My first retro-fit - any advice welcome!

electric_slug

10 µW
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Feb 3, 2023
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Hello, this seems a nice place, I did some reading and now it is time for me to ask for some friendly (if possible) advice ;)

I am a 105kg rider on a 12kg trekking bike with (occasionally) 30kg of luggage. The bike has 28" wheels and I would very much like to add a bit of electric assistance. I am not after "stealth electric moped" - I would very much like to rely on pedal power but have some support for the longer commute I am facing, being very much out of practice.

MOTOR PONDERING
Having read up on the available information here and elsewhere I am pretty certain that a hub motor with planetary gears in the rear wheel is the best way for me to head - the front wheel is built on an SON dynamo hub, and I recall the tribulations of putting the bottom bracket into the frame many years ago, and I am not eager to take that out :0)

My initial feeling is that I would like the bike to be 'legal' in the UK, Belgium and France which would limit me to rating of 250W. Oh, and I would like to have a very quiet motor if that can be combined with my other requirements.

I would be very grateful for recommendations from the current crop of motor choices! I would prefer to build the wheel myself, but there may be an unbeatable deal for a ready-built wheel that I should know about?

TORQUE THOUGHTS
I read some references to torque sensors being installed in the bottom bracket but did not read many details of the installation process - presumably this actually means replacing the BB completely?
Do motors exist that have the torque sensor built in? That would be lovely!

Many thanks!
The Slug
 
electric_slug said:
Having read up on the available information here and elsewhere I am pretty certain that a hub motor with planetary gears in the rear wheel is the best way for me to head - the front wheel is built on an SON dynamo hub, and I recall the tribulations of putting the bottom bracket into the frame many years ago, and I am not eager to take that out :0)

My initial feeling is that I would like the bike to be 'legal' in the UK, Belgium and France which would limit me to rating of 250W. Oh, and I would like to have a very quiet motor if that can be combined with my other requirements.
A DD (non-geared) hub will be a bit quieter overall, using an FOC or sinewave controller (which I'd use regardless, vs a trap/square controller), than a geared hub (because of the gears and the higher RPM of the motor running the gears). But the geared hub will, for the same power, have higher torque which you will probably need with the larger wheel diameter you have.



If you have anything other than flat terrain and no headwinds to deal with, a middrive running thru your shiftable pedal drivetrain will let you do more with the limited power. But if you want torque sensing, the only one you can use that will fit a standard BB and not require a custom frame built for it (or cutting your frame up to install a new bracket) is the TSDZ2. The rest only detect if you are or are not pedalling and engage fully at the chosen assist level, or else provide no assist, unless you use the throttle (for those that support a throttle).




If a front hub simplifies your motorization enough (which it may, depending on your pedal drivetrain / gearshifting setup, and frame/dropouts), the dynamo hub can easily be replaced with a DC-DC running off your ebike battery, or a separate lighting battery, if you are already electrifying the bike. It does mean your lighting would be functional only as long as you have battery power, but unless there are trips you will take via pedal-only power for at least some part, that shouldn't be an issue (unless something goes wrong with the battery system).


Regarding limiting power, the motor itself doesn't control that, the controller does, but you will need to check your particular local laws for exactly what they require to be legal if that is a consideration. Some of them don't even allow DIY bikes at all, and some require the *motor* to be limited in power, which is not actually a thing, but bureaucrats and lawyers that write these regulations typically have no idea how things actually work and just make words. In that event, your options are limited to whatever the law specifically *says*, such that if it says a motor must be labelled such and such, you would need to either get one with that label or put that label on whatever you use. If it says the *bike* must be limited, then that's easy--use a controller that's limited as required, or a system like the Cycle Analyst that can do this, etc.

Note that each locality you refer to has it's own laws, AFAICR, so your bike may not be strictly legal in all three simultaneously and may have to be modified or rebuilt for each one. Something else for you to research. ;)


I would be very grateful for recommendations from the current crop of motor choices! I would prefer to build the wheel myself, but there may be an unbeatable deal for a ready-built wheel that I should know about?
If you can build your own wheels, you can almost certainly make a much better wheel than anything a motor comes in from a factory. Use a good strong eyeletted rim (like another of whatever you've successfully used so far for your regular wheels) and good-brand 14/15g spokes like Sapim, etc.

To give specific motor recommendations, we'll need some more info: What is your bike frame; what are it's size limitations? (dropout width in rear, and/or in front fork) Do you require disc brake rotor mounts? Etc?


I read some references to torque sensors being installed in the bottom bracket but did not read many details of the installation process - presumably this actually means replacing the BB completely?
Nearly all of the separate DIY torque sensors currently available off the shelf new replace your whole BB with their own hardware. Some also replace your chainrings.

There have been systems that run off the chainline one way or another, but none of them are around anymore, so only found used. It wouldn't be too tough to design and build your own if you're up for that and have some experience at it.

There is a sensor type used on certain bikes (Some Stromers, Juiced, others I don't recall names of) that acts as the dropout, or installs "into" it, but it may require cutting into your frame to fit it or to allow it to work, as it puts a strain gauge across a gap such that chain tension on the axle changes it's output. I know you can find these on ebay/aliexpress/etc, but can't remember what they call it. There are some threads discussing it in reference to Juiced bikes, though.


Do motors exist that have the torque sensor built in? That would be lovely!
There is one geared hub I don't recall the name of that's been posted about that has a PAS sensor in the hub, but it may only be cadence, rather than torque/cadence.


FWIW, most controllers don't support torque sensors, only cadence, and usually only by detecting pedalling is happening, and providing full amount of whatever assist level is chosen. Most of them only have different speed levels, though some have "torque simulation" that essentially provides different battery current levels...but it is nothing like having actual pedal control over speed or torque.

But you can use a "dumb" controller that doesn't have any of that, just a throttle input, and then use the Cycle Analyst v3.x from ebikes.ca to interpret a cadence or torque sensor (or both) to give true pedal control over the motor system. I don't even use a torque sensor on the SB Cruiser heavy-cargo trike, just the cadence sensor, and almost every situation allows me to just pedal to control everything. Startups from a stop I sometimes have to use a thumb throttle as a "get started button" (most cases I could just literally have a button for this, but I have other considerations that require a throttle's presence as backup).
 
Thank you, amberwolf, for taking the time and write such a comprehensive reply!

Regarding DD vs. geared hub:
I do hope for some assistance on my commute, but I also use my beloved bike for e.g. a quick trip to the shops and I don't want to always have to grab a battery etc.
I am envisaging the electric assistance as a bonus, not as a core function, and from what I picked up so far (which may be wrong!) I understood that geared hubs provide less resistance when pedaled unpowered?
This is also the reason for hoping to keep the hub dynamo - it will give me light whether I am cycling with battery pack or without.

My bike frame is a 30 year old hand-built steel trekking bike from a small run made in Germany. The dropout width is about 135mm, and I am currently running Ryde wheels with 32 tires, and there is space for wider tires, but not "fat" ones, which I am not that keen on anyway.

Many thanks to the reference for Juiced bikes and further reading regarding torque sensors - I will do some more digging. Since my original rear hub is currently broken I am hoping to get the motor hub in and get cycling again while I keep researching the other components.

Cycle Analyst looks great, I will follow that route - it looks cheap for what it does!

Many thanks!
The Slug
 
electric_slug said:
I do hope for some assistance on my commute, but I also use my beloved bike for e.g. a quick trip to the shops and I don't want to always have to grab a battery etc.
I am envisaging the electric assistance as a bonus, not as a core function, and from what I picked up so far (which may be wrong!) I understood that geared hubs provide less resistance when pedaled unpowered?

I would get a kit like this, with the 28"; 36V 250W; Rear Wheel option. Then invest in the best battery you can afford. Skip the idea of a torque sensing bottom bracket, since a the power level you are looking for, the cost of going that direction will double your investment with very little benefit. Put that money toward the battery. The linked kit uses a KT controller, and their torque simulation PAS works well, even though it's not really torque simulation, it's smooth and predictable.
A geared hub is best for you, since you'll be pedaling unassisted at times and the direct drive motors will take some really strong legs to pedal without assist for anything more than a short ride.

https://www.ebay.com/itm/164855633511?hash=item2662295667:g:WjkAAOSwo9dgllxD&amdata=enc%3AAQAHAAAAsHXnna03JYb42RAgQGA4qa1XAIotiG5l8FZmmZQ3J9uogLp5IaV2d%2BReOili1T6D4cHUW9oe8fjbbrbq6ndgSzFXK26O1bcJeCFdSAQCT4z5s1DnINzHBDEmYRDBOjSwtRBqrfSOfMt4yF%2FZ7vDNM85LANXJ%2F4PHJNS7ytktCHjFTDmIoBORyQv9FKGOPeh1u7dHch5ZdwCvX0bfTQWMiAQRLrc4rirxyD7%2BQXa0Lzow%7Ctkp%3ABk9SR9zQrMnFYQ
 
When you first buy your kit before yes before you install the inner tube in the tire take the motor and the rim to a bike shop and have it trued and tightened the spokes unless you're able then make sure you tighten and adjust and straighten the spokes before the tire in the inner tube
If I was to buy a battery I would buy it from EM3EV and charger.
 
Thank you, E-HP - I found some mention of the KT controllers and they seem to be well regarded.
There is a lot of stuff in that kit that I don't need though, and I would prefer to build the wheel myself so I'll keep looking just for the right motor for now.
 
I recommend Bafang G310 hub motor, it is nominally 250W, light and almost silent. KT controller is a good pair.

Grin sells a slightly improved version but you can find one a lot cheaper from China as well.

https://ebikes.ca/product-info/grin-kits/bafang-g310-g311.html
 
ilu said:
Grin sells a slightly improved version but you can find one a lot cheaper from China as well.

https://ebikes.ca/product-info/grin-kits/bafang-g310-g311.html0-g311.html

IME that's a gross understatement. YES, Grin is a higher cost. But for many builders, the support and parts access make the price easy to swallow.
 
tomjasz said:
ilu said:
Grin sells a slightly improved version but you can find one a lot cheaper from China as well.

https://ebikes.ca/product-info/grin-kits/bafang-g310-g311.html0-g311.html

IME that's a gross understatement. YES, Grin is a higher cost. But for many builders, the support and parts access make the price easy to swallow.

Agreed. Though it's best to maintain a shopping/wish list and place orders once the shipping cost makes more sense.
 
E-HP said:
tomjasz said:
ilu said:
Grin sells a slightly improved version but you can find one a lot cheaper from China as well.

https://ebikes.ca/product-info/grin-kits/bafang-g310-g311.html0-g311.html

IME that's a gross understatement. YES, Grin is a higher cost. But for many builders, the support and parts access make the price easy to swallow.

Agreed. Though it's best to maintain a shopping/wish list and place orders once the shipping cost makes more sense.

Years back we did a few group buys from EM3ev. Saved everyone significant shipping But these days everyone is to spooked to trust transactions like that. A shame. I've offered several times to do a USA Grin group buy and save everyone the higher cost of shipping. But again all the scams have everyone too afraid. Oh well.
 
tomjasz said:
E-HP said:
tomjasz said:
ilu said:
Grin sells a slightly improved version but you can find one a lot cheaper from China as well.

https://ebikes.ca/product-info/grin-kits/bafang-g310-g311.html0-g311.html

IME that's a gross understatement. YES, Grin is a higher cost. But for many builders, the support and parts access make the price easy to swallow.

Agreed. Though it's best to maintain a shopping/wish list and place orders once the shipping cost makes more sense.

Years back we did a few group buys from EM3ev. Saved everyone significant shipping But these days everyone is to spooked to trust transactions like that. A shame. I've offered several times to do a USA Grin group buy and save everyone the higher cost of shipping. But again all the scams have everyone too afraid. Oh well.

I wish Grin had an update order option, maybe for the first 24 hours after an order. I always forget to order some minor part, but remember a few minutes after hitting the order button.
 
I don't doubt the usefulness of Grin's support and accessories. But just to give an idea of the costs, I got a good deal for the G310 two years ago, about 150 euros shipped. Now the same motor from Grin shipped to EU and taxes added would be almost 400 euros, which is not that easy to swallow.

The random AliExpress seller took a long time to ship it and it was different winding than what I ordered, but luckily it ended up being just fine or even better for my purpose. So with a premium price you'd more probably get exactly what you order.
 
ilu said:
I don't doubt the usefulness of Grin's support and accessories. But just to give an idea of the costs, I got a good deal for the G310 two years ago, about 150 euros shipped. Now the same motor from Grin shipped to EU and taxes added would be almost 400 euros, which is not that easy to swallow.

The random AliExpress seller took a long time to ship it and it was different winding than what I ordered, but luckily it ended up being just fine or even better for my purpose. So with a premium price you'd more probably get exactly what you order.
Um, so it's the same motor, just different? You ordered a motor by specification and got the wrong motor but it was cheaper.

There are significant differences between your budget 310 and the Grin version. The Grin version is around $240 plus shipping to the USA. Sadly you folks have that VAT. Not the fault of the resellers. eBay vendors have the dumbed-down version for $130. A cursory look at the online photos shows some of the differences.
 

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ilu said:
Grin sells a slightly improved version but you can find one a lot cheaper from China as well.

I am intrigued by this - does this mean, they are building clones or tht they buy the Bafang and then replace certain components to make them last longer?

Also, if I were to order from Grin (since the UK seems to have very little in terms of affordable but trustworthy suppliers...) - is there any sort of spare parts for the motor I may want to order right away to save me the shipping hassle etc. if I need them in a year or two?

Thank you!
slug
 
I noticed the link I gave earlier was faulty, I edited the post so it should work now. I'm not sure if they add temperature sensor and better magnet adhesive themself or if Bafang does it at the factory for their order.

You could buy a spare set of gears, but if you limit the power as recommended (either 40A phase current or ~500W input power limit) and especially if you can monitor the temperature as well, it's quite unlikely that you would need them (nylon gears fail with less force when too hot). The set costs only 30$ anyway.
 
Thank you very much for the fixed link - I did read up on their improvements and it seems to me that I won’t need them - on a 28” rim it is unlikely to spin too fast, and I can add a temperature sensor myself.
That might make it easier, although finding a good supplier in the UK has not been a success yet. I’ll keep looking.
Thanks again!
slug

Edit: The Bafang websie does not show his model, is it a legacy one that Grin still have stocks of?
I wish both Bafang and resellers would give more info, it's really hard to determine whether something is internally geared, or what the model number is. It seems one has to play the lottery a few times before striking gold?
 
Like E-HP said, pedalling a motor around with NO power will have double the resistance due to magnetic cogging and may not be ideal for longer rides. But ebikes are an addiction and the bicyclists who hate on them dont realise what they are missing! As said before, get the biggest battery you can afford, you can tailor the speed down if needed.
 
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