Please take me back to school battery electrics

[WheezyRider]

The hub-motor is spinning relative to the air, so it's like fan-assisted cooling, and it has a much bigger surface area to lose the heat from.

The surface area of an exposed on one side crank motor is 2piRL + piRR. For a hub motor it's 2piRL + 2piRR.
A BBS01 is about 4" dia and 4" long, and a typical 350w hub motor is 7" dia and 4" wide
That gives 62.8 sq ins compared with 241.9 sq ins. That's a massive difference, and when that hub-motor's surface is moving through the air much faster, it can probably shed about 8 times as much heat.

I can see your point, but in a hub motor, heat has to pass through two air interfaces before it can reach the outer hub surface, whereas crank drive coils can radiate directly to air through the casing. Also, there is good contact to the frame for heat conduction over a larger surface.

This guy calls hub motors "toast in a toaster" Would be interesting to see if someone has done some thermal measurements for crank vs hubs.

No One Gives A Rat’s Ass About Your ‘Street Legal’ Ebike : Build Something Awesome

Whenever I surf the web to find out what is happening in the ebike industry I get pretty depressed. The US ebike market is a wasteland of cheap underpowered hub-powered ugly ebikes and overpriced u…

electricbike-blog.com

 

[Sturmey]

One reason why I gave up on mid drive, although I use low gearing I just don't have a high cadence. I have the stamina but not the power to continually shift high rpm.
Hubs are so more forgiving though I gearing still needs to be used.

One thing that someone suggested and I tried lately was fitting shorter cranks to the middrive. In my case, I used 155mm steel cranks from an old 24 inch youths mountain bike and ground off the chain wheel. The shorter cranks make it a lot easier to pedal faster. It does reduce the torque a little but this is possibly only a problem with torque sensor bikes without throttle or custom software.

 

[vfr400]

I can see your point, but in a hub motor, heat has to pass through two air interfaces before it can reach the outer hub surface, whereas crank drive coils can radiate directly to air through the casing. Also, there is good contact to the frame for heat conduction over a larger surface.

This guy calls hub motors "toast in a toaster" Would be interesting to see if someone has done some thermal measurements for crank vs hubs.

No One Gives A Rat’s Ass About Your ‘Street Legal’ Ebike : Build Something Awesome

Whenever I surf the web to find out what is happening in the ebike industry I get pretty depressed. The US ebike market is a wasteland of cheap underpowered hub-powered ugly ebikes and overpriced u…

electricbike-blog.com

Let's make it easy. Bafang crank motors often blow the controllers and strip the nylon gear because they get too hot. Hub-motors just soldier on. I'm working back from that position.

 

[WheezyRider]

One thing that someone suggested and I tried lately was fitting shorter cranks to the middrive. In my case, I used 155mm steel cranks from an old 24 inch youths mountain bike and ground off the chain wheel. The shorter cranks make it a lot easier to pedal faster. It does reduce the torque a little but this is possibly only a problem with torque sensor bikes without throttle or custom software.

That's interesting. A while back I read that standard 175 mm cranks are too long for most people, often leading to knee problems, but the industry is fixated on 175 mm.

 

[Deleted member 33385]

Passive CPU coolers made of copper can be pretty effective - totally silent, no fans, therefore less to go wrong. Like this one, which won't do me any good, because the databse and graphics work I do would cook my CPU with this attached.

Nofan CR-80EH Copper IcePipe 80W Fanless CPU Cooler for All Intel & AMD CPU's

Buy from Scan - Nofan Copper IcePipe CPU Cooler, 80W, Fanless, For All Intel & AMD CPU's

www.scan.co.uk

... it'd supply sufficient cooling (depending on fanless case airflow) on a low loaded CPU on a media playback machine though (with a fanless power supply, and SSDs), if you want zero noise whilst listening to or watching Pink Floyd or whatever, without that annoying constant PC buzz. On the BBS01b, I'm starting to wonder if increasing the motor's surface area by attaching copper or aluminium heatsinks with long vanes attached to heatpipes...

Heat pipe - Wikipedia

en.wikipedia.org

..drilled into and meandering in and out of through the motor casing, would provide passive cooling worth putting in the effort to bother. Or heatpipes woven through the casing, and through a circular radiator running all the way around the motor... airflow would do the rest. Certainly more than it does now.

Or I could just try to find a metal cog to replace the nylon. There's one for the BBSHD:

Hallelujah : The BBSHD Steel Gear Is Finally Here

For years I’ve been anxiously awaiting someone getting their act together and mass-produce a steel gear to replace the crappy nylon gear in the BBSHD. The mad scientists at Lunacycle have des…

electricbike-blog.com

Other Bafang steel cogs:

Replacement gear cogs for Bafang 250 W motors.

Tune your motor with these planetary gears or replace worn gears. Nylon gears are the standard used in many geared motors. Please select the…

www.ebike-solutions.com

When the warranty runs out, I'll open the motor and see what nylon cogs I can replace with metal - "Full Metal Bafang" coming up! I've heard tale somewhere of Bafang 48V 750W controllers being compatible with the 250W BBS01b.

 

[Deleted member 33385]

One thing that someone suggested and I tried lately was fitting shorter cranks to the middrive. In my case, I used 155mm steel cranks from an old 24 inch youths mountain bike and ground off the chain wheel. The shorter cranks make it a lot easier to pedal faster. It does reduce the torque a little but this is possibly only a problem with torque sensor bikes without throttle or custom software.

Yes that is very interesting! I may actually try that. Bloomin knees!