Bafang Bpm, how many RPM?

[d8veh]

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.

[casainho]

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)???

[rojitor]

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.

[d8veh]

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.

[Haste]

casainho, what kind of battery are you using with the bpm?

[casainho]

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.

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 )

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.

[d8veh]

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

[casainho]

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.

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.

[miuan]

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.

[casainho]

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?

[miuan]

I tried front/rear motor and rear battery. Even with worse balance, rear is still a winner. Just be careful not to wash the front wheel out in corners. Lean forward if you corner hard.

[casainho]

I tried front/rear motor and rear battery. Even with worse balance, rear is still a winner. Just be careful not to wash the front wheel out in corners. Lean forward if you corner hard.

Thank you for sharing.

Could you please elaborate a list of the 3 main advantages and disadvantages of each one motor/setup?

[Russell]

IMO giving an RPM rating to a motor is bogus, it's much better to simply list the "RPM per Volts" then there's no second guessing. For example I just bought a Bafang BPM (from a board member here), the motor is marked "36V/500W 26(10)" and it spins at 8.3 RPM/V. At a nominal 36V therefore it spins at 299 RPM and at 48V nominal it spins at 398 RPM. Both measurements are no-load and calculated from speedo measurements so are bound to be off a bit. Still I'm left wondering when someone buys a "393 RPM" 48V motor is it the same exact motor as my 36V code 10?

-R

[Scottyf]

Pretty much bang on russel. The winds are the same. The stamp on the outside changes. But the kv is the same. It would be better to have rpm per volt as you've said though.

But I guess it's more difficult for Joe public to perceive that as real world speed. It also doesn't give you any torque figures.

[Haste]

Im lacing 210mm spokes to a 26" wheel using bafang bpm2. Can anyone post pics of their complete wheel...having hard time lacing it.

[Russell]

Im lacing 210mm spokes to a 26" wheel using bafang bpm2. Can anyone post pics of their complete wheel...having hard time lacing it.

Sounds like you're doing a 2 cross. If that's right here's a couple pic's of my front motor laced 2X;

GM Motor 025.jpg (89.34 KiB) Viewed 773 times

GM Motor 021.jpg (86.74 KiB) Viewed 773 times

-R

[Haste]

thank you! its kinda hard to lace a wheel without a truing stand. These hub motors get heavy and make it semi difficult to lace. Ill lace both sides one time and the wheel has so much play, and every other spoke hangs out like 1/2" out of rim..

[jateureka]

The BPM motors are offset so you should really be using 2 different length spokes.
Did you use a spoke length calculator to determine the correct spoke lengths for the spoke lacing pattern you are using?

[casainho]

Im lacing 210mm spokes to a 26" wheel using bafang bpm2. Can anyone post pics of their complete wheel...having hard time lacing it.

Please see my posts, I did shared a video and photos of my wheel.

[jateureka]

... its kinda hard to lace a wheel without a truing stand. ....

Turn your bicycle upside down and use it as your 'truing stand' to mount the motor in.

[Toby82]

motomech: I'm afraid you've got it all the other way round. Reality is, the lower the code number, the higher the speed. Actually, I'm pretty confident to say the code means number of copper turns, so assuming similar motor size to the MACs, the code 10 will be as fast as the 10 turn MAC etc. In my applications this has proven correct as I own and ride both of these motors.

More on the topic can be seen here:
viewtopic.php?f=3&t=12582
The numbers don't exactly copy what BMSBattery indicates, but it's in the ballpark.

When purchasing from BMSBattery:
393 @ 36V = code 8
393 @ 48V = code 10 (mine does 40mph in 700c rim for short periods at 74V)
201 @ 36V = code 13 (a friend of mine runs it at 74V and 26in, does about 30mph)
201 @ 48V = code 17? (I've ordered this one for my dad, will be able to confirm soon)

I know BMSBattery could do a better explanation of different wind speeds, but most should get it easily. Hell, one year ago, they had no speeds indicated online, and I had to spend almost an hour to see which code designation is in stock. So it's a huge step forward (for the chinese fwiw).

Hi Guys,
I just recieved my BPM motor from BMS Battery. I ordered the 36v 393 front motor. My motor code is 16(9). Having read this post prior to order I was expecting a code 8 motor. I emailed Bafang directly about the unloaded RPM of a code 16(9) motor and they responded with the following:

The unloaded RPM rating of motor code 16(9) at 36v is 330.
Any questions, please feel free to let me know.

I then emailed BMS battery to find out what their take on code 16(9) was and got the following response:

Hi sir,
The 393 is no-load RPM,and the 330 is normal RPM, thanks for your patronage.

I have now left the motor at my local bike mech to get laced into rim but when motor is returned I will test the unloaded RPM using a digital speed sensor I use at work for RPM calibration on test equipment. I'll then be able to confirm correct RPM rating.

[casainho]

I did abandon the idea to use the front wheel Bafang BPM because it is to strong for me:



Please read more here: Bafang BPM 500W broke again the aluminium fork dropouts

[Russell]

Hi Guys,
I just recieved my BPM motor from BMS Battery. I ordered the 36v 393 front motor. My motor code is 16(9). Having read this post prior to order I was expecting a code 8 motor. I emailed Bafang directly about the unloaded RPM of a code 16(9) motor and they responded with the following:

The unloaded RPM rating of motor code 16(9) at 36v is 330.
Any questions, please feel free to let me know.

I then emailed BMS battery to find out what their take on code 16(9) was and got the following response:

Hi sir,
The 393 is no-load RPM,and the 330 is normal RPM, thanks for your patronage.

I have now left the motor at my local bike mech to get laced into rim but when motor is returned I will test the unloaded RPM using a digital speed sensor I use at work for RPM calibration on test equipment. I'll then be able to confirm correct RPM rating.

Yeah they continue to confuse the hell out of their customers AND themselves by referring to their motors by RPM when they should state the RPM/V. Frankly you can't be certain of what you're going to get because they only give you a choice of "201" or "393" RPM motors but the actual RPM is different depending whether it's a front or rear, 350 or 500W and of course the voltage you operate at. Customers also add to the confusion by reporting no-load RPM without reporting the voltage, which with a fully charged battery will be higher than a nominal 36/48V.

That said my 36V/500W BPM code 10 spins at 8.3 RPM/V (unloaded and calculated from speedometer) or 299 RPM @ 36V (398 RPM at 48V), so 330 RPM at 36V sounds about right for your code 9.

-R

[d8veh]

It seems from the last two people that I spoke with, who recently ordered BPM motos, that BMSBattery are now shipping Code 13 as the 201rpm instead of code 15, which is the actual 201rpm version at 36v. The code 13 does about 20mph with a 36v battery.

[phproomer]

hello
Just for reference I ordered 500 w 36v 393rpm from bms battery and I recieved , 36 volts 500 watts 16(10) which seems to go 300 rpm at 36 volts, not 393rpm.