1st build, advice appreciated!

All
Building my 1st eBike, I've spent months reading the forums and am just about ready to order. Would appreciate advice/comments on my plans. I read (and hopefully followed!) the sticky on getting advice

I am an avid cyclist, This bike is for my wife who would like to join me on long distance rides. She dislikes upright bikes and rides a recumbent (Rans Rocket) w/ 20" wheels. Rider and bike (w/o electric assist) weigh ~170 lbs. We live in a hilly area and she can't make it up the hills at this point. Our goal is to have a bike that will help her up the hills so that she can develop better fitness. So I am looking for a light weight setup that is as efficient as possible at low (7 mph) speeds, no interest in faster speeds. While she will likely work up to 20-30 mile rides the motor would only be used on hills. Low cost is a goal since this is my 1st build; if things work well I will likely set up a recumbent tandem in a similar fashion and have a higher budget.

I'm leaning towards a Cute Q100h setup running at 24V (250W), the 201 rpm wind. I figure that will run around 7-10 mph max and be the most efficient at hill climbing speed. 24V because 250W is enough to assist a single rider, and the battery will be smaller and cheaper than a 36V.

I'm leaning towards a rear wheel since some of our hills are pretty steep and I"m concerned the front wheel will break free. That said, she'd need to drop from current 9 spd rear gears to a 7 speed freewheel so if front wheel would work it would be preferable.

I figure I'd order parts from either BMSBattery or ELIfebike, neither seems to be much better cust service than the other. I'd order a bare motor, square wave controller (KU65) with a thumb throttle, torque arms and a brake detector switch. I'll build the wheel myself. For battery I am thinking of 2 Dakota 12V LifePO4 from Clean Republic (http://www.amazon.com/12-Volt-Rechargeable-Lithium-Battery/dp/B00JK06CK8) in series, they now incorporate a BMS and are headquartered here in Seattle. In the longer term I'd like to try building my own 18650 battery packs using some of the approaches described on the forum but for simplicity I want to start w/ a ready to go pack.

Any advice would be greatly appreciated. One think I haven't figured out is an inexpensive way to estimate how many watt-hours she uses on a ride. Seems like it will be hard to estimate how much power she'll need since it's only hills of varying length and steepness. I'm hoping that 10ah will be a good start, and assuming that I could add 2 more in parallel if it's not.

Thanks for any comments and for all the excellent info contained in these forums. It took a while but I feel much more knowledgeable about eBikes having spent some time here!

Have you considered a Q75? It sounds like you've got a very good handle on things. Most people don't know what a watt hour even is by their first build.

http://www.amazon.com/gp/product/B001B6N2WK/ref=as_li_tl?ie=UTF8&camp=1789&creative=390957&creativeASIN=B001B6N2WK&linkCode=as2&tag=xbnijgbr-20&linkId=XRPRXJJX24BOD2OW You may want to purchase something like this to get a firm grip on her power consumption, at least with having this there will be no doubt about how much power she uses. You might even sort of plot her power usage after each ride to get a good feel for her growth in stamina, or maybe you'll learn she simply grows a bit lazier over time, hah!

As you note, it's pretty difficult to approximate the watt hours she will use when you consider the many variables in this scenario. http://www.ebikes.ca/tools/simulator.html You might play with something like this, though.

Thanks bowl, I had run across those watt meters. My only hesitation was that they're 1/2 the cost of a Cycle Analyst which seems like a much more capable device. Given that you can use those around the house to find energy hogs, maybe I'll take the plunge. It's mostly for her, to avoid her being 15 miles from home and out of juice

btw, did you mean Q85?

Hi Dr. Ben,

Over the last 10 years or so I put together at least a dozen different electric assist rides, including push trailers, front hub motors, both direct and geared, and several mid-drives. I think you indicated you wanted to keep costs down, but after working with two 500w BBS02's I would have to be pushed pretty hard to recommend anything besides a small crank drive.

Because the crank drive helps you turn the cranks it gets the advantage of all the existing rear wheel gearing. Because it freewheels, pedaling without using the assist works great. Installation is fairly easy and doesn't require any front wheel or rear wheel modifications. Using the low assist settings and the built in PAS it is very efficient and can be run using a fairly small battery.

The first one I did was for my 61 year old sister using a conventional bike. She loves it. I was also impressed with it and put one on a tadpole trike earlier this year, and I love it. Either one will allow you to easily climb a 20% grade (in low gear), and also allow you to cruise at any speed (up to about 25 MPH) you desire depending on the assist level and gear you use. Edit: Both of these are driving a 26" wheel, so would perform even better with a 20" wheel.

Welcome to the forum, and good luck with whatever you decide to do.

I have a Q75 in one of my bikes. It has two drawbacks. Firstly, it's sensorless, so controller choice is critical. These small motors generally do not run well sensorless unless you get a controller that is well matched to it. Many controllers simply will not work with one. Secondly, it's not very powerful.

I think that for the slight difference in weight, the Q100 is much better.

I know you want a simple system, but a controller like the S06S with LCD and PAS makes the riding experience so much better. You don't even need a throttle - just pedal. The KU63 gives full power with the PAS, which is not what you always want.

You want lightweight, so probably best to avoid LiFePO4, which weighs a lot more than alternatives. Do a search on Aliexpress for a 36v 30 cell battery, which will weigh about 4 pounds. Use "8.7ah 36v lithium battery" as your search ti take you to the ones with Panasonic cells, or search for the same on Google. 36v will give more flexibility on your choice of controllers. With a controller like the S06S, you can turn the power right down, and you can turn it up to get more torque when she needs it. There's no weight penalty in going to 36v. It's only the difference of 100g between 7S4P (28 cells) and 10S3P (30 cells). The weight of the controller and motor are the same. The much more common 40 cell 36v batteries (11.6ah) only weigh 3 kg.

A front motor will be fine for that bike. You won't get skipping at that power level.

d8veh says that a front hub would work at the lower wattages , and do use at least a 36 volt battery pack 11 or more amp hours, that will give your wife the range you want. If I go only 10-12 mph on a more powerful motor I have I could go over 25-30+ miles on a charge with about a 528 watt hour battery pack. I get less range if I go 17-22 mph
if you do want to go with a rear hub motor the Q100 c CST hub takes a cassette up to 9 speed, and even 10 speed if you use a 1-2mm spacer/washer .
When ordering anything from China, be sure you get plenty of the small items, if you want just one or two small items like a different controller or throttle, PAS sensor, the shipping cost is $ 35 or more .

drbenjamin said:

All

I'm leaning towards a Cute Q100h setup running at 24V (250W), the 201 rpm wind. I figure that will run around 7-10 mph max and be the most efficient at hill climbing speed. 24V because 250W is enough to assist a single rider, and the battery will be smaller and cheaper than a 36V.

I'm leaning towards a rear wheel since some of our hills are pretty steep and I"m concerned the front wheel will break free. That said, she'd need to drop from current 9 spd rear gears to a 7 speed freewheel so if front wheel would work it would be preferable.

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