Electrifying a cargo bike - Mid drive or Hub?

[Chalo]

yeah I wish there was a version of the BBS motors that had the power (actual motor) of the HD but had a larger down-ratio that brought max efficiency at right about 90-95 rpm. That'd be a real dream for pedelecs.

There's one serious issue with that arrangement that first became apparent with Stokemonkey, before any recognizably modern mid drives. Experienced cyclists try to maximize power by increasing pedal cadence. If that cadence is situated at a motor RPM that yields maximum efficiency, gross power is plummeting at the same time. So right when the rider is trying to make max power, motor power is dropping off precipitously. It made people think that Stokemonkey was much less capable than it actually was. Over time, riders could have developed the habit of gearing up and letting cadence drop to help the motor stomp out big wattage, but many became disappointed and never learned how to do it.

 

[nicobie]

Interesting. I once sponsored and helped a guy train for the 60 mph bicycle challenge. I wonder if a properly programed thing like that could be used as a 'rabbit' when training?

 

[smitty2k1]

I'm also looking to electrify my long tail cargo bike (Xtracycle Edgerunner with 20" rear wheel). I've really only been looking at mid-drives so far, since all new long tail cargo bikes seem to come with mid-drives, but the Grin All Axle looks interesting. I'm not looking to go above 20 mph but I will be hauling around ~300lb of humans and cargo (driver included). I'll probably install a throttle but don't plan on using it much.

However, I'm curious how the Grin hub motor works - does it have a torque or cadence sensor or does it use something different?
How would the Grin compare to say, a CYC Photon, when it comes to a "natural feeling" of pedaling? One of the reasons I like my cargo bike is it feels like an actual bike and is fun to ride, and doesn't just feel like a bike shaped object that you're pushing around.

 

[Epithemeus]

I'm also looking to electrify my long tail cargo bike (Xtracycle Edgerunner with 20" rear wheel). I've really only been looking at mid-drives so far, since all new long tail cargo bikes seem to come with mid-drives, but the Grin All Axle looks interesting. I'm not looking to go above 20 mph but I will be hauling around ~300lb of humans and cargo (driver included). I'll probably install a throttle but don't plan on using it much.

However, I'm curious how the Grin hub motor works - does it have a torque or cadence sensor or does it use something different?
How would the Grin compare to say, a CYC Photon, when it comes to a "natural feeling" of pedaling? One of the reasons I like my cargo bike is it feels like an actual bike and is fun to ride, and doesn't just feel like a bike shaped object that you're pushing around.

By default it has no pedal assist of any kind. But grin sells both cadence sensors and torque sensors separately that can be added on. The cadence sensors can be popped on pretty easy but the torque sensor requires removing and replacing the bottom bracket with the special torque sensing one.
Edit: Here's a useful link PAS Options - Getting Started

 

[amberwolf]

I'm also looking to electrify my long tail cargo bike (Xtracycle Edgerunner with 20" rear wheel). I've really only been looking at mid-drives so far, since all new long tail cargo bikes seem to come with mid-drives, but the Grin All Axle looks interesting. I'm not looking to go above 20 mph but I will be hauling around ~300lb of humans and cargo (driver included). I'll probably install a throttle but don't plan on using it much.

If you define your complete usage profile, including terrain / weather (hills, wind, etc) as well as the speeds you need to go in various situations, as well as acceleration desired, and how far / long you need to do these things, you can use simulators like those at ebikes.ca to determine how much power you need to do the job. Then you can use that to find out how much motor, controller, and battery you'll need to do it.

A basic simulation made without knowing most of the required info:

Motor Simulator - Tools

Our ebike motor simulator allows you to easily simulate the different performance characteristics of different ebike setups - with a wide selection of hub motors modeled, and the ability to add custom batteries and controllers and set a wide variety of vehicle parameters you'll be able to see...

ebikes.ca

uses a phaserunner and the GAA v2 standard wind in a 20" wheel, assumes total weight around 350lbs (probably be higher unless your 300lbs includes the whole bike already) and a 36v 26Ah battery.

This lets you go up to 19.7mph on perfect flat roads with no winds and no stops/starts for almost 50 miles. You can experiment with it to see how it performs in your *real* conditions and usages.

Graph	Syst A
Wheel Torq	10.5Nm
Mtr Power	362W
Load	363W
Efficiency	87.4%
RPM	329.7 rpm

Electrical	Syst A
Mtr Amps	11.6A
Batt Power	414W
Batt Amps	11.1A
Batt Volts	37.3V

Performance	Syst A
Acceleration	-0.00 mph/s
Consumption	21.0 Wh/mi
Range	48 mi
Overheat In	never
Final Temp	34 °C

However, I'm curious how the Grin hub motor works - does it have a torque or cadence sensor or does it use something different?
How would the Grin compare to say, a CYC Photon, when it comes to a "natural feeling" of pedaling? One of the reasons I like my cargo bike is it feels like an actual bike and is fun to ride, and doesn't just feel like a bike shaped object that you're pushing around.

The motor itself doesn't control this. The user-interface and control system does.

So with the Cycle Analyst v3 and the proper cadence/torque sensor to replace your present BB unit (that your pedals bolt to), you can set it up to do whatever you want it to, if you are willing to spend the time to first read up on how the CA works (there is a complete info page and manuals on the ebikes.ca pages, and quite a few threads about systems using them here on the forums), and then create a setup profile for the CA that matches your needs and intent, and then tune the system once built to respond the way you want it to, it could make the bike like a "bionic" version of itself, where it is simply easier to pedal it.


I use the CA and just a cadence sensor to control my heavy heavy-cargo SB Cruiser trike, and it works very well. It would probably work even better with the torque sensor, but I have yet to get time to implement and tune that. So I use the thumb throttle for a "go button" in the situations where I can't start it naturally with just pedalling--most of the time that's not necessary, so the throttle is rarely used.

 

[smitty2k1]

By default it has no pedal assist of any kind. But grin sells both cadence sensors and torque sensors separately that can be added on. The cadence sensors can be popped on pretty easy but the torque sensor requires removing and replacing the bottom bracket with the special torque sensing one.
Edit: Here's a useful link PAS Options - Getting Started

Thank you, that wasn't at all clear to me. Do people generally find hub motors with torque sensors to feel as "natural" as the mid drive units with torque sensors?

 

[smitty2k1]

If you define your complete usage profile, including terrain / weather (hills, wind, etc) as well as the speeds you need to go in various situations, as well as acceleration desired, and how far / long you need to do these things, you can use simulators like those at ebikes.ca to determine how much power you need to do the job. Then you can use that to find out how much motor, controller, and battery you'll need to do it.

A basic simulation made without knowing most of the required info:

Motor Simulator - Tools

Our ebike motor simulator allows you to easily simulate the different performance characteristics of different ebike setups - with a wide selection of hub motors modeled, and the ability to add custom batteries and controllers and set a wide variety of vehicle parameters you'll be able to see...

ebikes.ca

uses a phaserunner and the GAA v2 standard wind in a 20" wheel, assumes total weight around 350lbs (probably be higher unless your 300lbs includes the whole bike already) and a 36v 26Ah battery.

This lets you go up to 19.7mph on perfect flat roads with no winds and no stops/starts for almost 50 miles. You can experiment with it to see how it performs in your *real* conditions and usages.

Graph	Syst A
Wheel Torq	10.5Nm
Mtr Power	362W
Load	363W
Efficiency	87.4%
RPM	329.7 rpm

Electrical	Syst A
Mtr Amps	11.6A
Batt Power	414W
Batt Amps	11.1A
Batt Volts	37.3V

Performance	Syst A
Acceleration	-0.00 mph/s
Consumption	21.0 Wh/mi
Range	48 mi
Overheat In	never
Final Temp	34 °C

The motor itself doesn't control this. The user-interface and control system does.

So with the Cycle Analyst v3 and the proper cadence/torque sensor to replace your present BB unit (that your pedals bolt to), you can set it up to do whatever you want it to, if you are willing to spend the time to first read up on how the CA works (there is a complete info page and manuals on the ebikes.ca pages, and quite a few threads about systems using them here on the forums), and then create a setup profile for the CA that matches your needs and intent, and then tune the system once built to respond the way you want it to, it could make the bike like a "bionic" version of itself, where it is simply easier to pedal it.


I use the CA and just a cadence sensor to control my heavy heavy-cargo SB Cruiser trike, and it works very well. It would probably work even better with the torque sensor, but I have yet to get time to implement and tune that. So I use the thumb throttle for a "go button" in the situations where I can't start it naturally with just pedalling--most of the time that's not necessary, so the throttle is rarely used.

Thanks, though I wasn't concerned with power output but asked about torque sensing and the "feel" of hub vs mid drive. I've ridden bikes with cadence sensing (Bafang mid drives) and didn't care for them. I've ridden cargo bikes with torque sensing (Bosh and Shimano mid drives) and did like them quite a lot. I have never ridden a hub drive. I do understand that many of these DIY motors are tweakable and there are gains to be had by spending time understanding the system and fine tuning. My priority is really just to have a natural feeling and fun to ride bike.

 

[E-HP]

My priority is really just to have a natural feeling and fun to ride bike.

What does "natural" mean to you? If it's feeling like a pedal bike, then any assistance would be unnatural. If you mean feels like a pedal bike but your legs feel bionic, then that's not natural either, unless you have bionic legs already. A lot of people want the unnatural feeling of pushing harder on the pedal, and getting proportionally more assistance, without using the throttle. That's what I wanted when I bought my torque sensor a year ago; but I probably won't install it until the rainy season, if I get around to it. I use my throttle for PAS most of the time anyway, so I'm not in a hurry.

The fun part is easy, since any powered two wheeled vehicle is fun.

 

[amberwolf]

Thanks, though I wasn't concerned with power output but asked about torque sensing and the "feel" of hub vs mid drive.

There's no difference in the feel of hub vs middrive, unless you have the wrong gearing or wheelsize or motor winding for one or the other. If they're both setup for the same job, they'll both feel the same***.


I included the power output because it is tied to the other concerns you have. If you do the correct analysis of your power needs vs usage and riding situation, etc. (such as with that simulator), then you will be able to choose and setup the right stuff to make any motor system feel the way you want it to, for it's torque vs speed curve, which is all you really can do with the motor.

If you don't care to do this, then you'll have to just try setups until you find one that feels the way you want, and does the job you want and use that. It is easily possible that without first finding out your power needs to get stuff that does the job, you'll end up spending more time and money re-buying things to replace or upgrade parts that aren't capable enough--it's happened to plenty of people, and there's unfortunate examples around the forum over the years if you feel like looking for them.


The only functional difference between hub and middrive (if the MD goes thru shiftable gearing) is that you can change gears to use a smaller lower-power motor/controller/battery because you can up the motor RPM and then lower the output speed and raise the torque via that gearing, and you can shift gears just like you do on a pedal drivetrain to use that lower power to give you more speed when you need it, or more torque. On a hub drive, you have to use more power to get more torque, so the whole system has to be bigger and heavier just to provide the startup torque or heavy-load-on-hills torque, etc.

There are numerous mechanical differences, and installation requirements, etc., but those differ even between the various hubs and the various middrives, so there's no single post that can tell you all of those that wouldn't be a book of it's own.


*** There is one difference besides the potential size/weight difference: The hub will be in the wheel, and so it's mass is at one end of the bike. The middrive will be somewhere near the middle of the bike, usually, so that's where it's mass is. That can change the way it handles, but with most cargo bikes it is not noticeable because you already have so much weight at one end of the bike, especially when loaded.

My priority is really just to have a natural feeling and fun to ride bike

As previously noted, that's up to the control system, not the motor.

If your desired middrive includes a control system that you can't change, then you're stuck with whatever that control system allows or feels like, etc. Many people don't like the limitations of ones that come with many middrives, and so there are those that use the open-source firmware replacements for some of the systems, and some that gut the drive and use external controllers on them (like the *runner series from Grin), etc.

Almost no hubmotors include a control system, and can just be driven by whatever control system you choose based on your needs. The few that do include one pretty much only come preinstalled on OEM bikes, with no currently-produced examples I can think of.

 

[Hyak]

Homebuilt cargo bike. Plenty of miles. Huge hills. Usually with a 40lb dog and some groceries. BBSHD gets me up hills under load faster than I need to go. Have never replaced the chain. Have never needed service on the motor. Chews thru brakes tho! Meanwhile, there are lots of rear hub motor RAD Wagons around this area and they can't make it up the same hills without some serious pedal effort.

 

[Klang426]

Homebuilt cargo bike. Plenty of miles. Huge hills. Usually with a 40lb dog and some groceries. BBSHD gets me up hills under load faster than I need to go. Have never replaced the chain. Have never needed service on the motor. Chews thru brakes tho! Meanwhile, there are lots of rear hub motor RAD Wagons around this area and they can't make it up the same hills without some serious pedal effort.

Are you saying hub drives are no good or just that whatever hub is in the radwagon is no good? Aren’t huge hills one of the main weaknesses of hub drives?

How many miles do you have on the chain? Seems like some people say chain stretch/wear is a problem with middrives and others say it’s no problem at all…

 

[None]

I've owned mid-drive cargo ebike like Tern GSD, also Chinese cargo ebike purchased from Alibaba.
Both served me well, but one cost thousands more.
For the cost of a Tern, performance isn't worth the thousands of dollar more for carrying heavy load on an ebike.
Top speed & cruising speed on hills are not the priority for me.
Able to carry heavy load, stable handling & braking with heavy load are priority.
Personally, I prefer the simplicity of hub-motor.
The performance advantage of mid-drive doesn't justify the cost.
Less maintenance on drivetrain=more time spent riding.
That should be a consideration for anyone buying or converting an ebike.
BTW, I feel much safer walking away from a cheap cargo ebike when I go to the store or run my errands than leaving the $5k+ Tern unattended, locked up to a bike rack.

 

[Chalo]

Seems like some people say chain stretch/wear is a problem with middrives and others say it’s no problem at all…

That's the difference between folks who check their chains and expect precise shifting, and those who don't. We all know folks who are the same about their wiper blades, gutters and downspouts, etc.

 

[99t4]

Are you saying hub drives are no good or just that whatever hub is in the radwagon is no good?

Radwagon v1 owner here. The Shengyi 1000W hub/48v battery stock setup is fine on the flats and small hills but not powerful enough to maintain speed when climbing a steep hill, especially when loaded.

Aren’t huge hills one of the main weaknesses of hub drives?

Can be overcome with a bigger hubmotor and higher amperage controller/battery. My other ebike for example has a 1500W hubmotor, 35A controller, 48V, and it flies up the same steep hills that bog down the stock Radwagon.

 

[Bush mechanic]

Unashamedly biased, but 10 years riding a heavy long tail yuba with various rear hub motor configs (26"), I would put a good rear hub into that 20" wheel without a moment's hesitation.

If you can afford the outlay to get a suitable motor pre laced it's a fast, clean, and simple way to get started.

I do not have a Grin all axle but I ran it through a heap of different simulations recently while toying with the idea. It doesn't have enough torque for me in a 26" wheel but at 20" I would be happy to use it on my cargo bike.

 

[G8trwood]

Been running these same simulations for a tadpole cargo for driving grandkids around a sandy beach. Maybe a rear gmac vs if up front, the grin all in one, but that gets really pricey. Just noticed the leaf one sider in beach/snow configuration. Any experience for those for slower speed torque? Beach is flat but sugar sand. The lake campgrounds we go to are quite hilly to further complicate. 250 of me, a 100 bike, 120 kids.

 

[gromike]

if you plan to ride in loose sand you'll need a lot of torque if you want to go forward.

 

[99t4]

taylorpat334 are you a spambot?

 

[amberwolf]

Them and two others were all spamming for a company at the same time...probably all one person, same IP, etc. All gone bybye now.