Categories: all aviation Building a Biplane bicycle gadgets misc motorcycle theater

Tue, 15 Apr 2014

Electric Bikes, You Say?

I found myself up in Lynnwood last week (weird enough in itself), and realized that it had been years since I'd stopped in to Cycle Barn. There are lots of reasons for this, some good, some just passive, but no matter. I decided I should drop in, and expose myself to a bit of that new-bike smell.

While I was looking over the selection of lightly-used bikes parked out front, my eye was caught by the animated sign -- did that just flash the Zero Motorcycles logo? Curious, I went inside, and checked out the showroom. On the top floor, I spotted them: 2014 Zero S motorcycles just sitting around, like it's no big deal.

A surprisingly non-pushy woman came over and started chatting with me (perhaps the slimy motorcycle salesman is a thing of the past? I can only dare to dream). The magic, glowing words floated through the air, "Would you like to take it for a demo ride?" Why yes. Yes I would.

So I quickly found myself aboard a bright yellow 2014 Zero S. The woman gave me a quick rundown of how things work. The main differences between a normal gas bike and the Zero are the complete lack of controls on the left side (clutch lever and shift lever), and that the "start button" position on the right side is now occupied by a button marked MODE.

The MODE button selects between three different modes: Eco, Sport, and Custom. The Eco mode can be thought of as a governor, preventing you from giving the bike full power. This can make a huge difference to range. The Sport mode unleashes the full power of the controller. Custom can be set up to the owner's preference, but hadn't been set up on the bike I was riding. I don't have any idea how custom Custom can get.

The range thing is interesting. I was very surprised to learn that Zero claims 120 miles range for the bike I was on (with the 11.7 kWh battery) in city, and 80-some miles at freeway speeds. It makes sense, but it's so reversed from the normal gas engine expectation. The electric motor is more efficient at low speeds, and in a city environment you get the benefit of regenerative braking. On the freeway, you're battling wind resistance, which goes up with the square of speed.

In any case, I took a few test-squirts of the throttle in Eco mode, and experimentally switched to Sport. It didn't have a scary launch (the only thing I was worried about -- electric motors can generate up to 100% of their torque at 0 RPM, unlike gas motors; wheelie-town!), so I left it in Sport for the rest of my ride. The launch, in fact, was a bit disappointing compared to the amount of power available when rolling on at speed.

Rolling on throttle at speed was the really exciting part about this motorcycle. There's a common perception of electric vehicles as being underpowered and weak. Fortunately, Tesla has been changing that perception with their ridiculously hot Roadster and now the Model S. You can now add Zero to that list.

From a rolling start at around 30 MPH on the speedometer, I found myself going 75 MPH before I rolled off, and I would guess I was feeling about 1G pulling me back. It was under 2 seconds between 30 and 75. That's excellent performance no matter what you're driving. I'm sure that Zero has set up the acceleration profile in the controller to strictly limit launching torque so people don't accidentally flip the bike on top of themselves. The motor and controller are most likely capable of that, based on the roll-on performance.

Zero claims the bike with the 11.7 battery weighs 399 lbs, which sounds about right. It carries the weight higher up than my Ninja 250, so the bike felt a little ponderous in corners, since it's less than 50 lbs heavier than my little bike. The suspension was a bit soft for my tastes, and I read in a review that the 2014 model had changes to the suspension to increase comfort. The front brake was acceptable, and the rear brake finally provided me with a definition for the term "wooden." It was essentially useless on its own, compared to regenerative braking and the front brake. For perspective, my standard of a good front brake is the stock brake on my 2006 Ninja 250, with the addition of stainless brake lines. The fact that the Zero's front brake is not as good as that suggests that it's not at all good compared to actual performance brakes.

I brought the bike back and thanked the saleswoman. Zero lists the S model starting at $14,995 for the model I rode, which is simply beyond my interest at this point. It's a very cool bike, and one I would be excited to own, but I can't stomach the price.

This leads into part two of this post: musings on building my own electric motorcycle.

It just so happens I have a race-prepped 2005 Ninja 250 doing nothing in my garage, since I stopped racing, and haven't actually hit a track day in years. This has more than once led to the sort of chin-stroking ponder: maybe I should turn it into an electric bike.

My friend Alex has repeatedly pledged his assistance with metal fabrication and build help. We got to talking about it last night, which led me down the rabbit hole of looking at electric vehicle components.

As much for my own future reference as anything else, I'll lay out my thinking here.

The stock Ninja 250 puts out about 28 HP at the rear wheel if you wring it out. Most of the riding I do, in the 6k-9k RPM range, tops out around 20 HP, practically speaking. To cruise on the freeway at 70 MPH looks like it's using on the order of 10-15 HP, based on a very rough estimate from throttle position and a dyno chart. Using these numbers, I started pricing and sizing components.

The choice of battery technology and motor and controller are interrelated, but battery and motor-controller can be separated out.

For the battery, there are essentially two real-world choices: lead-acid, and LiFePO4. Lead-acid has the advantage that it is comparatively dirt-cheap, and the batteries are fairly durable. Unfortunately, its energy capacity per unit weight is also very low, so you end up with a heavy bike that doesn't have much range. Lead-acid batteries also have a limited discharge ability: if you used every amp-hour of a 20Ah battery, it would recharge a couple dozen times before it was dead. You have to leave them partially charged at the lowest point to keep from destroying them. So a 20Ah battery is really only worth 5-10Ah depending on what kind you get.

I calculated out some battery choices using the Zero's smallest battery pack (8 kilowatt-hours) as a standard, and it looks like I would need an improbable number of lead-acid batteries to meet that goal. However, a pack of 22 100Ah CALB LiFePO4 batteries would get me up to about the power density I want in a size that at least looks probable in the napkin-math. The downside to the lithium batteries, of course, is the cost. Where I could get up to a 72v system with lead-acid batteries for $1300 (with a very limited range of 10-15 miles), the lithium batteries will cost around $3500.

(Napkin math on battery space: the Ninja 250 has a roughly 9" x 18" x 18" space where batteries could go, for 2916 cubic inches. 22 100Ah lithium batteries are 2794 in3. So, probable, but not for sure.)

The major advantage of lithium batteries is energy density. That 22 pack of batteries holds just over 7 kWh of energy, which is enough to do over 70 miles of city driving using a conservative 100 Wh/mile. If they are discharged to zero? No big deal, charge 'em up again, they're fine. No deep-discharge problems with lithium batteries. They add up to 155 lbs, so the batteries alone will outweigh the 90 lb Ninja 250 motor.

So, if I can stomach the cost, I've got my battery question sorted.

Next up is the motor and controller.

For cost reasons, mostly, I restricted myself to DC motors. They're cheaper, they're pretty efficient, and they're relatively lightweight. The internets are scornful of brushed DC motors for EV applications beyond low-powered scooters and the like, since apparently they have a relatively high failure rate. So I kept my search to brushless designs.

It quickly became apparent that Motenergy is the one and only choice in commodity EV motors. So my search narrowed down to the point where I was really only considering two motors.

The first is the Motenergy ME1012, which looks like the ideal thing. It's rated up to 72v (my target voltage), and is typically described as being a 10 kW motor (about 13 HP) for continuous use. That lines up nicely with my estimation of cruising down the freeway on the Ninja 250 above. It's capable of a peak output of 24 kW or 32 HP, which is better than the 250's peak power when burning dinosaurs.

It's about 8" in diameter, and looks (again, napkin-math style) like it would fit on the 250 frame.

The close runner-up is the Motenergy ME1115, which is exactly the same thing, except it's newer, uses fancier position sensing tech, and can handle up to 96v (a factor which doesn't matter to me). It's also more expensive, but both motors are still $1000 or under, making them less than half the price of an equivalent AC motor. Both motors are 35 lbs, so that the "wet weight" of a loaded-up Ninja 250 (about 360 lbs) will be a bit of a distant dream -- the electric bike with 100Ah batteries would probably weigh over 400 lbs. It may be worth reconsidering the battery size, based on the weight issue.

All the reading I've done so far suggests that the correct controller to match these motors is the Sevcon Gen4 controller, in the Size 4, 72v variation. It's a spendy controller compared to a brushed motor setup (motor and controller cost a bit less than twice as much as a roughly equivalent brushed-motor setup), but the Sevcon controller is leaps and bounds ahead of the brushed equivalents in terms of tech. It is, practically, a new design, while most of the other controllers out there are using a decades-old design. Notably for me, it speaks CANbus, which means I can easily interface to it using microcontrollers, in case I want to do any fancy display programming of my own...

I totted up the bare prices of this controller ($925)/motor ($520)/battery ($3146) combo (without shipping or anything else) and came up with $4591. Obviously shipping will add a few hundred dollars, but that's the major components covered.

Of course, that is far from the whole story. Off the top of my head, I can think of the following items that aren't included:

So, in the worst case, that's roughly another $3000 on top of the $5000 for major components. The bike itself cost me $1100, so is amusingly one of the cheaper parts of an electric bike build, particularly considering that I got value out of it already as a track bike. It's definitely not a cheap build. It could be done for less. I'm not committed to doing this right now. But having done the major research to get me started (I'm sure there's another month of research necessary should I go through with all this), it looks more probable.

I'll have to think about the weight issue more. I only started doing research on that as I was writing this post. The advantages of going to a smaller/lighter battery are pretty noticeable: cheaper, less volume (so the bike doesn't have to look so slab-sided), and somewhat ironically, better range-per-watt-hour, since the motor doesn't have to accelerate the weight of the bigger batteries. The Ninja 250 is intended as a small, light bike, and I'd like to preserve that in the electric incarnation, if possible.

I've been thinking about doing something like this for a long time. Most of my riding is 10 miles to Capitol Hill and back. On my longest errand day, I go maybe 60 miles. Most of my trips are doable by bicycle, although on long days or days where I need to go multiple places, this becomes impractical. Having an electric motorcycle would eliminate 95% of my carbon emissions (since electric power in Seattle mostly comes from hydroelectric dams, and is carbon neutral). If I wanted to blow another $10k on solar panels -- and this is the real dream -- I could charge my electric bike without using any grid power at all. And, really, how cool would that be?

Posted at 14:05 permanent link category: /motorcycle

Categories: all aviation Building a Biplane bicycle gadgets misc motorcycle theater