First e-Build advice: Commuting Recumbent

[PeterT12]

Hi Guys, after some time lurking it is finally time for my first build! Hope to get some good advice from more experienced builders, so here goes: (Sorry for the wall of text, but I just want to provide as much info as possible)

The Basics
Bike is a rear wheel drive full recumbent, steel frame, no suspension. Currently setup with V-Brakes, but that might change.
Front wheel 20", rear wheel 26". Drive train is a standard 2x 8 Shimano setup.

Desired max speed on level ground: 40 Km/h, or a little higher (with significant rider effort, please see below)
(PS. I know that 25Km/h is the legal max. in the EU. But where's the fun in that?)
Desired max range: No max, but an absolute minimum of 40 Km range.
Preferred bike wheel size: Could be front (20") or rear (26")
Brake type of motor wheel. Currently V-brake. Will probably upgrade to Disc Front and rear.
Rider weight: 75Kg
Terrain: 100% flat, no hills whatsoever. (Location: Belgium)
Extra: Looks are not important, it's all about functionality. Stealth is not a concern.
Budget: Somewhere around 500€-600€ for a complete kit, if possible. Otherwise I will have to wait & save.
Builder skill: Pretty good. I do all my own maintenance and have built up a few bikes. Lacing a wheel wouldn't be an issue. But I have never touched anything e-bike'ish.

Intended use:
I commute twice a week to work, about 35Km each way. Currently I have a road bike (not an e-bike) and this takes me about 1h20 min. Terrain is fully flat with long stretches of open road with smooth road surfaces, about 20% is through urban area with some traffic lights. On the open roads, I can maintain 30Km/h quite happily, but I want to go faster than my legs allow 8)

I am looking to bring the time down to about 1h, while still getting my bike exercise. So I am switching to my recumbent which I want to electrify. I would need the motor to give me the final "push" to go from a top speed of 30Km/h (human powered) to 40 Km/h. What I don't need is a setup that does all the work for me, I just need some extra support for more speed. I find it quite hard to decide what type of motor/kit I need, as most high speed setups seem to assume you just sit on the bike and let the motor do all the work. Charging the battery during the day is possible.

What I came up with so far:
- Probably need a 48V Direct Drive motor and battery.
- Wattage is big factor. I read many people just putting in a 1000W motor, but that might be way too much since I will be doing most of the work?
- Since the motor is just for extra assistance, perhaps a smaller battery would suffice?
- From a weight distribution point of view it would be nice to have front wheel motor. Not sure if that is feasible in a 20" wheel, because it needs to have a much higher RPM?
- I have played extensively with the motor simulator, however without a good feel for the division of effort between me and the motor, it is hard to get useful data from it.

Any advice would be greatly appreciated!

 

[jesusjesus]

Imo
for your requirements,40kph, a 1000w motor will be fine, you can just use the throttle less.

(you could over volt the thing, as it usually will take up to 63v, thus increasing your top speed.)

i got mine here, has both 20" and 26" with 500w or 1000w.
http://e-mon-shop.de/

price is about the same as Chinese vendors (if including shipping and taxes), and its in the Eu zone and your have 2 years RMA.


now you need to look into batteries that will cost around 300euro, for your budget.

 

[dogman dan]

Rear hub, unless you have an internal geared rear hub shifter. 48v 1000w will be ideal. Or a 750w bottom bracket drive.

48v 20 ah battery, on good days you'll have excess range. On the worst, enough. Since a 20 ah battery is very large, it doesn't have to be the very best cells if you are on a budget. It can still be very small, and light, easy to carry.

If you do the very cheapest of 48v 1000w kits, and bargain basement battery, the whole thing can be under $700, in the US. In EU, likely more to get it into the country.

Much better though, to do a quality build, with a budget closer to $1500.

 

[wesnewell]

A fast wind 48V 1000W kit sounds perfect. One that has a 700rpm rating on 48V. Don't know where to get one in Belgium, but one similar to this.
http://www.leafbike.com/products/diy-bike-conversion-kit/26-inch-electric-hub-motor-kit/newest-version-26-inch-48v-1000w-rear-hub-motor-bike-conversion-kit-903.html

 

[PeterT12]

Great stuff guys, thanks! Will definitely post back here when I have something to show

One more question:
I am now looking at one of the kits from e-mon-shop.de (Thanks for the tip!).
They advertise their 36V 750W kit to be able to reach 44- 48 Km/h. Is that number realistic? In that case, would a 36V setup be enough for me?

 

[dogman dan]

The moderately fast wind motors, in 26" wheel, will reach 45 kph, when the battery is fresh. 48v, charged to 58v.

A slightly faster wind will easily reach 48, in 26" wheel.

Something not discussed, if your flat ride has a stop every half k, a slower wind motor will be more efficient than a fast one.
I don't mean crazy slow, so you only get 30 kph, but just one that gets you 40kph, vs 48 kph.

If you only stop every 2-3 k don't worry about it.

 

[wesnewell]

Please fill in your profile location.
https://endless-sphere.com/forums/viewtopic.php?f=3&t=66302

 

[jesusjesus]

as dogman wrote, not at 36v.
this is under the most optimal conditions.

24v-36v imo is like a pc with 2 gb ram, it will work fine. 48v and < is where the fun begins

but you have to think about the legal situation, and and above 35 kph you re pushing it. safety, my trike is not safe above 35kph, unless im away from trafic and in short bursts, but your setup might be better.

 

[cycborg]

I think describing my setup will help you, since we start from a similar non-assist situation. I ride a 20/26 recumbent, my weight is the same as yours, my non-assisted average speed is basically the same, and I wanted to reduce my commute time by a similar proportion. Main difference is that my area is hilly - no crazy climbs, but everything is either up or down.

Also, my commute is half the distance of yours, but I only charge once per day, so if you charge both at home and at work, then you could use the same battery specs.

My motor is a MAC 8-turn, which is one of the faster winds. I bought this used from an Endless-Sphere member along with a 32 A Grin/Infineon controller for $200. For batteries, I have three 4s 10 Ah Multistars in series. I bought these when they were on sale for $40 each; non-sale price is $60 each. Only other thing you’d need is a charger - I use a combination of chargers that I wouldn’t recommend for someone just starting out. But if you buy a typical e-bike battery as opposed to these RC LiPo bricks, they usually come with the charger.

When I’m pedaling at a rate that gives me a good workout without killing myself, I typically draw 2.5-3.5 Ah on my 16.5 km commute, which I do in about 32 minutes. When I don’t pedal at all and ride at similar speeds, my batteries discharge about twice as fast.

Your battery needs may be greater than this, since I think you want a somewhat higher average speed than I typically ride at.

Bottom line, you can probably do this within your budget, and without a huge battery pack, especially if you can get something used. Since you don’t have hills you could probably use a smaller motor than the MAC (500-1000 W rated; maybe look for something rated 350 W). As for the battery, a 48 V 10 Ah pack would be pushing it - in cold weather you might lose assist for the last several km. 15 Ah shouldn’t be a problem, 20 Ah would definitely be safe. But batteries tend to be the most expensive and heaviest part of the system, so a “safe” pack will stretch your budget and weigh you down - you have to decide where the sweet spot is.

 

[PeterT12]

Thanks jesusjesus and cyborg!
Very valuable info, especially regarding "real world" range and battery requirements. This is just the sort of thing that you can spend weeks trying to figure out, but never actually know unless you try it. Or, in this case, ask someone on this great forum!

I'm currently leaning towards a Q11 48V1000W rear drive set from bmsbattery. I have found that most people recommend running this with the KU93 controller, so i'll include that.
Together with a 12 or 15Ah battery, probably also from bmsbattery.

 

[dogman dan]

Re battery size. Yes, obviously he can do it on less than 48v 20 ah, that's 1000wh! The bent has much better range. I just don't have quite enough experience riding my bent to really be able to put the ranges spot on. I've not yet even ridden it with a CA attached. Mine is geared too low, so I tend to use it on shorter rides, not pedaling at all, or ride so slow the range is unbelievable.

Even on an upright bike, I used to get 22 miles out of a 750wh pack pretty regular, riding 25 mph or less. so about 35k distance at 40 k speed. So we know he can do better with a bent.

But I also had plenty of days that I needed all 750wh, AND riding slower, to make it the 14 miles to home. The thing about a long commute, is the effect of a cold windy day is amplified by the increased distance. So I am going to really stick to my advice, that he needs 48v 20 ah, the full 1000 wh, even on his bent.

I guarantee it, there will come a few days he sure as hell needs every bit of it. There will also be a day his charger plug breaks, or whatever, and he will need to milk it back home without the charge at work. And speaking of work, charging RC lipo at work sounds like a great way to get fired.

Just some shit I learned doing 30 miles a day to work and back for 5 years. On his budget, a big high quality battery won't fit. But a big but lower quality one might. But the best possible approach will be a higher quality battery, and possibly shave the size down to 15 ah if you go for the best quality battery. With a very good pack, then he will likely get all 750wh from it, and would likely only need about 10 ah per 35k most days.

So whatever fits best in the budget, very good 48v 15 ah, or cheapest possible 48v 20. go bigger if you go cheap. So look hard at that 20 ah pack from bms battery.

Or, one thing that could work nice. RC packs do make a great emergency spare. 3 ah pack of that stuff can give you 6 more miles, on some day you turn out to really need it. You could add that later, using money you have later.

 

[wesnewell]

At 370rpm, the Q11 is a slow wind motor, better for hilly area than flat terrain. On 48V it will top out ~40kph.

 

[rsilvers]

Range is very speed dependent. So going 40 kph will have much less range than going 20 kph.

You will get the range you need from a 48v true 12Ah, but for a recumbent, I would just a 20Ah pack just because you can find a good place to put it.

 

[PeterT12]

Thanks again for the useful info! I feel I have learned more in this thread than in weeks of random browsing.
Another question: This weekend I was offered a very nice (well, nicer then mine anyway) recumbent by a friend. I am thinking of using this as my project bike. The problem is that it is an aluminium frame. (Rear end of the bike is made of an aluminium road bike)

I've read a lot of horror stories about using high power motors with aluminium frames. However most of these seem to be about using alumnium front forks. I can see that that is a horrible idea (forks snapping/breaking). Suppose I would use an aluminium rear end combined with two torque arms, would that hold up to the 48V1000W motor? If the answer is "maybe" I will definitely be sticking to the steel frame, don't want to risk my life on this...

 

[dogman dan]

Aluminum frame will be fine with one good torque arm. Or two shitty ones.

Most of the real danger of aluminum and motors is when the motor is on the front. Even if you damage an alloy frame in the rear, it's just not usually near as hard on the rider as when the front wheel goes one way, and the bike another.

Definitely go for the new bent. If that one happens to have a 20" rear wheel, it will perform even better than your 26"rear wheel bike.

Beating the battery thing to death, 12 ah is enough. But a very long commute means you need a little bit bigger reserve for the bad days, IMO. All the ranges I was talking about were for 40 kph speed, but not on a bent. 15 ah would be enough for the warmer days, including a healthy reserve. But maybe not, if your route has a stop every block. Stops are as bad as a big hill for killing range. So re the slow wind motor, that IS what you want if you do have a stop every block. But a slow wind might mean a slow top speed too.

 

[rsilvers]

Stops are as bad as a big hill for killing range.

Now imagine human power rather than electric. And drivers wonder why cyclists don't stop at stop signs. Loss of momentum.

 

[dogman dan]

Just as not fun, if you choose a battery too small for your commute, and have lots of stops. You end up having to pedal only the first 20 feet after each stop to make your range. And sure enough, you don't want to stop then when no cars are coming, just like a regular cyclist hates it.

But choose plenty of battery, and your range worries vanish, and it takes all the sting out of stopping, or taking a longer but safer route.

Casual riders, do what you like. It's a joy to ride with the smallest possible battery. But a serious commute should have a lot of overkill on the battery size IMO. If nothing else, 2 years from now your battery will have lost some capacity.