Hello, first post , Cargo Bike retro fit advice and disscussion

[Simon.j.crossley]

Hi, Il introduce myself and my project,

I’m Simon long term cyclist, mountain biker, commuter and sort term father (I’m still learning) looking to convert a slightly odd ball Cargo bike to electric to aid the transport of my two children and stop my wife wanting a second car.

Link to pictures of the bike: LINK



As you will quickly notice unlikely to work standard electric hub due to single arm fork / frame. Mid drive is a possibility but not practical as the bike currently has idlers under the box that are not the best and wouldn’t take the stress of a motor as well as human power.

My plan: feel free to shoot it down or make suggestions, I have an idea how this will come together but not fully set on the plan.

1.Mount a lay shaft at the front of the box 17mm on pillow bearing
2.Add free wheel from the crank to the lay shaft
3.Hub motor mounted to the rear left (from above) sprocket attached to the disc mount to drive the lay shaft
4.Output from the lay shaft using adapter and screw on sprocket to rear geared hub
5.Rear Right mounted Nuvinci CVT hub input to the free hub output the rear wheel via disc mount sprocket to 20” rear wheel with free hub.


So where I need help is in the electrical side, which motor to go with to be robust and which controller to drive it.

Current thinking after lots of reading, I’m new to Ebikes in general and have only repaired and ridden them in the past.

Hub motor, restrictions must be less than 185mm outer diameter due to clearance, from a fabrication view front hub would be easier as its 25mm narrower. Must be disc mounted to get the output to the lay shaft.

This is currently where I stuck I need to pick a motor then work from there !

For the main part the fabrication will follow, I’m looking to get it made up and working using alu box section and tube clamps then if it works get it fabricated properly with Alu tube to reduce weight and flex. I have access to a skilled set of fabricators through work who work with aluminium daily.

In terms of what the bike will need to do, lug family around town, Sheffield and allow me to commute to work 7 miles away after dropping my 2 year old off at nursery. The local trip to the shops a climb of 300ft in 1.5miles. total weight me 85kg toddler 15kg plus 15kg of stuff , 20kg of bike plus electric / drive kit and battery. Maybe 160kg

Could of sketches of the drive train:

 

[Woosh]

I can't see how a rear hub motor would go on your cargo bike.
If I were to convert your cargo bike, I would try to locate first a replacement fork with standard 100mm dropout then use the XF07 on 20" rim kit.
https://wooshbikes.co.uk/cart/#/product/uid-192-xf07kit-13ah/xf07-front-hub-kit-with-13ah-battery

 

[Nealh]

Interesting idea and engineering, unfortunately I'm not an engineer but like the thought process. The lay shaft needs two outer sprockets so I assume you will have to play with sprocket sizes for gearing to allow the hub motor and Nuvinci to work at an efficient rpm, possibly they would have the same teeth count as the layshaft freewheel.

You will need a 328rpm hub for 20" wheels which will max out at approx. 19.5 mph assisted or for something with more torque opt for a 260rpm hub which will max out at approx. 15.5mph assisted.
There aren't many 250w after market hubs to be had but this Aikema is light and small, but you would certainly will need to reduce current to run it and keep it to about 17/18a at 36v. Though that said if you run it at 20a or a bit over and trash the nylon planet gears they are replaceable and I would buy a spare set any how as they would only add $13 to the purchase price.

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For after market set up there is only one make of controller to consider that is easy and reliable, KT (Kunteng) dual volt 9 or 12 mosfet sinewave controller. Although these are 20 -25a which is likely too much current the KT allows current reduction in it's settings.

 

[Nealh]

I can't see how a rear hub motor would go on your cargo bike.
If I were to convert your cargo bike, I would try to locate first a replacement fork with standard 100mm dropout then use the XF07 on 20" rim kit.
https://wooshbikes.co.uk/cart/#/product/uid-192-xf07kit-13ah/xf07-front-hub-kit-with-13ah-battery

I would be surprised if one with a long enough steerer can be sourced so taking that route a new extra long steerer would have to added to replace a stock one.

 

[Woosh]

there is no need to add a new freewheel nor gearbox.
If he does not mind how the conversion looks, he only has to mount the rear motor wheel parallel to the existing rear wheel. Job done.

 

[Woosh]

I would be surprised if one with a long enough steerer can be sourced so taking that route a new extra long steerer would have to added to replace a stock one.

I have them for 26" wheels but not for 20".

 

[Nealh]

there is no need to add a new freewheel nor gearbox.
If he does not mind how the conversion looks, he only has to mount the rear motor wheel parallel to the existing rear wheel. Job done.

But not if Simon wants hubs gears to replace the derailleur gearing he currently has.
The engineer in him has a plan and he has the work mates to prepare the fabricating.
The issue with all of this is chain line and will IGH systems work with the chain line on the opposite face ?

 

[Woosh]

4.Output from the lay shaft using adapter and screw on sprocket to rear geared hub

this part is not necessary and it complicates the thinking.

But not if Simon wants hubs gears to replace the derailleur gearing he currently has.

that's too, not easy and not particularly useful because after the conversion, they don't need to change gear often or at all so why getting rid of the derailleur?

 

[Simon.j.crossley]

Lots of replys where to start:

lets start with the engineering:

1) playing with drive train is required as the chain in currently running on poor quaility idlers and is very noisy, I think this might have been a prototype .

2) Replacing the fork is a no go as it strikes against the spirit of the bike. (Mike Burrows would be very upset)

3) woosh: Im lost how to mount paralel to the existing rear hub / drive train, chain back to the existing cassette ? maybe on the rear rack ?

4) chainlines etc the sketch is confussing because I have flipped it over so viewing from below . In terms of "bike" parts this should function, its similar to trike drive units. Both the ehub and geared hub are in their normal orientation. The lay shaft is needed to keep chainlines sensible.

5) In terms of RPM I have pretty good freedom. Im stuck with the sproket sizes currently availible but can work with them. I made a qucik spread sheet. With the design above (Woosh fair comments but at the moment I cant see another way) my restraint is the crank cadance to Motor RPM as both feed the layshaft.

5.1) legs vs motor speed .

42t chain ring to 14t freewheel
Motor fix cog 16, layshaft fixed cog 22t
This means at 40 RPM cadance the motors is at 165RPM
at 80RPM cadance the motors is at 330RPM
at 100RPM cadance motos is at 412RPM

Basically motor will always run pretty qucik which I though was a good think but like i say Im not an ebike man but an engineer and normal cyclist please tell me if this is wrong !

5.2) Actual speed

Using the same as above with the nuvini 0.5 to 1.7 ratio actual speed is very varriable with legs and motor speed been a little more restricted.

100 RPM - speed between 8.6 and 27MPH
40RPM speed between 3.4 and 11MPH
clearly extrmes here, I have hit 30mph on it down hill but dont think I will do that on the flat

Not Rear mech would be replaced by a single sproket mounted on the freehub







Electrical:

1) Nealh, thanks this is the type of Info I need as I dont really know what im looking for!
Contollers etc are all balck box to me so happily take advise and will follow

2) motor wise I was reading about the bafang G360 as a heavy but robust motor but cant find any to go out and order,

3) Motor RPM, stated wheel size , and torque . There is a relationship here that I cant quite work out ! and RPM / V seems to come into it !

4) I will likely go 48v rather than 36 volt but not really sure there is much reason behind this

 

[Woosh]

3) woosh: Im lost how to mount paralel to the existing rear hub / drive train, chain back to the existing cassette ? maybe on the rear rack ?

a rear hub motor does not need to be connected to the drive train. In fact, you can remove the chain and can still ride the bike home with your hub motor. The cadence sensor will pick up the pedaling, the brake sensors will still stop the motor when you brake etc.
Just imagine you mount a tiny motor wheel on one of these to see the logic:

 

[Nealh]

The bike isn't able to have a rear hub, it doesn't have a conventional drop out.
The front fork is like the Cannondale lefty and the rear D/O if you like a righty.
No way to a fix a hub direct to the D/O.

 

[Woosh]

that's why I said if he does not care about how the conversion will look like, he can just weld a rear wheel parallel to the existing one. The wheel will push the bike when energised.
The best solution is still to change the leftie fork for a normal fork.

 

[Nealh]

The G360 isn't any different from a lot of hubs, though is an updated version of the Bafang CST I am using.

 

[Nealh]

Buying direct from Bafang isn't possible unless you are imorting in bulk or buying as OEM bikes or kits.
For good front drive you are limited, Woosh sell the XF07.

Or BMSBattey/China sell all of the below but non are 250w.
Getting a marked 48v 250w hub isn't easy, though vendors do sell them on liExpressunless. Other wise they are supplied OEM or a special order OEM as Woosh spec them for their kits.

Bafang 48V500W BPM2 Front Driving Hub Motor RPM 201

Bafang 48V500W BPM Front Driving EBike Hub Motor.

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Bafang 36V350W BPM2 Front Driving Hub Motor RPM 201

Bafang 36V350W BPM Front Driving EBike Hub Motor.

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Q128 48V400W-500W Front Driving V-Brake Hub Motor RPM 328

Q128 48V400W-500W Front Driving V-brake, rim-brake E-Bike Hub Motor. Waterproof hall sensor connector.

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