Best way to DIY an Ebike ? - Page 1
Forum section: electronics / projects

author: ArchieAltz
author_rank: Contributor
timestamp: October 01, 2025, 10:54:32 pm
content: So me and my friends are in high school and we want to make an Ebike for some competition.My question is how do we acomplish this in a solid manner . The legal limit for Ebikes is 25 km/h for the speed and 250W continuous for the motor so we will have to make due with that.Where do we source a motor and what's the best way to get Li-ion batteries for our own battery pack ?Any help is appreaciated.

author: SteveThackery
author_rank: Super Contributor
timestamp: October 01, 2025, 11:57:21 pm
content: To be clear, kits for converting standard bicycles to e-bikes are widely available on eBay. I assume these are no good for you? And that you must develop your own from scratch?If the latter, I would suggest you choose a different project. You must consider the motor, the transmission, the battery pack, the battery management circuitry. Then you need the control electronics, with speed sensor and pedal cadence sensor. Optional would be a variable assistance control and start-up facility (ie a throttle control which will propel the bike up to 4mph from standstill without pedalling).It's a lot for a 1st year project, in my opinion.

author: ArchieAltz
author_rank: Contributor
timestamp: October 02, 2025, 11:51:21 am
content: Quote from: SteveThackery on October 01, 2025, 11:57:21 pmWe can get the kit motors though I don't really know if I should trust a chinese Ebike kit to be reliable.

author: Marco
author_rank: Super Contributor
timestamp: October 02, 2025, 11:58:13 am
content: What kind of competition? If it's a kind of ebike race with a spending limit, show the rules. If it's a competition to show DIY engineering skills ... well depends on your skill and willingness to learn new ones.You can always kitbash some open source projects and a commercial motor/battery for bike conversion together.https://opensourceebike.github.io/Bafang especially has a huge amounts of users and their motors are sold for conversion.

author: BILLPOD
author_rank: Frequent Contributor
timestamp: October 02, 2025, 02:05:37 pm
content: Good Morning ArchieAltz, Much will depend on the skill level of you and your friends. Electrical knowledge and experience is quite high in such a project. Also, mechanical skills are very important.There's also a big difference in designing from scratch, or adapting an existing bike. I recommend looking into conversion 'kits' for ideas. A monumental project, indeed. Good luck to you and your friends, and please come back here and let us know your decisions, and/or progress.

author: eugene
author_rank: Frequent Contributor
timestamp: October 02, 2025, 02:31:45 pm
content: Quote from: ArchieAltz on October 02, 2025, 11:51:21 amSome products from China are high quality and reliable, some are not. Maybe find a forum with experienced ebike builders to help you choose a good quality kit?

author: UnijunctionTransistor
author_rank: Frequent Contributor
timestamp: October 02, 2025, 04:08:59 pm
content: E-biker here.Two words of advice: throttle control. Don’t underestimate the complexity and safety requirements for this apparently simple device.You mentioned the “best way”; I would also recommend conversion kits. There is still a significant amount of labor and ingenuity required to convert a regular bike, but at least the safety aspects of it, like the throttle control mentioned earlier or the battery management mentioned in other posts, will have been debugged for you.

author: Marco
author_rank: Super Contributor
timestamp: October 02, 2025, 07:47:20 pm
content: The rules for ebikes in Bosnia Herzegovina are probably harmonized with EU, so no throttle on ebikes.

author: SteveThackery
author_rank: Super Contributor
timestamp: October 02, 2025, 09:01:59 pm
content: Quote from: ArchieAltz on October 02, 2025, 11:51:21 amOf course you should. Where do you imagine most e-bike components are made?

author: SteveThackery
author_rank: Super Contributor
timestamp: October 02, 2025, 09:06:22 pm
content: Quote from: Marco on October 02, 2025, 07:47:20 pmI think that is incorrect, @Marco. I think they are allowed, but must only function up to 6kph. In other words it's to assist you pulling away safely, but no more than that.

author: langwadt
author_rank: Super Contributor
timestamp: October 02, 2025, 09:07:54 pm
content: Quote from: Marco on October 02, 2025, 07:47:20 pmI think you can have a throttle as long as there is no drive unless you also turn the pedalsbut it is probably still not possible to legally diy because it has to be type approved for use on the road

author: Calvin
author_rank: Regular Contributor
timestamp: October 03, 2025, 08:24:43 am
content: Hi,You can find conversion Kits and single parts quite cheap on AliXpress and Alibaba.Our inventive chinese friends build motors, controllers and batteries in any size and power class.You can find wheel motors for front and back as well as middle motors (Bafang e.g.) to be built into the frame (matching frames also at Aliexpress).The middle motor has become the almost standard and is power and speed limited ... and regularly quite noisy (trapezoidal commutating controllers instead of sinusoidal ones)It builds compact and lightweight though, which is good regarding bike agility.But since all the torque is developed via a gear and transmitted to the wheel via the chain, those components are stressed heavily.The power density is much higher and the associated heat power loss is concentrated on a smaller weight and volume.Back wheel motors on the other hand are mostly direct drives with with no gears and almost nothing in to fail.As size isn´t a issue, they can deliver up to 5kW and more.Direct drive also means that the chain and gearing is stressed much less and You can use standard gearing from Shimano, SRAM or something cheap from china like Zitto.As weight is consideraly higher than for middle motors and due to the mounting position, the bike agility is lower.But recuperation, resp. motor braking can be really helpful going steep downhill and it increases range.I also found it impossible to find a bike frame with rear suspension that allowed mounting a sufficiently big battery (>1kWh).So, these motors rather lend themselves for city- and trekking-bikes, less so for full suspension, performance mountain- or gravel-bikes.And that is why I built, based on a trekking bike frame and this is where the wheel motor excels.The reasons I did DIY were threefold.a: The ridicolous prices that are charged for eBikes since the market exploded over Covid. I mean come on 4.000€ up just for a half decent bike still with cheap chinese components and easily 9000+ for A-branded gear?b: I wanted a motor assisted bike to commute to work on a daily base.c: I found out the hard way that manufacturers like Shimano build in obsolescence, resp. unneccessary and costly ´safety imroving measures´ regarding battery supervisory circuitry.When I built my bike I used a Controller and Display fromhttp://www.szktdz.com/and a motor fromhttps://www.angyang.com.cn/product/8/, which is of the back wheel type.Powered by a 1300Wh battery fromhttps://unitpackpower.en.alibaba.com/?spm=a271p.trueview.1.1, which I recommend, because they build with genuine Samsung, LG and Tesla battery cells.So far I´m absolutely happy with the performance of the setup ... 5700km since dec.´24 without issues.Kunteng controllers are well regarded and displays like the LCD-8H are just great.You can configure almost any parameter after your wish in the setup menu.A 1500W B50 Motor by Angyang (or Jun-Yuan) for example is listed at Alibaba for less than 90€!Lower powered motors are even cheaper.Btw. the legal limit in many european states of 250W means average power .... which is good for about 30km/h max on flat terrain wo. wind.750W is the limit for short term power.Bafang offers middle motors and matching frames via Alixpress at affordable costs.This allows for ´professional looks´ and motor integration.regardsCalvin

author: SteveThackery
author_rank: Super Contributor
timestamp: October 03, 2025, 04:41:51 pm
content: We are still left with a degree of uncertainty.ArchiAltz: please tell us whether you are allowed to just buy off-the-shelf stuff (either individual components, or complete kits) and fit it to a convenient bike, or if you have to develop all the components yourself.I think this is a very unsuitable project for first year students. Either you can buy and fit a kit off eBay, in which case it is far too easy for an assignment, or you must develop your own system from scratch, which is far beyond what first year students should be asked to do.

author: SteveThackery
author_rank: Super Contributor
timestamp: October 03, 2025, 04:45:36 pm
content: Quote from: langwadt on October 02, 2025, 09:07:54 pmActually, no, so long as the throttle doesn't work above 6kph you don't have to pedal. It is considered a 'starting aid', but can also be used to assist when walking alongside your bike, pushing it.

author: SteveThackery
author_rank: Super Contributor
timestamp: October 03, 2025, 04:57:33 pm
content: A small rant. I am totally in favour of all the EU rules regarding e-bikes. The 25kph limit for assistance is reasonable, as is the need to pedal (so it only assists you).But there is one rule which I completely disagree with: the 250 watt maximum continuous power.Speaking as someone who is old, fat and knackered, I can say with certainty that 250W is nowhere near adequate for helping me get to the top of most of the hills I routinely encounter. This means that an e-bike is pointless for me, because I don't want one which I have to dismount and walk up most of the hills.250W assistance is reasonable for people who are averagely fit, but absolutely not for people who are elderly or well below average fitness. In fact, I would argue it is discriminatory against old, fat and knackered people.I think the continuous power rating should be raised to 1kW, whilst still keeping the 25kph assistance limit. That would get almost anyone to the top of most hills, even people who are very unfit. I genuinely believe we would see a significant uptake amongst older people if the bikes had enough power to ride with comfort, even in hilly areas.Anyway, sorry - a somewhat off-topic rant!

author: voltsandjolts
author_rank: Unknown
timestamp: October 03, 2025, 05:26:50 pm
content: I agree.But I would also like to see some assistance above 25kph, just enough to compensate for the drag and weight of the motor and battery. Maybe 50W or so.Above 25kph a pedal-only bike is much easier to move!

author: Marco
author_rank: Super Contributor
timestamp: October 04, 2025, 11:02:05 am
content: Quote from: SteveThackery on October 03, 2025, 04:57:33 pmSince there's no certified way to measure the 250W, does it really matter? 250W of mechanical power at the wheel gets you up a 1:10 incline at 15 kph ... and even more is easily arguable as legal, because hills go up and down, so things average out.

author: Marco
author_rank: Super Contributor
timestamp: October 04, 2025, 11:12:40 am
content: Quote from: voltsandjolts on October 03, 2025, 05:26:50 pmA floppy bag of water on top of a light racing bike is less dangerous to bystanders than one on a far heavier e-bike.

author: voltsandjolts
author_rank: Unknown
timestamp: October 04, 2025, 11:28:38 am
content: Quote from: Marco on October 04, 2025, 11:12:40 amMy bike is 19.5kg and I'm just over 100kg.Maybe ban tandems since they are much faster and twice that weight.

author: Terry Bites
author_rank: Super Contributor
timestamp: October 04, 2025, 02:07:58 pm
content: All sensible people hate fast ebikes and their riders.Just so you know!

author: ArchieAltz
author_rank: Contributor
timestamp: October 04, 2025, 02:19:29 pm
content: Quote from: Terry Bites on October 04, 2025, 02:07:58 pmI think We'll keep with the rules and regulations with this one.

author: NivagSwerdna
author_rank: Super Contributor
timestamp: October 04, 2025, 03:01:02 pm
content: Although obviously off topic relative to the original poster's question...I converted my old 1990s MTB to electricity during COVID times and have used it ever since to commute. At the time it made sense to buy a Bafang motor (other flavours are available) and a battery from China and it's certainly a way of getting something that violates the rules but I think the economics have now changed... it's arguably not worth the effort and many more manufacturers offer reasonably prices bikes now.One thing to bear in mind if converting is that a regular bicycle isn't really designed for the extra mass and torque of a ebike conversion kit. So you will find your brakes and drive train will be challenged... on a ready made bike these factors will have been considered so you will get a more sturdy frame (even more mass), appropriate brakes and a beefier drive chain.In my old age I don't have a throttle, have speed and power restrictions so my set-up should not offend plod... I could do with better brakes though.

author: SteveThackery
author_rank: Super Contributor
timestamp: October 05, 2025, 09:34:30 am
content: Quote from: SteveThackery on October 03, 2025, 04:41:51 pmARCHIALTZ: please answer my question!If you want help you'll have to co-operate.It is disrespectful to ignore people who are trying to help.

author: ArchieAltz
author_rank: Contributor
timestamp: October 05, 2025, 03:35:51 pm
content: Quote from: SteveThackery on October 05, 2025, 09:34:30 amSorry didn't see that one , anyways we don't have strict regulations AFAIK. We as a teamwill discusswhether we use off the shelf parts of really make our own system but I think thatwe will go with the more complex route, we are pretty passionate and stubborn.

author: eugene
author_rank: Frequent Contributor
timestamp: October 05, 2025, 05:31:08 pm
content: Quote from: Terry Bites on October 04, 2025, 02:07:58 pmThat's sounds like a serious issue, Terry. Personally, I hate it when anyone pilots any machine (ebike or otherwise) at a speed that is unsafe for others. I hold no contempt for the machines themselves.Maybe that's what you meant to say?

author: UnijunctionTransistor
author_rank: Frequent Contributor
timestamp: October 05, 2025, 08:48:43 pm
content: Any vehicle, driven recklessly, is an issue with the driver, not the vehicle itself.I once witnessed an E-skateboard being driven both recklessly and fast through a pedestrian area, hitting an elderly person in an electric wheelchair. Even though the wheelchair adds significant mass and lowers the center of gravity, the impact was strong enough to topple the wheelchair and causing the poor elderly person to sustain significant injuries.Obviously the fault was with the irresponsible individual riding the board.

author: jonovid
author_rank: Super Contributor
timestamp: October 05, 2025, 10:10:32 pm
content: Chinese ebike kits are available from 200W to 2Kw from 24 to 50 volts from basic to ridiculously overpowered offroad.most will fit on standard Chinese bicycle frame sizes. including BMX frames. front, mid, or rear Alixmid crank motor is best for underpowered 250w . front hub motor is the cheapest & rear hub motor is the best for high power direct drive units.get the waterproof wiring harness with the o-ring seals on the plugs. more expensive but worth add reliability. bicycles do get wet.most Chinese ebike kits come with hell sensor throttle control , brake levers with sensors , & crank sensor. again get the waterproof types.I recommend buying two battery packs with a cradles. so you can swap out the battery.you also get a spare cradle & charger if you need it .a whole kit will bolt on to a standard Chinese bicycle frame in about 2hrs . lots of youtube videos showing how.most Chinese Electronics are 98% reliable check the AC mains supply voltage of your charger compatibility. EU US UK ... & the plug

author: ArchieAltz
author_rank: Contributor
timestamp: October 06, 2025, 01:33:47 am
content: Quote from: jonovid on October 05, 2025, 10:10:32 pmWe were thinking about a more hands on approach , we'd source a BLDC motor and create our own mounts and at the very least a battery pack (very well aware of the dangers of homemade Li-ion battery packs so it will be done in a controlled environment with all the safety measures and a EE will be supervising us). AFAIK there's 6 months till this competition and we're pretty determined to create something on our own . If not I think that creating just a battery and a solid enough installation of a kit motor will net us an OK placement on the competition.

author: jonovid
author_rank: Super Contributor
timestamp: October 06, 2025, 06:03:30 am
content: I did 6 months research into ebikes back in 2019 looking at core design Not expensive brand nameswatching many youtube videos of other ebike builds some successful some not, so avoiding mistakes.then setting on buying a Chinese ebike wheel hub kit that is still running reliably. now on my second set of battery packs.having get 3 yrs out of them.