Just wondering. An ebike from mway etc usually costs around 3-5k. A DIY ebike with a torque sensing mid-drive (so not a motor in the wheel, but one just like the Bosch and Yamaha) can be built for about 1.5k (including a brand new bicycle)
I just finished building mine and very happy with the result. I’m wondering if there is any interest in this, and if anyone else here did it?
This sounds like a fun idea I’ve been thinking about for some time now. Would live to hear more details how you did it! 
i was more looking into something that can replace my road bike’s front wheel and do the recuperation trick when breaking, but i have not found anything so far.
@boschika
could you elaborate please?^^ what did you build, where did you get the parts? thanks!
very cool - did you follow a specific tutorial?
So it’s not that complicated, but you do need to be confident and make your hands dirty. I put extra care in planning my build and cabling it because I wanted a nice looking end result, but there are also others who don’t care as much and have cables everywhere. Neater takes more time, but it’s up to you.
I bought a mountain/hybrid bicycle new (because a used bicycle here costs the same as a new one in Germany.) I went for a name brand but others have had success with pretty much any bicycle, including department store kind of bicycle. Giant bikes are also very popular because they’re easy to find and reasonably priced. Things to look out for are: disc brakes (a must in my opinion because your bike will be much faster and 8KG heavier with motor + battery), and a square tapered bottom bracket (motor only fits these.) Some also prefer a front suspension, but I personally didn’t go with it because it’s extra maintenance and a decent one adds cost. Some go for a cyclocross bicycle with full suspension, but that makes it very tricky to fit a battery and the motor, and will usually require serious hacking and welding/custom part fabbing.
I then bought a TSDZ2 mid-drive direct from China for singles day (11.11, a big sales day in China)
And the battery I got from em3ev which is the best money can buy with a Black Friday and wire transfer discount.
I chose the TSDZ2 because it’s the only aftermarket mid-drive that has torque sensing (meaning that it senses how hard you push down on the pedals and multiplies this effort, when the other motors just sense that the pedals are rotating and applies full force right away), and because there is an amazing open source firmware you can flash on instead of the stock firmware.
As for the battery, I didn’t want to worry about range when going on summer adventures so I got a 17Ah 52V battery (825Wh.)
Buying the tools to put it together cost me about 100.- or 150.- because I was able to plan ahead and buy most tools from amazon.de or aliexpress. Some of the tools I had to buy here because I needed them in a hurry, and that cost more than all the other tools combined. But basically you need a crank arm extractor, a bottom bracket nut, allen keys, a tool to shorten your chain (not always required, my chain for instance was still the right length after the conversion), anti-seize paste. I also needed to re-route my rear derailleur cable so I had to buy a Shimano kit for that (housing + cable) and pliers to cut it to size.
The motor + a 850C color display cost me 360.- shipped from HK and arrived within a week by DHL
The battery cost around 550.- including shipping and a quality 90/100% charger (excluding UPS’s insane brokerage fee of 30.- to collect 5.20 worth of tax due)
On my bicycle, the tricky part was that the cables are routedunder the bottom bracket, but the cable guide holding them in place was too thick to fit between the frame and the motor. So I had to take this out and put full housing on the cable so it would fit without the guide anymore.
On my other bike, the inside of the frame in the bottom bracket area was not machined well and had a bump that made the motor not fit through. Luckily, that frame is aluminum so it’s relatively soft to file down and correct that.
Oh and you’ll need to do some soldering to build the display flashing cable if you don’t want to spend an extra 50.- buying an official one, or to to add a temperature sensor onto the motor to avoid overheating and demagnetizing the motor. I didn’t include the cost of the soldering iron and accessories for that because I already owned it all. It pays for itself very quickly after you’ve repaired a couple of things that you would otherwise need to throw out and rebuy because a 3$ component burnt out.
I haven’t flashed the open source firmware yet because I’m still in the process of building my flashing cables, but I’ll get around to it this weekend probably. Even without the open source firmware, it’s a very fine setup. There is a 7-8% grade to go back home, I used to climb this at 6-7 km/h and arriving all sweaty on top (even in the winter.) With the motor on minimum assist level, I climb it at 12-13 km/h and while it ups my heart rate, I’m not sweaty when I arrive. I could crank the assist level all the way to the maximum, then I barely have to push on the pedals to climb. The bottom line is that with a motor, I can either relax and let the motor do the work when I’m lazy, or I can pedal as hard as I did without a motor but get further and faster before I’m tired.
This is the battery I bought: https://em3ev.com/shop/em3ev-52v-14s5p-jumbo-shark-ebike-battery/
This is the motor I bought: https://eunorau-ebike.com/products/48v500w-tongsheng-tsdz2-mid-drive-motor-kit-with-torque-sensor?_pos=4&_sid=ec2abcd31&_ss=r
This is the amazing open source firmware: https://github.com/OpenSource-EBike-firmware/TSDZ2_wiki/wiki
Good resources to learn more and plan your build are https://old.reddit.com/r/ebikes and https://endless-sphere.com/forums/viewtopic.php?f=30&t=93818. You can see on reddit where people post their bicycles that it runs the whole gamut between neatly tucked cables and rat nest.
And for general bicycle repair/maintenance/removing the bottom bracket/etc, park tool makes amazing videos on youtube.
Happy to answer questions as well.
Great job! we are a family with 3 bikes, 2 electric and one non-electric foldable.
I would love to see some picture
I have a small workshop myself in the garage, more kind of like an hobby, and repair the bike myself. I didn’t build one from scratch, but we bought a Moustache with Bosch 1st gen (a bike from 2012) in 2016 for 1400 chf. Over the year I’ve cut cables to changes the onboard computer (the old one broke), added lights when I found out that some of the cables had 12 Volt on it (bought them from AliExpress; it is crazy in europe you can’t buy replacement part almost, the culture of always “buying new”). Bought a new bosch battery as well just last year, that was the most expensive part (400 chf)
The bike performs very well. In the end though I mostly use the foldable non-electric for commuting. And I even attach the trailer with my 2 kids and bring them around town. It is a nice workout 
I’m not sure I agree with you about how all the ebikes are so expensive here and how much cheaper is in the rest of the world. Swiss people sell 2nd hand bike that are basically new for a fraction of the price. It takes time to scout the web but you can find great occasions.
I chat with bike shop occasionally, and sometime they have great occasion as well. The moustache bike (a very expensive brand) we bought was bought from a shop.
I’d love to build one but I don’t have space and time to do all of that. Especially the soldering. (why a motor doesn’t have a temperature sensor?)
Wouldn’t a motor with that power need a yellow license plate? Do you know if the liability insurance would pay in case of an accident with such a self built vehicle?
I built ours in our apartment. I needed something like 2 square meters to do it. You don’t need soldering. I have bought the temperature sensors a while ago but didn’t install them because it’s a bit of a production to open the motor etc. Not impossible to do, just a bit of hassle. For building the flashing cable, it can all be done on a table. I got a silicon matt from aliexpress so that I can solder on it without damaging the dining table under. Do it with an open window (or better yet, outside) and block your breath so that you’re not breathing fumes while soldering.
With the open source firmware, you can display what power the motor is running at. And if you stay in the 250W range most of the time, it won’t overheat. The danger is if you’re making a steep ascension for longer periods of time then the motor runs harder and heats up more.
Installing the motor itself was not suuuuper hard, but you still need tools. A bike stand makes things a lot easier too.
The power a motor develops is a gray area… There isn’t really a way to measure how much power the motor outputs because it depends on so many factors. The sticker on my motor says 250W but it can run at 500W or 750W for a few seconds to start. If running for longer than a few minutes at this power, it would destroy itself. But it can run at 250W for ever without overheating/damaging itself. If I’m going up a steep hill, it will need to run at 600W and I’ll be going 7 or 10 km/h; any less than that and the assistance will be too weak to have any effect. Is it a 750W motor then or a 250W?
The speed however is limited to 25km/h, after which the assist cuts out and it’s just up to my legs to go faster (if I can!). So it doesn’t require a plate or insurance. This is something I was worried about so I asked the local police, and that’s what they confirmed.
Of course, I could reprogram the motor to never stop assisting. I had this for a little bit to test, and I was able to get to 35-40 km/h as my cruising speed. But I leave it at 25km/h because I don’t really need to go that fast, I’d need insurance then (and I suspect it’s hard to insure a DIY bike, you’d probably need to pass some kind of inspection etc), and I found it dangerous as well because you tend to do more stupid stuff when going fast: you become impatient, you behave in a riskier way, while having less time to react and so you put yourself at more risk.