Off the grid

A FI­NAL OFF-THEGRID PURGE LED TO A PRAC­TI­CAL PROJECT THAT GAVE LOTS OF PLEA­SURE IN THE MAK­ING

The Shed - - Contents - By Mur­ray Grim­wood Pho­to­graphs: Mur­ray Grim­wood

— Mur­ray gets around to build­ing an elec­tric cargo bike so he can farewell the au­to­mo­bile at last

The off-grid men­tal­ity be­comes per­va­sive. You re­al­ize you don’t have to pay for — or main­tain — stuff that you don’t use. Which leads to purg­ing the un­nec­es­sary. After 15 years of no power bill, we’d purged most of the fat in our house­hold en­ergy use, but one thing stood out — the car. It has al­ways an­noyed me that we’ve lugged a tonne of metal for 20 min­utes each way, climb­ing and drop­ping 500m twice in the process, just to bring a few bags of gro­ceries home. So I talked my­self into build­ing a cargo bike.

The tar­get was that the $2K bud­get for build­ing the bike should be saved by us­ing

the bike in­stead of the car over a two-year pe­riod. It would have to be elec­tric-as­sist, prefer­ably us­ing a separate charg­ing sys­tem from the house — in other words, with its own pho­to­voltaic (PV) pan­els.

I’m no stranger to bikes or to car­ry­ing cargo on them, but I’m 64 and we’re talk­ing about a three-hour re­turn trip (bikes be­ing slower than cars) with three se­ri­ous climbs. I’d built a sin­gle­wheel trailer and hauled 95kg on it over the Rail Trail, but it’s a long rig. I’d also had a fair bit to do with re­cum­bents but this time around de­cided to stick with con­ven­tional rider po­si­tion­ing — partly be­cause I wanted to create some­thing oth­ers might be more in­clined to copy.

Fun to build

Front cargo looked in­trigu­ing and twofront-wheel tilt steer­ing sug­gested it­self for the in­tel­lec­tual plea­sure in­volved — to say noth­ing of as­suag­ing my la­tent petrol­head­ery. For good mea­sure, I de­cided to build in tim­ber us­ing ply­wood, strip tim­ber, and judicious use of carbon fi­bre, again for the plea­sure in­volved.

When con­fronted with a de­sign prob­lem like this, I have a cir­cle of peo­ple to bounce ideas off, usu­ally done over co­pi­ous cups of cof­fee.

One such is a naval ar­chi­tect with a very use­ful CAD pro­gramme. We bounced, we cof­fee’d, we sketched, and we re-sketched. A con­cept took shape: slightly un­der 2m long; 600mm wide; twin wish­bones up front; tilt­ing; sus­pen­sion all around; disc brakes all around; 20-inch wheels up front and a 26-inch one be­hind; a water­proof — prefer­ably rigid — cargo bay for­ward, a nod to aero­dy­nam­ics (given the long down­hills in­volved and the fre­quency of head winds); and the back half to be es­sen­tially a moun­tain bike. The e-mo­tor was left in the yet-to-de­cide bas­ket, but the bat­tery would live low down in the cargo bay.

A CAD combo

CAD al­lows you to build — and dis­card — mul­ti­ple prototypes with­out ma­te­rial cost. Of course, this can still be done in the time-hon­oured man­ner, known to gen­er­a­tions of boat­builders as ‘loft­ing’. We use a mix­ture — my friend draws things on his CAD, gives me a ta­ble of off­sets, and I loft the shapes out, old school. Don’t laugh — I’ve sailed a schooner built from a whit­tled half model, her frames scaled up from lead strips bent around it. Old still works.

After 15 years of no power bill, we’d purged most of the fat in our house­hold en­ergy use, but one thing stood out — the car

CAD al­lows you to build — and dis­card — mul­ti­ple prototypes with­out ma­te­rial cost

I’d also had a fair bit to do with re­cum­bents

Be­low and right: Try­ing out a re­gen­er­a­tive­brak­ing hub mo­tor, retro­fit­ted by a friend to his moun­tain bike

Wedges hold­ing strips to­gether while glu­ing

Try­ing out the cargo space

An early eval­u­a­tion in the de­sign process — an idea incorporat­ing mid cargo, foam and fi­bre­glass con­struc­tion, and a sin­gle front wheel

Left: Spoke thread­ing is a la­bo­ri­ous han­d­op­er­ated process

Be­low: Twin-wish­bone ar­range­ment on a re­cum­bent trike

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