First Build - Madsen Cargo Bike

Hi All,

I'm new to the forum, and I am considering my first electric bike build.

I would like to electrify a Madsen cargo bike that my wife and I own. It has a 26" disc brake wheel in the front and a 20" v-brake wheel with a derailleur in the rear.



We use our bike primarily to take our three kids to the park and to run errands.
I would guess that the longest trip we’ve made was about 8 miles round trip.
However, my kids are getting heavier, and it would be nice to extend our range a bit, so that we could go 10-20 miles round trip at somewhere around 15-20 mph. Thus our interest in adding an electric motor.

Here are the constraints involved with this project. I weigh about 215 lbs., my 3 kids, together, weigh about 130 lbs. We live in Portland, Oregon. Most of the biking we do is relatively flat, but there are some hills down to the river, and then up and over the bridges here. They are moderately steep, and moderately long. My CFO is telling me that I have $500-700 to spend on this project.

I have done a lot of reading on this forum regarding direct drive hubs, mid-drive hubs, and geared hubs. I would like to use a geared motor of some type so that we can use the bike without electric assist when necessary.

At first I was interested in a Bafang mid-drive kit, but I need a system that is foolproof, and it seems that proper gear shifting is rather finicky with that system. So, now I am considering either a Bafang BPM2 500W 36 or 48V system.

So, my first question is, will the motor be powerful enough? Keep in mind that we are used to pedaling without a motor. Related to that question, is do we need 48v, or is 36v enough?

Secondly, which would be better, a front hub system or a rear? I have seen several other people use a 500w hub on the front of this bike, and I haven’t read about any issues with it. The bike has a steel fork, and I could add torque arms.



The rear wheel drive sounds safer, since the frame can handle more torque than the forks. However, from what I have read, I would need to buy a 7 speed freewheel in order to fit within the 135mm dropouts (because of the bucket I would imagine it would be hard to spread the dropouts). Would I also need to change out my derailleur, since it is indexed? It is a SRAM X5 8 speed.

Thank you for any guidance or input you can give me!

John

I think we talked on the Ebike chat. Your project budget is a real problem to do that much. If you choose a geared hub motor, when it gets hot, and it will, it will not shed heat near as well as a direct drive can. This could overheat it, and is why we suggest 300 pounds for the upper limit of our geared motor.

For sure, a rear hub would have much better performance with the 20" wheel. But the really affordable kits is not the geared motors large enough to do your task. Don't choose a tiny geared motor for that bike.

You might re think having freewheeling hub. If you can save back just a tiny bit of your battery, it takes very little power to just tickle the throttle enough to eliminate the slight drag from a direct drive motor. People make a big deal out of the drag, but it's not a big deal. A nearly dead battery can still power the motor enough to eliminate the drag. The drag is not that much when going slow anyway. Descending a huge hill heavily loaded, the drag is actually quite a help!

So maybe a cheap dd kit, rear motor, 20" wheel from amazon or ebay. You'll have good performance, just not quite as good as the heavy duty kit. Still work great on most terrain, only would get a bit hotter climbing the very steepest, very longest hills.

You'd have to put a 7 speed shifter on the bike, to go with a 7 speed gear and have perfect indexing. The derailleur itself can remain the same. If you use it as is with a 7 speed freewheel, you will still get decent indexing on most of your gears. So set the tension on your cable to index good on the gears you uses the most.

But the best bet, likely also costing more than your budget, will be a mid drive, like a bafang or whatever, that drives the chain in your lower gears. This way you get the freewheeling, and the ability to crawl up steep hills super slow.

Welcome to the forum. What you want is certainly possible, but probably not in your budget. What you need is a torquey motor than can move large weight up hills. That will necessitate both a good motor, and a good battery that can handle the higher power outputs. Your budget will cover the battery, but that's about it.

Small geared hub motors don't get along with high weights and hills.

A Direct drive would work, but does add a tiny amount of drag when not under power. They also need more power from the battery, so a better battery is needed

The best alternative for you maybe a geared through-the-crank drive like the BBS02: http://em3ev.com/store/index.php?route=product/product&product_id=166
That would allow you to keep your rear gears and derailleur. With the motor powering the bike through the chain, You can gear down for hills or gear up for speed as needed. 500w might do, but the 750w kit is the best option.

As for the battery, a 48v 10AH would be all you need. Forget 36 volts when planning to use it in the bicycle equivalent of a pickup truck. you'll need the extra oomph that 48 volts can give.

Tell the CFO, that every time you go 20 miles on the bike, vs the car, it puts about 10-15 bucks in your pocket.

So the budget it will take, $1000-$1500, will pay itself off in a year or less. ( just 10, 20 mile rides) Then it's mostly just keeping a good battery on it, needing a new one every 2-3 years.

NOT putting miles on cars, not down there paying for repairs to it, and most crucially more years without a loan payment on it puts even more money in your pocket. That can put hundreds a month back into your budget. That money wasn't even included in the 50 cents a mile or so you gain by taking the bike vs the car. You'll save even more, when you can take the bike so much farther.

Couple examples of a bargain motor kit that will work good for you. Important for you to go with the rear motor, for better performance heavily loaded, using "regular" hub motor kits.

http://www.ebay.com/itm/20-Rear-Wheel-48V-1000W-Electric-Bicycle-Motor-Conversion-Kit-LCD-Display-/371229674881?pt=LH_DefaultDomain_0&hash=item566f034d81

http://www.amazon.com/Electric-Battery-Powered-Bicycle-Conversion/dp/B00QVTY3FM/ref=sr_1_cc_1?s=aps&ie=UTF8&qid=1429613777&sr=1-1-catcorr&keywords=1000w+bike+kit%2C+20%22+wheel

Then spend real money, on a really good battery. Get at least a 48v 15 ah. Budget, $700-$1000 for just the battery. You'll need a strong battery, large enough to really handle those longer trips that save you money. A cheap battery only good for short trips will not put the cash back like a big one will.

A 9 Continents clone in a 20" wheel on 48V would be a pretty good system for the use you outline, it would be about as trouble free as you're likely to get without spending a lot more money, would take you right around 20 mph on that rig on the flat and do the climbs you outline doing. The key to riding something like that is to save yourself on the flats by resting or pedaling at an exertion level and cadence you can handle easily while using the motor to make a good cruising speed and then bust your ass at full throttle and a high cadence to keep speed up going up hills, if you slow too much it gets hard on the entire system, battery, controller and motor. Once you crest a hill then coast down the other side maybe using a touch of motor to maintain speed or even some regen to put a little back in the batteries depending on the slope.

You'll probably only use the top two or three gears once you have the motor on, a 1000 watt system makes you feel like a very strong rider rather than being a moped, so all you have to do is index the shifter for the higher gears.

If you start with a high current capable battery it doesn't necessarily need to have a lot of amp hours (range) at first, get used to the system and show the benefits to the CFO and she'll authorize further capital investment in another parallel pack which should slightly more than double your range or let you go faster. When you ride for a bit you'll figure out how to balance range with speed.

That is such a cool project, get it motorized and you and your kids will have EV grins every time you're aboard.

Which high current, low capacity battery would that be, safe to have in a house with three kids?

Cheap out on the motor, in 20" rim anything direct drive with 48v will do your hauling fine. But get a decent battery, 48v 15 ah. To save money, you need the range to park the car more than you have been doing.

Hi Everyone,

First of all, thank you all for your considered responses and enthusiasm!

Dogman Dan,

I don’t think we’ve chatted before, so I must have a doppelgänger. There are a lot of bikers here in Portland, so the chances of someone else considering the same build, are not as great as you might think. My neighbor 2 houses down even has a Madsen!

Drunkskunk,

I really like the idea of the BBS02 and being able to leverage the gears on the bike. But I’m still worried about the shifting. I’ve read reviews here:

http://electricbikereview.com/8fun/bbs02/

and here:

https://www.youtube.com/watch?v=dDti2qvf3TM

where it has been mentioned that shifting under the load of the motor grinds the gears and can even cause the chain to break. It’s giving me images of my wife calling me at work because she forgot to let up on the motor when shifting, and needs me to come pick her and the kids up because the chain came off the sprocket and she can’t get it back on. Am I being too pessimistic?

That being the case, I’m leaning toward Dogman Dan’s strategy of getting the direct drive motor for it’s power and simplicity.

It sounds like the one thing everyone agrees on is that a 48v battery is the way to go. As Dogman Dan mentioned, it would be good to keep things as safe as possible with kids in the bike, so I was thinking of going with LifePO4. Does that make sense for this build?

I love Jonathan’s idea of buying a smaller battery (10ah?) to get the project going, and adding a 2nd battery in parallel. Is that just not technologically possible?

If not, could I buy one of these?

http://www.ebay.com/itm/NEW-48v-15a...bike-Kits-Powerful-8-Weeks-Gift-/131244468263

That would keep me withing my budget, even if I have to wait 8 weeks!

I would also consider building my own battery pack as mentioned in this thread, if it would keep the price down:

http://www.endless-sphere.com/forums/viewtopic.php?f=14&t=17912&start=0

I may be able to stretch the budget upward a bit if needed, but I do need keep the CFO happy so that I stand a chance of being approved for a 2nd bike project I'm considering, which would be a folding commuter bike.

John

I made my own battery 12s12p from 144 18650 cells but it's quite a chore, not something I would want to do anywhere small kids could get at it.

I was actually thinking of some of the 48V 10Ah batteries that BMSbattery sells but the shipping charges on those are fairly high from what I've seen.

Looking at Ebay you can get a 48V 15Ah made from 18650 cells and sourced in the US for a low enough price to get your project on the road for fairly close to the dollar figure you originally quoted if you go with a $250 1000W DD hub kit.

http://www.ebay.com/itm/Electric-Bi...108?pt=LH_DefaultDomain_0&hash=item4d1361fadc

For the bicycle equivalent of a minivan a BB drive would be nice but it's more expensive and as you point out there are potential pitfalls with a non-enthusiast rider. I started off really wanting a BB drive because my area is rolling hilly and I was worried about climbing but once I started riding a direct drive hub motor on a regular basis I realized riding style and where you add the pedal energy in the hill cycle counts for a lot so I no longer feel the need for the BB drive.

Probably easier to teach a non enthusiast rider to pedal hard at the steep uphills when the motor wants to bog and loaf the rest of it than the finer points of gear changing a BB drive under electric power.

As long as a person realizes they may need to dig into shrink-wrap to troubleshoot BMS and cells, those cheap eBay packs can work out okay. Just assume there's no hope of a return if cells are really shitty.

I think many of the reliability and shifting issues you’ll hear about with BB drives tends to be related to higher power users. Something you see over and over around these parts is that most folks craft a mini-motorcycle merely resembling a bicycle.

Target the goal of operating at highest performance level of pedal bicycle, instead of low-powered motorcycle, reliability really isn’t much concern, IMO.

Another issue which plays into the BB or Hub decision is tire service/repair. Ride enough you’re much more likely to suffer from flats than from chain or shifter issues. Many more options for tire repair on the road when not bolting a hub motor/wheel into the equation.

You seem to be doing your due diligence - good luck and many happy miles on EV power. Once you get this project on track and you begin looking into folding ecommuter I’ve got 2 words for you: Swift Folder

O.K., so we spent some time discussing the project over the past couple of weeks, and decided that if we're going to do it, then we need to do it right. After weighing all the great responses from everyone here (thank you!), the CFO approved doubling our budget ,so that we could purchase a 750w Bafang Mid Drive Kit with a 48V 15Ah battery. I'm still a little nervous about shifting with the motor, but I'm hoping that if we just take it slow in the beginning, we can develop our skills. It can't be any worse than learning to drive a stick shift (grind grind), can it?

Since we need to invest so much time learning to e-bike, I decided to forgo building my own battery, and purchased one from Ping instead. After reading numerous posts here, they seem like the Honda of batteries - a safe bet in terms of quality and reliability, for a good price.

I will keep you all posted on our progress and post pictures of the build as it progresses.

Thanks again for all of the advice and encouragement!

Ykick said:

Once you get this project on track and you begin looking into folding ecommuter I’ve got 2 words for you: Swift Folder

Click to expand...

That looks like one cool bike!

Sounds like a good plan. Shifting won't be a huge problem, it's just shifting when under full throttle that can be harsh on the chain and gears. The key is to shift early, before you hit the hill and need to downshift desperately. Or if shifting up on the flat, just get off the throttle and pedal through the shift, then back on the throttle.