Electric motorcycles have come a long way since their inception, but the lack of a gearbox has kept them from being fully embraced by many enthusiasts.
A couple of weeks ago, Brammo’s Empulse RR (ridden by MCUSA’s Steve Atlas in the Electric Superbike Racing: Brammo Part I, Part II and Part III articles) kicked amps and took names at the first round of the 2011 TTXGP series. One of the first things Steve had to get used to was the lack of a clutch and shift lever on the road racer. In the first few years of the EV motorcycle scene, Brammo, Zero and other EV makers repeated the mantra that, since electric motors make peak torque from zero rpm, a gearbox was superfluous.
Yet recently, Brammo announced it had made a deal with SMRE, an Italian supplier, that would be making six-speed gearboxes for several future Brammo models, beginning with a forthcoming dirt bike and supermoto-styled street bike.
So what gives? Do EVs need gearboxes or not? And if they do, is it logical that we go from a single speed to six? To get up to speed on the engineering case for a gearbox, I called two old friends: James Parker, an iconoclastic freelance motorcycle designer who I happen to know has put a lot of thought into gearboxes for EVs; and Lennon Rodgers, a Massachusetts Institute of Technology PhD. candidate who’s leading the school’s TT Zero project. Lennon then referred me to Charles Guan, another MIT brainiac for a crash course in electric motor theory. Finally, I called Brammo CEO (and fellow Kansas Citian) Craig Bramscher.
Brammo has shifted its focus to attract existing motorcycle riders by adding a gearbox in select models.
What I learned was that there is an engineering case for a gearbox, but there’s a little more to it than just ensuring electric motors stay in their peak-power rev range. The decision to add gearboxes to new models also reflects a shift in Brammo’s strategic marketing plan.
But I’m getting ahead of myself. Remember all those times e-moto builders told us, “And you don’t need a clutch or gearbox?” Until now, virtually all e-motorcycles have been single-speed, direct-drive bikes.
That was half right. It’s true that electric motors make peak torque as soon as they begin to spin, so you don’t need a clutch and low gear to start moving from a stop. In fact, there’s so much torque from 1 rpm that it can almost be a problem for e-moto designers. It’s hard to program a motor controller to feed power in gently enough for smooth takeoffs from a full stop. That was a real flaw in the early electric motorcycles that I rode, including the first Brammo prototype and early Zero products. In stop-and-go traffic, I got into the habit of giving bikes a bit of juice while holding the brakes, and then easing off the brakes to start smoothly.
At slow speeds electric bikes are – pardon the pun – a gas. That wave of low speed torque creates the impression e-bikes are a lot more powerful than they actually are. The thing is, as speed picks up, e-bikes run out of steam. From the saddle, it feels as if the bike goes up a hill. If you’re used to riding modern sport bikes, which of course generate a lot more power as revs climb, bikes powered by electric motors feel really anemic at high speed.
This isn’t limited to two-wheeled EVs. “Look at the Tesla,” James Parker pointed out. “It has the 0-60 time of a supercar, but the top speed of hot hatch.” In fact, one of the things that delayed Tesla’s first model introduction was the fact that the car maker felt it needed a two-speed transmission to achieve both its acceleration and top-speed targets, but there was nearly an insurmountable
While single speed gearboxes are the norm with electric bikes, it’s rare to see in a gas motorcycle like this 1913 BSA.
engineering challenge in building a two-speed box that could handle both the EV’s substantial torque loads and the large ‘jump’ between ratios. Parker, in fact, has designed just such a box for motorcycle use (but since it’s not yet patented, I can’t tell you how it works.)
Basically, any electric motor spins at a speed determined by the voltage being fed to it. More volts equal more revs. So if you consider your options, in terms of getting more top end with a single-speed electric setup, you’ve got two choices: you can operate at higher voltage and let your motor spin faster, or you can produce more torque, and choose a higher gear ratio. Remember Tesla’s gearbox problem? They eventually solved it by operating at 375 volts, which is quite a lot more than any electric motorcycle I know of. Most bikes run at under 100 volts.
The most common, and simplest, electric motorcycles rely on brushed, DC, permanent-magnet motors. The Agni, and the Lynch motors are this type. As voltage climbs up over 100V, arcing becomes a problem. That’s one of the things that limit motor speed. Torque (and hence, the tallest gear you can run in a single-speed setup) is proportional to current. The inherent problem with increasing current is that an electric motor is basically a resistor, and the heat generated by a resistor increases with the square of current. Double the current, and you’ve got four times the heat to dissipate; triple the current, and you’ve got nine times the heat. That’s why heat buildup is a common limiting factor in air-cooled motors – especially in racing applications.
I got a primer in electric motor theory from Charles Guan, a senior at Massachusetts Institute of Technology who has honed his electric motor skills building, among other things, the world’s fastest electric shopping cart. (Don’t worry, America will never lose the battle for shopping cart supremacy) What I was trying to get from him was, what was happening inside electric motors when torque fell off at high RPM?
Internal combustion engines use gears to reach a peak torque range, but electric motors have a parabolic power output – meaning its powerband is much wider.
The reason I was even asking that question was, I come from an old-school, internal combustion background. The rev limit of a racing ICE can almost always be raised. Want more revs? Lighten and balance reciprocating components, and install stiffer valve springs. Or better yet, go Desmo; get the head and throttle bodies on a flow bench, tune the exhaust for better scavenging, find a faster-burning fuel… there’s always something you can do (although the cost of building the motor goes up exponentially.)
Charles sent me a graph that illustrates torque fall-off in a typical electric motor as a simple product of the motor’s physics. He explained it this way:
If you observe the torque-speed curve for a typical DC electric motor as used on most electric bikes today, you will notice that an electric motor produces incrementally less torque as it reaches top speed. Therefore, an electric vehicle will monotonically approach a top speed and you will feel less and less force as it reaches that speed.
The reason internal combustion engines have transmissions is that they cannot spin at zero speed (they stall), and their maximum power output (the “powerband”) is usually pretty narrow as a function of speed. You’d shift gears to make sure the engine is always operating near that peak region. An electric motor has a parabolic power output profile with the peak at 50% speed but decreasing shallowly around that, so the useful powerband is much wider.
Therefore, EVs have historically championed the “no gears” line because motors already produce peak torque at zero speed (which is why many EVs feel like they have way more horsepower than they do) and the motor can operate efficiently over a wide rev range.
The reason that they are now adding transmissions is that a transmission lets you effectively change the T-S curve’s slope (its steepness). If you’re cruising at top speed, as you can observe from the graph, the motor consumes and produces very little power, typically just overcoming drag.
Adding a transmission to an electric motor will allow users to access more torque.
Adding a second gear would force the motor back towards the higher power region while making you go faster.
It’s interesting that Charles’ natural conclusion was that, given the relatively wide power curve of electric motors, you’d add a second gear. Lennon Rodgers, who is the leader of MIT’s EV motorcycle project team (they’re racing a single-speed motorcycle in the TT Zero race on the Isle of Man next month) also told me, “I can see that EV manufacturers will design some slick two speed transmissions in the next few years.”
So, why is Brammo going for six-speed, if two-speeds would do? James Parker guessed that the reason was, it was cheaper and easier to source an off-the shelf six-speed gearbox than to engineer a two-speed box from scratch. (As Tesla learned, it’s not easy to make a two-speed gearbox with a single huge jump between ratios. The larger the jump between ratios, the harder it is on transmission components. This is something you can see in ICE transmissions, too. The largest jump between ratios is between first and second gears, and although modern gearboxes fail rarely, when they do fail it’s usually second gear that goes crunch.)
Brammo CEO Craig Bramscher didn’t put that exact spin on it, but he pretty much confirmed that Parker’s guess was at least half-right.
“The key point, that electric motorcycles don’t need a gearbox, is still true,” Bramscher told me. “But the need and the want are different. You don’t need a 1,000cc sport bike, either, but you want one. As we pushed the envelope [of single-speed bikes] we found that in order to get the full motorcycle experience and appeal to enthusiasts, you could either have a bike that went 110 or 120 mph and had acceleration that was just OK, or you could have trouble keeping the front end down, but you’d only go 80 or 90.”
One of the reason Brammo is opting for six gears instead of two is that six-speed gearboxes are much easier to source.
Bramscher continued: “So for several years we worked on what we thought was the logical next step, which was a two-speed gearbox. Tesla, as you know, worked on that, too. But the challenge is, the jump was too large; it was hard to synchronize and it was expensive and it wasn’t readily available, so you were talking about a five million-dollar investment. Avid motorcyclists also told us they liked shifting gears.”
That “avid motorcyclists” comment is noteworthy. Two years ago, when I first interviewed Craig, he focused on the simplicity of clutchless, single-speed electric motorcycles and described Brammo’s potential customers as people who aspired to ride a motorcycle, but were intimidated by current gas-powered bikes. Selling Brammo bikes in Best Buy stores was part of a strategy to make the purchase less intimidating; it was just another appliance or electronic gadget. Obviously, since non-riders vastly outnumber riders, the idea of appealing to non-riders sounded good to potential investors, too.
Over the last couple of years, though, both Brammo and Zero have found that non-riders are hard to convert, even to clean, silent electric motorcycles. The perception that motorcycles (especially street bikes) are dangerous is still a barrier to entry, and so are special licensing requirements. Anecdotally, I hear that most electric motorcycles are actually being sold to existing motorcyclists. My own observation supports that; everyone that I know who actually owns one either is, or at least has been, the owner of an ICE bike, too.
“If you talk to Harley-Davidson or anyone else, new customer acquisition is the most difficult challenge,” Bramscher admitted. “But we had to start [with non-riders] because we didn’t really have the performance to appeal to existing motorcyclists. Where we think we’ll be with this next round of bike is: we’re making great motorcycles that just happen to be electric.”
While Brammo is targeting more experienced riders by adding gearboxes, it will continue to produce ‘twist-and-go’ models with single-speed motors.
Not that Brammo is completely giving up on the simplicity of twist-and-go. “Brammo will always make some motorcycles with a single speed,” Bramscher said. “We think that’s the ‘on-ramp’ to motorcycling for the aspirational customer. A couple of years ago, where the technology was, we had to go after the novice rider, because the performance just wasn’t there to satisfy [sport bike] riders. So part of it’s the evolution of the industry, part of it’s the evolution of our company and part of it’s getting to the point where EVs are on parity with internal combustion engines. We think we’re close on a couple of fronts there.”
While a six-speed transmission offers about four more ratios than any electric motor needs, it offers two things Brammo wants; an affordable and readily available way to provide both acceleration and top speed. And it offers something existing motorcyclists also want, or at least are used to: a clutch and something to keep your left foot busy.
The clutch and gear levers that will soon adorn Brammo bikes represent a shift of more than just gears… they indicate a fundamental shift of business strategy. Rather than focus on new riders, Brammo’s now going after existing ones. That’s why the company is (again, like Zero) busy signing up new dealers, too.
What does it all mean for the emerging EV motorcycle industry? Well, I suppose if you were the kind of guy who sees the battery as half-drained, you’d say that the shift in emphasis to giving existing riders something they’re familiar with – and reaching them through existing motorcycle dealers – means that electric bikes will not turn millions of new riders on to bikes any time soon. It might follow, logically, that sales of electric bikes will cannibalize sales of conventional ones.
If you’re inclined to see the battery as half-charged, you’d conclude that gearboxes – even with several ‘extra’ gears – are another step towards functional parity with ICE bikes. The electric promise is still the same: a bike that’s as fun as the ones you’re used to, but nearly pollution free, that you’ll be able to operate for pennies a day… soon.