20inch rear hub conversion

Vetinari

Just Joined
Jul 19, 2020
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Hi everyone,

First post here, although I have been reading around generally. We are just about to get a recumbent trike for my daughter who has balance issues and we are planning to electrify the rear hub (20 inch) to help here come on walk/rides with the rest of the family.

Ideally a system that is super easy to operate, mainly for pedal assist, but would be good for it to be possible for her to run it purely on a throttle if necessary. We won’t be going huge distances and she isn’t very heavy, so a modest battery and motor capacity should be sufficient. Simple visual display for her to use, even if there are more complex setup menus to delve into.

Any recommendations on what would be a good system and where to buy from. I am used to looking after the rest of the family bikes, doing electrics etc so fitting a kit feels like it a very doable. Would prefer to simply buy the whole wheel ready to go and either swap over or buy a new cassette. The trike will already be pretty pricey, so not paying someone vast amounts of money to fit something no better than something I could fit seems pointless.

Any pointers appreciated

Thanks
 

vfr400

Esteemed Pedelecer
Jun 12, 2011
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How many speeds are there on the rear cassette? This is important to determine the right kind of motor. Also, how fast do you want it to go - modal speed and max speed? This is also very important for choosing the right motor. The legal limit of assistance is 15.5 mph, but to get good power at that speed, you need a motor that can do 20 mph if it were unrestricted.
 

Vetinari

Just Joined
Jul 19, 2020
3
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How many speeds are there on the rear cassette? This is important to determine the right kind of motor. Also, how fast do you want it to go - modal speed and max speed? This is also very important for choosing the right motor. The legal limit of assistance is 15.5 mph, but to get good power at that speed, you need a motor that can do 20 mph if it were unrestricted.
It is an 8 speed cassette. She will not be going fast in this. It will be mainly off road paths/tracks and we will be setting the cassette up for lower gearing. Think gentle rides with the family or riding whilst the family is walking with the dog, rather than cycling along the backroads from village to village.
 

vfr400

Esteemed Pedelecer
Jun 12, 2011
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If you go for a rear hub-motor, you need a cassette motor, and it's ideal speed would be 260 rpm. Most ready-made 20" electric bikes would use motors with around 330 rpm. A 201 rpm 36v motor becomes a 260 rpm one when you run it at 48v. At 48v, you get 30% more torque available, so I would always choose that as the voltage.

The motors to look out in sequence from smallest and lightest upwards are AKM 85CST, AKM100CST (Q100CST), MXUS XF08C, AKM 128CST (Q128C), Bafang SWX02C.

At 48v, you want a 15 amp sine wave controller. At 36v, a 20 amp one.
Have a look at BMSBattert.com, topbikekit.com, elifebike.com and greenbikekit.com

Alternatively, you can get a crank-motor kit, like a Bafang BBS01 or Tongsheng TSDZ2. Installation is slightly easier, but reliability isn't quite as good as a hub-motor. Motor speed doesn't matter because you're driving through the gears. These motors are designed to work at normal cadence.
 

Vetinari

Just Joined
Jul 19, 2020
3
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Thanks vfr400. We will definitely be going down the route of a hub motor. If I understand your comments correctly, you are suggesting buying a wheel with a 36v motor at 201rpm, but then run the rest of the system at 48v.

Does anyone have any recent experience of typical delivery times?

Thanks for the help!
 

vfr400

Esteemed Pedelecer
Jun 12, 2011
6,944
2,674
Basildon
You can use either a 48v 260 rpm motor or a 36v 201 rpm at 48v. Essentially, they're the same motor, even though the markings might be different.