Reduction ratio, front hub motor

Joined
Mar 22, 2015
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27
Hi all,

From you experience, could you please advice me what are the practical differences between motors with various reduction ratios?

I am choosing a motor for the installation in a front hub. Bafang motors are either 1:11, 1:4 or 1:5 and do not know which one to choose :eek:

Here are the motors:
http://www.szbaf.com/en/components/component/motor/fm-g01250v.html
http://www.szbaf.com/en/components/component/motor/fm-g02250d.html
http://www.szbaf.com/en/components/component/motor/fm-g01350v.html

Cheers
 
You are missing what the real differences are, Size!
The first one is a true "mini", much like the Q100 "Cute or MXUS.
The last one is a large geared motor, too big and powerful for a frt. mount, I.M.O.
The middle one is still somewhat large for a frt. mount, depends on the fork.
Tell us what bike you will be using, what battery, what the riding conditions will be like and how fast you want to go.
Then we can make some recommendations.
 
I've never seen those motors for sale. The choices for front motor are normally:

SWXU not sure of the size, but smaller than a SWX. It has a speed and high reduction ratio to get the necessary torque
SWX 120mm size for 15 mph, not for a heavyweight rider or steep hills
BPM 180mm size and heavier. 350w and 500w versions with different winding speeds. Better for heavyweights and hills.

The only sensible reason to fit a front motor is if you have hub gears. You shouldn't go over 350w on the front unless you know what you're doing and have a specific reason for it.
 
d8veh said:
I've never seen those motors for sale.

Is that true? Hmm, I haven't looked at purchasing yet, so why the coding names are different them?


d8veh said:
The only sensible reason to fit a front motor is if you have hub gears.

Yes, I do, Internal hub at rear :)
 
motomech said:
You are missing what the real differences are, Size!
The first one is a true "mini", much like the Q100 "Cute or MXUS.
The last one is a large geared motor, too big and powerful for a frt. mount, I.M.O.
The middle one is still somewhat large for a frt. mount, depends on the fork.
Tell us what bike you will be using, what battery, what the riding conditions will be like and how fast you want to go.
Then we can make some recommendations.

True, I missed that point :) So, what do you reckon, from the range of small motors, for how long can they be pumped at 500 W before the damage occurs? I would need about 3 minutes of 24V*20A = 480W delivered for climbing two hills on my commute ;) Is that too long?
 
Reduction ratio relates to internally geared motors. A motor with a reduction ratio of 10 means the motor turns internally 10 times for every 1 time it's shell turns externally. The primary benefit to this relates to acceleration and hill climbing efficiency. Electrical motors have efficiency curves that are tied to a motors RPM, the faster a motor turns the more likely the wheel is in it's ideal RPM maintaining a higher efficiency.
 
baikiewheelie said:
motomech said:
You are missing what the real differences are, Size!
The first one is a true "mini", much like the Q100 "Cute or MXUS.
The last one is a large geared motor, too big and powerful for a frt. mount, I.M.O.
The middle one is still somewhat large for a frt. mount, depends on the fork.
Tell us what bike you will be using, what battery, what the riding conditions will be like and how fast you want to go.
Then we can make some recommendations.

True, I missed that point :) So, what do you reckon, from the range of small motors, for how long can they be pumped at 500 W before the damage occurs? I would need about 3 minutes of 24V*20A = 480W delivered for climbing two hills on my commute ;) Is that too long?
If you are looking for a sm. geared motor, many of us like the Q100H (Cute) series.
They come in 2 "winds", which are usually measured as rpm @ 36V(a function of the reduction ratio and the # of wire "windings" on the poles).
24 Volts is pointless(hope that doesn't mean you intend on using a pair of SLA batt.s).
The choices come down to:
201 on 36V=16-17mph
201 on 48V=17-18mph
260 on 36V=18-19mph
260 on 48V=20-22mph
If you are fit and not too heavy, all these combos could handle your commute.
I like the 9-FET 350 W controller from Elifebike, but they also have a 9-FET 500W model.
And BMS Battery has some nice Li-on Batteries.
Here is a thread where chiridder and I are discussing his Q100H build.

http://endless-sphere.com/forums/viewtopic.php?f=2&t=55477&hilit=q100h&start=100

You can also click on my name()or D8veh)and search the posts for Q100H.
.
B of S-nice explanation of red. ratio.
 
motomech,

Thank you for the info. May I ask you why 24 V is pointless? Is it because their efficiency is low? The reason I am asking is that it wouldn't be easy for me to assemble 36V batt pack in a small water bottle.

Regarding controllers, I am not there yet with my research and learning :) But in general, any particular reason why you wouldn't go with higher power (500W instead of 350W) and simply restrict from full throttling all the time?

Cheers,
P.S. Sorry for double posting, somehow I though it would be a good idea to "distill" this question into a separate post since noone has ask it explicitly before (or at least I couldn't find any results searching in topic titles).
 
baikiewheelie said:
motomech,

Thank you for the info. May I ask you why 24 V is pointless? Is it because their efficiency is low? The reason I am asking is that it wouldn't be easy for me to assemble 36V batt pack in a small water bottle.

Regarding controllers, I am not there yet with my research and learning :) But in general, any particular reason why you wouldn't go with higher power (500W instead of 350W) and simply restrict from full throttling all the time?

Cheers,
P.S. Sorry for double posting, somehow I though it would be a good idea to "distill" this question into a separate post since noone has ask it explicitly before (or at least I couldn't find any results searching in topic titles).
I plan t use 7s4p top-notch Li-Ion battery pack which could easily output 20A in total (5A per single cell), so 24V*5A*4cells = 480W of power.

Nader style battery huh?
There are some fundamental problems with your plan.
High capacity batteries in a tiny packages violates laws of physics.
And, 24V driving a 260 rpm motor equates to 13 mph(Ebike CA motor sim. using Outrider standard motor).
That is slower than you can pedal, so what would be the point of installing a motor?
Nader doesn't give us much in the way of actual spec.s, but 10S(36V)/5Ah seems to be the Max that can be stuffed into a water bottle.
https://www.electricbike.com/mini-hub-motors/
Given that rather limited battery capacity, why would you want to run 20 Amps?
You should be thinking of small 6-FET controllers in the 10 to 14 Amp range.
And assuming your goal is super stealth, these would be the units to use to that end.
But be advised, tiny controllers do not like to be tucked away from the air stream..
 
FYI, I am currently using a Q100H w an ELB 350W 9-FET controller' and a 10S/5Ah battery pack.
http://www.elifebike.com/peng/iview.asp?KeyID=dtpic-2014-3K-SAUG.5TSEX
Top speed is 18 mph and it climbs well for a mini.
Range is about 8 miles, but I carry an extra pack.
This is not a sm.controller, but it is not prone to over-heating, so I place it inside a bag.
I also have a 10A 6-FET ELB controller, which is very low power, but works well on bike paths;

http://www.elifebike.com/peng/iview.asp?KeyID=dtpic-2013-5G-GN6T.6Y9YQ

This is a very sm. unit(smaller than a pack of cig.s.), but it must have airflow over it.
You might consider the sine-wave 6-fets from either ELB or BMS Battery.
 
For a first build, it's better to copy someone else's setup than plan your own from first principles or use a complete kit. It might be better if you say how heavy you are, how far you want to go, how fast and what type of hills you have. Then we can advise you.
 
motomech, d8veh,
Guys thanks for keeping conversation going. My plan is the following:
1. Fit 30 batteries into a bottle. Done.

2. Choose voltage and parallel config to maximize efficiency and battery longevity. I am thinking which config is better 7s4p or 10s3p?
Here is what I estimate:
10s3p: 36V * 15A = 540W, each cells is drained at 5A (3p*5A=15A).
7s4p: 24V * 20A = 480W, each cells is drained at 5A (4p*5A=20A).
So, it seems that 10s3p is marginally more efficient (by 540/480 = 12% )! Is that what you guys mean when you say 24V motors suck?

motomech, to it seems that "10S(36V)/5Ah seems to be the Max that can be stuffed into a water bottle" is not entirely right. I calculate the following way:
Each battery has 9.5Wh energy capacity at 5A drain current. So the total bottle pack will have 9.5Wh * 30 batts = 285 Wh, a number almost twice larger than given above, right?

d8veh, :) I ask first before I build to minimize mistakes and I am having fun estimating, planning and calculating it all. I weight 75 kg / 165 lbs. The return commute is 22 km / 14 miles. There are 4 hills, each can be driven up in 3-4 minutes, thats when I will use e-power. Bottle pack, as shown above contains 285 Wh at 500 watts drained power and it will last somewhat 20 minutes (accounting efficiency losses in the motor and controller) at max that "more than enough for me" power.
 
... . There are 4 hills, each can be driven up in 3-4 minutes, thats when I will use e-power.

Many have this idea before they actually ride an Ebike, but few, if any, end up using a hub motor in this fashion.
I can't explain why, but even a lightweight, free-wheeling systems create more of a penalty un-powered than one would think.
Experienced riders who want to use their legs, carry enough battery set the motor a few mph lower than they want to go and use their legs to add those lacking miles per hour.
The result is more ground covered at faster rate while still getting a work-out.
Way more fun too.
If this is your intention, you would be better off with something like the Kepler friction-drive, not a hub motor.
 
motomech said:
... even a lightweight, free-wheeling systems create more of a penalty un-powered than one would think.


Hi motomech, good point. However, the other day I tried solarbike.com.au electric fixie, 17kg. Absolute fun, easy to ride on flat, climb the hill like superman, hehe.

Mine will be even more lightweight (around 12 kg), carbon fiber assembly 7 kg + 5 kg electric conversion (2.2 kg motor + 2 kg battery (30 cells) + 0.3-0.5 kg (controller) + 0.2-0.3 kg wires) :)

Actually, I have realized that mainly I will be using the e-power to accelerate eg. to gain momentum.
 
Another question I have is about RPM.

Say Q100H can be bought with 201 or 260 RPM (presumably these figures given at 36V). So the larger the diameter of a wheel, the higher will be the driving speed, right? But how about the torque? Is there anything more to it than just simply lower RPM, more torque?
 
The slower the motor turns, the more torque it makes, but once you go below 50% of maximjm speed, efficiency decreases, so the power drops off and the motor heats up.

If you use a 700c wheel instead of a 26" one, you will get 8% more speed and 8% less torque at the same motor speed.

The worst thing you can do is use a motor that's too fast compared with its power. The 260rpm Q100H in a 700c wheel would be OK as long as you do not weigh over 100kg and don't have steep hills. It would be OK for hills if your weight is 75kg or less. You can go up to 48v with the 260 rpm motor in a 700c wheel if you're light, your bike is light, you pedal hard to keep the speed up and you don't have steep hills.
It might be a good idea to increase the current a bit above 15A to increase the power and torque a bit, which will help to keep the motor more in the efficient zone. .
 
This is actually just what I wanted to hear, I have been debating on getting the 201 vs 260 wind q100h, and I think I have decided on the 260. I live in one of the flattest states in the US, weigh 150lbs (68kg), final bike weight will be around 42lbs (19kg). I am going to put the 260 hub in a 700c wheel with 48v Li Ion battery and from what you posted it seems like I should only need to pedal on hills to keep the speed in the 15-25 mph range? Motomech recommended I go with the slow wind in the larger wheel, but as far as I can tell the only benefit would be hill climbing which I have few of, right?
Thanks!
 
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