What Q128C version (and which controller) do you recommend?

[joscha]

Hi everyone,

I'm planning to convert my Scott Sub 20 2013 700cc into a pedelec.

The bike itself weighs 11kg plus change and I'm 80-85kg and moderately fit. I don't mind pedaling, but my friends I usually cycle with are all on electric motors now and I can't keep up with them without support . Also I like tinkering around with things, so this project is 2/3 practical and 1/3 fun for me.
As you can see from the picture my bike is quite sleek, that's why I want to use "small" LiPos, controller and batteries instead of for example an oxydrive kit with the "heavy" 3.8kg bafang motor and big 11AH battery. Range is not really relevant for me, I'll just carry replacement batteries with me if I'm driving for a longer duration.

So far I am planning to get the following components:
- Cycle analyst v3 (ca3-dp)
- Q128C (I'd like a cassette motor so I can keep my 9 rear gears + cassette)
- 2x6S 5A LiPos in series for 44.4V nominal, around 50V max
Plus the following peripheral items:
- PAS
- Electric Brake Magnetic Sensing Switches (I have hydraulic brakes)
- Torque arms (my frame is made of aluminium)
- Three way switch to select different speed profiles (i.e. Road Legal, Offroad, No assist)

Now I have 2 Questions:
- Is the Q128C an ok choice? I couldn't find too much information about it online. Basically I'm looking for a <3kg motor that supports cassettes. An alternative would be the swxh2-r, but it seems to be more expensive.
Also, which version of the Q128C should I get? It's available in 201 and 328 rpm for 36V or 48V. Ideally, I'd like the motor to support me up to 25-30mph. By that I don't mean that the motor alone should get me to that speed, but it should assist in getting there and not put additional load in terms of increased roll resistance/weight on me. At the moment I manage to get up to ~28mph (slightly downhill, unassisted) if there's no wind, I'd like to keep it that way .
For this reason I'm considering the 48V and 36V 328rpm versions. According to some formula I found on the internet the 328rpm@36V motor in conjuntion with a 12s lipo at nominal voltage should yield a theoretical max speed of 33mph, and 25mph for the 328rpm@48V motor.
Do you think the 328rpm@36V version at 44V will have enough torque for me to achieve around 15mph on 5% elevation with me putting in ~100W through pedaling or should I rather get the 328rpm@44V version of the motor?
For comparison: a friend has the 11AH oxydrive kit, i.e. 15A controller with bafang swx02 code 10 (~315 rpm@36V) @ 700cc, which I feel has more than enough torque to get up hills. However the top speed he get's out of it is rather unsatisfying as I'm actually faster unassisted downhill than him. (It's that guy: http://www.pedelecs.co.uk/forum/threads/which-motor-kit-to-get-bafang-cst-or-xiongda-36v-or-48v.21169/). Of course aero dynamics also play a role here, but still...

- Second question: What controller do you recommend? I was thinking of getting the Lyen mini monster (http://lyen.com/), mainly because of it's size to power ratio. However, I guess I wouldn't need a programmable controller with the cycle analyst, right? So maybe there is another smallish controller that I could rather use? What do you think?


Thanks for reading, and apologies for not being able to keep the text shorter.

Joscha

 

[Deleted member 4366]

The Q128C is too new for anybody to have any experience of it yet.

First thing, forget about the three-speed switch. If you get a decent controller and LCD, you don't need it, and that probably means the CA too, unless you have some other reason for wanting one.

Your big problem will be to get the speed you want. A 36v 260 rpm motor will give you about 24 mph with 12S lipos, but the Q128C doesn't come in that speed. You'd have to get the Q100H, which is a freewheel motor.

This shop has the controller you need it's similar to the BMSB S06S, but 48v. You can get the LCD from him too. In his listings, he shows a Xofo cassette motor, but that listing is all mixed up regarding the different motors. In the photo, it looks like a XFV, but it could be a squashed photo of the XF-K(V), which is the same as the big Bafang CST motor. You'd have to ask him which one it is and what rpm it is at 36v, but I doubt that you'll get any sense out of them. Worth a try though. Xofo make clones of Bafangs, so a lot cheaper, and they claim better.

http://www.aliexpress.com/item/Regeneration-Electric-Bicycle-Brush-less-Controller-48V-6-MOSFET/1749495210.html

http://www.aliexpress.com/store/product/Electirc-Bike-Motor-36V-250W/914437_1792921456.html

The Oxydrive kit has the perfect motor for you. Can't you buy an upgrade motor for your mate and get his one.

A 328 rpm motor will be too fast for its power. It won't work efficiently. You need to choose a motor that has its highest efficiency at your modal riding speed. Optimum efficiency comes at about 2/3 to 3/4 of maximum speed. Also, when your motor is too fast, you spend a lot of time drawing maximum current, which will overheat the controller. As a rough guide, you will be drawing maximum current all the time you demand full power when your speed is less than 50% of maximum.

The next option would be to get a crank-motor. You can do any speed with one of them. You just have to choose the right power.

 

[joscha]

Thank you for your advice.

Reasoning behind the CA was that I might be tempted to install a torque sensing crank set at some point in the future, and would have to replace the display then anyways. I'm not entirely happy with how PAS feels. Also I usually prefer to buy high quality items once instead of buying cheap multiple times.
Reason for the switch is that I'd like to have an off/zero assist switch, just for subjective peace of mind. I do realize that this is not really necessary or a good implementation of an "emergency stop".

About the xofo motors: To clarify, you recommend the xf-v(k) (http://www.xofomotor.com/display.asp?id=780), right?. Because the smaller xfk (http://www.xofomotor.com/display.asp?id=783) is too weak?
I'll try to contact the seller and see how he responds.

My mate unfortunately does not want to sell his oxydrive kit motor.

I was considering a bbs02 mid drive at some point, but it takes away the possibility to ride the bike without assist which i'd like to retain, and i cant make due without the front shifter. Especially not with the added resistance that a disabled motor in the system would bring.


Actually, there is one thing that I don't understand though. You say 328 rpm is too fast for its power, but then say that the oxydrive motor would be perfect for me. However, as far as I know, the oxydrive motor is specced at around 320rpm@36v, just like the q128c? What am I missing?

Best regards,
Joscha


Edit: Btw, I was originally looking for a 260rpm@36V motor, but couldn't really find any that supports cassettes. The hub motor market is horrible for unexperienced people.

 

[STEVEMANFA]

Just to let you know the oxydrive 11Ah is back on offer at £450.00 if this is any good to you

 

[Deleted member 4366]

The Oxydrive motor is around 270 rpm. It's about the same speed as the bigger one, but slightly less torque.

I didn't recommend one Xofo motor over the other. The bigger one is heavier and of course bigger, so it can give more power. Both motors can give adequate power with the right controller and battery. I have used the bigger ones at 30 amps 36v. They're slower than the Bafang CST, giving about 19mph at 36v, but they seem to be a lot more free-running.

 

[daenny]

I got the 11ah oxydrive kit (as stated above). And it's a code 10 motor at 36V. And the free spin speed is around 40kph (according to the dispaly) so that would be more like 310rpm, right?

 

[Deleted member 4366]

I've been given some wrong information by the factory. Code 10 is normally about 300 rpm at nominal voltage (36v). Fully charged, your battery will be 41.5v, so a no-load speed of 40km/h can be achieved in a 26" wheel. On the road, the power would significantly drop off after about 35 km/h, so that's about the maximum speed you'll go on the flat with strong pedalling. This would be a good kit for a roadbike or light-weight hybrid conversion.

 

[daenny]

Yes that's exactly true. I can get to 30-36kph very easily, even uphill. But everything faster is almost impossible, only on a downhill, where the motor is essentially not doing anything anymore. So to get higher speeds, I would need more voltage, right? I am also thinking on testing with 12S lipo, just for the fun of it. Do you have any experience with this motor on 44.4V? I guess I would need a new controller, etc?
PS Sorry for the thread hijacking

PPS: e.g. buy this https://bmsbattery.com/controller/698-sine-wave-controller-for-09-case-controller.html#/137-color-black/43-voltage-48v, and two 6s lipos?

 

[joscha]

No worries, im anyways on standby to see whether the aliexpress vendor gets back to me about rpms and model of the xofo or not..

 

[Deleted member 4366]

So to get higher speeds, I would need more voltage, right? I am also thinking on testing with 12S lipo, just for the fun of it. Do you have any experience with this motor on 44.4V? I guess I would need a new controller, etc?
PS Sorry for the thread hijacking

PPS: e.g. buy this https://bmsbattery.com/controller/698-sine-wave-controller-for-09-case-controller.html#/137-color-black/43-voltage-48v, and two 6s lipos?

12S lipos will give you 20% more speed plus more power to hold the speed.

That BMSB controller won't fit in your case. The Oxydrive has a standard Lishui controller. The battery case is cleverly designed to fit it, so you would probably be able to replace the controller with any standard 6 FET Lishui one, though I haven't tried it yet. Most 36v controllers can manage 12S lipos, although sometimes the LCDs get confused if they're dual voltage. They don't seem to like the in between voltages.

For testing, it would be better to get a 48v controller and stick it in a bag somewhere. You'll be lucky to find one with the right connectors, so you'll need a new throttle and PAS too. When you add everything up, it's getting complicated and expensive.

 

[joscha]

Well, I got a response from the aliexpress vendor. According to him the motor is as xfk. Unfortunately he just ignored my question about RPMs

 

[Deleted member 4366]

When they ignore your question, that means that they don't know the answer, the answer is uncomfortable or they didn't understand the question.

We often have terms and expressions that they don't understand. I keep reminding myself about a defect report one of my guys sent to a German factory regarding a car seat frame that hadn't been welded properly, and he wondered why he hadn't had a reply. "Nature of defect: Sidearm adrift". I guess the German translated that as, "gun floating on the sea at the mercy of the wind and tide", and thought the sender was nuts.