Zero electric motorcycle


Charging at Tsawwassen Mills with a J1772 adaptor

Various Links

The lefthand brake saga

I sometimes take my motorcycle aboard my sailboat (see e.g. 2008 vacation), which involves taking it up and down a ramp. I also occasionally transport it in a pickup truck.
The technique is to walk alongside the bike to provide stability with 3 points of contact (two wheels plus one foot on the ground), given that the boat may be moving. To get the bike up, I drive it up with the engine. To get it down, I back it down with the engine off, in first gear, using the front brake (acting on the front wheel) and clutch (acting on the rear wheel) to control the descent. Since the bike is on a slope, most of the weight (and hence most of the stopping force) is on the rear wheel.
Problem is, the Zero has no clutch, and the electric motor provides no braking whatsoever at zero speed. Using the front brake alone, the tire slips.

After some discussion on forums, asking Zero support, and talking to a couple of mechanics, I decided to fit a left-hand brake acting on the rear wheel. Zero in fact makes a parking brake as an option, but it's expensive and as far as I can tell it's a lock, not a normal brake.
I could not just use a right-hand assembly upside-down, because the hydraulic cylinder is integral to the lever assembly and would be the wrong way up. Initially I ordered a left-hand hydraulic clutch assembly from banggood on the advice of a Ducati mechanic (at least, he suggested I look on banggood but did not recommend a specific item). That turned out to have too small a reservoir; probably intended for a smaller bike. On returning to a local bike store, which had initially been unable to help, the owner found an assembly somewhere on a shelf that did fit and had a good size of reservoir. I fitted that on the handlebar, with the brake hose feeding the ABS controller in place of the foot pedal hose. I was able to bleed the hose out through the reservoir, and the system worked quite well - I had two hand brakes to back the bike down a ramp.

Then I realized that I did, in fact, occasionally want to use the foot pedal - when stopped to use my phone or GPS. So I thought I would combine the two, with a dual banjo bolt. Having stolen the original rear brake hose to connect the left-hand lever, I had another hose made up with the requisite fittings. Bleeding the system did not go well - I realized that the upper cylinder was leaking out through the lower cylinder hose.
I only needed one reservoir, so I decided to block the connection to the original lower one. I did that with epoxy and a steel washer, blocking off the channel from the brake cylinder. I still had not fully understood what was going on in the brake system. I managed to bleed out the system successfully, and the hand lever worked OK, but if I used the foot brake, the system leaked into the upper reservoir. There is a small channel connecting the reservoir to the cylinder, which is open when the brake is not engaged, but is closed by the piston when the brake is operated. This makes the system self-bleeding - air bubbles rise to the top and out into the reservoir when the brake is not used - but means that my simple connection could not work. When I looked online again I found references to a non-return valve that might work, or systems that used two sets of calipers. In the event, I secured the hand lever in a half-depressed position with wire, closing the channel, so that I can use the foot pedal when stopped. To use the the hand lever for backing down a ramp, or when riding, I have to pump the brake a bit before it works to the full extent. Overall, it's "good enough".

To solve the problem of having no parking brake (cannot put the motor "in gear"), I made a sprag from a length of steel rod. If I insert that through the rear forks between the wheel spokes, it stops the wheel turning.


The sprag

The battery story

I bought the base model FXS with one modular battery. That's enough to commute to work and back, charging overnight. I'd been thinking all along of buying a second battery at some point, to double the range, but they're not cheap. Without the second battery, there's a big hole in the frame. I thought that looked a bit stupid, so I made a battery-shaped box out of fibreboard and duct tape and painted it black. That's it in the top photo, behind the real battery with the reflective stripe. I used it for storage, for e.g. a USB charger cable.

According to Zero's website, the bike should go at full speed with just the one battery, but with slightly reduced power. In practice, I found that as the battery discharged below some 40%, it would start to limit the speed. When I installed the Zero app on my phone and downloaded the system logs (3rd-party decoder online), I found some entries "current limiting" that corresponded to these slowdowns. So I bought the second battery a bit earlier than I might have otherwise. No more slowdowns - they were really a bit embarrassing, on the highway returning home.

I also bought a fast charger at the same time; two batteries would clearly take twice as long to charge. From what I'd read, I'd expected it to install inside the bike. In actuality, it's a large external unit that plugs into a fast charge connector on the bike that I never even realized existed - it's hidden beneath a rubber dam on the right-hand side, underneath the motor. As it turns out, you can charge with the built-in charger and the external one simultaneously, for about a 3x speed-up over just the internal one. For normal use, it's much too much trouble. It takes a bit over 3 hours to recharge from my commute with the built-in charger, and of course it still takes a bit over 3 hours with two batteries because I'm still riding the same distance. Even charging from dead would take less than my nominal 8 hours of daily sleeping time.

The bike comes with a regular 110V power cord, stowed in the rear fork pivot. That's fine for charging at home, or from ad-hoc outlets, but most EV charging stations use J1772 connectors. I bought an adaptor online; it has internal circuitry to trigger the EVSE relay so it's slightly more complex than just a plug and socket. It's visible in the photo. Since buying the fast charger, I added a Y cable and another 110V socket so if I keep the charger in the top-box, I can charge at 3x speed on the road.


Charger connected to DC charge port, with J1772 adaptor.

"Fuel economy"

An internal combustion engine is inefficient, and produces little torque, at low RPM. So a normal motorcycle has a gearbox, to match the engine RPM to road speed. It also means that the bike is most fuel-efficient at higher speeds where it is in a high gear and the engine is operating at an efficient RPM. The fuel economy curve looks something like this:


(from fueleconomy.gov) - the efficiency rises with speed, then plateaus and drops as aerodynamic drag (scaling as the square of speed) becomes more significant. See also Optimal Vehicle Speeds for Best Fuel Economy (simulations)

An electric motor is equally efficient at all speeds, so the efficiency curve is dominated by aerodynamic drag. The drag coefficient of a rider on a motorcycle (no fairing, not crouched over the tank) is much worse than that of a car, so the effect is quite pronounced.


Zero FXS compared to Nissan Leaf

The figures for the Leaf are from the on-screen display. For the Zero, I did a screen capture of the phone app and ran the video file through OCR; the bike logs from the app are too granular (I'd have to hold each speed for a much longer time).

The inference is clear - to get more range, slow down.

Andrew Daviel