Tire change #3 and #4

The previous Goodyear "Street" tire was showing cords after only 369 km (229 miles).  I replaced it with a heavy-duty "electric scooter" tire (QIND Q-211).  The scooter tire is a lot beefier, but the nominal size is the same, 57-203.

Initial inflation to 25 PSI caused a little tire rub (probably at the "hairs" that hang off).  Lowering the pressure to 10 PSI reduced rubbing.  Low tire pressure makes the contact patch wider, so more rubber is available to wear.  It also improves shock absorption, but raises rolling resistance (not so important) and the risk of bottoming-out (which is hard to quantify).  The operating weight of the front wheel is only 40-60 lb¹ (measured with a bathroom scale) and I approach large bumps slowly, so I think low pressure is ok.

This tire was super tight to put on.  I used 12" motorcycle tire levers and also zip ties to hold the seated bead against the rim while working the tire on.

For unknown reasons, after the tire change I had to adjust the V-brake left and right spring tensions a lot to prevent brake drag.

I recommend this tire for anyone who wears out multiple tires per year and is willing to deal with a tight bead and minimal clearance.

Update: The Q-211 tire lasted 3620 km.  It ended with a gradual flat (first one) and some cords visible.  I had periodically pumped it to 20 psi or so.  At softer, more comfortable pressure, the tire and tube slowly rotate against the rim because of driving torque.  This would cause the valve stem to rip out.

    

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¹ Equals 18 to 27 % of vehicle weight, depending on upper body position. Shifting the wheelchair rear wheels backward would improve the Firefly weight distribution but degrade manual wheelchair handling.

Door opener

Doors are difficult to operate with the Firefly on the wheelchair, because the attachment makes the wheelchair long.  After fighting with our home's entrance door one time too many, it was time to build an electric door opener.  This door has the peculiarities that:

1. Gravity pulls it shut.
2. The door sticks at the frame and does not fall all the way closed after cracking it open.

The opener is activated by Bluetooth remote control buttons.  It uses a motor attached to the wall to pull the door open by winding a string onto a pulley (after unlocking and cracking the door open by hand). Gravity makes the door fall shut when the motor releases the string. 

Main ingredients (total cost under $200) are:

• Stepper motor (Sparkfun ROB-13656)
• Pulls the door open
• Strong enough to open the door, but weak enough to not crush people or things.
• Motor driver (Sparkfun BOB-13752)
• Energizes the motor
• Raspberry Pi Zero W (MicroCenter)
• Receives Bluetooth signals and generates motion commands
• Talks to the motor driver via SPI.
• NEMA23 bracket (Amazon)
• Attaches the motor to the mounting board
• Mounting board (Amazon)
• A spare 10" x 10" wooden pizza peel that was in the drawer
• Holds circuit boards and motor
• Pulley / drum (McMaster 6245K214)
• Let the motor wind string like a winch.
• String (McMaster 2057T75)
• D-ring (McMaster 3076T35)
• Attach string to door
• Power supply (12 V, 3 A) from unused equipment
• Jumper wires (MicroCenter)
• Bluetooth LE buttons
• Initially "Scosche Tapstick"
• Later cheap "iTAG" buttons from eBay / China
• 5 Volt regulator (7805)
• Power the Raspberry Pi from 12 V supply.
• Miscellaneous: fasteners, pin headers

Some custom software on the Pi is needed to send appropriate commands to the motor driver, and dispatch these commands after receiving Bluetooth events.  So far, this system has cycled the door 476 times with only the occasional software tweak.

Tire change #2

Old: Schwalbe Big Apple (50-203, $25)
New: Goodyear 12" Street Folding (57-203, $15)

The rubber had worn through to the light brown base material in one spot.  Schwalbe Big Apple lifetime: 515 km.

The new size has minimal clearance.  To prevent rubbing, I had to adjust the fender (loosen screw at fork, push fender away from tire & re-tighten).

Tire change steps:

1. Flip Firefly upside down
2. Disengage V-brake
3. Unplug motor cable
4. Remove disc brake (5 mm Allen wrench)
5. Remove wheel (17 mm wrench)
6. Let air out of tire
7. Remove old tire with motorcycle tire irons and replace (easy peasy)
8. Pump to 30 psi
9. Reassemble

Note that despite its name, this Goodyear tire does not actually have a street tread, and I can't recommend it.

Battery boost

The Firefly gets its zip from the Lithium-ion battery.  Here are some tips:

To reduce cold-induced low-voltage cut outs, set parameter C12=0 (28 V).  See the S-LCD3 manual for information on various parameters, and how to change them.  This sacrifices some margin of safety. so keep your eye on the voltage display and try not to drain the battery below 33 V (at rest).  This is based on the following experience, which I believe was due to increased battery resistance at low temperature:

I rode a fully-charged Firefly to visit a friend where the distances were 10 km out and 7 km back. While there, I left the Firefly outside in 30 F weather. On the return trip, the unit cut out repeatedly. At first while climbing hills, but later on flat terrain. The display flashed an empty battery symbol and the motor went dead. After a few seconds, it would recover. At some point, I started watching the battery voltage on the display, and the cut-outs occurred at about 30 V. Final resting voltage was 35.4 V.

According to internet wisdom, keeping the battery fully charged for long periods reduces its lifespan.  But Micah Toll writes (he also has a website) that it should be fully charged "occasionally" to balance the individual cells.  Whether trying to maximize the battery lifespan is even worthwhile depends on personal circumstances.

The original battery (at least mine) is a 36 V, 6.6 Ah THUNDER-DT from a company in Kunshan, China called Reention (formerly ksreention).  DT stands for down-tube, the intended mounting location on a bike.

Rendering (ssztec) of the original battery with 30 cells (green).  The circuit board (blue) probably holds the battery management system (BMS).  

It turns out that Amazon lists a larger (taller) battery from the same manufacturer that fits the original receptacle.  [Update: AliExpress lists higher capacity models that are less expensive.]  Mine was rated for 11.6 Ah and upon receipt, I measured 11.85 Ah (see graph below).  This battery contains 40 cells (4 parallel x 10 series), and I believe the type is Panasonic NCR18650PF Samsung (perhaps 29E) with 2900 mAh capacity.

One notable difference is that the new battery always generates output voltage at the contacts and the pressing the "power" switch just shows the charge level.  On the old battery, this switch turned the battery output on and off.

Discharge test through a precision 75 Ohm resistor (red line) and battery voltage vs. distance traveled (blue circles) over several days.  The final range of 33.9 km is almost twice the original.  Energy efficiency is about 22 km/MJ, which is quite high.

To swap batteries, it is necessary to replace the original mounting rail with the longer one that accompanies the new battery.  While the taller battery will fit onto the original rail and can be taped to the frame for testing, it won't lock into place.

1. First unlock the old battery and remove it from the rail.  
2. Then remove the rail from the steerer tube (four 4 mm Allen screws)
3. Remove the battery base with all the wires from the rail (two 4 mm Allen screws) and leave the base hanging off the Firefly.  This box houses the motor controller that drives current through the motor.  
4. Attach the new, longer rail (which comes with the battery) first to the controller box and then the Firefly. 
5. Slide the new battery onto the rail and lock it in place.

Voilà, the Firefly range is almost doubled!

Summer, 2020 update:  About 3500 km later, the battery is going strong with about 40 km range.  At one point, a loose contact caused intermittent cutouts.  This was solved by taping the battery to the steering tube rather than relying on the rail lock.  Here are pix of the innards.

Fall, 2021 update:  After about 5000 km, the battery started cutting out and I replaced it.

Mud flap

Dirt, water and leaves were being sprayed up by the Firefly wheel. Especially the wheelchair's flip-back footrest mechanism was catching a lot of wet debris. The picture shows some of the schmutz after it dried (a lot already fell off and made a mess at home).

So I super-glued and taped a rubber sheet (cut to L x W: 5.25" x 5", 1/16" thick) to the fender. The mudflap is effective, and after many trips with plenty of wet leaves, nothing new has stuck to the footplate.  It reduces the open tire aperture to less than 1 inch from about 3.5 inches.  Because the material is flexible, ground-contact is not a problem.  In the photo, the bottom of the tape (2" wide Polyken) corresponds to the fender bottom. 

2/19/2019 Update: The link at the top shows pictures with a mudflap. So the manufacturer has either added one since mine was made, or removed it since the photos were taken.

Headlight location

Days have gotten shorter, and how should we pierce the inky blackness?  With a headlight of course, which the Firefly's designers helpfully included.  But the original location, so close to the ground was not ideal, and the battery above forced a near horizontal beam direction.  The shallow angle illuminated the ground in front poorly, and rudely shone up into people's faces.  For illumination and civility, it's better to place the light higher up and direct it downward.

Placing the Firefly's lamp higher, required disconnecting its HIGO connector and unscrewing from the mount.  Then I cut the cable halfway between connector and lamp, to splice in a few feet of extension (without crossing the wires).  Finally, I took an attachment clamp from an old bike reflector, to mount the lamp higher on the steerer tube.  Now the light is still weak and oddly blue, but it makes a useful bright spot, and shouldn't bother passersby.  The old light location is a good spot for a front reflector.

Tools and supplies needed:

• Old bike reflector
• Old USB cable for extension
• Wire cutter / stripper
• Soldering iron
• Heat shrink
• Electrical tape
• Phillips #2 screwdriver

September, 2020 update: At some point, I removed the stock headlight and have been relying on a handlebar-mounted Cateye AMPP800.  It is important to point the light downwards, to avoid blinding oncoming pedestrians.

Tire change

After 1000 km, the original tire (ETRTO size 47-203) was getting bald (not the only thing doing that), and it was time for a replacement.  The new tire is a Schwalbe "Big Apple", size 50-203.  The Schwalbe tire went onto the rim by hand and seems like a quality product.  The original was really tight and I used steel motorcycle tire levers to remove it.  Unfortunately I scratched the inner rim and didn't think of sanding down any sharpness before putting on the new tire.  Hopefully this doesn't cause a flat.

After loosening the outer wheel nuts, the axle had a 5 mm or so total gap between the inner wheel nuts and fork legs.  A pair of washers whose thickness matched the gap had been put on the outside of the fork, and the fork legs were being bent to close the gap.  Putting the washers on the inside allows the wheel to be mounted without bending the fork.

The V-brake needed adjustment to match the new wheel position.  Making this adjustment had the benefit of significantly reducing brake shudder.

PS: For reference, the inner fork spacing is 5.375" (137 mm).