ultra light,40 mph w/fairing,93+mi range,bicycle

I have gained a great amount of knowledge and insight into electric bicycle building through the members of this site. I built a pedal assist trike and learned much about power to weight and its effects on motor heating and battery pack integrity. It is 72V/60ah,LiFePO4.

The subject: I want to build a strong enough, but very light by electric bicycle standards, e-bike that I can pedal assist to about (65kph-55kph) 40mph(not slower than 35) for 93miles with elevation gain of about 2500ft.(Remember elite long distance road racers regulatory go 50 kph) Some extra weight added for added fairings, day pack wt., and foul weather gear. Is it possible to do this with some mid drive unit of not much over 48V and maybe 60-80 ah.. High pressure road tires, good 3/4 full fairing, full pedal assist(20mph road bike effort), Best battery pack to build for this? and how to support its wt... Is there a mid/central drive motor that would work and not deter from proper pedaling action. Lighter will add to efficiency gains, as the vertical gain and speed over distance is large. I don't feel the x5 or other such hub motor is up to task(heat and eff. issues) Larger bldc /ac syc motors are difficult to mount and too much wt. aloft. I don't want 100, or even 80 kph, just 65kph for about 150km. (that's 40mph for 93mi). I want to go from the ocean to the nz alps.. and back after recharge. This should be possible, just looking for a brainstorm on the matter.................

Velomobile territory. The key thing is going to be reducing your aerodynamic resistance to the level experienced by those road racers. Remember, they only pull time at the front for a short time, then rotate back and hide from the wind in the peloton. So none of those guys is pulling the whole race at 50k really. Even breakaway guys do it by sharing the load with 3 or more other riders, or they do it on a steeper stage solo. Nearly impossible to break out of the peloton sole on a flat day, riding into wind.

Or, you will need to forget about being that light, since you will be packing a much larger battery than you think. Looks like you realize that already, since you are talking about 48v 60-80 ah. In lifepo4, 60-80 pounds. I couldn't call an 80 pound battery light.

That's about 4000 watt hours. So at 1000w, 4 hours traveling 30 mph on flat, 120 miles. Definitely doable by carrying that much battery on an unfaired bike. The hill does complicate things though. 1000w won't go 30 mph up the hill. Or even 10 mph if it's very steep, and your rig weighs 350 pounds. If you are pulling 3000 w to go up that hill fast, then your battery now needs to weigh 240 pounds, meaning you will need 6000w to go fast up the hill. etc.

But if you lower your uphill expectations to 25-30 kph, then 2000w should do it, and you will get about 60 k of range. I just don't see how the steep part of your hill will go on the battery size you want. But going slower, pedaling accounts for a much higher % of total watts, so the steep part can be climbed on less power than would be the case if all of it was steep.

You are quite correct though, that a mid dive can be more efficient climbing the big hill than most hubmotor setups. But that efficiency is going to be happening by gearing down and going slower, unless your mid drive is also a big heavy powerful motor. Bottom line, 1000w only hauls weight up mountains so fast. So your ride up the mountain with mid drive will either be slower, or take a lot of wh. and in any case will take more power than back down.

I'd look into charging half way up somehow. Then you can cut your battery in half. 40 pounds less battery will help more on that hill than any fairing.

Also, it's still definitely doable with a hubmotor, particularly one able to climb at 2000w no problems, such as an x5, or any other hubbie with wide magnets.

Fairings and bodywork streamlining hold awesome appeal in a perfect world. But, real riding conditions are never quite so perfect.

What if/when the wind gusts strongly or you get buffeted around by larger much faster vehicles? More often than not, what was once helping you slip/slice through air is now acting like a sail and blowing you around all over the place.

Use the online calculator here to estimate your power requirements http://www.kreuzotter.de/english/espeed.htm. It even includes some different bikes fared and unfarred, with tail box and without. To get it outputting power required delete the power amount in the Power box and enter a speed, 40mph in your case, though you can switch it to metric too. At a mininum you'll want low and sleek with a tailbox like the Kreuzotter race bike, but more faring can be even more efficient through the wind. I entered you at 180lb and the bike at 80lb with that bike and came up with a 644W requirement for 40mph on flat road with no wind, but that's power at the wheel. To be conservative I used 80% overall efficiency (no pedal effort included) and came up with a pack requirement of 1.9kwh. Is there no place to stop along the way for a break and recharge to cut pack requirement in half, or do you need to go straight through?

I'm not sure why you're eliminating hubmotors right off the bat. The last thing I'd want is a blender sound inside a noise amplifying faring. I'd even spend the extra on a sine wave controller to ensure silence. A continuous run with little grade is exactly where hubmotors really shine, and weight is really of little concern. Just make sure it gets adequate air flow, and I'd ventilate (though not the holes in a pizza pan approach) it to keep it cooler and more efficient.

Whether in wheel or not an unstressed motor is the route to greatest efficiency, and that means a larger motor than one that is just big enough to do the job without failing. Lower rpm means less noise, another big plus for a hubmotor, even if run outside of the wheel.

In the interest of efficiency, don't paint yourself into a low voltage box either. Motor losses come in the form of heat, and heat loss from resistance in the copper is dominant. That means with most systems running a higher voltage will be more efficient, since that means lower current for the same power. Copper losses go up by the square of current, so limiting current pays healthy dividends. Ideally you'll want to start with a high efficiency motor, and then set it up so that peak efficiency (where copper losses and iron losses are equal) occurs at the load and rpm of your desired cruising speed.

Regarding batteries, the latest and greatest 18650's is the way to go, because they have the greatest energy density, so for a given pack capacity they're the lightest and most space saving option readily available.

Sounds like a great project. Take lots of pics of the process, both the build and the ride, and share them on ES.

John

ps- There are some nice thin somewhat flexible solar panels now available quite economically. To the extent your fairing needs a skin anyway, I'd consider having that skin add power back to your battery. It wouldn't be able to provide all the energy, but every little bit helps. Plus it would make your ebike much more of an attention getter.

Good stuff John.

I agree that at the speed he wants to go, a hubbie might be the best approach. And 48v might not be the ideal voltage then. Only if he wants to climb that hill on 1000w would a BB drive be better, and no way he's climbing any grade above 5% very fast ( like 65 kph) on only 1000w.

I would not completely rule out a chain drive, but maybe the approach could be a hub motor directly driving a chain. To hell with running it to the crank, we know pedaling at 65 kph is pointless.

One approach that could work well is two motors. One a high speed setup for the flatter parts, then the second for a slow crawl up the steepest parts through the chain, and pedaling. But it would be much simpler to just use a big hub, and carry enough battery to go faster up the steep.

Aero remains very important if he will travel 65 kph, even down hill it will matter. Low as possible for sure. Check out Cedric Lynch, the inventor of the Agni motor. He had a great looking velomobile. I saw it on a movie about electric motorcycles at the Isle of Mann TT. Uphill if you slow enough, aero will matter less, at some point it's hauling weight up a hill. But much of your ride will not be so steep and aero will be key for efficiency on the low grade or even downhill parts of the ride.

Re what the hill will cost your, and what speed you will be at going up it, it will help if you can break down the ride some. x miles at less than 1%, x miles at 3%, 4% etc etc. If 80% of your ride is 2% grade, build for that is what I mean.

Ideal would be if your ride will be 70 miles of flat, or rolling hills. Then a place you can charge before tackling the last 20 miles of steep climb. That would allow you to carry a lot less battery weight. That weight will hammer you on the final climb for sure.

Brief shot of Cedrics velomobile here. https://www.youtube.com/watch?v=KnqoH0YaCsE

I say just get the zero motorcycle at this point. It is production. It is proven so potentially it will last longer. Also it is probably a lot cheaper than what you are going to build.

The only downside is you have to register it. And have a license to operate a motorcycle here in the states.

Everytime someone mentions velomobile i just think instantly $10K minimum.

Save yourself the hassle of building and servicing and get yourself an electric motorcycle.

Now if your goal is to learn how to build an electric bike velomobile that is capable of this speed and range with great reliability, then go for it. Just know you will be spending a lot of money and time for something that probably already exist ina much better form. Understand the cost of such venture and the rewards. Then make your decision on that.

FWIW, I think Cedrics Velomobile would be classed as a motorcycle. Likely also true for anything able to climb a steep hill faster than 20 kph. 2000w minimum. Much more to climb a hill faster.