bafang 8-FUN gear ratio

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bafang 8-FUN gear ratio

Postby jeson » Sun Sep 18, 2011 10:13 am

Hello Every one
I was wondering if its posible to change the gear ratio of a bafang 8-fun, I mean open the motor and change parts inside ? , the thing is that I have a 36v , 500w, 201 rpm built into a 20 inch wheel, and its slow, the torque is incredible I can mount any hill with my 100Kg !:-> its even sometimes anoying to have such a torque. so I would like to raise the rpm to 300 or 350..even if I loose torque, there are a similar motor with 393rpm, you think I can get some parts from that engine and put in mine? ..
thanks a lot ..
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Re: bafang 8-FUN gear ratio

Postby John in CR » Sun Sep 18, 2011 10:30 am

The easy answer is to raise the voltage to 48 volts and lower the current. That will give you more speed, less jerkiness with the throttle, and the reduced torque from lower current will make life easier for the plastic gears inside, which is the weak point in the system.

You should also get yourself a Cycle Analyst. The current throttle option will give you the smoother response that you're looking for.
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Re: bafang 8-FUN gear ratio

Postby jeson » Sun Sep 18, 2011 10:46 am

thanks John,
it it posible to do that with the 36 volts, battery I have ? the way to do that is to hack the battery itself ? because I dont have room for extra cells in the battery pack, or its posible to use a transformer ?
also the bms battery controller is 36 volts , will be able to still use it ?
maybe my quastions are kind of dummy , but I am new to all this , this is my first ebike built :->
thanks
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Re: bafang 8-FUN gear ratio

Postby spinningmagnets » Sun Sep 18, 2011 10:53 am

If you boost the volts higher from the 36V pack with some type of transformer, there will be a roughly 30% loss of watts.

It may be possible for you to parallel a 12V battery with the 36V pack, but I'm afraid the best suggestion by far is to get a 48V pack, which will give you a roughly 25%-30% increase in top speed.
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Re: bafang 8-FUN gear ratio

Postby jeson » Sun Sep 18, 2011 6:09 pm

trying to find a cheap solution, the battery change is costy , back to the original idea, anybosy knows if I can change the gear ratio by changing parts from the bafang 8-fun motor ?
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Re: bafang 8-FUN gear ratio

Postby GrayKard » Sun Sep 18, 2011 7:09 pm

The only geared motors I know of that have different ratios from the factory are the smallest Ananda aka Cute motors. As far as I know the Bafang use different windings to achieve their speeds.

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Re: bafang 8-FUN gear ratio

Postby Kurt » Sun Sep 18, 2011 9:12 pm

The only geared motors I know of that have different ratios from the factory are the smallest Ananda aka Cute motors. As far as I know the Bafang use different windings to achieve their speeds.

Gary

I was wondering about this the other day. It makes sense to just change the windings to achieve different kv rating. I recently just purchased a code 9 bafang motor as I wanted a fast wind for a 20" wheel. What got me thinking that they might actual change gear ratio's is what was written on the motor .

It has code 9 36v 500w then it has 26 for the wheel size. Why mark the wheel size on the motor if all gear ratio's are the same?

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Re: bafang 8-FUN gear ratio

Postby Russell » Mon Sep 19, 2011 2:24 am

I have owned both 6.4 RPM/V and 9.4 RPM/V Bafangs and the difference is in the motor windings so you can't simply swap the gears. Notice I did not say the motor was this or that "RPM" because it is meaningless unless the voltage is spec'd too.

Here is a picture of a Bafang opened up

GM Motor 027.jpg
GM Motor 027.jpg (84.61 KiB) Viewed 648 times



You have a couple options for more speed that are fairly easy on the wallet and easy to implement:

1) Buy an identical Bafang motor but in a faster wind then swap the cores. Swapping cores saves you having to re-spoke the new motor into the rim. Put the old "slow" core in the new case and sell it to recoup some costs.

2) Wire another battery in series with your existing battery to up the voltage. I did this early on by using a 12V SLA in series with a 36V LiMn pack. You'll want to match capacities as close as possible, for example I used a 9Ah SLA in series with a 6.4 Ah LiMn (the SLA ran out of juice first).

Of course upping voltage will increase the torque even more. If that's not desireable you could either mod your present controller or buy another lower power controller. I experimented with one "20A" controller and was able to adjust the current from 27A to 13A simply by adding or removing solder from the shunt (shown below).


9Cfront 049.jpg
9Cfront 049.jpg (88.64 KiB) Viewed 648 times



Or

Sell your present motor/wheel and buy a new one. Most vendors spoke the higher speed motor in a 20" wheel, but it's good to check with them.


-R
Jeep Comanche 29er w/EBK geared motor, 42 lbs + 14 lb rear trunk bag w/15AH battery, tools, etc. 24 mph w/36V 10S Li-ion, 22A controller, 700Cx40mm tires.


Past Bikes: Raleigh 700C, Kona Smoke 2-9, Mongoose Hatchet dual suspension
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Re: bafang 8-FUN gear ratio

Postby Kurt » Mon Sep 19, 2011 5:04 am

I agree that the motor wind there for kv rating of the motor core is what gives you the different speeds. It dose seem silly to change gear ratios to achieve this as it would be costly to manufacture different gear sets.

I was told my code 9 was 8.9 rpm - volt. That was the fastest wind I could get . What's the fastest they make code 8 ?

I also think my motor looks a little different to the one in the pic inside. The windings are exposed and the motor casing is more of a open frame. I guess to allow better heat transfer

It still has me stumped then Why they mark a wheel size on the motor casing? Mine has 26 on it but its doesn't make sense even if the marking was just a recommendation to the wheel size 26" you would expect my code 9 to be marked 20" or 24" and 26" to be marked on a slower wind like code 12 or so. :?

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Re: bafang 8-FUN gear ratio

Postby dogman » Mon Sep 19, 2011 6:25 am

Most likely they intend the faster windings to be used in small wheels. So putting a wheel size on the motor case is one way to no mix em up.
THE LIPO RULES. NEVER ABOVE 4.3V NEVER BELOW 2.7V DON'T PUNCTURE

Ideal charging /discharging range for Lipo, 3.65v minimum 4.1v maximum

See battery technology section, FAQ thread at the top of the page for lipo noob info.

See the frankenbike longtail at the thread below.
viewtopic.php?f=6&t=28389&hilit=bouncing+betty
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Re: bafang 8-FUN gear ratio

Postby Kurt » Mon Sep 19, 2011 7:46 am

dogman wrote:Most likely they intend the faster windings to be used in small wheels. So putting a wheel size on the motor case is one way to no mix em up.


Yes but that doesn't work out as I have one of the faster winds code 9 and mine has 26" marked on it. I think they go up to code 15 or something like that. What are they recommending for a 20 " wheel then? Would be nice to know what is the fastest code.

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Re: bafang 8-FUN gear ratio

Postby jeson » Mon Sep 19, 2011 8:40 am

thanks every body for you answers,

I think this is a good option given by russell, as spoking again the wheel will get me crazy , beside having to order the spokes with the special length ...

...
1) Buy an identical Bafang motor but in a faster wind then swap the cores. Swapping cores saves you having to re-spoke the new motor into the rim. Put the old "slow" core in the new case and sell it to recoup some costs.
...
buy the way I checked the code of the engine, its code 13 ...
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