Newbie making light-weight longtail ebike?

[Flailing_Tentacles]

Hi friends,

I'm planning to convert my Bike Friday Haul-A-Day cargo bike to have some electric assist. In its human-powered form, it's ~35 lbs, and has 20-inch wheels. My goal is to be conservative with weight additions, add mainly hill-climbing power (I'm in the SF Bay Area), with a range of about 10 miles or more. I want to keep the "bike" part of my bike intact. I want to pedal hard and get tired.

My commutes are ~10 miles long, with two hills up to 350 feet each with grades mostly below 10% but sometimes briefly 15%. I like to bypass traffic by climbing hills. Maybe a motor would help me do that more. I tend to keep it below 20mph/33kph except on downhills.

For motors: I was looking at mid-drives, but as I read more, it seems I should be looking at geared hub drives to save money and weight.

I'm looking at the Q128c and the Bafang 500w CST, each with highest RPM available because of my 20-inch wheels. My understanding is the sensors, batteries, controller choices for these are pretty straightforward and I could probably copy them from another successful build with the same motor.

My concerns with this are that I would have a lot of extra-tweaking, soldering, unexpected troubles from a cheap geared hub motor, or that I'm grasping and the dark and don't know what kind of trouble I'm getting into.

Is this a good idea?

Thanks.

 

[d8veh]

The 328 rpm Bafang CST would give a top speed of about 20 mph. It's a good strong motor, but heavier than the Q128C. Both motors have the standard 9-pin connector. Connecting them up is very straight-forward.

 

[dogman dan]

Not because of the height of the grades, but because of the steepness, Mid drive for the win. It's San Francisco.

Seriously, I don't know where you got the idea they were heavier than a hub. Maybe they are a pound or so, but not enough to care about.

Put a Bafang BBs02 on it. You won't be sorry.

I'm not saying the hub motor won't work, it will, and work fine. But the mid drive will do so much better when you are overloaded.

 

[Cephalotus]

A high power middrive will eat your bicycle chain and cassettes quickly.

You also may loose your lower front gears which can suck on very steep climbs.

The middrive motor is more effective at lower speeds.

If you can climb the hills without a motor today and if you are willing to pedal strongly I would suggest a hub motor. It's cheaper, easier to install and your drive train will last longer. You can keep 3 front "gears". It's typically more efficient and more silent at 60-100% of its top speed, the problems of hub motors start driving for longer time at just 50% of top speed and slower at high power. (at low power you can drive hub Motors also at low speed with no Problems, but it is the low speed parts where people often want to have maximum motor power)

 

[Flailing_Tentacles]

Thanks for the input!

I'm located more in the East Bay, Oakland/San Leandro/Hayward area. Over here, the riding involves more long gradual hills rather than short steep ones like in San Francisco proper. Some of my commutes involve climbing 900 feet--but mostly from long ~5% grades, only briefly reaching ~15% grades for only a few hundred feet. The pattern of riding here tends to be a choice between dense trafficky flat paths, or open hilly paths with less traffic. On human-power, I tend to get where I'm going faster if I take the hill paths, because there are fewer stop lights, and I get long downhills with few stops.

I've considered the BBS02 for a long time, and I understand its weight advantages are almost the same as for geared hubs, but the price difference appears to be substantial. Any BBS02 configuration I choose seems to approach ~$1000. Geared hub motors in contrast seem to be below $700 with battery, and less running costs (chain/cassette/rings wear). Am I mistaken here? I am excited for a mid-drive, but that may be for another bike, when I'm out of graduate school and carrying heavier loads.

Cephalotus--It sounds like you are saying that with geared hub motors I will want to be running it at 60-100% top speed when the motor is on, or 12-~20 mph? That is to prevent wear on the electric part? 12-20 seems like my normal speed unless I'm going downhill. Would this be realistic if I'm running the motor at ~5%-10% grades frequently?

 

[green79]

I've ridden a Haul-a-day with a Bafang motor and have a Big Dummy with a rear geared hub motor (also a Yuba Spicy Curry on the way). The one thing I did not like about the Bafang is that it the assist is on/off. I have a bottom bracket torque sensor on my big dummy and it is a much more natural riding experience. My route home has a 15% grade and my geared hub motor, an Ezee, works great. The other advantage is that it is relatively easy to remove a rear hub motor and return it to a normal bike, e.g. if you want to do some longer tours on the weekend and not haul around extra weight from the motor. I have not tried the CST but a local guy that I know rates them highly and installs them on Haul-a-days - I like that you can just use a normal cassette with it and not a lower quality freewheel.

 

[spinningmagnets]

First off, here's a chart to make calculations easier. It lists the speed you will get from wheel RPM's at various diameters, yours being the 20-inch.

https://endless-sphere.com/forums/viewtopic.php?f=28&t=16114

The listed 328-RPM is "unloaded" at 36V, so...in a 20-inch wheel, it should be approximately 19.5 mph (30-km/h). Boost that to 48V and then we have 19-MPH X 1.3 [for 130%] = 25-ish MPH. Add the load of riding uphill, and actual speed at 48V in a 20-inch wheel will be near 20-MPH.

As much as I'm a fan of mid drives for hills...the hubs you mention are cheap, and you are saying the hills are long but not too steep, so...a rear hub couldn't hurt. Buy a high-quality 48V battery. If you fry a $150 hub kit, its not a big loss. I think there's a chance the geared hub might work for this, but...if your hills are just a tad bit much, you can always upgrade to the 48V BBS02.

Make sure to specify the 48V controller with the 328-RPM hub...

 

[Flailing_Tentacles]

So a "high quality" battery would be something along the lines of a Lunacycle battery like this one?

 

[dogman dan]

If your total weight of bike, you, cargo, will be not over 300 pounds, and the grades under 10%,, then you will be just fine with a 500w rated geared hub motor.

If you go the hub motor though, you'd prefer to run it on 1000w, that is, 48v. The Bafang you'd only need 36v.

I never meant to suggest a high powered mid drive. But I did not specify,,, the Bafang, running on 36v, 750w is what I meant. Still hard on chain yes, but very effective if his loads were going to be over 300 pounds, and the hills steep.

In fact, the 350w bafang might be plenty. I was amazed at interbike, what the 350w mid drives could do.

 

[WoodlandHills]

If you use a 3 or 5 speed IGH with a singlespeed ebike chain your chain and thus your sprockets will last as long as the skinny chain you will be using with a derailleur and a cassette. The torque of even a small mid-drive means you don't need as many gears since you will have the strength of 4 TDF riders..... :lol:

 

[ScooterMan101]

Since you have a rigid front fork, have you thought about a front hub ?

Grin Technologies, makes and sells Great Products. http://www.ebikes.ca

here ...... http://www.ebikes.ca/shop/ebike-parts/motors/mg01-fst.html

I do not know about front hub motors and going up hills, I would hesitate , only , if I only road off road with loose dirt,
but for the road/pavement the front might work well for you.

Perhaps people with front hub motor experience can tell you better .

 

[spinningmagnets]

I believe the 3-speed IGH's are likely stronger than a 5-speed from the same manufacturer, but...the 5-speed will likely have a much wider gear spread.

Karl mentioned the Sturmey 3-speed fat version worked well on his BBSHD (no breakages so far) but I think I would only risk the 5-speed with the smaller BBS02.

I mentioned that I thought the geared hub listed above would work OK, and to clarify...if that geared hub was in a 26-inch wheel, it would run a little hot (not good for hills), but the faster version in a 20-inch wheel should be just fine.

 

[WoodlandHills]

The new SA rotary C-50 5-speed is a different animal from the earlier models in that it is touted to be both an all new design and intended for "heavy duty" usage, possibly even for ebikes. I only had about 150 miles on mine when I got hurt, but it seemed to be well matched with the BBSHD. A temporary problem is that the C-50 is so new there is zero selection of cogs available. I run a 34t on my Nexus 3 and would like to do the same with the C-50, they both have a DD middle gear with all steps between gears being 25%, so the C-50 is essentially a Nexus 5 and I want to gear it the same.

 

[Flailing_Tentacles]

OK, I think I want to try out the bafang CST option. I'm not sure about the whole parts list that I will need though.

I've seen these parts used for this motor on a different thread:

Controller

Hall sensor

LCD

Speed sensor

I'll also need a battery, 20" rims, spokes, and torque arm. Any recommendations for those or alternatives to what I've listed?


Thanks for the help everyone!