Alta 101 - Intro to Electric Motors
This is part of a little series we’re going to do to help the layperson understand electric vehicles, how they compare to gas vehicles, and how they compare to each other. Henry Ford did the same thing on his blog when his Model A was replacing horse and carriage. If you’re a professional or even an armchair engineer, you may want to skip it.
Vehicles, both gas and electric, can be split into two parts: input and output. In a gas vehicle, energy input is stored in your fuel tank and energy output comes from burning that fuel in an internal combustion (gas) engine. In an electric vehicle, the energy input is stored in a battery and energy output comes from an electric motor. Simple, right? Bear with us here.
In 101 we’ll look at energy output, aka the “fun side.” At Alta, we separate of electric drivetrains in two types, economy or performance, generally defined by their voltage and their motor technology. Systems that run on less than 100V or use brushed motors are generally simple and inexpensive to build, and are fairly reliable. Brushed motors are called such because they make a mechanical connection between the two moving parts of an electric motor which brush against each other to transfer electricity. This is a very simple way to make sure each part knows where the other part is, but it causes friction and the brushes wear out eventually. You’ll find these in your blender, your cordless drill, and in most electric scooters and golf carts. The basic technology has been around for 130 years and constitutes what we call the economy category. However, this technology doesn’t quite cut it for high-power applications like electric cars.
To get the power output needed to match the gas engines in modern cars and motorcycles, electrics require voltages well over 100V. For efficiency and low maintenance, they need brushless motors. Brushless motors don’t have a mechanical connection between the two moving parts, so they are more efficient and lower maintenance, but require sophisticated systems of sensors and controls to make each of the two moving parts know where the other one is. As an analogy to the gas world, you can think of it as the difference between your pull-start lawn mower and your car. Both run on gasoline, but the car requires some serious brain power and delivers considerably more power and efficiency as a result.
A lites-class (250cc four-stroke) gas race bike puts out around 35hp in stock trim, though usually up to about 40hp after tuning. To put it in perspective, with the rider on them these bikes have the power:weight ratio of a modern Porsche 911 Carrera. To compete, Alta has had to develop a high-voltage, brushless, liquid-cooled drivetrain from scratch. This allowed us to create a motor that is about twice as powerful and half the size of off-the-shelf electric motors like the Agni 95. From initial testing, we can say, the thing absolutely rips and if you look at the chart of rear wheel torque of the RedShift vs. a lites class motocrosser below, you can see why. Rear wheel torque is what actually pushes you and the bike forward. In the chart, you’re seeing that the gas bike matches our top end in 1st and second gear, but only for a moment at its peak. The rest of the time, and in the rest of the gears, anywhere the red line is above the blue one the RedShift is pulling ahead. In fact, even in first gear, the gas bike isn’t winning because it’s traction limited – you can’t actually use all of that torque without spinning up the wheel, which is why racers start at the gates in 2nd gear.
Why the RedShift gets the holeshot every time.
Size matters, and in this case, smaller is better because as you’ll find out in class 102, we need as much space and weight for the battery as possible. The Alta motor is about 4″ in diameter by 9″ in length – about the size of your fancy new water bottle. In bench testing, it cranked out about 46hp with a bit of headroom left to go, though for production we’ll keep it at about 40hp. It’s the most advanced motor ever planned for a production electric motorcycle, but that’s what it takes if the goal is to be better than what we already have in gas bikes.
Next up, Alta 102 – Intro to Batteries. Stay tuned…