For a long time I've thought that it would be a fun project to put together an electric bicycle. However I've been stymied by the cost and questionable quality of the existing kits, and the complications and compromises of the various DIY methods that are out there online. I have some ideas for how to go about making a cheap and simple electric bike, but I'll be the first to admit that I'm nobody's idea of an engineer so I thought I'd run some things by y'all and see what insights you have.
My overall goal here is to have a bike that could take me to work and back, seven miles each way across mostly flat roads, at a reasonable pace and if necessary with a recharge between the trip out and the trip back. I'd like to be able to pedal the bike as well. It needs to be reliable and to be able to transport about 225 lbs of bike, rider, and gear at say 15mph over flat ground. I also want to keep costs, weight, and complexity to a minimum.
I have already ruled out the idea of buying a purpose-built electric bike. They are very pricey for what you get (my understanding is that this is due mostly to economies of scale, plus the fact that a decent new bike is already at least several hundred dollars even without electric running gear) and somewhat counter-intuitively tend to be built rather cheaply in order to keep costs down. Also they are usually not the best as far as pedaling; aside from the inevitable extra weight of the electric drive system, they usually seem to use heavy high-tensile steel frames and to omit the kind of transmissions that allow traditional bikes to be fast and efficient. Most importantly though, I want to be able to enjoy the fun of building something useful on my own.
There are kits out there that purport to allow one to convert a standard bike into the kind of electric bike I am interested in (Here's an example
, note that it does not include batteries) but they tend to be expensive -- around $1,000 once you factor in a set of good batteries -- and my understanding from reading reviews is that they are built rather cheaply in China and tend to have pretty inconsistent build quality and reliability. That's out of my price range, especially for something that is possibly not going to last very well, so I've been thinking a lot about hacking something together out of repurposed parts.
The plan is to start with a used but good-condition hybrid or mountain bike, something like what I was asking about in my Ask from last week
. (I haven't bought anything yet as a result of that question, but I got some great ideas and anticipate getting a new bike soon, thanks!) This would give me a nice sturdy frame to work with, something well built from aluminum or chromoly steel, with street-appropriate tires and a transmission that would allow for decent pedaling. I think something like this would be an ideal platform to build an electric mod around.
Currently my favorite idea in terms of the electric "upgrade" is to build it around a powerful cordless drill with a brushless motor. The model I've been looking at most is the Milwaukee 2604-20
, an 18v cordless drill with a brushless motor (for quieter running and longer life -- most cordless drills use brushed motors which inevitably wear out, especially under sustained heavy use) lithium-ion batteries, and an all-metal gearbox that can be had for about $250USD on eBay complete with two batteries and a charger in new or lightly-used condition. It's gotten excellent reviews in the contractor community for being one of the more powerful drills in its class, and for being able to run for a long time on each battery. Milwaukee tools also seem to have a good reputation for durability, reliability, and overall build quality. There are similar drills from other brands as well, but that's the sort of drill I'm looking at. (All these drills seem to be built in China also, but built well rather than cheaply.)
The advantages to building my system around a cordless drill mostly come down to simplicity. Basically a cordless drill provides a motor, a chuck, a speed controller, a transmission, and a battery all in a single package. The only part that I'd need to add myself would be a throttle, which would be cable-actuated either by a hand brake lever or a twist handle. I would also need a similar system to disengage the drill, though depending on where I end up mounting it I may be able to simply put it into neutral with the button on the drill itself. I'm not remembering clearly whether cordless drills will spin freely when in neutral, but even if I need to use a freewheel hub or some kind of disengagement device like a derailleur or a movable cog I should be able manage.
I can think of a few ways to make a drill drive the front wheel. I could simply use a roller pressed against the tire or rim, though I am aware that this method tends to sap a lot of power from the system and I'm already worried about it being underpowered so I probably won't do that. I could mount the drill directly to the axle on the front wheel (after swapping to a suitable axle) but then I would end up with a rather large, heavy drill hanging off the side of the bike and making it unbalanced. The third option I have in mind is to use a chain drive to connect a cog on the drill to another cog on the front wheel (which would probably have to be switched out for a back wheel that was modified to work with the front fork). The last option sounds like it's probably the most practical (I could simply mount the drill on the back side of the front fork, assuming suitable clearance) albeit it's the most complicated as well.
So far so good, but I'm not convinced that the underlying plan is a sensible one. I'm concerned that a cordless drill won't be able to do what I want it to do, and the specifications available for drills don't really give me the kind of information I need in order to work out from first principles whether or not this is a real option. I'm concerned that a drill won't be powerful enough to drive the bike, that it won't be durable enough to hold up to sustained use, and that the batteries (even if I carry a spare in my bag) will not give me the kind of range that I need and/or that they'll wear out quickly and be unable to hold a charge. Drill batteries are a lot cheaper than big LiFePo4 bricks
, but if I'm having to buy a new set every week or two then it becomes sort of a pointless endeavour. There's also the issue of theft and weatherization, but I'm convinced that I can deal with those problems.
What do you think about all this, hivemind? Have you ever tried something like this, or seen or heard about it being tried either successfully or not? I've seen a few instructables and such that involve building an electric bike with a cordless drill, but none of them have satisfactory end results. They all use very weak drills and crude drive systems however, and I think I can do a lot better there. I've seen some debate on online forums around this idea, but nothing that seems really conclusive -- people seem to be making a lot of uninformed assumptions that don't seem like they'd necessarily hold up in the real world if I "did it right".
If you do think that this is potentially a workable concept, I'd appreciate advice about the best way to set this system up so that it would work well or about any pitfalls or hurdles that I haven't thought of. If you think it's a poor idea overall then I'd love to know why you think so and would especially like to hear about any designs or concepts that you know of or have thought of that you think would be superior. My knowledge of electronics and mechanics is pretty rudimentary but I am fairly handy in general (and bikes are one of my stronger suits, albeit I recognize that I am no professional in that area either) and am looking at this project as a learning exercise so I'd be happy to expand my skills as long as whatever I have to construct comes with clear instructions. I think my absolute maximum budget for this project, not including the original bike and assuming that I have all the necessary tools to pull it off, would be something like $500USD. Less would be better of course, as long as I'm not sacrificing my performance minimums -- 15mph sustained top speed over flat ground, seven mile range, 225lb load, ability to pedal, and a reliable system that will stand up to years of frequent use.
All your advice is greatly appreciated. I'm very much looking forward to hearing what y'all come up with.