Friday, September 15, 2017

Fossil Free Friday: $500 Simple DIY Electric Bike Formula (The Electric Stuff and $ Total)

Welcome! If you're just now joining us, this is the third in a four-post series. Post 1 introduced the overall plan. Post 2 was all about the right bike to convert. Post 4 will be all about the stuff that I could not stuff into the first three posts.

Our goal has been to build a bike with similar or better capabilities than the Sondors Thin (base model) and to keep it under $500 (with shipping).

I had originally hoped to buy a Bafang-based full conversion kit that would be close to the Sondors' performance and quality, but I didn't find it in the price range, so here's the new plan - buy a comparable controller combo and a separate hub motor with no rim. The plan came in under budget, but ended up adding another step to the build. We will have to pay a local bike shop to lace up the hub motor and rim.

The Controller and Electronic Components (AliExpress)

Lots of goodness to be found in this set. The LCD screen is the same as the one on the Thin. It makes it possible to have five different levels of assist and to keep up with lots of stats like speed, distance, battery level, cruise control, and where to find the best pie in town. The controller is a sine wave model (more power and very quiet) that will let you move up to a 48 volt battery pack if you find yourself needing more power or less money. It will also let you add power regeneration/reverse functionality (but you'll need a direct-drive motor, not the geared model we have chosen here). Brake cutouts are crucial on a bike with pedal assist (unless you enjoy rushing uncontrollably into traffic).

The Hub Motor (AliExpress)

(add $60-$80 to have your local bike shop lace this motor into your wheel)

Before you jump into this part of the project, talk to your local bike shop to see if they are willing to lace up the rim to the hub motor and how much they will charge. Some bike shops will be interested, but others have no interest in working on e-bikes. It's better to find that out ahead of time. While this added step may seem a pain, in most cases you will end up with a much better built/balanced wheel than one mass produced in a factory. (And it's good to be on a first-name basis with a local bike mechanic.)

While you are having your wheel laced up, be sure to ask your mechanic to remove the rear sprocket from your old wheel. This will keep you from having to purchase a $10 sprocket removal tool. The sprocket should screw directly onto your new motor without needing any tools.

While this is not the Bafang I'd hoped for, it is a reproduction of that motor and costs 1/2 of the original. I probably should have mentioned this a little earlier, but I went with the geared motor for a few reasons:
  • they are very light weight and efficient
  • they are much smaller (and stealthier) than a direct-drive motor
  • they freewheel when you try to pedal the bike without electric power
  • most e-bike manufacturers favor geared motors for light duty e-bikes

The Battery Pack (All Purchased on Ebay)

One place we'll rock it in our conversion - coming up with a lithium phosphate battery pack (and charger) for less than a $100. Check it out:
All the pieces and where to find them:

Charger ($8 shipped)
The hardest part of the battery pack setup is splicing the pigtail onto the charger. You may need to borrow a digital multimeter from a friend (or borrow a friend who knows how to use a multimeter to test DC voltage).

So, did we make it? Well, not really, but we stayed pretty close, kind of. If we'd budgeted a little lower on the bike or maybe had a buddy around who laces wheels up for kicks, then maybe. But we haven't factored in wiring, zip ties, connectors, electrical tape, and a place to stash the battery pack and controller. There's still a little money to be spent, but we're still looking pretty good.
Even so, with a little luck or ingenuity, you can see it can be done, especially if you already have a bike hanging around just waiting for the electric treatment. Also, if you don't mind sacrificing things like the LCD or the geared motor (instead of a direct drive), you could get there for a lot less. So, yes, it can be done.
And hey, if it breaks down, you'll have a pretty good idea of what it takes to fix it! (Ah, the satisfaction of DIY!)
So, how about it? Feeling inspired? If so, let me know how it goes, or if you have any questions.
May you end up with a low-cost, high quality, eco-friendly machine one way or another!
PS. Stay tuned for Part 4 where we explore a lot of random stuff that did not make it into this post, including the formula for an even cheaper e-bike and for a powerful mid-drive bike for less than $1000. (Woohoo!)