2wd bafang SWXH/SWXK5 @ 2000 watt 70 kph build

Hi all, I'm new to the forum, but I've been doing heaps of reading and am looking to build my first proper ebike

I've followed kepler's super commuter build (http://endless-sphere.com/forums/viewtopic.php?f=6&t=47139) and am keen to follow the same basic philosophy, but with slightly higher speed potential, but still the same level of stealth (well a bit less, I will be running 2 hubs after all)

I'm aiming for a top speed of around 70kph (45ish mph), and am hoping to achieve this with 2 small bafang motors, an SWXH on rear hub, SWXK5 for front, oil filled and running at 1000 watt each, achieved through a 24s lipo battery pack (probably 4 6s in series) running at 96 volt.
This means each motor will only need a max of about 11 amp through them, and I'm fairly confident that with the oil they should be able to take this, using a CA3 to control max watts/current and overheating. I also have an electrical background so modifying the controllers to be 100V capable shouldn't be too much of an issue.

Looking at the bike calculator (http://bikecalculator.com/veloMetric.html) I will need 2000 watts of power to reach 70kph, which works out well for the 2 motors.
The motors themselves are also internally identical, with different cases for front/rear use. Both come in a 201 rpm @ 36 volt winding, which at 96 volts gives me
201 / 36 x 96 = 536 rpm
536 x 2200mm wheel circ = 1,179,200mm/Min or 1.1792km/Min
=70.752kph
So this also works out well with the 2000 watt at 70 kph figure from the calculator. It's also with a fairly median sized wheel circumference, so I can change that around to move free wheel speed up or down.
General cruising speed would likely be around 40 kph.

The issue I'm facing is that I can't use the simulator because there is no way for me to do a 2wd simulation, and the closest motor on there is the cute q100 with a high speed winding, so I'm not sure how the heavy bafang and high torque winding will fare facing 96 volt, 10.5 amp.

I'm also not sure how required rear suspension will be on this setup, front is a definite. Battery and controllers would be quite light as amp requirements are not high, nor is range, but I would be worried about damaging them without the extra shock absorption of rear suspension. I'm also worried about control-ability at top speed without the rear damper, let alone not being shaken to pieces.

I'm also assuming wheel spin shouldn't be an issue because I'm using quite small motors, but again I haven't used these before

Any input would be much appreciated!


UPDATE: Motor candidates have been changed to the one in http://endless-sphere.com/forums/viewtopic.php?f=30&t=53939
Its a slightly faster wind,70kph correlates with a 66v pack, if the Kv on that thread is correct.
The motor also has a larger gear reduction, not to mention coming half oil filled from factory so the bearings are likely already sealed so a complete fill for better cooling should be far easier!

Dual mac 6-8t motors would be better
Not as easy as you think

I have an alternate idea for you. You might want to consider the cute Q100H motors from bmsbattery ( yeah, i don't like BMSbattery, but they are the only vendor ).

Why?

1) The Bafang SWX motors are rated for 250w by bafang. Q100H is rated at 350W and the motor dyno graph shows that it's near it's efficiency point at 350W, so that's realistic.
2) Q100H motors are 2.1kg.. bafang says that the SWX motors are around 3kg, but doesn't give an exact figure.
3) Q100H motors hit a peak of 83% efficiency; bafang mentions an >79% efficiency, but i can't find a dyno graph so let's assume it's 80% peak?

Whether these motors can be oil cooled or not, i can't tell you. They are newer and a lot of people haven't played around with them yet. But they contain a 12:1-13:1 reduction, rather than the typical ~5:1 reduction that geared motors have, so if you look around, you might find lots of reports about the old Q100 and it's mediocre power, but these are different.

Even a single 8T MAC motor would probably have better performance than 2 250w motors being pushed to their limit. Wouldn't be as stealthy, but the weight would be about the same and more power would definitely be put to the ground at 2000W.

jesset33 said:

Dual mac 6-8t motors would be better
Not as easy as you think

Click to expand...

My only qualm with the mac motors is that they are bigger, and I'm trying to make this as inconspicuous as possible, as well as heavier and over double the price each.

I have an alternate idea for you. You might want to consider the cute Q100H motors from bmsbattery

Click to expand...

I'm hesitant to use the cute's as they are lighter, and in this situation the extra thermal mass would be useful due to the high power through them, although I will look into them as an option as the extra efficiency and gearing does sound good

wil said:

... and I'm trying to make this as inconspicuous as possible, as well as heavier and over double the price each.

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LOL. a bike doing 70km/h will NOT be in inconspicuous anyway

Yeah, less thermal mass, but maybe you don't need as much due to the higher power rating, as you'll be generating less heat in the first place.

Dual MACs is insane and will give you power levels close to 'the crown' or a crystalyte HS4080. The sad part though is that two MACs would weigh the same as a single HS4080 and give you lesser efficiency in the end. It's kind of pointless, unless you just want to balance the bike's weight better. ( not fun to lift the rear when the motor is 20lbs. )

Dual MACs is insane and will give you power levels close to 'the crown' or a crystalyte HS4080. The sad part though is that two MACs would weigh the same as a single HS4080 and give you lesser efficiency in the end. It's kind of pointless,...

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There's always the tradeoff, and temptation to go for more, which is why I'm trying to limit myself in size, I could go for double SWX's or I could go for a single MAC, which is bigger, in which cause I may as well go for double MACs, so the hubs look the same, but then I may as well just go for the lyte... etc etc until your at industrial motors at 50kw and no rear tyre left.

LOL. a bike doing 70km/h will NOT be in inconspicuous anyway

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Haha well maybe not at those speeds but when I'm just puttering about I'm hoping it will be!

The bike calculator that you used appears to be computing the 'power necessary to propel the bike' - similar to the 'Load Line' in the ebikes.ca simulator.

This is not the power you must expend to achieve that speed. If you set that simulator transmission efficiency to something like 75-80% you will get a fair approximation of the 'battery power' reported on the ebikes.ca simulator. Regardless of the technical aspects of the build, you have a target power shortfall of several hundred Watts.

The Load Line curves upward very rapidly over 50kph, requiring ever increasing power to gain each kph - for a road bike on the drops it only requires about 510W of battery power to hit 40kph, 1000W to hit 50kph, and 2370W to achieve 70kph (over 4x the power to hit 40kph). If you are targeting 40kph as your cruising speed, I think your build might be better served to go after a more conservative top end and lower the voltage to get your bike into a safer operating range instead of flogging the gears and clutches at 96v - way above the max recommended for MACs or BMCs.

As far as 2WD using the ebikes.ca simulator is concerned - drag out Excel and locate a motor with characteristics similar to those of interest. Scrub the 'speed' cursor along the speed axis and manually record a dozen or so data points from the summary data tables under the plot. Then just use Excel to duplicate the simulator Load Line and motor power curves against speed - but use two times the motor power. This is a PITA, but gives quite good results for 2WD estimates.

^--- word.

Consider also that you will be either saturating or almost saturating the motor, so if you want to hit 70kph, you may need as much as 2,500+ watts, as efficiency will be in the 70%-50% range..

...that's why i recommend a motor that is closer to what you want, rather than beating the piss out of a tiny motor. If it can handle it thermally for extended periods of time due to the oil cooling, then that's great. But your battery is going to suffer, thus your range..

I wish some company made a mid-range 500w rated motor that was lighter than the bafangs and MAC/BMC hubs.. but those just don't seem to exist.

Well it looks like this build might be off the table then after that, and I might have to change to a MAC hub, or maybe the Q100H suggested above, but I will have to see how they turn out with other people first, or revise my speed goal to a more reasonable 60 to 65kph.

As far as 2WD using the ebikes.ca simulator is concerned - drag out Excel and locate a motor with characteristics similar to those of interest. Scrub the 'speed' cursor along the speed axis and manually record a dozen or so data points from the summary data tables under the plot.

Click to expand...

Great idea! I'll be using it from now on working out what I'm going to do, ill probably also be able to scale motors to their various windings if their not on the ebikes.ca simulator with this as well. If I make something decently usable I'll upload it too

I wish some company made a mid-range 500w rated motor that was lighter than the bafangs and MAC/BMC hubs.. but those just don't seem to exist.

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You and me both! Joint venture? :lol:

Vladimir w/ Greyborg has a motor you may want to find out more about. It's 380w, oil filled, 3 kg, steel gears and has 135mm spacing.

It is mentioned on page 16 in their brochure: http://issuu.com/zelenavozila/docs/zelenavozila

You will want to ask him if it's capable of running the voltage/speed you want to achieve. If it can, it would save you a fair bit of hassle.

Good Luck


ps, I'm not sure it's disc compatible if that is important to you.

pss, this is V's email if you care to learn more: epmpartner@yahoo.com

newb said:

Vladimir w/ Greyborg has a motor you may want to find out more about. It's 380w, oil filled, 3 kg, steel gears and has 135mm spacing.

It is mentioned on page 16 in their brochure: http://issuu.com/zelenavozila/docs/zelenavozila

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I'm emailing him now asking about it, it does sound like these could work, but where did you get the information on it being rated for 380w? I can't seem to find information for it on http://www.zelenavozila.com website, or any of the distributors, and the catalog states it as 800 watt capable.

If I do manage to get any technical details from him, or even a motor name I'll post the information, these could be good little motors, high gearing, oil filled and with helical gears, but we will see!

wil said:

where did you get the information on it being rated for 380w?

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The weight and power rating were included in emails he and I exchanged back when I was their Australian distributor. Actually I have 3 different power ratings for that motor (don't know why) so go with whatever he is currently stating.

wil said:

I can't seem to find information for it on http://www.zelenavozila.com website, or any of the distributors, and the catalog states it as 800 watt capable.

Click to expand...

Discussed with some specs in another thread: Steel-Geared Hub Motor

Website and catalog are a bit of a struggle - here's a snap from the catalog for the impatient....

teklektik said:

Discussed with some specs in another thread: Steel-Geared Hub Motor

Website and catalog are a bit of a struggle

Click to expand...

Oh cool, thanks for that thread teklektik, i'll be following it but a quick run through of the maths gives us top acceptable speed
3750rpm / 7 = 535rpm
535 * 2200 /10/100/1000 * 60 = 70.7 km/h @ 65 volts
Which gives us a requirement of 18.46 amp to reach 1200 Watt

I also received an email back from Vlad, he rates them for 48 V 15-18 A. = 750-900 W

I would wonder if the stator side could be oil filled separately from the gear side for the cooling benefits, if so then the high power might be possible for short time periods

neptronix said:

I have an alternate idea for you. You might want to consider the cute Q100H motors from bmsbattery
...
1) The Bafang SWX motors are rated for 250w by bafang. Q100H is rated at 350W and the motor dyno graph shows that it's near it's efficiency point at 350W, so that's realistic.
2) Q100H motors are 2.1kg.. bafang says that the SWX motors are around 3kg, but doesn't give an exact figure.
3) Q100H motors hit a peak of 83% efficiency; bafang mentions an >79% efficiency, but i can't find a dyno graph so let's assume it's 80% peak?

Whether these motors can be oil cooled or not, i can't tell you. They are newer and a lot of people haven't played around with them yet. But they contain a 12:1-13:1 reduction, rather than the typical ~5:1 reduction that geared motors have, so if you look around, you might find lots of reports about the old Q100 and it's mediocre power, but these are different.

Click to expand...

You seem to be thinking of the SWXU which is comparable to the Q100. The SWXH and SWXK series are rated at 350 watts and are physically larger and have stronger larger gears etc. My wifes SWXK routinely sees peaks of just over 1000 watts on thill to her work with no problems.
I've ridden bikes with all three and SWXK is a far more capable device than the other two.

There is also a thread from Marcs, another member who has an oii cooled SWXH and runs insane amounts of power at high speeds in a trike. See his blog for more.

I completely understand a small pole count motor performing extremely well in a small wheel, as trikes typically have. You can increase the constant power rating by spinning it faster.

This is how MWkeefer also gets away with beating on his little MXUS motors on high voltage, he has a few folding bikes with 20" wheels.

Bafang's web page does say that these motors are 250w units though.

I don't think those kind of speeds can be reached realiabily with any pair of Mini's.
Didn't MWkeefer smoke a MXUS in a big wheel @ 16S?.
As my Sig. states, I got 28 mph at 12S with a pair 328 Q100. 15S would put it near 30 mph.
I know the Bafangs are more powerful, but I'm not sure they are true 328 rpm @36V motors so they might run out of rpm unless over-volted to near destruction.
I tried adding ATF to several minis, it always runs out the wheel bearing all over the brake

motomech I've just updated the intial post, but it looks like the motor candidates will now be the one in http://endless-sphere.com/forums/viewtopic.php?f=30&t=53939. It seems far more likely to be able to take the abuse they will be given

Also when oil filling, depending on the motor you need to remove the old bearings and press in sealed ones so as to minimize leakage. This doesn't stop leakage through the wires though~

wil said:

motomech I've just updated the intial post, but it looks like the motor candidates will now be the one in http://endless-sphere.com/forums/viewtopic.php?f=30&t=53939. It seems far more likely to be able to take the abuse they will be given

Also when oil filling, depending on the motor you need to remove the old bearings and press in sealed ones so as to minimize leakage. This doesn't stop leakage through the wires though~

Click to expand...

I put in sealed bearings. The ATF is very viscous and flowed past the seals like they wern't there.
The seals in bearing are more to keep water and dirt out, than oil in.

Update!
Bought my scott scale 50 the other day

A touch big, but buying second hand and looking for discs and front forks beggers can't be choosers, especially for what I paid for a $2000 new bike! I'll move the seat forward all the way and throw a slightly shorter front stem on it and call it a day

Will order motors, controllers, batterys, CA, chargers, BMS etc after I move houses (1 week)

I'm also collating all of hobby kings lipo at it's australian warehouse into an excel to ease battery choice for australians, I will probably run 3 5000mah 6s in series, but will buy 4 so I can run 12s2p for extended range when needed (my commute will only be about 7km each direction)