Ed Nisley's Blog: Shop notes, electronics, firmware, machinery, 3D printing, laser cuttery, and curiosities. Contents: 100% human thinking, 0% AI slop.
A great musical interlude on the patio announced an airlift of construction materials eventually producing this pile inside the top cover of the propane tank:
Carolina Wren – nest started atop propane tank
The male Carolina Wren switched from the Tweedle of Great Nestbuilding to the less musical Mighty Chirr of Disapproval, presumably because he noticed a mouse (or, perhaps, chipmunk) occupying the lower ring of the tank. Rodents and birds do not coexist well at all; I have no doubt a mouse would climb right up the tank for a supply of breakfast eggs.
I must blow the crud off the tank before the next fill.
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
IMO, the bike would burn rubber at the motor’s full 24 A current …
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.
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.
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 cablemanagement cleanup …
I clearcut a stand of spearmint and turned it into three jars of what should become mint extract:
Homebrew mint extract – start 2021-06-17
The left jar has 3 ounces of mint mostly covered with 80 proof vodka and the other two jars each have 5 ounces submerged in 180 proof grain alcohol.
Nine days later:
Homebrew mint extract – 2021-06-26
The vodka is now on the right and shows a weird layering caused by the leaves extending above the light yellow liquid; I’ve been inverting the jars every few days. The grain alcohol looks more like the previous iteration, with uniformly decolored leaves in dark green liquid.
A closer look:
Homebrew mint extract – vodka vs grain alcohol – 2021-06-26
What’s happening in the vodka jar does not look like a nominal outcome …
These two discrete LM3909 circuits recently stopped blinking:
LM3909 AA alkaline – Green and Blue
The green LED (on the left) took six months to wear its pair of not-dead-yet AA alkalines from 2.7 V down to nearly zero.
The blue LED in the radome took two months to go from 1.0 V (!) to nearly zero. It didn’t start very bright and went decidedly dim along the way, but the LM3909 circuitry still managed to jam a few microamps through the LED.
In both cases, one of the cells was reverse-charged by a few hundred millivolts, although neither leaked.
Both got another set of not-quite-dead AA cells and they’re back in action.
The Smell of Molten Projects in the Morning 