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