ryguythewiseguy said:
Desired max speed on level ground: 50mph
Desired max range at what cruising speed: 40 miles at 30mph
Preferred bike wheel size, or wheel size of bike you want to convert: 26" wheels (will take advice based on my use case)
Brake type of motor wheel. Disc or not: Disc brakes or whatever is needed to save my life
Rider weight: 220lbs
Terrain. mostly flat, some short hills under 20% grade all road and asphalt with minimal offroad
Budget:$3000
Based on the above, and this quote in your profile "building a bad ass bike that wont get me pulled over on my commute to work.", you're basically building a motorcycle, and you'll likely want to build one that's registerable as such.
If you look around the web at ebike law in Illinois in general,
https://www.google.com/search?q=chicago+ebike+laws
you find that it's max of 750w, which won't get you the speed you're after, unless you're building a streamlined recumbent type. It's also limited to a max of 28mph for the highest class of ebike, so you can't go that fast on a bicycle-class type regardless.
So to get the speeds you want, converting an existing gas motorcycle is your best bet, but the budget is probably going to have to stretch beyond $3000; youre basically building a motorcycle-class ride, and it takes more money to do that than bicycle-class.
That said...if you want to risk it anyway, you can build with a good enough frame, suspension, brakes, and wheels, and be relatively physically safe doing it, but you will probably want to use motorcycle / moped wheels and tires so you have less problems at the higher speeds. You don't want a sudden flat at the higher speeds--one in front could kill you at 50MPH (even 30), even if you're wearing full MC gear. (though I expect wearing such gear will get at least curious looks from LE you pass, unless you have MC plates on the bike; dunno what LE is like there in Chicago).
If you go the bicycle route, I'd recommend not building something that looks like a motorcycle, and keeping as bicycle like as possible, or else you're likely to attract LE and other attention you don't want. Going those speeds is going to do that anyway.
Suspension...there's bicycle suspension for DH bikes and the like that's probably good enough for those speeds, depending on how bad your roads / paths really are. But if it's really bad on any stretch you have to go fast on, you might consider MC stuff instead.
If you're using MC wheels and forks you can also use MC brakes easily enough, without machining adapters to make them fit bicycle wheels and forks (there's posts around the forum on doing that, too, if you like).
'First, if you want more than just a list of parts to build with, and want to understand something about the relationships between the bits you're going to put together and why people make some of these recommendations, you should go to http://ebikes.ca/simulator, read the entire page, and then play with different systems to see what might best do what you're after. This will give you some knowledge of how the system as a whole works, and what parts you may be able to use less of and what you need more of, between motor, controller, and battery, and if a particular wheel size vs voltage, or whatnot, might work better for your purposes.
The data below are guesstimates based on experience and reading other's builds, and not using the simulator or other tools. If you use the simulator and similar tools, and read thru other build threads to do the same thing you want to, you may be able to get more precise numbers.
Battery...if you only need 40 miles at 30mph: If we assume 60-80wh/mile or so for power usage, then you'd need 40 x 80 (worst case, let's say, not counting headwinds or crosswinds), then that's around 3200wh. That's a pretty big pack. My SB Cruiser trike's almost-40lb-EIG pack is only about 2000wh, so you can estimate around 60lbs for your battery. You may be able to use much less, if your aerodynamics are better than expected, and/or you don't have to do much stop/start traffic stuff, not much in the way of winds, etc. But most likely you'll need at least 2000wh, around 40lbs of battery, depending on the type you use and it's casing/etc. You will want to build it with some percentage (25% or more is what I'd go for) extra capacity to account for detours, headwinds, pack aging, etc. Most likely a 72v pack is a better option than a 48v or 52v pack, for the speeds you're after.
Every moment you spend at higher speeds than the 30mph cuts deeper into your range than staying below that. Every moment you spend below 25 or even 20mph wil gain you significant range over riding at 30+. The power requirements go up nonlinearly (quite a lot) the faster you go.
You may also want to build a battery heater into the bike's pack container, so in winter you don't have less capacity and capability, or charging problems.
There's DIY and premade---if you're unexperienced with batteries I'd go with a prebuilt one, as learning enough about the process and materials and such to DIY takes a while, and while the actual failure percentage is probably low, the failure results can be devastating, and can destroy the whole building (or complex) the battery was in when it ignited from it's failure. The same failures can happen to any battery, but the risk is much higher for DIY stuff by inexperienced builders (and cheap "shrinkwrap" batteries...if the price seems low, so likely is the build and materials quality).
Motor: for 50mph you're probably going to need 5kW+. There've been a number of fast builds based around QSmotor's "8kw" hubmotor, which also comes in a MC rim, handy for that kind of speed. Depending on total weight and slope of hills and speed needed on those hills, and headwinds, you may need higher power. (an 8kw motor can do probably twice that for short bursts of up to a few minutes, and 8kw all day, if it's realistically rated). I wouldn't go with MXUS as I'd call their build and materials quality on the poorer side of middling, based on my experiences with two different generations of their 3K motor. No experience with QSmotor either, but the pics I've seen of interiors appear much better than MXUS. The motor and wheel is likely to weigh 40-60lbs, at a guess, depending on MC vs bicycle rim/tire, size of motor, etc.
You can go with middrive stuff instead, chain or belt drive with the motor on the swingarm or in the frame, instead of the wheel. You'll probably have better ride quality like this, for rougher roads, as the suspension can act more quickly, and the motor will probably be lighter (because it spins faster to get the same power, but could be more vulnerable to overheating on long peak power demands unless it's actively cooled). It is just mechanically more complicated to build than hubmotors, unless you buy a frame designed for that, and the motor/etc that frame is built for.
Controller; there's a lot of good controllers out there, but if you buy from places like QSmotor they have some they pair with their motors as compatible; might as well try those first. I'd personally avoid Kelly because of stuff I've seen on the forum about various problems, including bricking the controller just by having the motor rotating while the controller is plugged into the programming interface (computer via USB)--that's a pretty major flaw to leave in a design, when I'm sure it's not that hard to fix. They do warn not to do this in the manual, but it's an easy thing to have accidentally happen, and Kelly won't help you if it does. Plus, sometiems Kelly stuff just explodes without any apparent cause, after operating perfectly for quite a while. Sevcon is complicated to setup, and requires extra hardware that can cost more than the controller to do so. ASI is supposed to be pretty good and customizable. Generic cheap controllers...you get waht you pay for. Lots of other types out there, including build-it-yourself like Lebowski, with various powerstages designed by several poeple around the forum. At a guess the controller is going to be 5lbs+ and the size of a hardcover book or trade paperback, if not quite the same shape; depends on how it's designed and how it works.
Wheel size: smaller wheels give better torque for the same motor/battery/controller than a bigger wheel, but get you less top speed. Higher voltage fixes that. But they also have worse ride quality than a bigger wheel, on less than perfect pavement and offroad. A bigger motor / more current from the controller / battery fixes the torque issue of the bigger wheel.
Torque will get you going faster and help you climb hills. If acceleration time is not important, you don't need as much torque. IF you need to get going quickly from a stop, torque is important.
