Velociraptor™ Intelligent Motor Controller, the Back Story

For those of you new to electric transport, the heart of any electric drive system is a piece of power electronics called the motor controller. Its function is analogous to the fuel injection and ignition systems combined on a car. It’s what makes the motor spin and determines how much power you get out of it. When we say a motor is, say, a 1000 Watt motor, what we’re really saying is that the controller is allowing the motor to produce 1000 watts. The only sense in which the motor itself is a 1000 Watt is that its design is robust enough for a controller to push it that hard without damage. Velociraptor can easily push our 1000 Watt motors to 1500 Watts or more. The only question is how long they’ll last at the higher power level.

For all of the years since EcoSpeed’s founding in 2003 we have, like almost all other e-bike kit manufacturers, purchased motor controllers made by manufacturers, all in Asia, that specialize in making them.

The problem with that is that almost all of the manufacturers that make controllers for e-bikes are focused on low cost. That wouldn’t be a problem if they also had both high performance and high reliability. But, sadly, they don’t. The controller is the second most common component to fail on e-bikes. Some controllers we’ve purchased have had failure rates approaching 50% when new. We duly replace failed ones under warranty and take care of our customers, but quality like that is just not in keeping with the EcoSpeed philosophy.

Others that we’ve sold have been more reliable but, and here’s the dirty little secret no one selling e-bikes talks about — the reliability and life you get from your battery is largely determinined by the controller. It turns out that the most reliable controllers on the market are the high current ones, which are also the ones that are hardest on battery systems. And, the battery is the number one most common component to fail

 

The Velociraptor Project

Three years ago we started a project to do something about that. Designing a state of the art motor controller from scratch is not a project for the faint of heart, or for small companies like EcoSpeed. But, we’re located here in Silicon Forest where some of the most advanced electronics in the world is developed and manufactured, including the processors in your PC. So, full speed ahead, we dived in.

The internal design of a motor controller is very similar to an audio amplifier. In fact, with some simple software changes, Velociraptor could drive a pair of speakers at high volume. And, therein lies the reason why commercially available e-bike controllers are so unreliable. Just as any self respecting audiophile wouldn’t expect much from a 1000 Watt amplifier that sells for a hundred dollars, it’s simply not possible to make a quality motor controller at the same power level that costs much less than a high quality audio amp. In fact a motor controller is harder to make in some ways because it has to run off batteries, be small enough to fit easily on a bike, and be weatherproof. The latter is no small feat since it means that the case has to be sealed so the usual vents and cooling fans are out of the question.

Velociraptor Design Criteria

The number one design criterion for Velociraptor is that it be able to survive harsh transportation use. Temperatures from Minnesota winters to Phoenix summers, gentle beach walk cruising or towing trailers up the Rockies — all are in a days work for an e-bike motor controller. So, we use high quality US made power transistors rated for voltages and currents well beyond what they’ll encounter in heavy use. And, we built in protection circuitry that detects conditions that might damage the electronics and either shuts off the system or modifies operation to prevent harm.

A second design criterion is that it’s better to have some assist than no assist. On a hot day, for instance, a conventional e-bike controller climbing a steep hill will keep heating up until it either shuts off automatically, best case, or fails, worst case. Either one leaves you stranded trying to get up the hill on pedal power alone. If you’re lucky and it simply shut down, it may take up to a half hour for it to cool enough to turn on again.

Velociraptor, in contrast, will smoothly reduce power as it heats up beyond a certain point. Eventually it reaches a temperature and power level that it can sustain under the conditions. You don’t get full power, but you do get some. And as the controller cools, even slightly, power starts to increase.

Finally, we decided that Velociraptor should be programmable. Conventional controllers do just one thing. They operate off of a single battery voltage, sometimes two, and at a single output current. Programmability means that Velociraptor can operate at any battery voltage or output current that’s within the limits of the hardware. It can also do things like power curve shaping where current varies with rpm. For instance, current can be reduced at very low rpm to reduce stress on the power transistors and increased at high rpm for increased performance.

Programmability also puts you in control of how your bike works. You get to decide on trade-offs like high performance or long battery life or, long range or high speed.

Intelligent Battery Interface

The thing no one ever tells you about batteries, is that how long they last depends on how they’re used. Forget cycle life specifications –those numbers battery makers publish telling you how many charge and discharge cycles their battery can go through before it’s useless. Those numbers only have meaning inside the battery maker’s lab under completely controlled conditions. Out in the real world all bets are off and how long your battery lasts depends mostly on your motor controller and to some extent on how you ride.

With most motor controllers, the only factor you can control is your riding style. The controller just does whatever it does and, if it pays any attention to the battery it’s connected to at all, it just has a simple low voltage cutoff. That’s where it suddenly shuts off if your battery drops below a preset voltage, even for a fraction of a second. That may or may not protect your battery, but it certainly can leave you stranded.

Velociraptor uses an innovative intelligent battery interface. What that means is that the controller actually measures how the battery is performing 1000 times per second and adjusts its operation accordingly. Plug in a new, fully charged, battery of the appropriate size and the controller will note that and allow full power operation. If the battery is old, or too small, or almost out of charge, or if it’s too cold, Velociraptor will reduce power output to minimize battery stress.

And, like the rest of the controller, this feature is programmable. That gives you the power to decide. If high performance is more important to you than long battery life you can have that. Or, if you want to use a very small and light battery for best pedaling performance without worrying about shortening the battery life, that is yours also. In keeping with our philosophy here at EcoSpeed, the important thing is that you get to decide.

Additional Features

Velociraptor is built around the new high performance 32-bit ARM Cortex M3 CPU. This gives us plenty of computing power to implement innovative new features. After several design spins, many blown controllers, and dozens of 80 hour weeks on end writing code, we’re far from done. We have lots of ideas for new features that we’ll be adding over the coming months. Because they’re being done in software, any Velociraptor controller will be upgradeable to take advantage of any new features we develop.