Nine Continent Vs. Bafang

[Russell]

I’ve said in the past that the overall efficiency of the Bafang geared motor and the Nine Continent direct drive motor on a bike are essentially the same and here is a bit more data to support that idea. I’ve recently upgraded to a 48V/10Ah LiFePO4 battery and have started a battery log where I record more detailed information than I normally record on my cycling log. Here is the trip data for my Kona/Bafang and my Raleigh 9C with the speed suppressor connected. The course is the same 31 mile route and the weather in each case was almost identical too.

9/11 Kona/Bafang/48V10Ah/15A controller

Distance: 31.1 miles
Average speed: 18.8 mph

Amp-hours used: 6.146
Watt-hours used: 312.9
Peak Watts: 791
Peak Amps: 15.31
Min Volts: 48.46

Wh/mi: 10.06



9/13 Raleigh/9C/48V10Ah/22A controller with speed suppressor

Distance: 30.9 miles
Average speed: 18.6 mph

Amp-hours used: 6.196
Watt-hours used: 315.1
Peak Watts: 1095
Peak Amps: 22.12
Min Volts: 47.36

Wh/mi: 10.20



The bikes are similar in components but they feel quite a bit different. The 9C equipped Raleigh is a hoot with the 48V battery and 22A controller. With the speed suppressor engaged the top speed on the flats is cut by 40% to about 18.5 mph with all assist gone by just over 21 mph. Acceleration from a stop is basically unchanged but then it slows considerably. You’d basically have the same situation if you installed some sort of mechanical stop on your throttle limiting it to 60%. It’s easy to cruise at 19-20 mph with normal pedalling but over that speed the bike feels ‘heavy’. The Kona with the 36V Bafang running at 48V will peak at 23.5 mph on the flats and has some assist all the way up to the high 20’s. With the 15A controller it requires more rider input on hills than even the restricted 9C but it feels livelier. In any event when I recorded the data for today’s ride I was struck by how close the average speed and power used for the two bikes were over the same course at essentially the same speed. In both cases I used the throttle for almost the entire ride.

The debate between geared and direct drive will never end but on the issue of efficiency I’d say from my experience it’s a tie. The DD motor’s inherent slightly higher motor efficiency is offset on the bike by its cogging torque and the geared motor’s slightly lower motor efficiency due to the mechanical gears is offset by its ability to freewheel.

-R

 

[jag]

The debate between geared and direct drive will never end but on the issue of efficiency I’d say from my experience it’s a tie.
-R

I think the conclusion is plausible, but I'm sceptical of any figures where an unmeasured amount of human pedalling has gone into it. I'm suspecting that even though one thinks one pedals with roughly the same power, actual power can easily vary 10-20% (or maybe more).

A more scientifically valid comparison would be to find a course where hills are moderate enough that both Bafang and 9C will get up w/o assist, pick a day with no wind, and then run the course at constant and equal speed with both motors.

(Sorry if this sounds too scientifically picky... that's what I do for a job.)

 

[Russell]

Oh I've got far more data than just the one example I posted above. I haven't done any statistical analysis on the data but with few exceptions the power I consume on a ride doesn't depend on which bike I ride, the Raleigh/9C or the Kona/Bafang, what determines how much power I use is how fast my average speed is. It doesn't even seem like hills affect the power I use much because I do circle trips and what goes up must come down. Also once in condition after the winter hiatus my input is amazingly consistent, I've even had back to back rides where I've used exactly the same amount of battery power over the same route at the same speed.

As I said the debate will go on because everyone has their own preconceived ideas and without a perfectly controlled test the results are always going to be in question. For me however there is little doubt, for the riding I do the motor makes little difference to the power I consume from the battery. However that said for purely assisted rides I prefer the Bafang and for mainly motor-powered rides I prefer the 9C.



-R