Category: Electronics Workbench

Over the decades, we have devoted considerable time and attention to adjusting the reach and travel of the brake levers on Mary’s bike, so I ordered a pair of brake sensors for the Bafang BBS02 motor to mount on the existing hardware:

The sensor is the black block secured to the brake mount (with good outdoor foam tape), with the bar magnet similar secured to the handle. The magnet ended up slightly off-center from the switch due to the overlapping joint between the lever and the mount; I can’t detect any difference from having it centered.

The Bafang switches included cute little disk-shaped neodymium magnets which weren’t suited for the levers and stuck out in all directions without getting particularly close to the sensor. As a result, the least pressure on the brake handle produced a hair-trigger switch activation.

So I harvested two bar-shaped magnets from a defunct Philips Sonicare toothbrush head, reducing the rather large assortment I’ve been saving for just such an occasion by one item. Each brush head contains a pair magnets attached to a steel backing plate, seen here after removing the lower magnet:

I don’t know how Philips attaches the magnets, but a few shots to the steel backing plate with a drift punch breaks the bond without any obvious damage:

Neodymium magnets have a nickel plating to prevent corrosion, but AFAICT the only way to know whether I’ve cracked the plating is waiting to see if the magnet falls apart. If it does, I promise to be more careful with the next toothbrush head.

They’re magnetized through the thinnest section, not along the length like an old-school bar magnet, but the disk magnets are similarly magnetized and I think the net effect is about the same.

The bars fit the brake handles more closely, put more of the magnet closer to the switch, and allow about 5 mm of travel before tripping the switch.

Pending more road testing, the switches seem more usable.

Protip 1: Demagnetize your tools after working with neodymium magnets.

Protip 2: Don’t put a loose magnet anywhere near your bench block, because it will shatter when it snaps onto the block from a surprising distance.

The shift sensor detects motion of the rear derailleur cable so the Bafang BBS02 can briefly cut motor power while the chain moves across the sprockets:

This should be a drop-in fit on most bikes, but the Tour Easy’s front brazed cable stop is a little shorter than the ferrule. Trimming a plastic tube poses little problem:

The ferrule now fits neatly in the stop, although the sensor casing sits at a slight angle because the stop’s centerline puts the cable slightly closer to the frame than the back of the sensor body will allow. You could mount it elsewhere, but the cable stop sits directly above the motor and doesn’t require an extension cable.

The sensor works wonderfully well, with the motor pausing for perhaps a second during the shift: just shift normally and it’s done.

A red LED (the small dot to the right of the label) blinks when the sensor detects a shift, so you can verify its operation on the work stand.

The Bafang BBS02 motor claims a 750 W power output, although I suspect that’s measured at the instant before it flings its guts across the test lab:

With a nominal 48 V battery supplying the motor’s nominal 24 A (some say 25 A) current, it dissipates well over 1100 W, although that’s obviously a short-term thing. With 750 W calling for 15-ish A, most likely it will (ideally) suffer thermal shutdown long before the battery runs out.

Torque being more-or-less proportional to current, its nominal 160 N·m torque at 24 A scales downward by the same factor as the current, for 100 N·m at 15 A.

The as-received Bafang BBS02 motor controller configuration provided far too much torque for our riding style; I think it’s intended for much younger folks tackling off-road trails on what used to be called mountain bikes, rather than assisting us with normal street riding.

For example, the default maximum current was 24 A and the first step of pedal assistance was 28% = 6.7 A → 45 N·m: a pretty hefty shove right off the starting line. The Tour Easy was pretty much uncontrollable in the driveway, which is a Bad Sign.

I started with the “Limitless” configuration (wherein the assistance for all steps continues up to the 20 mph overall speed limit) and reduced the maximum current to 15 A.

The first assistance step of 5% = 0.8 A → 5 N·m now compensates for the additional weight of the Bafang motor + battery and feels like the unloaded bike.

The second step was 37% = 8.9 A → 59 N·m and is now 7% = 1 A → 7 N·m, so Mary can ride along with a little oomph for minor hills.

The third step was 46% = 11 A → 74 N·m and is now 16% = 2.4 A → 16 N·m, enough for the admittedly gentle hills along Vassar Road.

The throttle uses the ninth step setting (100% = 15 A → 100 N·m) to provide a “get out of Dodge” boost at intersections.

So far, the BBS02 configuration file looks like this:

[Basic]
LBP=42
LC=15
ALC0=0
ALC1=5
ALC2=7
ALC3=16
ALC4=25
ALC5=37
ALC6=51
ALC7=67
ALC8=85
ALC9=100
ALBP0=0
ALBP1=100
ALBP2=100
ALBP3=100
ALBP4=100
ALBP5=100
ALBP6=100
ALBP7=100
ALBP8=100
ALBP9=100
WD=12
SMM=0
SMS=1
[Pedal Assist]
PT=3
DA=0
SL=0
SSM=3
WM=0
SC=10
SDN=5
TS=10
CD=8
SD=1
KC=100
[Throttle Handle]
SV=11
EV=42
MODE=1
DA=10
SL=0
SC=10

Mary says she’s getting entirely enough exercise and, frankly, so am I. We have yet to try faster paces and steeper hills.

For reasons not relevant here, Mary’s Tour Easy recumbent now sports a Bafang BBS02 Mid-drive motor:

It pretty much Just Fit, although the lithium battery sits atop mounts conjured from the vasty digital deep:

Many cables connect all the doodads, which a custom-made e-bike can hide inside the frame, but … that’s not an option for us.

The Bafang BBS02 kit is basically plug-n-play, at least if you own a standard-ish bike. I included some useful options for our setup:

• Mini color display
• 48 V 11.6 A·h “Ultra Slim” battery
• 2 A charger
• 46 tooth chainring
• Brake sensors for existing levers
• Gear shift sensor (original design)

Changing the controller parameters, usually called “programming”, required firing up the Token Windows Laptop:

• USB-to-serial adapter
• Quasi-official software
• Original hacked software
• Some background
• Detailed parameter descriptions

As you might expect, I set up a relatively sedate and low-powered pedal assist mode in place of the default rocket sled mode.

The motor design seems a decade old, so Bafang (née 8Fun) has had time to work out some of the original design misfeatures. It definitely has shortcomings, but nothing insurmountable so far.

Early results suggest Mary is now riding her familiar bike over much flatter terrain.

Some background reading:

• Bicycling magazine can follow the money
• Powered bikes are quasi-legal in NYS
• Why powered bikes are widely ignored

More on all of this as I compile my notes …