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Discussion Starter · #1 ·
I've read a few people on here, in the past, mention building e-bikes, so hoping some knowledgeable people can point me in the right direction...

I've decided I quite fancy an e-bike for my daily commute. It's only 4.5 miles (9 mile roimd trip), with a short steep incline, which is why I'd like an e-bike, to help me get to work without needing a shower once I get there!

Now, the thing is... I'm a bit tight, so like to keep the cost down!... But, I do have access to equipment to help with a DIY build, such as a laser cutter, 3D printer, PCB manufacture, etc.

Having had a quick look at things on tinternet, I'm thinking a front hub motor (bought already mounted on a 26" wheel), and I know I'll need a controller and throttle, plus the expensive part... A battery. Is that it?

What DIY forums are there, and sources of kit that I'll need.

I don't mind buying bits separately and putting them together, but I just don't want to buy complete rubbish!
 

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I'm thinking a front hub motor (bought already mounted on a 26" wheel)
I’ve built a front hub motor ebike. make sure you have a decent “torque arm” on the motor. The one I had initially applied all the force to the aluminum dropouts of a standard fork I had via a flat sided axle and snapped it in an instant. Make sure the counter torque is applied far from the axle to minimize leverage forces on the dropouts... or my solution was a custom steel fork with highly reinforced dropouts to handle the torque generated at the axle.

For example, suppose you have a 1cm diameter flat side axle on the motor (larger than standard 8mm fork dropouts), to calculate the force on the dropouts applied by the axle, multiply the torque of the motor in newton meters at peak motor current by 200 to get the force on the dropouts in Newtons, which will be very high no doubt... likely significantly higher than the normal force. This can lead to rapid unscheduled disassembly of the part of the fork that holds your front wheel onto the bike.
 

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in high power systems that generate a lot of torque, or in setups with weak dropouts, the forces present can exceed the material strength and pry the dropout open. When that happens, the axle will spin freely, wrapping and severing off the motor cables and potentially causing the wheel to fall right out of the bike.
To give a sense of the magnitude of these forces, a hub motor with a 12mm axle generating 40 N-m of torque will exert a spreading force of just under 1000lb on each dropout
. A torque arm is a separate piece of metal attached to the axle which can take this axle torque and transfer it further up the frame, thus relieving the dropout itself from taking all of the stresses.
 

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Discussion Starter · #4 ·




in high power systems that generate a lot of torque, or in setups with weak dropouts, the forces present can exceed the material strength and pry the dropout open. When that happens, the axle will spin freely, wrapping and severing off the motor cables and potentially causing the wheel to fall right out of the bike.
To give a sense of the magnitude of these forces, a hub motor with a 12mm axle generating 40 N-m of torque will exert a spreading force of just under 1000lb on each dropout
. A torque arm is a separate piece of metal attached to the axle which can take this axle torque and transfer it further up the frame, thus relieving the dropout itself from taking all of the stresses.
Thanks, something that could be easily overlooked, but could cause big issues.
 

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The first question that needs answering is what bike are you thinking of converting?

The second is probably whether you intend to stay within the rules/law for your conversion, as motor power and thumb ‘throttles’ are areas you need to think about.

Do you still intend to pedal, or are you wanting something to power you up the hill without any input from you?

I’ve converted 4 bikes to e bikes now, but all with TSDZ2 mid drive motors.

Check out endless sphere;

 

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Discussion Starter · #6 ·
The first question that needs answering is what bike are you thinking of converting?

The second is probably whether you intend to stay within the rules/law for your conversion, as motor power and thumb ‘throttles’ are areas you need to think about.

Do you still intend to pedal, or are you wanting something to power you up the hill without any input from you?

I’ve converted 4 bikes to e bikes now, but all with TSDZ2 mid drive motors.

Check out endless sphere;

I've come across Endless Sphere, and had a brief look, but saw it was states based, so didn't dwell long. Not that there's anything wrong with a states based site, but was hoping to see where parts are available over here and what's possible over here.

My aim is not for the electric to fully take over the drive, but provide assistance, so still pedalling, as I just don't want to end up at work dripping with sweat (there's quite a steep hill on the way).
 

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I've come across Endless Sphere, and had a brief look, but saw it was states based, so didn't dwell long. Not that there's anything wrong with a states based site, but was hoping to see where parts are available over here and what's possible over here.

My aim is not for the electric to fully take over the drive, but provide assistance, so still pedalling, as I just don't want to end up at work dripping with sweat (there's quite a steep hill on the way).
What’s possible over there, is still the same as over here. There are a limited number of off the shelf systems, coming out of the same factories. The technical discussions are still valid, although they aren’t concerned with the UKs legalities around bikes.

UK suppliers tend to be expensive, I buy all my motors etc from PSW Power’s German warehouse.


With Brexit looming, not sure how straightforward that will be.

Personally, I don’t like front hub motors, they corrupt the steering and can wash out quite easily, but accept they’re easier to fit up to a point.

Mid drive feels the most natural, but you need a suitable bike for conversion.
 

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I put a cheap 250W front hub onto an old mountain bike to make a 1km 1 in 10 hill and the rest of a 30km commute reasonably easy. Its legal, I don't find any handling problems with the front hub. A 250W direct drive doesn't put enough torque into the front forks to require any reinforcement although I am about to fit torque links anyway just for safety.
 

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Discussion Starter · #9 ·
I've seen a 20" wheel bike that I can get for around £250.

I was thinking it could be a cost effective way of getting all of the kit I need to change over onto my bike (as the bike looks garbage!).

The only doubt I've got is the battery, it's 24v 7ah, and I've read that for a decent amount of power you should be looking at 36-48v minimum. However, £250 for the motor, controller and battery, plus everything else needs, seems good, even if I end up scrapping the rest of the bike!
 

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I've seen a 20" wheel bike that I can get for around £250.

I was thinking it could be a cost effective way of getting all of the kit I need to change over onto my bike (as the bike looks garbage!).

The only doubt I've got is the battery, it's 24v 7ah, and I've read that for a decent amount of power you should be looking at 36-48v minimum. However, £250 for the motor, controller and battery, plus everything else needs, seems good, even if I end up scrapping the rest of the bike!
A relative bought one of these, all junk
 

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The other safety thing I recommend is put the front hub motor on a front fork and preferably bike frame that’s made from steel not aluminum. If a magnet sticks to it that means it’s steel. Steel bends but aluminum snaps suddenly if and when when you exceed the material strength. With an aluminum fork, even with a torque arm, if its powerful enough the next point of failure I’d be worried about with an aluminum fork is where the fork enters the steerer tube, which transfers the pulling force from the motor to the rest of the bike. Not only did I have a steel fork but I also had a steel frame that additionally had steel gussets reinforcing where the rest of the bike frame meets the steerer tube. I had about 4000w, 72v, 40mph top speed, able to do front wheel burnouts on dry pavement.

I used this frame (notice the heavily reinforced, steel front end) :

 

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Not trying to scare you but when my pal developed a hub motor for a skateboard we discovered that hub motors do in fact put extreme stress on the axle itself and all associated parts. We discovered that standard steel 8mm skateboard axles simply are too weak to handle the torque output of the motors so custom trucks with 12mm axles had to be produced. When we calculated the stress applied by each motor to the axle we found it was about 20x greater than the force applied to the axle by gravity from simply standing on the board. This is a true color but contrast enhanced picture of the 8mm skateboard axle after the hub motor sheered off while accelerating at low speed in a parking lot:
138736
 

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With a torque arm, the load on the fork is similar to a disk brake, just way lower. So if you have a fork that can take both kinds of brake, attach the torque arm to the disk brake mount, and use rim brakes, everything should be strong enough I guess?
 

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With a torque arm, the load on the fork is similar to a disk brake, just way lower. So if you have a fork that can take both kinds of brake, attach the torque arm to the disk brake mount, and use rim brakes, everything should be strong enough I guess?
This why I prefer mid mount motors, they keep the forces/stresses where they’re supposed to be, and within the design limits of a bicycle drive train, at least with UK legal limit motors.

Torque arms and going back to rim brakes removes probably the only benefit of a front hub motor, ease of installation.

I was out on one of my TSDZ2 conversions yesterday evening, just a 250w version and in the maximum assist mode it made mincemeat of the hill out of my village, the main reason I got into e-bikes in the first place, everywhere is uphill from here!
 

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This why I prefer mid mount motors, they keep the forces/stresses where they’re supposed to be, and within the design limits of a bicycle drive train, at least with UK legal limit motors.

Torque arms and going back to rim brakes removes probably the only benefit of a front hub motor, ease of installation.

I was out on one of my TSDZ2 conversions yesterday evening, just a 250w version and in the maximum assist mode it made mincemeat of the hill out of my village, the main reason I got into e-bikes in the first place, everywhere is uphill from here!
Mid drive retrofits are not difficult: have a look at Wooshbikes for an idea on what is involved.
 

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Mid drive retrofits are not difficult: have a look at Wooshbikes for an idea on what is involved.
I know, I’ve done 6 of them now, 3 for mine/my family’s bikes and 3 for friends.

Hub motors have a place, I’ve got an e-bikemotion x35 rear hub system on a Lapierre road/gravel bike, and it’s a discreet and lightweight system.
 

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Discussion Starter · #17 ·
I know, I’ve done 6 of them now, 3 for mine/my family’s bikes and 3 for friends.

Hub motors have a place, I’ve got an e-bikemotion x35 rear hub system on a Lapierre road/gravel bike, and it’s a discreet and lightweight system.
So how difficult is a mid drive conversion?

I'm reasonably decent with a set of tools, done discs and pads on the leaf, as well as a full suspension swap on my old mazda mx5.

Are there any specialist tools needed, or will a set of spanners do?
 

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So how difficult is a mid drive conversion?

I'm reasonably decent with a set of tools, done discs and pads on the leaf, as well as a full suspension swap on my old mazda mx5.

Are there any specialist tools needed, or will a set of spanners do?
If you’ve worked on bikes before, it’s not difficult. You need a bike with a standard bottom bracket shell width, 68-73mm, and the tools to remove the old bottom bracket.

Crank arms are square taper, no special tools to install them, but you’ll need pullers for the old cranks.

The mid drive motors come with their own spanner for tightening the motor shell mounts.

You’ll need space somewhere to mount a battery, the bottle mounts usually, and then it’a just a case of running wires neatly, fitting the controller on the handlebars, speed sensor on the chain stay and a magnet on the spokes to pass it.

This is one of my conversions, the batteries are in the black triangle bag, no room for a traditional bottle battery on this frame. I’ve also fitted a smaller front chainring, the kits are easily adaptable to take standard 5 x 104 BCD chainrings.

If you’re converting a standard hard tail, it’s even easier.

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I recommend endless sphere web site too.

With their help ten years ago I converted A recumbent trike for my 9 mile commute to work. It had a 15Ah 18s battery pack, I limited the current to 100A max in the controller but it could still quite happily do 42mph down the cycle track!
 
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