Cargo bike motor recommendation

frk1206

100 mW
Joined
Apr 22, 2022
Messages
37
Hello everyone!
After testing existing $10k cargo bikes at the local bike store (Tern, Reise Muller, Radwagon) I've realized they are all underpowered and decided to build my own. I''ve built many bafang BBS02 and BBSHD mid drive bikes with custom battery packs so I know the drill.

I'm thinking of buying a old radwagon and using that as the basis. Ofcourse the easiest thing for me is to go with a middrive setup with either a BBSHD or a Cyc X1 Pro mid drive setup but after having destroyed a couple of derailers and snapping a chain i'm wondering if hubs are better.

I live in a very hilly area (Oakland, CA) and the hills can approach 8-12% grade for a mile or more. Total load on the cargo bike with me + kid + bike would be around 300lbs. Are there any hub motors that would work? I'm assuming the dropout on the radwagon is in line with other bikes at 150-180mm but I haven't been able to measure it yet.

Is there a hub motor that would work? I'm okay with using a heavy motor like the QS 205 alongside a custom 72V battery pack but I'm worried it would overheat or just become a wheelie machine once I load the bike up with all the cargo + kid in the rear. Anybody have any experience with this? I'm mostly going < 20mph - so I feel like the DD motors would be wasteful at that but the geared ones would overheat. Confused!

Thanks!
 
Direct drive hubs can be the most efficient option, as long as they run in an efficient part of their speed range. For your application, that would mean using a relatively low RPM per volt motor, or using a low battery voltage.

In your situation, I'd strongly consider twin hub motors. That's double the torque, thermal mass, and cooling, with no increase in unloaded speed.
 
If the motor is wound (kV, RPM/volt) to go the speed you want at the voltage of the system you want, then it will be as efficient as it can be under a given load at that speed.

When you run it at that load at a *lower* speed, there is less BEMF and so higher current and more heating, etc.

You can see how this works at the http://ebikes.ca/tools/simulator.html if you like, using the various existing simulated parts, using your actual conditions.

So, for example, here's a generic system under the worst case conditions you list, using 20" wheel (because a lot of cargo bikes use those to clear the cargo deck lower):
https://ebikes.ca/tools/simulator.html?batt=B3626_GA&cont=PR&autothrot=false&wheel=20i&mass=150&grade=12&hp=0&axis=mph&blue=Lbs&black=grade&throt=100
It's using a 72v battery with a phaserunner and crystalyte h3540 (default motor in the list) in 20" wheel, 330lbs total weight (because that was the closest default, and I think you'll end up wiht a heavier bike than expected to do battery and motor enough for this). I didn't play with different stuff to find a better combination of parts; just did this to get you started with the idea. :) I picked the PR solely because it's the highest power controller in the default list so it made making the simulation easier. Had to use 72v to get the ability for 20mph under these loads.

To do 20mph it takes 2616w battery power, and 1917w motor power, to maintain this speed on the 12% grade, and would overheat the motor to greater than 250C in 5.3 minutes, using 131wh/mile. WIth the (huge) 72v 23Ah battery chosen, you'd get about 12 miles of this kind of load (if you had a motor that could survive that).

WIth that kind of power usage, then on a DD hub I'd personally go for a QSmotors QS205 50H, despite it's high weight, because it should take that all day, and they're made significantly better than the MXUS equivalent (which is a little lighter, but lower quality).

Alternately you could use a pair of the 1500W leaf hubmotors, one at each end of the bike in the same size wheel with the same winding; divides the load between them and also gives redundancy in case of system failure, especially if you use separate batteries for each. I use just one battery to power both motor systems on my cargo bikes / trikes, but it would work either way.


So...if you don't mind the maintenance issues, a middrive thru your gears would save you weight (and make a stronger wheel) over a hubmotor guaranteed to be able to handle the power required for the time required.


A hubmotor will work, and will be less maintenance, but it will be heavier (probably a lot heavier), and it will make the wheel it is in weaker. (and if you ahve suspension it will also make that work less well, probably a lot less well, as it wasnt' likely designed for that weight in the wheel).

For myself, and my heavy cargo needs, dual hubmotors for 2WD have worked more reliably for longer periods than the chaindrives (which in my case went thru the pedal drivetrain to enable gearshifting), however the difficulty of doing roadside tire / tube repairs somewhat negates that. Also, for best torque I ended up with smaller wheels, which give a worse ride quality and are not as strong as regular wheels because of the shorter spokes and worse bracing angles from the narrower hubmotor flanges, etc.

My next version of the SB Cruiser cargo trike is very likely to use motors that drive the (regular bike style) wheels via single-ratio chains (not thru the shiftable pedal drivetrain), so that I can have single-sided wheel mounts that make it very easy to quickly change whole wheels for roadside tire/tube problems, etc., *and* to enable creating the "perfect" gear ratio (compromise) for best acceleration from a stop to 20mph with the worst-case cargo load, with the right top speed, and give me stronger wheels of a larger diameter for a better ride quality. It would eliminate the problems caused by power thru shiftable gearing, but it doesn't eliminate the chain and sprocket wear.



frk1206 said:
After testing existing $10k cargo bikes at the local bike store (Tern, Reise Muller, Radwagon) I've realized they are all underpowered and decided to build my own. I''ve built many bafang BBS02 and BBSHD mid drive bikes with custom battery packs so I know the drill.

I'm thinking of buying a old radwagon and using that as the basis. Ofcourse the easiest thing for me is to go with a middrive setup with either a BBSHD or a Cyc X1 Pro mid drive setup but after having destroyed a couple of derailers and snapping a chain i'm wondering if hubs are better.

I live in a very hilly area (Oakland, CA) and the hills can approach 8-12% grade for a mile or more. Total load on the cargo bike with me + kid + bike would be around 300lbs. Are there any hub motors that would work? I'm assuming the dropout on the radwagon is in line with other bikes at 150-180mm but I haven't been able to measure it yet.

Is there a hub motor that would work? I'm okay with using a heavy motor like the QS 205 alongside a custom 72V battery pack but I'm worried it would overheat or just become a wheelie machine once I load the bike up with all the cargo + kid in the rear. Anybody have any experience with this? I'm mostly going < 20mph - so I feel like the DD motors would be wasteful at that but the geared ones would overheat. Confused!

Thanks!
 
Chalo and Amberwolf are right IMO: for very high power on cargo, 2wd is king. Maybe one DD for regen, and one geared for torque. I still gotta ask: do you need that much power, especially at low speeds: I carry 2 kids on a long john with an rh212 DD hub along the swiss jura - so total weight around 180-200kg and it works. Sometimes barely, but it works. I'd think the next level aka leaf 1500w would be plenty. That motor can handle 2.5kw easily. Not sure why you'd need 2 of them.
 
frk1206 said:
I'm assuming the dropout on the radwagon is in line with other bikes at 150-180mm but I haven't been able to measure it yet.
You didn't say which Radwagon version but I'm pretty sure the pre- V4 (22" wheels) ones were in the range of 135mm OLD rear dropout width.

I'm with the others in a 2WD setup, possible dual Leafmotor 1500 so you can custom order the winding count to maximize the efficiency at your projected speeds. The rigid forks are pretty stout.
 
99t4 said:
qwerkus said:
I still gotta ask: do you need that much power, especially at low speeds...
Because of brutal hills?

Dunno Oakland, but I doubt it beats the local 1300m mountains - hence my question. Starting at 500m altitude, 12km long trip, it takes me around 60min to reach the top including a couple of pauses to cool down the motor. The only real problem I encounter is when starting on a very steep slope. Utterly sucks with only one front DD hub. When I already have momentum, that thing just flies uphill - quite impressive, so I can only image what a leafmotor would do. Sadly totally illegal where I live.
 
If the load is really not over 300 pounds, a longtail of some kind with 20" rear wheel should work fine with a 9 continent type 500w rated dd motor. Near its limitations, but not over it. This is the kind of motor common in a 48v 1000w kit.

But hell yeah, any much heavier DD motor given 2000w will do er nicely, even in 26" wheel, and with a weight limit closer to 400 pounds.

Pick any heavier, more powerful DD motor that fits your bike, and your budget, and feed it 52v 40 amps. You'll be able to carry the kid up the rocky mountains. It won't take that much more watt hours to climb a hill than a slow mid drive, but it will burn them at a faster rate, riding up it at 15 mph or more. So you do need a strong battery to pull 40 amps and not get angry.

A mid drive would of course do er too, and very efficiently, but at 5 mph its a bit slow getting there if the hill is 5 miles long.
 
Chalo said:
Direct drive hubs can be the most efficient option, as long as they run in an efficient part of their speed range. For your application, that would mean using a relatively low RPM per volt motor, or using a low battery voltage.

In your situation, I'd strongly consider twin hub motors. That's double the torque, thermal mass, and cooling, with no increase in unloaded speed.
Or even better, mid drive with rear wheel gears with a front wheel little geared up either connected to the same pas or throttle only, to give a extra push on those hills or if the bike is very loaded/heavy
 
This BBSHD longtail has been hauling my fat but up the 400' of vertical at 10% grade between town and my residence with 40lb pup and groceries for several years. Original drivetrain, battery and motor have never needed repair or replace. Recommended.

Screenshot 2022-06-11 193245.jpg
 
Hyak said:
This BBSHD longtail has been hauling my fat but up the 400' of vertical at 10% grade between town and my residence with 40lb pup and groceries for several years. Original drivetrain, battery and motor have never needed repair or replace. Recommended.

Um. Have you checked the chain elongation lately?
 
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