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Electric motor/hub gearbox considerations for the thoughtful



 
 
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Old March 24th 20, 03:57 PM posted to rec.bicycles.tech
Andre Jute[_2_]
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Default Electric motor/hub gearbox considerations for the thoughtful

On Tuesday, March 24, 2020 at 2:10:11 AM UTC, pH wrote:

I think I saw another Rohloff hub in the wild....drool, drool. I was driving, but don't think it was a hub motor. Saw no evidence of a battery bank anywhere.


My Rohloff is often mistaken for a hub motor, and even the SON dynamo in the front wheel is often so traduced. This despite the fact that an electric motor bigger than either sits in front of the bottom bracket.

the only ebike/kit I would consider would have to have the throttle-only option. I don't like being "told" I have to pedal to have motor assist. I want it whenever I feel like it if I want it at all.


Hang on.

First of all, let's agree that the pedelec paradigm is counterproductive. It makes the electrical assistance directly proportional to the rider's input at the pedals. Consider a hill. The cyclist's input normally falls off as he ascends the hill. The electrical assistance consequently declines with his declining input. Useless. The goes for breaking a heavily loaded bike away from a standstill even on a level supermarket carpark. Conversely, the cyclist is speeding downhill and pedalling madly to towards spinning out, the electrical assistance picks up proportionately. Why?

I can't speak for every maker of electrical motors or controller software; my experience is limited to installing Bafang aftermarket motors in a touring bike, one front motor, one central motor. In each case I shopped only with the dealers who didn't cripple the software.

The Bafang central motor BB** be bought bare, with a certain amount of self-protection software built in; it is probably already a pedelec. Don't buy it, regardless of how attractively priced it is.

Instead buy a full kit, either including or excluding the battery if you want to fit a bigger battery than available in any of the packages offered. The full kit includes a communication facia about the size of a large bike computer, and wiring to a controller with three buttons which between them can offer an amazing amount of programming, plus wiring to a throttle (only one -- if you want it on the other side of the handlebar from your Rohloff rotary gear change, you have to buy a different throttle control, about ten bucks), plus wiring for a motor cutout to work with your standard rim or disk brakes (switches for Magura Rim Hydraulic Brakes available but optional) which turns the motor off when you brake and on again the moment you let the brake lever go.

This bunch of wires and switches gives you access to the most important thing you want: it gives you a setting which delivers full power regardless of how the pedals are turning. It is very important that you buy a kit on which this facility has not been crippled. There's a whole bunch of stuff for which several years later I haven't even read the manual. There are two options of reprogramming everything, using the buttons on the switch I mentioned above, and a plug-in link operated by a computer, presumably useful to downhill racers; I didn't bother with it because the facilities on the full kit are already enough.

Now, having selected full torque availability at all settings, available through the thumb throttle, you now have a nine-speed electric gearbox/cruise control under the same thumb. It is smart to put the on/off and "gearbox" switch control on the same side as the thumb throttle so that you have to take your thumb off the throttle select another assistance or "gear" level.

Now, unless you're one of those unfortunates whose dick is stretched by the complication of his machinery, you don't really need to control nine levels of assistance. I worked out by abstruse math which I did by mental arithmetic of course (and had checked by proper engineers, not the clowns on RBT whose mathematical incapabilities you can check on any helmet thread here) that my hills and lanes (especially wet grass middlemen on the narrowest country lanes) required for my own safety and the bike's stability not change more than two electrical "gears" at once, especially in the lower *real* gear range of the Rohloff HGB on the same bike. So I reprogrammed the control electronics for five gears, which serendipitously turned out to be exactly right for my hills, my riding style (I came to cycling too late to learn a butterfly cadence, so I'm a masher), and my method of controlling my input by my heart rate, read off a monitor also on the handlebars. All of this programming was done with the standard on/off switch cluster's three buttons, which also switch on the lighting for the fascia, and provides a very useful parking facility where you walk beside he bike and it propels itself up stairs and so on. As standard the software will limit the speed of the bike to 15mph/25kph but the facilities allow you to choose any governed speed or none. The throttle overrides the "gear" settings.

Once you grasp how all this works, you don't need those huge 750 motors used by the country-side shredders and people too cheap to buy a real motorbike. 250W, or 350W if you're a heavyweight, will do fine; the important thing is not to skimp on the battery so you can have "a whole lotta coulombs" as Jeremy Clarkson would say -- the more Ah in the battery, the faster the rate of current delivery, which is why the reserve meter on the Bafang dash shows not the amp-hours available in the battery but the instantaneous current availability. I rode a 750W bike last year and didn't care for its suddenness, even though I rarely ride in traffic, and the owner who had a battery of the same size (huge) as on my bike complained about the limited range, about half the range on my bike. The lower-powered Bafangs are quite powerful enough, and more fun to ride, than the 500 and 750W models. A 350W Bafang motor is quite sufficient to turn a careless rider with a heavy thumb on the throttle over backward onto his head.

With the bigger Bafang motors a Rohloff or Pinion gearbox is essential because a Shimano Nexus or Alfine will be ripped apart; with the smaller motors a NuVinci may suffice if you take care to always start off on the throttle with the electric "gears" at zero. NuVinci also makes a model with an automatic gearbox, which after my experience with the Smover (a fully automatic Di2 for commuter bikes, including electronic active suspension, once sold in Europe to OEMs) I would heartily recommend.

(Curmudgeon alert.)


Too late.

A key thread on this subject is on a forum where lots of Rohloff equipped touring owners hang out, and several have over the last few years fitted electric motors; sorry about the digressions, but if you read the whole thing you will have a better understanding of electric motors with Rohloff HGBs than probably 99% of people who buy their electric bikes off the shelf:
http://thorncyclesforum.co.uk/index.php?topic=10883.0

Andre Jute
No hypocrisy he I gave up the car forever in 1992.
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