Tag: Improvements

Making the world a better place, one piece at a time

Bafang BBS02: Improved Motor Reaction Spacer
The original BBS02 reaction spacer for Gee’s Terry Symmetry didn’t work quite the way I expected:

Bafang BBS02 – reaction block displacement

The motor evidently vibrates enough to propel the block forward, shearing the double-sticky foam tape which was never intended to resist force in that plane. I thought the block was located at the point where the motor casing was tangent to the frame tube, so as to equalize the forces in both directions, but … nope.

A revised design based on measurements informed by new knowledge:

Terry – Bafang motor spacer – improved – solid model

The upper curve is now symmetric and the whole block mounts more rearward under the bottom bracket lug, where some tedious work with a machinists square located the real tangent point:

Bafang BBS02 – reaction block improvement

The motor sure doesn’t look like it’s tangent, but a dry fit showed all the curves laid against the case and tubes.

The brazing fillet means the step fitting the downtube can’t sit snug against the edge of the lug, but most of the reaction force should go through the section into the lug, near the center of the block.

A crude marker will keep track of any motion:

Bafang BBS02 – reaction block marker

I think the symmetric curve against the motor has enough projection to keep the block from wandering off, even if I haven’t gotten the location exactly right.

Stipulated: H ope is not a strategy.

The OpenSCAD source code:
```
MotorOD = 111;              // motor frame dia
MotorOffset = 10.0;         // motor OD tangent wrt lug edge
ShiftSpace = 6.0;           // motor to frame space

LugLength = 25.0;           // length of section over BB lug

Spacer = [5.0 + LugLength,DownTube[ID]/2,4*ShiftSpace];
SpaceAngle = 0*atan(1.8/Spacer.x);            // tilt due to non-right-angle meeting
echo(str("Spacer angle: ",SpaceAngle));

module MotorSpacer() {

    difference() {
        translate([LugLength - Spacer.x/2,0,0])
           cube(Spacer,center=true);
        translate([0,0,DownTube[ID]/2])
            rotate([0,90 + SpaceAngle,0]) rotate(180/FrameSides)
                cylinder(d=DownTube[ID],h=DownTube[LENGTH],$fn=FrameSides,center=true);
        translate([DownTube[LENGTH]/2,0,DownTube[ID]/2 - DownTube[LENGTH]*sin(SpaceAngle)/2])       // concentric with ID
            rotate([0,90 + SpaceAngle,0]) rotate(180/FrameSides)
                cylinder(d=DownTube[OD],h=DownTube[LENGTH],$fn=FrameSides,center=true);
        translate([MotorOffset,0,-(MotorOD/2 + ShiftSpace)])
            rotate([90,0,0]) rotate(180/48)
                cylinder(d=MotorOD,h=2*Spacer.y,$fn=48,center=true);
    }

}
```
Nothing like actual riding to reveal what needs more thought!
2021-07-12
Seedling Shelter Frame Deployment

Mary bound up a mesh cover for the shelter frame and deployed it to protect some yummy seedlings:

Seedling Mesh Shelter – installed

Those will become the next round of lunchtime sandwiches:

Turkey Sandwich with Excessive Lettuce

It’s a quarter-pounder: 4 oz of turkey, 4 oz of lettuce, and a layer of Swiss and good stinky Provolone cheese. Yum!

2021-07-11
Tour Easy: Amber Running Light
Having seen a few bikes with amber “headlights” and being desirous of reducing the number of batteries on Mary’s bike, this seems like an obvious first step:

Fairing Mounted Side Marker – First Light

It descends from the fairing flashlight mount with an entry to suit a 15 mm truck side marker body:
```
LightBodies = [
  ["AnkerLC90",26.6,48.0],
  ["AnkerLC40",26.6,55.0],
  ["J5TactV2",25.0,30.0],
  ["InnovaX5",22.0,55.0],
  ["Sidemarker",15.0,20.0],
  ["Laser",10.0,30.0],
];
```
The rest of the code gets a few cleanups you’d expect when you compile code untouched for a few years using the latest OpenSCAD.

The markers are allegedly DOT rated, which matters not for my use case: SAEP2PCDOT.

The mount is grossly overqualified for a wide-beam light with little need for aiming:

Fairing Mounted Side Marker – test light

Eventually, the marker should slip into a prealigned cylindrical holder, with a dab of epoxy to keep it there.

The lights are a buck apiece, so there’s no reason to form a deep emotional attachment. They are the usual poorly molded and badly assembled crap, although the next step up from a nominally reputable supplier is a factor of five more expensive.

It’s generated for the left side of the fairing, although I think having a pair of them would improve conspicuity:

Fairing Mounted Side Marker – installed

Being automotive, it runs from a 12 V supply, which comes from a boost converter driven by the Bafang 6 V headlight output. The absurdity of bucking a 48 V lithium battery to a 6V switched headlight output, then boosting it to 12 V to drive a single amber LED with a 1.5 V forward drop does not escape me.

It’s possible to slice the lens off (using a lathe), remove / replace the resistor, then glue it back together, which would be worthwhile if you were intending to drive it from, say, an Arduino-ish microcontroller to get a unique blink pattern.

Given the overall lack of build quality, it might make more sense to slap a condenser lens in front of a Piranha LED.

Bonus: contrary to what you (well, I) might expect, the black lead is positive and the white lead is negative.
2021-07-06

Bafang BBS02: Assist Power Levels

Although Gee’s Terry Symmetry is sized for female bodies, I managed to ride it up and down the driveway while watching the power display:

Voltage		52.5
Rated Current		24
Max current		18
			Power	Power
PAS	Assist	Amp	Calc	Observed	Ratio
0	0%	0.0	0	0	~
1	4%	0.7	38	26	69%
2	6%	1.1	57	52	92%
3	9%	1.6	85	78	92%
4	13%	2.3	123	104	85%
5	20%	3.6	189	182	96%
6	30%	5.4	284	258	91%
7	50%	9.0	473	453	96%
8	85%	15.3	803	675	84%
9	100%	18.0	945	900	95%

Bafang BBS02 on Terry Symmetry – actual voltage

The variations in the last column suggest my data-taking is … wobbly, at best.

I think the displayed power does not come from actual current and voltage measurements, because recalculating the power using the nominal 48 V battery value produces an unnatural agreement:

Voltage		48
Rated Current		24
Max current		18
			Power	Power
PAS	Assist	Amp	Calc	Observed	Ratio
0	0%	0.0	0	0	~
1	4%	0.7	35	26	75%
2	6%	1.1	52	52	100%
3	9%	1.6	78	78	100%
4	13%	2.3	112	104	93%
5	20%	3.6	173	182	105%
6	30%	5.4	259	258	100%
7	50%	9.0	432	453	105%
8	85%	15.3	734	675	92%
9	100%	18.0	864	900	104%

Bafang BBS02 on Terry Symmetry – nominal voltage

The motor controller may measure the actual winding currents while generating the BLDC waveforms, but the values may not be available to the display at the end of the cable. If Bafang documented the commands & responses, we’d know for sure, but they don’t.

Those assist values come from Mary’s Tour Easy, a much heavier bike than the Symmetry, but the first few levels work well in my limited tests. The highest levels may be too peppy for Gee’s normal routes, but having some serious boost in reserve can defang (hah) the worst hills.

Terry Symmetry - Tour Easy — Terry Symmetry – Tour Easy

IMO, the bike would burn rubber at the motor’s full 24 A current …

2021-07-01

Bafang BBS02: Terry Symmetry Shift Sensor & Cable Guides

The Bafang BBS02 came with (because I added it to the order) what looks like a genuine shift (“gear”) sensor made by the original company in the Czech Republic:

Terry Bafang – shift sensor – installed

On a typical bike, it mounts against a cable stop with the cable housing holding it in place against its other end:

Tour Easy Bafang BBS02 – shift sensor – installed

The Terry Symmetry has only two lengths of housing: in front of the adjuster on the downtube and behind the stop brazed to the chainstay. In either position, the sensor would move as the shift cable flexed and (IMO) put unreasonable stress on the electrical cable running to the motor.

Yes, the Tour Easy has those same two lengths of housing, but the forward one joins a sheaf of wires & cables that barely moves.

Fortunately, the sensor fits neatly between stations 1 and 2 along the downtube, with a snippet of PTFE lIned housing holding it firmly in place, with the 3D printed battery mounting blocks including paths for both cables:

Terry – Bafang battery – all stations – solid model

The shift cable originally ran from the adjuster in the front to the guide under the bottom bracket along a slightly diagonal path I could not possibly match. Instead, the path is now parallel to the downtube from the front adjuster:

Terry Bafang – OEM shift stop

.. to the rear block, where it angles downward over the motor to the bottom bracket:

Terry Bafang – shift cable clearance

The front block at station 1 has a Delrin / acetal bushing to align the cable with the rest of the blocks:

Terry shift guide – acetal installed

Yes, it’s a round peg jammed in a hexagonal hole:

Terry shift guide – acetal hole

Turning it from stock is well within the capabilities of Tiny Lathe™:

Terry shift guide – acetal cutoff

For great slippery, a similar UHMW PE bushing supports the cable bend at the rear of the station 4 block:

Terry shift guide – UHMWPE installed

The Basement Laboratory Warehouse Wing disgorged an overly large rod taxing Tiny Lathe™ to its limit:

Terry shift guide – UHMWPE turning

Memo to Self: next time, just saw off a stub and move on.

2021-06-30
Bafang BBS02: Motor Reaction Spacer
The Terry Symmetry’s rear shift cable passes along the side of the downtube and through a plastic guide channel under the bottom bracket shell. The Bafang BBS02 motor must press against the bottom of the downtube, so the shift cable rubs against the top of the motor.

The solution is a small block shaped around the point of contact to cradle the downtube, the bottom bracket shell lug, and the motor case:

Terry – Bafang motor spacer – solid model

A strip of double-sided foam tape holds the block to the motor and the reaction force from the motor’s torque presses the block against the downtube:

Terry Bafang – motor reaction block

Seen from the other side, looking parallel to the shift cable, you can see the tight clearance:

Terry Bafang – shift cable clearance

The block holds the motor 8 mm from the downtube, just enough to give the cable some breathing room.

The block is slightly taller on its front end, because the motor doesn’t meet the downtube at a right angle:

Terry – Bafang motor spacer – tube angle – solid model

I determined the proper angle by taping waxed paper to the top of the motor, sticking a trial (non-angled) block to the downtube, coating its bottom surface with hot-melt glue, then squishing the motor against the block. The cooled glue was flush with the block on the rear and 1.8 mm thick on the front, a 5° angle over the 20 mm block.

Definitely easier than correctly figuring the geometry from first principles: tweak the model to include the measured thickness, compute the angle, tilt the tube, and print another block that fits like it grew there.

With the block in place and the motor held against the downtube, tighten the retaining nut against the “fixing plate” by giving it a few gentle whacks with a hammer, then tighten the jam nut.

The OpenSCAD source code snippet:
```
// Motor Reaction Block
// Holds motor away from downtube enough to miss rear shift wire

MotorOD = 111;              // motor frame dia
MotorMountRad = 85;         // BB spindle center to motor center
Space = 8.0;                // motor to frame space

Spacer = [20.0,DownTube[ID]/2,4*Space];
SpaceAngle = atan(1.8/Spacer.x);            // tilt due to non-right-angle meeting
echo(str("Spacer angle: ",SpaceAngle));

module MotorSpacer() {

    difference() {
        cube(Spacer,center=true);
        translate([0,0,DownTube[ID]/2])
            rotate([0,90 + SpaceAngle,0]) rotate(180/FrameSides)
                cylinder(d=DownTube[ID],h=DownTube[LENGTH],$fn=FrameSides,center=true);
        translate([DownTube[LENGTH]/2,0,DownTube[ID]/2 - DownTube[LENGTH]*sin(SpaceAngle)/2])       // concentric with ID
            rotate([0,90 + SpaceAngle,0]) rotate(180/FrameSides)
                cylinder(d=DownTube[OD],h=DownTube[LENGTH],$fn=FrameSides,center=true);
        translate([0,0,-(MotorOD/2 + Space)])
            rotate([90,0,0]) rotate(180/48)
                cylinder(d=MotorOD,h=2*Spacer.y,$fn=48,center=true);
    }

}
```
Mary’s Tour Easy didn’t need this block, because all the cables run elsewhere, but I did capture a piece of closed-cell foam between its vestigial downtube and the motor to prevent chafing.
2021-06-29
Bafang BBS02: Terry Symmetry Battery Mount Tee Nuts

The two middle mounting blocks under the Bafang battery plate have 5 mm holes for the screws going into the water bottle studs brazed to the frame. The outer blocks clamp around the frame and it seemed like a good idea to secure the plate to them, as well:

Terry Bafang battery mount – trial installation

Those two blocks have a recess for an M5 tee nut:

Terry – Bafang battery – station 2 – bottom view – solid model

I snipped off the prongs with hardened diagonal cutters and filed the stubs to a uniform height:

Modified M5 tee nuts

Applying a hot soldering gun to the plate melted the stubs into the block:

Terry Bafang battery mount – tee nut in place

An M5 screw with a wingnut atop a big washer kept the tee nut properly aligned while pulling it into the melty plastic; I was pleasantly surprised at the lack of drama.

A ring of JB Plastic Bonder urethane adhesive glued the nut to the block:

Terry Bafang battery mount – tee nut gluing

The adhesive starts out runny and flows under the nut, so there’s more surface in play than meets the eye.

Clamping the partially cured goo to the frame atop a layer of waxed paper squashes any protruding adhesive lumps flat and prevents them from marring the tube’s paint:

Terry Bafang battery mount – tee nut adhesive molding

Anchoring the battery to the bike at four spots makes it utterly immovable, which seems like a good way to ensure longevity:

Bafang BBS02 – Terry Symmetry full assembly

That’s a test assembly predating the cable management cleanup …

2021-06-28