Bafang Bpm, how many RPM?

General Discussion about electric bicycles.
casainho   1.21 GW

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Re: Bafang Bpm, how many RPM?

Post by casainho » Mar 12 2012 5:48pm

PUTA MADRE, I almost killed myself!!

I went to make a quick test drive after my mechanic got the motor laced and the brake disk ready. The first thing I verified was that the wheel skidded (and I weight near 100kg). I drove for 60 meters and my mechanic told me after that I went for more than 50km/h, that I were quicker than a motorbike!! He told me that he were afraid.

At the end of the 60 meters I braked and turned back, were I decided to pull the throttle to full and again the wheel skidded and I quick decided to make a small raise the wheel so it could run at full speed and than skid even more when touching in the road, BUT, when the wheel touch the road it instead broke the fork!!! I took a fall, and I am ok but I could be dead for now if this happened when I got high speeds.

Image

Image

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So, I would like to know in what kind of bicycle are people using this motor...... can you please share some pictures? Are there some special forks to handle all this power??

My mechanic told me that he was afraid because the motor is heavy and large... we think that the wheel got movement and with all his weight and being large it can't be quick stopped... that is what happened when I did the small raise and when it touched on the road.

right now I am really afraid to use again this motor and bicycle. I don't even know if I trust on the 250W motor and this bicycle, since I got top speeds of 40km/h.

Any suggestions/help for a cyclist that is now afraid to use electric bicycle at higher speeds than 25km/h and with a motor more powerful than 250W? thank you.
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Re: Bafang Bpm, how many RPM?

Post by cwah » Mar 12 2012 6:42pm

You need 2 good torque arms on the bike fork. Otherwise the forkend may not be able to handle that power and just crack as it did.
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Re: Bafang Bpm, how many RPM?

Post by casainho » Mar 12 2012 6:48pm

cwah wrote:You need 2 good torque arms on the bike fork. Otherwise the forkend may not be able to handle that power and just crack as it did.
Thank you!! Do you know if I can find it on some online shop? or will I need to do them for myself? -- I wish I can buy it on BMSBattery or something like.
Developer of the Flexible OpenSource firmware for EBike motor controllers (TSDZ2 and KT) and LCDs (KT-LCD3 and Bafang 850C color LCD).

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Re: Bafang Bpm, how many RPM?

Post by cwah » Mar 12 2012 6:59pm

The ones from doc seem quite strong (but not very pretty):
http://endless-sphere.com/forums/viewto ... 31&t=29129
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Re: Bafang Bpm, how many RPM?

Post by rojitor » Mar 12 2012 7:39pm

For front kits two torque arms is a must and c washers are very important as well.Image

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Re: Bafang Bpm, how many RPM?

Post by casainho » Mar 12 2012 7:45pm

rojitor wrote:For front kits two torque arms is a must and c washers are very important as well.
Now I remember to see some "special" washers that came with the Bafang motor, it they are the C washers.

I can't find a site/shop with clear information for arm torques to ALU front forks/fron hub motor......
Developer of the Flexible OpenSource firmware for EBike motor controllers (TSDZ2 and KT) and LCDs (KT-LCD3 and Bafang 850C color LCD).

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Re: Bafang Bpm, how many RPM?

Post by rojitor » Mar 12 2012 8:36pm

Try here meu amigo http://www.crystalyte-europe.com/home.php?cat=299 or maybe even here because they are partners http://www.greentarget.pt/

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Re: Bafang Bpm, how many RPM?

Post by cwah » Mar 13 2012 1:37am

What's the difference between torque arm and C washer? They look very similar to me.
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Re: Bafang Bpm, how many RPM?

Post by rojitor » Mar 13 2012 4:05am

I guess you see a similar shape with doc's torque arms cwah, they are nothing alike though, a c washer weighs like 2 grames and is smaller than your thumbnail,like 1/10 size of the axle nut, it is designed to make the perfect pressure on the dropouts.

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Re: Bafang Bpm, how many RPM?

Post by cwah » Mar 13 2012 4:08am

Ok, it's like the standard washer I already have on my motor axle. Thanks.
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Re: Bafang Bpm, how many RPM?

Post by casainho » Mar 13 2012 4:13am

Seems to me that C washer handle the motor torque and spreeds it on the axle. This C washer fits the motor to avoid it rotating and damage the axle, but sure, it may not be enought, I wil go also with the arm torque.
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Re: Bafang Bpm, how many RPM?

Post by rojitor » Mar 13 2012 4:29am

c washer
Image

torque arm
Image

check this thread out : http://endless-sphere.com/forums/viewto ... =3&t=31521 it is a very good example.
If you use front kits you will break eventually the dropouts.... but they will last long if you use double torque arms and c washers.

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Re: Bafang Bpm, how many RPM?

Post by casainho » Mar 13 2012 8:10am

rojitor, thank you for all that info!!

And I am sharing now a picture of the washers BMSBattery sent me. I must say that I didn't know about this and so I didn't told to my mechanic. He didn't used the washers in a correct way, I guess. Anyway, just the washers aren't enough, I guess.

Image

Rear Driving more safe than Front Driving hub motor?

With the little time I had in my hands the Bafang BPM 500W front wheel hub motor, before it shot out and broke the fork drop outs, I verified the front wheel did skidded a lot!! I think that will be a problem when making a turn, if the front wheel loses traction. Also if the fork/drop outs brake and the wheel shot out, I think I will jump front the bicycle and probably be dead.
1. Isn't safer to put the motor/wheel with traction on rear wheel?? -- I am now thinking in use the Rear Driving Bafang BPM motor.

2. Does anyone knows if the 350W version is really 350W or if 350W is just the peak wattage and the normal wattage is 250W? -- I am afraid to use the 500W version, it seems to have much more power than what I need and so it is dangerous...

Thank you for all the help.
Developer of the Flexible OpenSource firmware for EBike motor controllers (TSDZ2 and KT) and LCDs (KT-LCD3 and Bafang 850C color LCD).

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Re: Bafang Bpm, how many RPM?

Post by Scottyf » Mar 13 2012 9:24am

A front wheeled setup with a high powered gear motor is just asking for trouble as you've found out.
You need good solid torque arm's to avoid those problems.

The rear ones are usually stronger as standard on most bikes.

Sorry to see you broke it but you really needed torque arm's on this kind of setup.

The only time you don't need them is on little 250w front setups that don't kick out more than 400watt. An even then its best to have them just in case.
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Re: Bafang Bpm, how many RPM?

Post by rojitor » Mar 13 2012 3:39pm

. Isn't safer to put the motor/wheel with traction on rear wheel?? -- I am now thinking in use the Rear Driving
Bafang BPM motor.
Indeed, rear motor is safer, one or two torque arms recommended,and those washers of yours are a good ideaImage
I use this on the rear motor and two torque arms.

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Re: Bafang Bpm, how many RPM?

Post by d8veh » Mar 14 2012 5:20am

I built two bikes with the BPM motor in the front wheel. They are OK up to 25amps and 44v (about 1.25kw from the battery), but you must have torque arms to stop the axle breaking the forks. I made my own. torque arms.

Rear wheel installation can also give problems. This motor makes a lot of torque and can be dangerous at low speed with 40 amps. It's OK on a good road surface, but on grass and mud it's difficult to stop it spinning and you can high-side if not careful. At 25 to 30 amps it's better. If you fit a rear motor, you also need good torque arms.

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Re: Bafang Bpm, how many RPM?

Post by casainho » Mar 14 2012 11:43am

I would like to go with a rear motor however all of them uses a thread for the changes/transmission and the lowest change have 14 teeth while my current have 11 teeth and I get now as maximum about 40km/h pedaling (the same maximum velocity of current Cute-85 motor). With 14 teeth I will get only about 30km/h while the Bafang will go up to the 50km/h... I want to pedal over all velocity of 50km/h... How are you guys doing with rear motors? Not pedaling?

About the controllers, mine for Bafang 48V 500W says over current = 30A, does it means it powers the Bafang at start with 1440W (48V*30A)???

Image
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Re: Bafang Bpm, how many RPM?

Post by rojitor » Mar 14 2012 3:49pm

Yes 1440w your maths are right. I pedal only at low speeds, in the middle of the traffic i pedal all the time and between towns i go fast so i don't pedal at all.

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Re: Bafang Bpm, how many RPM?

Post by d8veh » Mar 15 2012 3:43am

I wouldn't take too much notice of that 30A written on the controller. The only way to be sure is with a meter. I had a KU123 that gave 40amps and a 25A controller that only gave 14A.
Your main problem is that the motor gives maximum torque at low speed, which makes it difficult to control. Look at some of the threads about smoothing the throttle.

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Re: Bafang Bpm, how many RPM?

Post by Haste » Mar 15 2012 9:41am

casainho, what kind of battery are you using with the bpm?
1997 Marin Hill Hawk. Bafang BPM 2 10T. KU123 30 amp controller. 12s LiPo.=32mph

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Re: Bafang Bpm, how many RPM?

Post by casainho » Mar 15 2012 5:43pm

rojitor wrote:Yes 1440w your maths are right. I pedal only at low speeds, in the middle of the traffic i pedal all the time and between towns i go fast so i don't pedal at all.
Thank you for your info. I guess you don't pedal when you go fast because you don't have gear for that velocity, which is something I don't like to do. I want to exercise myself, it's good for my healthy. Because of that, I think I will need to go with front wheel motor since the rear motor only have gears of 14T instead of cassette type which have 11T (as my current setup).

About the 1440W, 30A at 48V, I think that I will buy and use a KU63 controller which powers the motor at 48V*20A = 960W at start.
d8veh wrote:I wouldn't take too much notice of that 30A written on the controller. The only way to be sure is with a meter. I had a KU123 that gave 40amps and a 25A controller that only gave 14A.
Your main problem is that the motor gives maximum torque at low speed, which makes it difficult to control. Look at some of the threads about smoothing the throttle.
Yes, I was thinking in used a resistor divisor (only 2 resistors) to limit the maximum throttle/possible motor power. I came from a 250W motor and I just want a bit more power, maybe more 50 or 100W (mainly for days with wind) and a bit more velocity (~6km/h). 500W seems a lot to me and also I want to travel 68km with a battery(s) charge.

So yes, I think having a "soft start" would help me on safety and avoid strong torque forces on dropouts. Let's see if changing from KU123 to KU63 will also help me on that.

I am reading this and this threads about throttle control (I see a cheap Arduino/AVR board being used for that :-) )
Haste wrote:casainho, what kind of battery are you using with the bpm?
48V 10Ah Li-Ion Alloy Shell EBike Battery Pack.

Front VS Rear motor

I wanted to go and try a rear motor mainly because seems to be more safe to me however I see 2 main problems on using rear motor:
- I loose speed on the gears because of the 14T freewheel (now I have 11T cassette and I get about 40km/h while pedaling)
- maybe I would get wheelies and loose traction on front wheel due to bad weight distribution as explained here:
Assuming the battery is located at the rear of the bike, you get a better weight distribution (as opposed to a typical front wheel drive).
Also, practically you get a two wheel drive (rear wheel pedaling and front wheel motor assistance). A two wheel drive is better for use on slippery surface because you get better handling (Just like a four wheel drive automobile). Another thing is that the front wheel motor assistance won't cause any unintended wheelies on sudden acceleration.
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Re: Bafang Bpm, how many RPM?

Post by d8veh » Mar 16 2012 4:15am

The KU93 is the controller you want - not the KU63. The KU63 is for a 250W motor and won't be powerful enough.

You can get a 11T free-wheel from Ebikes.ca. You can also get your torque arms from there.
http://www.ebikes.ca/store/store_ezee.php

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Re: Bafang Bpm, how many RPM?

Post by casainho » Mar 16 2012 4:31am

d8veh wrote:The KU93 is the controller you want - not the KU63. The KU63 is for a 250W motor and won't be powerful enough.
Yes, thank you.
d8veh wrote:You can get a 11T free-wheel from Ebikes.ca. You can also get your torque arms from there.
http://www.ebikes.ca/store/store_ezee.php
What is safe to ride (with battery on back side), the motor on front or rear side?

BMSBattery just started to sell torque arms. I sent them an e-mail explaning my accident and the dropouts broken and they told me they will offer me the torque arms.
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Re: Bafang Bpm, how many RPM?

Post by miuan » Mar 16 2012 5:31am

casainho wrote:BMSBattery just started to sell torque arms
Wow. They have made some serious progress during recent 12 months. The price is great and the fact that these are specially made for 12mm axles is cool too. I hope they are at least 4mm stainless steel.

Go get the DNP 11 tooth freewheel, it's a must for every high speed ebike.

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Re: Bafang Bpm, how many RPM?

Post by casainho » Mar 16 2012 6:08am

miuan wrote:
casainho wrote:BMSBattery just started to sell torque arms
Wow. They have made some serious progress during recent 12 months. The price is great and the fact that these are specially made for 12mm axles is cool too. I hope they are at least 4mm stainless steel.
Let's ask them for the size of the torque arms.

I would like to get help on this question:
What is safe to ride (with battery on back side), the motor on front or rear side?
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If you like my work, please consider making a donation. I am being using the donations to buy needed resources for my developments. My paypal: casainho AT gmail.com.

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