I’m a firm believer in seeing what works and using it. If you’re an engineering student, or like tampering with the elemental forces of the Universe, you’re not going to agree with me, but if you’re looking to get a bike rolling in a reasonable amount of time with a reasonable investment, and with a good chance of success, I figure you want to see what everyone else is using, see how well it works and go with that.
I know. Playing it safe is so boring. Well, until you get on the (working) bike and go for a ride…
The easy way to do this is to simply look at what a supplier is putting up for sale. Thunderstruck Motors, Cloud Electric and Electric Motorsports probably have the most common and complete lineup of good stuff… all great companies to deal with, from what I’ve heard too. They also all sell complete packages- the motors and controllers to match- a very helpful thing, especially when you consider warranty issues. If you buy the package from one place, you get someone who’s going to stand behind what they recommend.
Here’s the basic breakdown. First, the PMDC lineup.
(Shown above- Mars ME0709, Agni 95R, and Perm 132)
Permanent Magnet DC
Permanent Magnet DC motors fall into two basic classes- brushed and brushless. The brushed models, like the Mars motors, are probably the most basic motor design you can go with, reasonably priced, and well proven in the light motorcycle/robot market. You’re looking at around $500 for a 72V brushed model. The controllers are in the $600 range. Brushless motors are basically very similar, but rely on the controller more since the controller performs the same function as the brushes. You don’t, however, have to worry about maintenance- there are no brushes to wear out.
By the way. There’s a very confusing tendency to refer to the Mars motors as an “Etek”. I have a whole big post about that, you can read all about it, here, but the bottom line is there are no Etek motors anymore, unless you get something used or NOS. Just sayin. Also, I put together an explanation of axial and radial air-gap motors here.
The Agni and Perm are called a “pancake” design- an axial design that gives you high efficiency, more RPMs per volt, more RPMs period (the Agni spins up at 6500RPM) and a really handy shape for an electric motorcycle. (When did they start calling the shape the “form factor”? Around the same time that curtains became “window treatments”?) With the increased efficiency you get a higher price- around $1000 to $1400 for the Perm, and around $1400 for the Agni. Many of the race bikes run the Agni- some run two.
Series-wound DC motors
Probably the second most common motor type is the series-wound DC design. These things are the workhorses of the EV industry- very common on car and truck conversions. They’re big, heavy, but strong as an ox- and well tested in the field. They have, as far as I understand it, huge amounts of low-end torque, but a limited high-RPM… great for lifting loads and getting you rolling. They also can take higher voltage- the D&D motors shown on Cloud Electric can handle up to 144V- way higher than a PMDC. You’ll see them used in the bigger bikes, as well as the drag racers and experimental bikes- they’re a lot more common as simple industrial motors.
I’m showing a Netgain WarP 9″ “ImPulse” here, just because I like the name. Sue me. These sell for around $1500 and the biggest issue with them is that they’re long- sometimes a little tough to fit into a frame and line up with the drive sprocket. You’ll also see guys pulling motors out of various salvage applications- forklifts being a popular one- and modifying them for bikes and cars. This can be a tricky row to hoe- you can assume you’re going to have to do some modification to the motor, like the output shaft- and it may be a job getting the controller to work well for a bike. It’s not a solution I’d use, but I can see how it’d be a fun challenge if I had the time and resources.
AC motors may be where we see the most development in the coming years- it seems to be where everyone is going, especially in the racing community. AC motors have higher RPM capability and you can control the performance more, due to the nature of the physics of the motors and the controllers. You’re going to see this in the better regenerative braking performance- “regen” of the motor- something we really haven’t talked about, and, honestly, something I don’t feel, after everything is said and done, is worth the extra overhead. More on that later, but if you’re looking for regen, you probably want to look at an AC induction motor.
The standard package seems to be the AC-15 ($3200 with controller and kit) or the AC-20 ($3800 with controller and kit). The AC-20 pulls 72-108V, 550A, ~50HP and 110FT-LBS . They call it the “RACE MOTOR”. In capital letters. It’s a little more pricey than what we’ve looked at, but I think you can pull more out of it if you know what you’re doing, or want to learn.
As I’ve said, AC motors seem to be where people are heading- in particular, liquid cooled AC motors. Several of the newest models of motors we’re seeing are offering a liquid cooling option, with various levels of benefits. See more about that in my motor cooling stories.
Sepex (Separately Excited) DC motors
“Sepex motors are almost identical to traditional Series motors except for the way their field is wired and controlled. Unlike the Series motor whose armature and field windings are wired together in series, the SepEx motors field and armature windings are excited separately by special SepEx controllers that have wire leads to both the armature and the field. Separate control of the armature and field creates distinct advantages over a standard series wound motor, notably adjustable regenerative braking, higher rpm, longer power band, higher efficiency, and easy reversing.“ As far as I understand it, they’re also the top end of the efficiency range of any motor. You do, again, have a problematic “form factor” to wrestle with- maybe not a great solution for a small bike, but certainly workable for a bigger one.
With the Sevcon PowerPak controller, the D&D runs at 425 A, 84V, 25 hp, gives you 4500RPM and sells complete for around $1500. Honestly, it seems like a great price for a very versatile package- something you could set up to run easily, and then spend countless happy hours tweaking away to your heart’s content…
All in all, the motor decision is, in my opinion at least, not ultimately about performance. The performance comparisons between any of these options is going to be offset by the other various factors of the build- the weight, the fit, and I come right back to motor basics. That is, the motor you choose has to be able to handle the load you want to give it, that is the bottom line. The ultimate performance of the thing has more to do with the batteries- how much current and voltage you can feed it for how long, and how fast- and other things like the weight of the bike. You figure that out, then pick a motor that can handle it.
You chose a motor to fit your build, you don’t build a bike around a motor. You build a bike around the entire system. That’s where you look at what’s been done, what works, how it performs and how much you can afford.
Everything else is what my friend Adam lovingly refers to as “motor prOn”. …and hell, we all need a little motor prOn.