[HNaTTY]

I built an e-bike last weekend, I have just 35 miles on it so far and I've convinced 1-2 friends to get one already. I love riding but my enthusiasm in winter is severely diminished; this has rekindled it for me.

Anybody here who is interested in an e-bike should strongly consider building up an existing bike rather than dropping $4k on one of the ones mentioned in this article. All the ones mentioned in the article are underpowered and overpriced.

I built a front-suspension mountain bike with a mid-drive motor called a BBSHD. Setup of the bike with the motor kit took about 3 hours and there were no major issues. Some custom tools might be needed to remove the bottom bracket, a bike shop would likely charge less to do it for you than the tools cost.

Last bit of advice, if you do get a DIY kit, make sure to get a high-quality 18650 battery pack. Don't go LiPo and certainly don't go lead-acid. Your battery pack will last longer if you don't always charge it to 100%, but you should charge it to 100% the first half dozen cycles to balance the batteries.

[zik]

I've ridden a few converted bikes and a few purpose built e-bikes. In my opinion the purpose built ones are far better than any conversion I've ridden. In fact I now own a Gazelle.

[HNaTTY]

In my opinion the current generation of mid drives are better than the vast majority of hub-drive motors, whether we're talking about the Bosch or Yamaha or Bafang etc... "Better" is a very slippery word. The Gazelle bikes have the Bosch mid-drive system which has torque sensing, but only puts out 250 or 350 watts and your bike cost $3 or 4 thousand dollars. Considering the moderate range and instantaneous power, while it's in line with similar bikes, I feel that it isn't a good value overall. Once bikes with this kind of performance are readily available for, say, $1200, the world will bend around them. But not before.

[zik]

250W is all that's legal in my country so that limit is fine by me. I can still go as fast as really makes sense on the bike paths I commute on.

[mustafab]

I am really interested can you tell more about how to build it ?

[HNaTTY]

Here's a video of the installation: https://www.youtube.com/watch?v=SmMtUVO5XZA

The folks that made that video are probably the biggest DIY kit sellers and a big (and controversial) force in the e-bike community. I bought my kit from them including the battery pack.

First: remove the front derailleur (you'll likely have to break the chain to do this, your chain may have a quick-link, otherwise you'll need a chain breaker tool, check YouTube for instructions), remove the shifter cable all the way up to the handlebars, remove the shifter from the handlebars. This mid-drive only has one sprocket on the front, and you retain the stock gears on the back.

Next: remove the pedals, crank arms, and cranks aka front sprockets. Then remove the bottom bracket (special tool may be needed here).

The motor slides right in the hole, you cinch it down on one side, re-attach crank arms and pedals and chain, and from there it's a matter of plugging everything in and a little cable management. Zip ties will be needed.

Here's an incredible riding video to motivate you: https://www.youtube.com/watch?v=tZrleBFAleQ

[marme]

it should be noted that the motor installed in that first video is 1000 watts which makes the bike legally a moped by federal law in the US which means you must register it with the dmv and get a plate for it, some states outlaw mopeds completely. It must be 750 watts or lower and max speed under 20 mph to be still be considered a bicycle which does require registration or drivers license. Lots of people put the 1000 watt motors because they have little to no markings saying they are 1000 watts so as long as you are not caught going above 20 mpg you will never get in trouble for it.

But they sell 3000 watt motors that can easily reach 50 mph. If you get clocked by a radar gun going 50 mph on a bike there is no amount of reasoning that will not get your bike impounded as an illegal/unregistered moped. To understand the equivalence 750 watts is approximately 1 horsepower so a 3000 watt motor is 4 hp. The average 49cc moped/scooter outputs 2-5 hp so it makes sense they would make you register an ebike with that much power as a moped

[kazinator]

You can exceed 20 mp/h with a 250W motor: namely, your legs. :)

[HNaTTY]

The law in my state defines a bicycle as a "device having two or three wheels with fully operable pedals and an electric motor of less than 750 watts (one horsepower), whose maximum speed on a paved level surface, when powered solely by such a motor while ridden, is less than 20 miles per hour". So you are allowed to go faster than 20 if you're pedaling.

Bonus fun fact: in my state, you can't get a DUI on an e-bike because it is not a "motor vehicle".

[alistairSH]

While true, not many casual cyclists can maintain 250W for more than 10-15 minutes. And 750W is an all-out sprint for many casual cyclists. 1000W-1500W is a sprint for trained cyclists.

So, that 1000W motor is, in theory, as fast as my sprint, but for a much longer time period. And also in excess of the speed limit on a residential street.

[HNaTTY]

The power output (watts) is a function of (volts * amps) so if you have a 48v battery, you can output ~15 amps and get 750 watts. The amperage output is controlled by software, and these mid-drives are programmable. When you buy the kit, you can have it programmed for 750 watts or 1600 watts for off-road use only.

FWIW, on the bottom is a sticker that says "750W".

[agumonkey]

> Here's an incredible riding video to motivate you: https://www.youtube.com/watch?v=tZrleBFAleQ

Anybody remembers Street Hawk ? :)

[fillskills]

How much range do you get on yours? I am interested in this one because it has 30 mile range and replaceable battery. Price is pretty decent at less than 1500. Link: http://www.genze.com/e-bikes/

[HNaTTY]

That bike has a 36v, 8.7ah battery. I have a 52v, 13.5ah battery. Watt-hours is volts times amp-hours, so you're looking at 313wh and I've got 702wh, so more than twice.

That bike has 1.75" tires and I've got big 3" wide tires, and I'm only running about 10-12psi, with front suspension sucking up what feels like half of my pedal power, so rolling resistance is much higher and efficiency is much lower for me.

The "efficiency" is calculated as watt-hours per mile. You'll see different numbers depending on all sorts of factors (pedaling, speed, terrain, tires), but we can just hand-wave it all away (science!) and say 20wh/mile. That gives you about 15 miles and me about 35.

I've only run the battery down once so far, and that was only from a 90% charge, with a lot of mud, snow, and general screwing around. The battery cut out at just over 25 miles.

[fillskills]

Thanks for detailing it out. Really appreciate that. I will mostly be using the e-bike for daily commute. I was looking for something that is good battery life, cheap, comfortable, long life. Your analysis helps a lot in figuring out the a big part of it.

[HNaTTY]

A bit more info on the 20wh/mile number that I totally made up.

The bike you linked has a 250w motor. Running it at 100% for an hour, if you were able to average 12.5mph for that time, that gives you 20wh/mile.

Based on the watt-hours we calculated earlier, and the manufacturer's claim of 30 miles, we have to assume they're figuring 25mph at 250w of power. This is technically possible according to (http://www.analyticcycling.com/ForcesSpeed_Page.html) but clearly we're in "best case scenario" land.

[owenversteeg]

Nice comment! Just a things I'd figure I'd add, cause I know a bit about batteries and this is HN after all:

- LiPo cells are really LiIon cells, the name is misleading. There exist true LiPo cells but unless you're a battery researcher you probably don't have one.

- 18650 batteries _are_ LiIon batteries (just as LiPo batteries are) they're just a specific form factor: a 65mm long cylinder with diameter 18mm. (Technically, 18650 is just a form factor, so you can have a non-LiIon 18650 - and I have two non LiIon 18650 cells - but it's exceedingly rare for an 18650 to be non-LiIon and I don't believe you can buy them.)

- Pretty much all batteries are only made in extremely large amounts and sold to large companies for either industrial, automotive, or consumer electronic uses. 18650s are made for industrial and automotive uses. RC, e-bikes, vape pens, etc are just a blip on the radar compared to the enormous battery consumption by industrial, automotive, or consumer electronic uses. This means that none of the battery companies make cells for these uses. This means that the companies that make battery packs for RC uses or e-bikes are making packs out of leftover cells from larger companies. If you buy, for example, a pack online for your quadcopter, it is probably made by a factory that takes 10 cell-phone, or laptop, or power drill cells and puts them together.

- Because there are space/weight losses associated with getting the reaction to happen in a cellphone battery sized space, and there are losses from packing ten cellphone packs together, "LiPo" packs are generally a bad idea.

- However, 18650 cells are relatively space/weight efficient to begin with, and there are a bunch of large companies pouring many billions of dollars into improving their 18650 format battery processes, so they're by far the best thing to use when you're concerned about weight/power/capacity.

- Lead acid packs are, like you said, a horrible idea, unless you have strange constraints. If you need the ability to treat them horribly, or need high power, get lithium ferrophosphate cells. If you need to treat them horribly, need high power, AND need extremely low cost, then lead-acid cells may be your best bet.

- Building your own battery packs will save you an enormous amount of money. If you don't like working with electricity, hiring someone else to build your packs will save you a bit less money, but it's definitely worth it. When you build your own packs, you know what you're getting, as the vast majority of these pack websites overcharge you for fake cells. I build very large packs occasionally. If anyone's curious on how to build their own, or wants sources to find good cells cheap, my email's in my profile.

[joshu]

Any docs on parts you used or how you researched and acquired them? I am actually building a gokart that would take advantage of this stuff.

[HNaTTY]

My favorite sources of information about e-bikes come from endless-sphere.com, electricbike.com, electricbike-blog.com, and the /r/ebikes subreddit. Also I've obsessively watched almost every video with "BBSHD" in the title on YouTube in the last several weeks. I will say that the technology is moving pretty quickly and the state of the art today will be the underpowered overweight crap of tomorrow. There is a LOT of room for better technology and the price can come down further as well, all it'll take is an expanding market and competition to bring new innovations to market.