I hope to have pictures of my finished bike up soon. I painted it purple have christened it the eGrape, or Vitis electricus var. Labrusca, the fox grape (a wild North American native, an unrefined early approximation). Someday I hope to follow up with the high performance Concord or Red Flame. or maybe just the economical Thompson seedless.
Anyway, a condensed version of my Labrusca plans and components follow:
Parts
A bike from the garage of Nigel (he works in the lab upstairs, and we've
been bouncing eBike/eTrike ideas back and forth).
Two 12V Revcor Permanent Magnet motors (essentially the same as what ZAP
uses) from Wilde EVolutions
(about $48 each).
Four 6V sealed lead acid batteries (7 amp-hour capacity each) from Alltronics for about $8 each. (If
you want to stick with all 12V, then B.G. Micro has them really cheap.)
Switches, diodes, heat shrink tubing, circuit breakers, and other
bits and pieces from Al
Lasher's Electronics here in Berkeley, and All Electronics Corporation in Los
Angeles(?).
And some hardware from the local Home Depot.
Power Control
The batteries are connected to the motors via a double-pole double-throw
(DPDT) switch
that will allow me to have the motors either in series (low power) or in
parallel (high power).
The connection between the batteries (two pairs of 6V batteries) is
made/broken by a pair of microswitches (two, in order to carry the high
current) on the handlebars. (You can see the schematic here.)
That
way, if I'm not actively telling the motors to run (if, say, I wipe
out or something), they'll turn off.
Regenerative Braking
There's a lot of debate as to whether regerative braking on an eBike is
really worth it, but I decided that it would be a good thing to at least
experiment with.
So, my right brake lever actually comes from a moped among Nigel's
collection, and it contains a small microswitch (originally controlling
the brake lights on the moped) that I wanted to use to control a regen
braking relay. But I had trouble finding a 6V relay that could handle
sufficiently high
currents, so instead I'm using a second pair of microswitches.
The
batteries are connected in parallel in the braking circuit (not in
series as they are in the drive circuit) and the motors can be arranged
either in parallel or series by the DPDT switch mentioned above. ZAP says
that with their setup (motors in series, 12V battery) you only get
charging if you're going over 12 mph. Hopefully,
with my setup, you get charging if you've got the motors in parallel
and you're going over 12 mph, or if you're going 6(?) mph with the motors
in series. Based solely on the sounds made by the motors (I haven't
metered it yet), it sounds like having 6v regen makes a *huge*
difference.
Diodes in the braking circuit make sure the voltage from the
batteries doesn't make the motors speed up (which might send me in front
of a passing automobile).
Mounting the Hardware
Fortunately, Nigel happened to have an extra friction roller that I could
use. I think ZAP sells them for about $20. You basically just jam the
drive shafts of the two motors into the two slots at the ends of the
roller. I've held the two motors together using 1/4" all-thread
(basically a super-long bolt with no head, and threaded along its whole
length) and a bunch of nuts locked against each other. Two pairs of
mounts on the motor have all-thread, the third pair hangs over the wheel,
so they can't be connected (but I use them to pull the roller against
the tire).
The motors are connected to the seat stays on the bike by half of a door
hinge. The hinge pin is replaced by the all-thread joining one pair of
motor mounts. Nigel welded the hinge plate in place for me, but you could
probably get away with bolting it where the bike's rear reflector or rack
is usually attached, maybe with a couple of U bolts for rotational
stability.
Two long springs from the hardware store pull down on the third set of
motor mounts, to keep the roller against the tire. An extra gearshift
lever acts as a low tech manual clutch to pull the roller off of the
tire when I don't want it there.
The motors are held in place by a tangle of heavy gauge baling wire. I
wanted to use medium gauge fencing (like you use for gardens or small
animal cages) but the hardware store didn't have any at the time I wanted
it, so I got the baling wire instead. Not pretty, but it works.
Things I'd Do Differently or Want to Try
Relays: I've got way too much #10 wire running around the bike.
It's kind of ugly. I'd like to convert to relays; I found some nice
solid state relays that can handle high currents that could be used with
6V regen if I wanted. Then I could use that microswitch in the brake
lever for a clean, transparent interface.
Electric clutch: I've got a nice 12V solenoid that I'd like to use
to
automatically pull the roller down onto the tire only when drive or regen
is engaged (and then use a spring to lift the roller off at all other
times).
The solenoid supposedly has about a 3 pound pull at 1/4".
Lighting: Maybe I'll also get around to hooking up some flashing
LEDs and
a headlight someday.
