...

And on the side where the wires exit, it could help protect 'em in the event of a spill.

Instead of a thread-on thingie with fins, what about a larger piece of stock which ran up alongside the forks? More mass, more surface area, more airflow across it... and imagine the styling possibilities. Me, I'm thinking Buck Rogers

Just keep in mind you want good contact with that hot threaded axle, so something threaded and even some thermal grease. A chunk of metal is beneficial for short-term needs, but the thermal transfer process is a pretty slow one anyway, especially through the steel axle, and in continuous operation what matters is surface area unless you are able to somehow stimulate a change in the flow over the surfaces.

 

[dogman dan]

Re the CO2, wouldn't a little flask of liquid nitrogen be.....Cool. But as I've said before many times, a huge diameter bearing on the hub would allow an axle with lots of room for all kinds of things. Forced air cooling, water cooling, fatter power wires, integrated torque arms, etc etc etc. Even small quantities of forced air going into the motor would allow tons of heat out. But current designs don't allow much room in the axle for it.

 

[John in CR]

Re the CO2, wouldn't a little flask of liquid nitrogen be.....Cool. But as I've said before many times, a huge diameter bearing on the hub would allow an axle with lots of room for all kinds of things. Forced air cooling, water cooling, fatter power wires, integrated torque arms, etc etc etc. Even small quantities of forced air going into the motor would allow tons of heat out. But current designs don't allow much room in the axle for it.

Dogman,
I'm installing a bearing in left side cover with an inner diameter of 50mm. Real phase wires and intake vents will be there. The exit vents are between the spoke flanges, making it a "squirrel cage" type centrifugal fan. It should make for a great little stoke monkey type of drive. I hope the gears hold up. Pics soon. I just need to make the piece for axle to bearing and swiss cheeze it.

 

[dannyboyohyeah]

I thought about this and did a little experiment.
I took various sized rubber grommets...you know...the ones you can get at Ace hardware in quite a variety of diameters and wall thicknesses, for passing wires through something, like an 1/8" panel...took various of these, cut out circles of an old innertube and rubber cemented them to the outside face of the grommets. (to keep out the water). The holes in the side-casing would need to be evenly spaced and placed, =distance from center to balance. So you keep a fistful of these onboard somewhere. When it starts to rain, you pop them into place. (this is of no help to you dirt-riders, I'm afraid). The rubbercement bonded quite well. Trim them to perfect afterwards. Voila....perfect for those Arizona-like afternoons, I believe. I'm going to try it, anyway. You might want to wait for a test result to see how the roadgrime really gets in there.

 

[amberwolf]

There are also versions of those grommets made with a barrier already in them, which you simply poke a hole in or cut out as needed to pass wires thru. Some are pre-slit in quarters, like the ones in automotive firewalls, but you'd want the ones with no pre-slit.

Just in case you don't want to deal with the cutting and gluing.