Learning Curves Bafang BBSO2

With the BBSO2 installed on Rover II the real lessons begin. Curiosity killed the cat. What will it do to Rover II's chain line? Let's review the goals

1. I want to cruise comfortably regardless of headwind, hills, or hard rolling resistance without wrecking my knees
2. I still want a comfortable but reasonable amount of exercise. As long as the pedals go round my leg muscles are gaining
3. High speed is not a goal with 20-30 kph on the open road  reasonable for my area. The legal e-assist speed in Ontario is 32 kph.However you can coast as fast as you want unassisted. In Minnesota its 20 mph e- assisted or otherwise. 
4. I want to meander along at 10-15 kph on the walks and trails in town where there is significant pedestrian traffic
5. I want to be able to go further, finding over 35 km per trip on my home route unassisted is about all my knees will tolerate.  50 to 70 km on a charge would be nice.

My kit included a new 750C colour display. It was just released and like most things e-assist, instructions were scant. A link on the Luna Cycle Forums https://electricbike.com/forum/forum/ask-lunacycle/luna-cycle-new-products/32467-new-750c-color-display-for-bbshd-and-bbs02 got me started. This display has a few bugs and shortcomings I hope will be addressed by a firmware upgrade in the near future, but on the whole it seems decent. I have not changed any of the controller settings that came with the unit. They are the stock settings as supplied by Luna. I have a programming cable and will look at them in the future.

The main screen combined digital and graphic displays provide an uncluttered easily readable info on speed, watts consumption and assist levels. Smaller print provides more info on trip, odometer, battery level, time and other items you would expect on a bike computer. There are some issues with glare under certain conditions, but still generally fine for me. Navigating around the computer brings up a whole bunch of info I do not understand and is not yet active for the BBSO2.

The one main change I have made is to the E-Assist Levels. I changed it from the default 5 to 9. This fit my route conditions and my style  better. Now in Level 1 power consumption appears to be around 90 watts and for much of my paved route without a headwind I run in 6th gear at 21-23 kph.aiming for a cadence of 60-70 rpm.With a stiffer headwind or grade I go to Level 2 and appear to be drawing 170-190 watts, Really ugly northwind the other day, I went to Level 3 drawing about 300 watts. Don't know how accurate that watt readout is and it bounces around a fair bit you look for an average.

I also changed the speed limit assisted maximum to 32 kph to be in accordance with Ontario law. It does work and interestingly the throttle assist only increases the speed to that max. Also higher e-assist levels will draw higher watts up to the speed limit and then cut back to lower watts. The level seems to 'hunt' for proper wattage when you are against the upper speed limit, but is more stable when 3-4 kph below the max. Hmmm?

On a bit of a down grade with a tailwind I use Level 1 in 8th gear running  29-31 kph with a 65-70 cadence. Again wattage drops way down at 31-32 as no load.(There is no cadence readout on this computer I just calculated  using BikeCalc.com) Here I may do some coasting and stop cranking in which case the power assist stops and you pump again when you want/need it.
I've found setting the lower level of assist now in Level one more my style when riding slower on variable gravel road surfaces, even running in a lower gear.

Shifting and pedaling with a PAS e-assist rather than a torque sensor like in the Tongsheng TSDZ2 or some of the other OEM mid-drives i.e.Yamaha. Bosch is described as a little different, but the essentially the same problem. (No personal experience on other systems) You don't want the e-assist pumping out power when you are trying to shift.

On the BBSO2 this is easily accommodated , particularly on a trike. Some use a gear shift sensor, but I think they are wholly unnecessary on a BBSO2. Think of it as driving a stick shift particularly truck carrying a heavy load. When you pause pedaling the chainring stops (it's right in front of you and very visible) as power to it is shut off, and will not start until you resume pedaling. Shift your gear- up or down- and turn the pedals a little bit -sixth or quarter turn- and a little shot of power will spin the chain ring a bit pulling the chain through the rear derailleur smoothly without undue stress on the chainline as you have only momentarily sent power to the chainring. You cannot of course change gears at a complete stop or under heavy load without the 'crunch' on the rear sprocket, just like you cannot engage gears on a stick shift under heavy load or at a full stop without  properly using the clutch. Sound complicated? It's not.

Never operated a trike with a Nuvinci hub, but bet it would be sweet with this e-assist.

Finding the proper cadence is important on I believe all e-assist, as DC motors have efficiency curves. The BBSO2 'sweet spot' appears to be in that 60-70 rpm cadence. Maybe even faster but I find higher cadences uncomfortable and subject to fishtailing. Certainly 20-30 rpm cadences don't feel like they are putting out power comparable to what the watt meter is showing.

								Speed KM per Hour				at Cadence			24" Wheel
Gear	Cogs	5	7	9	11	13	15	17	19	21	23	25	27	29	31	33	35	37	39
8	48x11	10	14	18	22	26	30	34	38	42	46	50	54	58	62	66	70	74	78
7	48x13	12	17	21	26	31	35	40	45	50	54	59	64	69	73	78	83	87	92
6	48x15	14	19	25	30	35	41	46	52	57	63	68	74	79	84	90	95	101	106
5	48x17	15	22	28	34	40	46	53	59	65	71	77	83	90	96	102	108	114	121
4	48x20	18	25	33	40	47	54	62	69	76	84	91	98	105	113	120	127	134	142
3	48x23	21	29	38	46	54	63	71	79	88	96	104	113	121	129	138	146	154	163
2	48x26	24	33	42	52	61	71	80	90	99	108	118	127	137	146	155	165	174	184
1	48x34	31	43	56	68	80	93	105	117	130	142	155	167	179	192	204	216	229	241

In town when I don't want/need e-assist, I simply reduce to Level 0. The freewheel clutch in the drive motor incurs no drag as nothing in the motor is turning. Do not notice any difference in pedaling resistance between this and a simple bottom bracket.

The BBSO2 has a Thumb variable throttle control I rarely use. It has amazing torque that would certainly shorten the chainline life and perhaps the internals of the BBSO2 as well as the battery range if used injudiciously. But it is always available regardless of Assist Level as long as power is on. occasional boost going up a hill. Very handy for spinning the chain line when I have the trike suspended and setting up the shifting on the rear derailleur. On a test across a level strip the trike would quickly spin up over 30 kph, but was drawing over 900 watts so would quickly drain the battery.

Ride is as smooth with 20.5x2.12 Big Apple fronts and 24x2 Knobby rear. In fact it seems as good at 25 kph as it was at my humble 15 kph I used to ride unassisted. it is virtually silent, with the knobby rear tire and the chainline tubes providing the most noticeable sound. Gravel roads are readily navigable, with the only caution really loose gravel and washboard.

Range. Not sure yet. I have done 50 km on a combination of gravel and tarmac roads with a bit of grade and some headwind. Voltage showed I was down to 46.2 at end of trip. Battery voltage 'sags' during operation and then rebounds a volt or two after a few minutes rest. Motor gets barely warm to the touch sometimes and battery case not at all. I have been charging the battery in slow mode to 80 or 90%capacity with the occasional charge to 100% as recommended.