Hi! Current thoughts on a mid(tandemish?)drive cargo bike

[eishethel]

Hi, I'm new to this, but have been riding a bike for a very long while.

After riding a direct drive cargo bike and using a geared hubbed fat bike for a bit, neither really was quite what I had a, for lack of a better word, craving for.

The super mundo was a more appealing idea, but also kind of fell short in a few ways.

*deep breath*
Currently, my thoughts are to use a mundo(v5) frame, a 800w direct drive front hub, and a 1.2kw-ish(20amp) brushless dc motor for the mid drive (@3600rpm and a 10x reduction) With all the above operating at 60v.

The rear hub would be a nuvinci. I'm not sure about adding an internally geared front crank, but it is a possibility. according to some math, the crusing speed would be around 26mph with the numbers we had for the various ratios, and we'd only need a freewheel to connect the riders input to the motors output spindle, and I think the rear hub and center portion could potentially be directly connected without a freewheel. The gearing is to keep rider input valid to cadence between 7mph and 27mph. With a reducer crank, that goes to 3.5mph which should be enough to get anything up a hill with the motors helping that the frame will hold. The front hub is mostly to pull the bike up to 36mph and for extending the life of the brakes.

With a bit of math, in theory, I might be able to get a overall controller to handle the shifting too to keep it range appropriate, and to avoid putting over whatever the max torque the rear hub can handle automatically.

The ratios from cranks to center and center to rear are 5:1 and 1:2 I the speeds are based on a 26 inch wheel (by notes)

unless my obervations are wrong, the way it's inline with the drive drain is a lot like a tandem bike? hence the title of the topic.

the super mundo was nice, but a large rotating thing just makes me feel uncomfortable and worried my skirt will be departing being an article of clothing. this keeps everything in a chainguardable zone.

With tire pressure sensors, you also get a bit more input on how much energy will be needed for the rider and cargo, so more accurate estimates and force reductions with heavier loads. Also, 'stall warnings' if you are attempting steep climbs with heavy stuff on the bike.



...my other random thought, was 'bike by wire'. the cranks are a generator. there is a battery. there is also a virtual shifter which gives you a range of gearing that your bike will try to mimic. legs spin cranks, the bike tries to spin the tire as if the two were connected. It gives a pretty intuitive way to control speed way, way faster than you should be comfortable moving.

 

[eishethel]

Another ride and a dinner later, and I've got a few thoughts to finish.

I'm utterly clueless on exactly _what_ motor to use. I'd like to both ends of the shaft supported by bearings of some nature. I'm also a bit unsure whereabouts to try to find a weatherproof 3phase brushless dc motor of the appropriate power with a 10x reduction.

I live in seattle, so operating when it is very rainy is a requirement. Also why the default power is kind of high to begin with; so many hills.

As far as a drive for the motor(s), that's...mostly taken care of, sort of, with whatever specs I wind up deciding on.

But I can't even figure out what the mounting is going to entirely look like, til I find the correct motor. :s

 

[amberwolf]

Have you heard of the stokemonkey? Uses a hubmotor as middrive thru the cranks. You could find (or rewind) motors to run at higher RPMs and gear them down, if you like--but using a hub like the SM does means it's already narrow to fit between the cranks and it's about as weatherproof as common motors get.

There are a lot of middrive designs around ES, too, if you look in the non-hub motor section. Could give you ideas, or solve problems you haven't realized might exist.


For myself, since I deal almost completely with "flat" roads, my solutions to the problem of moving heavy stuff (furry or not) has become hubmotors in each wheel, independently throttled, simply becuase of the issues I had with frame flex causing chain derailment on the high-torque powerchair motor thru the pedal drive train systems I built on CrazyBike2 originally. If I could've solved those reliably, I mgiht've stuck with chaindrives...and someday I intend to go back and try again.


BTW, there have been reports about the NuVinci sucking up a significant part of the power thru it as heat, under sustained higher power inputs. I've got one of the old autoshifting systems here intended to try as a middrive but never have gotten that build very far (life and some major events changed plans).

 

[eishethel]

the stokemonkey Is a nice setup, but it's also a large whirling cylinder where I'm looking for a smaller nonwhirling cylinder, but more or less is about the same idea, with a not quite the same stuff.

namely, this is having an output shaft with the two gears directly attached to it. I know it'll produce a bit of drag if the system was entirely unpowered, but even without a boost, I think I can get the motor to at least act like it's not there when the pedals are turning, and to make the rear hub 'feel' like it's not got a lot of friction. With the ranges intended, in theory even if it's draggy and heavy I think it could still be pedaled home or to an outlet.

one issue is pretty simple though, and why I don't want to simply use a powered rear hub...Call it a personality quirk or such, but, I utterly detest Derailleurs and refuse to have them on a bike I call a daily use one.

Which is a bit frustrating; in terms of what I think would make a great powered bike, I used to use a raleigh 3 speed. swapping the SA hub out for a powered one and a rear gear somewhere around where the top gear used to be, and using a schlumpf for the cranks, or even that tiny post installed motor...or even one of the boosted cranksets that seem to be findable nowish, would make a great daily driver...even if my old bike was kind of too short a wheelbase for my height and required some modification to get a post high enough to use, it was still one of the best bikes I've ever used. And it was, in fact, a bit older than I am.

But it'd be likely about the same cost to power a cargo bike or that modernize and power that style of 3speed, and the cargo bike lets me (in theory) haul a passenger, so that's what I'm going with.

My honest desire is actually a combo internally geared and motored rear hub of around 1500w, but I doubt such a thing exists currently.

Hopefully, if total power can be regulated when under load, there will be minimal frame flex~ Also, large solid cargo bike. The mundo seems to be the most solid of the various cargo bikes by review...

Thanks for pointing me in the correct direction! ^.^

 

[APailthorp]

My honest desire is actually a combo internally geared and motored rear hub of around 1500w, but I doubt such a thing exists currently.

Sounds like this:
http://www.ebikes.ca/shop/electric-bicycle-kits/tdcm-igh/tdcm-igh-kit-basic.html
Not as powerful, but thought I'd make sure you found it - I didn't the first couple of times I browsed/searched around for options.

 

[dogman dan]

That much power can be a bit hard on a nuvinci.

You have a dd hub motor right? Might be worth looking into how it might perform in a 20" wheel.

I was impressed by the clever cycles edgerunner, and the ODK cargo bikes. With less budget, I just more or less copied the edgerunner or the mundo.



The result is the single best e bike I've built to date. Able to carry up to 80 ah of battery, 40 ah of it in the forward bags. Tows a trailer like a dream. Currently on a mere 1000w dd motor, but plan to eventually lace up a larger hub motor.

would have upsized the motor a long time ago, but it works so good as is!

 

[amberwolf]

the stokemonkey Is a nice setup, but it's also a large whirling cylinder where I'm looking for a smaller nonwhirling cylinder, but more or less is about the same idea, with a not quite the same stuff.

If you're willing to do the DIY for it, look up Crossbreak's geared hub middrive thread. He modified a geared hub to output via the axle, rather than the shell.

 

[Drunkskunk]

Golden motor make some inrunner motors that you might be able to use, but it's not a perfect fit to your desire. Inrunner motors are where the shaft spins and the case stays stationary. outrunner motors are like a hub motor: the case spins.
The problem is cooling. the smaller the motor, the more important a constant airflow is going to be. if you get much smaller than something like the stoke monkey at the power levels you want, then you lose your weatherproofing. The solution to that is a shroud around the motor to keep the weather off. However, if you add a shroud, then you eliminate the issue with a large spinning chain and motor, and the stoke monkey or other similar setup starts to make more sense again.

If you don't mind the noise, and you can accept putting small motors in a shrouded, high airflow weatherproof container, then you might take another look at outrunner motors. there are a large number of RC outrunners available in the size and power you want.

 

[dogman dan]

FWIW,, once you power up beyond what you get from typical mid drive kits,, why not just run chain to the left side?

Use a big powerful motor, and you sure don't need to shift anymore. But you can still also dial in gearing to what you desire by going with a chain drive.

Where this thread is headed,, it belongs in the non hub motor section, so the gurus in that type of bike will see it and help. So I'm moving it there.