Rear hub motor choice

jbond

100 W
Joined
Oct 1, 2010
Messages
204
Decisions. Decisons. Which would make a better base for a stealth 48v-15A rear drive motor on a bike with mechanical 160mm disks and Shimano Acera 9sp rear mech? The Cute/QBK 10 CST using the existing 9 speed cassette, or the Bafang/8Fun SWXH with a DND 9sp freewheel. The Cute has a LHS cable exit which might be a bit neater. And the CST using the existing cassette might fit and work better with the existing drop outs and mech. Conversely the Bafang might be more robust and cope better with being overdriven. There may be some differences in disk clearance, spoke dishing required, drop out width and so on. The base bike is a Genesis Tour De Fer road touring bike, 700-35c tyres.

Anyone got any direct experience of the comparison?

GBK-100CST 36V 250W e-bike cassette freewheel kit http://www.greenbikekit.com/electric-bike-kit/rear/100cst-cassette-freewheel-e-bike-kit-36v-250w.html
Bafang SWXH 36V 250W Rear driving conversion kit http://www.greenbikekit.com/electric-bike-kit/rear/bafang-swxh-250w-36v-rear-driving-e-bike-conversion-kit.html
9SP DNP 11T FREEWHEEL http://em3ev.com/store/index.php?route=product/product&path=41_56&product_id=113
 
Have the SWXH that I laced into a Weinmann 700x35 rim to save the shipping on a full wheel kit, I used Bikewagon's ERD in the Grin spoke calculator and they were 2 mm too long. Maybe I got the wrong nipples or ERD was off. Hard to mis-measure the hub.

No load speeds are 24 mph and 33 mph at 36V and 48V, but actual max speed is 22 mph on either voltage, using a BMSBattery 14A controller and accurate bike computer. Someone else can explain why that is so.

The hub motor is 6.0 pounds. I keep batteries in the bag on the rear rack. Controller is now mounted under the rack,as it got hot in the bag. The bike uses between 7 and 10 watt-hr/mile. I ordered a 3 pound 54V 7AH rated Luna Mini. That would be 350 watt-hr, but figure 300 usable. Should easily get 30 miles range, and infinite if I just pedal. Very little drag from the hub motor.

MA230032.jpg


Stealth? A roadie was behind us in slow traffic on the bike path the other day, and picked it up immediately. He liked it though. Probably saw the glow of the wattmeter.

What would I do today? The shipping on that GBK kit to USA was $178. I'd still buy a bare motor or watch ebay, as 700cc 500W 36V geared motor kits for under $179 shipped come and go there.
 
jbond said:
Decisions. Decisons. Which would make a better base for a stealth 48v-15A rear drive motor on a bike with mechanical 160mm disks and Shimano Acera 9sp rear mech? The Cute/QBK 10 CST using the existing 9 speed cassette, or the Bafang/8Fun SWXH with a DND 9sp freewheel. The Cute has a LHS cable exit which might be a bit neater. And the CST using the existing cassette might fit and work better with the existing drop outs and mech. Conversely the Bafang might be more robust and cope better with being overdriven. There may be some differences in disk clearance, spoke dishing required, drop out width and so on. The base bike is a Genesis Tour De Fer road touring bike, 700-35c tyres.

Anyone got any direct experience of the comparison?

GBK-100CST 36V 250W e-bike cassette freewheel kit http://www.greenbikekit.com/electric-bike-kit/rear/100cst-cassette-freewheel-e-bike-kit-36v-250w.html
Bafang SWXH 36V 250W Rear driving conversion kit http://www.greenbikekit.com/electric-bike-kit/rear/bafang-swxh-250w-36v-rear-driving-e-bike-conversion-kit.html
9SP DNP 11T FREEWHEEL http://em3ev.com/store/index.php?route=product/product&path=41_56&product_id=113

The Bafang weighs 3 Kg, while the Cute weighs 2 Kg. The Bafang might accept more power(mass dissipates more heat), but if you are going to stay w/ 15 Amps, you don't need a bigger motor than a Q100.
The CST is nice, especially if the donor bike has a decent drive train, but sometimes they can be a bit of a pain to fit. The CST model, to make room for the cassette, the motor is pushed over towards the brk. side and the wheel requires "dishing" to center the rim. I have done two different bikes w/ the Q100C. W/ the Rocky Mountain, I never could get the motor centered to my satisfaction. The second build, a GT Idrive was a "piece of cake" everything just fell into place w/ minimal dishing. It depends on the bike. If I had to guess, I would think it would fit well in your donor bike.
I just finished the GT and have I posted a little bit w/ pic.s. Here is some of it as it applies to your proposed build;

2 keys to stealth is color and and profile. It's best to start w/a dark bike. IWrapped all the wires that go back to the controller in blk. spiral wrap and secured w/ velcro tie downs. Don't use plastic zip-ties, their tabs are a dead give-a-way and the velcro ones secure more gently. Burned the holes in the seat bag with my soldering iron.

100_0103.JPG

As for the system, the first thing I do is see what the largest frt. chain ring that will fit. In this case, a 48T replaced the 44T. With the 11T sm. gear on the original cassette, 48/11 is good for about 20 MPH and since this is an assist bike, it didn't need to go any faster than that.

Q100V CST (201 low-speed), 12S lipo(46V) driven by a 15 Amp controller and 26" wheels and that's what got, 19 to 20 MPH. Simple 3-speed limiting controller works fine w/ a system this low-powered.

View attachment 1
The torque arm.

100_0107.JPG
I use Lipo. There is 10.4 Ah in the sm. frame bag and 3Ah in the bottle, for a total of 13.4 Ah. About $300 for me to put together.

Your bike, w/ the 700 tires, should hit about 21 to 22 mph on a 48 V battery and you should be able to add another mph w/ your legs. This is w/ a "201" speed motor. That's fast enough for a bike without suspension.

If you settle on a Q100C 201, the next choice will be battery and controller. There is reems of material on the options here. You can search using key-words like SO6S, bottle battery, SLCD-3, BMS Battery, etc. Or just search back thru my posts.. Many go w/ a BMS Battery Li-Ion batt. and that opens the option of using a bottle, Shark, or Dophfin batt. w/ intergrated sine wave controller. The 18A max would be the best choice for the CST.
 
My current ride is an Alien Aurora with a 36v350w BPM and a 36v15AHr LiNMC rack battery. I'm trying to put a bike together with about the same performance but lighter and neater with a better basic bicycle. The Aurora is a rigid MTB style, 26" wheels but low quality. I'm in the UK.
 
No question. Just clarification of where I was coming from with the original query. And thanks for your input. It does sound like the Q100 is going to do the job.
 
docw009 said:
No load speeds are 24 mph and 33 mph at 36V and 48V, but actual max speed is 22 mph on either voltage, using a BMSBattery 14A controller and accurate bike computer. Someone else can explain why that is so.

I don't know the specifics of your motor, but if you are running 15amps, you don't have enough power to go beyond 22mph. My motor wants to do about 26mph, but it can't get above 22mph without more power. my noload speed is 30mph. I'm guessing your noload rpm is 260 @ 36v, or 350 at 48v.
 
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