Step 8: How about a real vehicle controller?
But there are such things in the world as inexpensive brushless motor controllers which aren't rudimentary and lightly built. They don't need a weird throttle converter, instead being able to use a 3-wire voltage source directly as the command. They tend to have real current (torque) control, variable electronic braking, and some times come with useful accessories such as a main relay driver or light controllers. It's like they were built for vehicles or something.
Luckily, in the past two or three years, specialized small EV controllers have become very common and also inexpensive. Here's some general characteristics about them.
They are sensored controllers
Positive starting from zero throttle and no desynchronization from control inputs too fast to follow. Then downside is that you'll have to add sensors to your motor if it doesn't have them already.
Current control and regenerative braking
A brushless motor's inverter circuit is implicitly capable of performing regenerative braking - where kinetic energy is capture from the motor and returned to the battery. There is nothing magic about regen , despite it being a marketing tagline for all sorts of consumer electric accessories (and cars). Regen is not available on most R/C controllers just out of cost reasons and no real necessity. While regen can only capture back a few % of the energy contained in a moving vehicle, it can contribute to longer brake life and less necessity to use mechanical braking to make a small speed adjustment.
Current control emulates the dynamics of a gas-powered vehicle better by keeping the acceleration constant. It also means the motor is limited from producing too much torque, which is handy for large brushless motors with very high torque capability.
Multiple inputs and outputs including reverse
Typically, an EV controller has at least two analog inputs: one for a throttle pedal or knob, and the other for a variable electric brake. It might also have inputs for throttle and brake switches which are tripped as soon as you step on either, and can signal to the controller that you indeed want to either go or stop (A single analog input cannot distinguish between you flooring it and a loose wire, possibly leading to dangerous situations). The brake switch would signal the controller to stop driving the motor because you want to stop instead. Maybe that's bad for doing burnouts, but it's not good to fight your brakes with your engine or motor anyway.
Other switches and doodads include key switch inputs, reverse inputs, status light outputs, datalogging, etc.
Because vehicle controllers have to be more rugged, they are generally built inside sturdy metal cases which also act as heat sinks for the power semiconductors.
Common small EV controller examples
Like quite a few other situations in life, a Chinese company offers a solution for the entry-level and basic functionality seeker where American and European manufacturers could (or actually would) not. The undoubted champion of inexpensive small EV controllers is Kelly Controller . Back in 2007 and 2008, they were really shady... but things have improved alot there, apparently. Kelly's KBS line of brushless controllers has everything I just described up there and the typical price is about 2 dollars per amp... real amps . Not barely-on-the-edge-of-destruction amps.
Kelly KBS Series
These things are about the size of a 12oz drink can (except square) and the chunkiest model can process up to 7Kw (72v, 100A) peak and 3-4 kW average. The one I've had the pleasure of dealing with the most is the KBS36051 , which is a 20/50 amp type. I've found that 20 amps is a little sluggish for most vehicles, but that doesn't mean you can make fun go-karts using them.
If you want more power, the KBL type goes up to 500-600 amps and 120+ volts. Now that's getting into electric car domain, so I'm actually not going to recommend them to small EV builders. They are also legitimately the size of a house brick or more.
Kelly controllers can be extensively calibrated using the the shady visual basic application they come with and a USB-to-Serial dongle.
Shady Electric Bike Controllers
These some times pop up on eBay for $50 to $200. They function kind of like Kelly controllers, but are more rudimentary, not calibration-enabled, and were often produced for a specific model of electric bike sold in Asia. They come in fixed voltage and current ratings (and are internally current limited to that fixed amount).
I have no specific product page link for these things, and the actual wiring harness changes depending on the model you get. They're made in nameless factories throughout southern China and have no brand name attached. There are definitely several "bloodlines" of them, and they might even warrant an entire Instructable on what the hell they actually are. I can only recommend going to eBay and searching "brushless e-bike controller " to see what I mean.
Because of the indeterminate wiring conventions, I can't recommend these to complete beginners, but if you have been hacking around with EVs for a while, they are great starting foundations for modding controllers. Speaking of which...
Community-modified Shady Electric Bike Controllers
There is a large community of electric bicycle builders who have spent some time reverse engineering those controllers and are now selling upgraded versions of them as kits or whole modules. The largest concentration of these users are at the Endless Sphere Technology forums.
*NEW* January 2012 Sensorless E-bike controllers, a.k.a "Jasontroller"
As I recently discovered, there are several nameless e-bike controllers which can run fully sensorless. They are my current recommended small EV control solution because their sensorless startup and run algorithm is optimized for vehicles, which are inertial loads (as covered before). Instead of forcing the motor to start by dead-reckoning a minimum frequency, which would mean jerking your vehicle to several mph, these controllers ramp up to speed in startup mode. While the "ramping" takes less than a second, the effect is very pronounced and different from R/C controllers - the launch is smooth and generally seamless and without "cogging" or pole slipping. Being generic e-bike controllers, they also feature current limiting and a variety of different brake inputs. The only downside so far is that they do not perform regenerative braking...and they're kind of big.
As the only place I have found which retails these controllers is eBay, I can only link to confirmed sellers and general search terms. They are usually advertised directly as "Sensorless", or in some amusing roundabout way as "Without Hall". Current, bobzhangxu is the only seller which clearly advertises some of the controllers in his store as sensorless capable. The controllers I have investigated personally are retailed by him.
I have performed a full teardown and inspection of a "350W" type in this site post (and the next several posts show integration into some of my vehicles, including the hub motored RazEr and the titular Melonscooter). I like these things alot now, since fiddling with proper Hall sensor timing is both critical and very much a pain unless you have an adjustable sensor mount. The nice things about them are:
- They're sensorless. Not like crappy R/C airplane sensorless, but actually optimized with ramping functions for inertial loads.
- Cycle-by-cycle current limiting, so they are fairly robust. Like their sensor-only brethren, this current limit can be violated and messed with in multiple ways, including bypassing the current-sense shunt or changing the MOSFETs out.
- They are fairly large. Even the 350W is the size of an average single-serving juice carton or so, much bigger by volume than an R/C controller, but still smaller than a Kelly.
- They're not that power-dense or robustly designed. Low cost means cheap components and modest over-rating ability. The circuitry is fairly generic, the gate drive is discrete and made of really cheap small transistors, and almost everything is thru-hole or large surface mount packaged.
Being sensorless and not particularly high performance, they like motors with a reasonable winding resistance and inductance - something R/C motors are not known for. I've killed some by accidentally powering the motor with the drivetrain locked or restrained, and the resulting massive fast current spikes overcome the in-built protection and seem to destroy the gate drive circuitry. They seem to have some trouble starting up large airplane motors such as the melon (as-tested on melonscooter),so I would recommend them on the 60mm type motors at most. Else, you may elect to rewind your motor to a reasonable BEMF constant. They're designed with bike wheel hub motors in mind, which have many poles, are slow, and usually high resistance and inductance - a case proven by testing these on RazEr.
Finally, they have a commutation frequency limit. This is a point where the ESC can no longer keep up with the motor, and as a result could lost synchronization and draw huge current spikes. While airplane ESCs, with their simpler commutation dead-reckoning scheme, can usually commutate up to 3000+ electrical Hz (maximum speed of switching the phase outputs from one motor state to another - this has nothing to do with the PWM frequency), the Jasontrollers seem to be limited to only 500 electrical Hz or so. To convert eHz to mechanical RPM, divide by the motor magnet pole pair count, then multiply by 60. This implies that for an average 14 pole outrunner, the highest attainable motor speed should be no more than about 4,700 RPM. Again, this implies that they were built to drive bike hub motors. If you want to utilize these controllers effectively, you should make sure your motor doesn't regularly go over 4,700 RPM, which with a fast and high Kv airplane motor, could prove difficult.
When you're ready to make the jump from super hacked and rudimentary to something more legitimate, a real EV controller is the way to go. Kelly is generally the most well-documented and supported mass production upgrade path, but there are options worth experimenting with if you want to go out on a limb and learn something about how motor controllers work.