BHT ALTernative low kV for single reduction mid

[nutnspecial]

Greetings 2025
I was lucky enough to get some BHT motors back in the day, to make my single reduction mid drive. It is still running strong and I'd love to see how it does against the new CYC gen4 with a cassette and also the single reductions.

I'm aware most if not all middrives including surons use lighter higher kV motors needing 2 reductions.
Not interested in that. Less noise and better durability/reliability with a 'slower' motor. Like I think zero's are pob single reduced, and maybe some of the e dirtbikes too. . . .

Am accumulating parts to build another improved and possibly higher power of the same mantra design, but am having ZERO luck finding anything equivalent to these old BHT with rpm's/volt.

Looking for bldc's weighing at or close to ~15lb max with about 20 to 25 rpm per volt.

BHT weighs 11.2lb and spins ~2500rpm @ 100v. It works excellent for this ~72lb bike and lighter rider when geared for 40mph max. Throw 60-80a thru the controller and it's a great balance with alot of wattage in a small package, decent enough for prolonged low end grunt and what I consider a max reasonable topspeed.

I've tried many search terms and the problem lies with all the basic motor suppliers giving pretty generic spec ranges of volts and rpms, tho it's pretty obvious they are at least double the kV I'm looking for.


/////EDIT////// adding datasheet from Drum from bigblock alt motors thread linked below. Rather than my kV guesswork here is the data in blackwhite

 

[amberwolf]

Are you willing to consider motors not direclty designed as middrives and/or for ebikes?
Are you set on a specific mechanical design / motor mount?

Neither "BHT motors" nor "mantra design" come up with any usefully consistent image results, so don't know what you're looking for structurally.

 

[scianiac]

There are reasons why most motors have higher Kv, it's easier to design motors like that. You can make any motor you want a range of Kv by changing the winding but depending on operating conditions you'll just end up with an inefficient motor by changing Kv to operate the motor outside it's intended RPM range. Designing efficient low RPM motors requires a bit more skill in design and manufacturing. I think though depending on your target speed I would just use a lowish Kv motor and more reduction, with a suitable frame you can put quite a large sprocket or pulley on the rear and if you design it right those don't even have to be very heavy.

RPM and current are the variables here, if you are trying to make high power to weight from the motor you need to either have a special motor, normally with a very high pole count, or you need to spin that motor fast to make power without incurring tons of resistive losses. High pole count motors do exist often with quite low Kv but they are mostly open frame outrunner motors for propellers, for the size you are talking that would be large agricultural drones or paramotors.

I'm guessing those BHT motors were just probably 5 pole pair or something low like that with just a low Kv wind on them as they were designed to run at higher voltage than you were using them, to be run at low power and speed, or just poorly optimized.

However in a bike there is some nuance here, because how much time are we really spending at high current vs just crusing along so maybe a low RPM motor is not so inefficient. Well that depends on motor design, specifically the magnetic design of the motors. When I tested my LR Small Block it has pretty low magnetic losses so even with my very very low gearing and factoring in my average current which is pretty low I sitll can spin it faster and it would be slightly more efficient. I think many of these motors we are already spinning them too slow for optimal efficiency even factoring in average current and not peak current. Reason being I think is high gear reductions are a pain and come with their own drag and high rpm starts to cause other issues like noise.

 

[nutnspecial]

What battery to use for 1000watt 48 volt BHT?

I ned info about what battery to use for this BHT 1000w motor at 48volt I don't know what controller to use yet, maybe a Lyen? or Kelley? I was thinking about this green works pack that I saw on one o fhte threads. But it is only 40volts. maybe he reconfigured the packs to get the right...

endless-sphere.com

??FREEWHEELING BHT?? or other powerful motors?

to freewheel or not to freewheel- that is the ? I'm trying to find real world examples of moderate power via single reduction put to the rear wheel, preferably successfully using freewheels for motor and pedals. I am reworking the bht on my klein mantra as the 1st iteration needed much...

endless-sphere.com

A few pics of the motor from the threads noted. A handful here have used bht.

It was only marketed as a '1000w ebike cart motor', emphasis on 'cart' and other slow moving torquey stuff I think. (but has does well in my app with 6-8kw on accelerations to ~40mph)
I imagine it was intended in the east for tuk tuk type stuff?
AW- along with a WB freewheel (if wanting to coast/pedal/no regen), this would probably be excellent at moving a heavy trike up to 15 or maybe 20mph fast

There are reasons why most motors have higher Kv, it's easier to design motors like that.
. . .
Designing efficient low RPM motors requires a bit more skill in design and manufacturing.

I figured this, but especially in the specialized field of mtn bikes and ebike stuff the complexity and cost of manufacture doesn't seem to be stopping alot of these products and designs. Sky is the limit, look how much cyc is getting for their specialized kits.
I can only assume it's simply because most are not trying to make a mini zero style bike with single reduction, and for heavier slower stuff hubmotors and crank drives are acceptable to most?

There still has to be s o m e t h i n g out there, it was such a simple motor and not crazy expensive.

I can go back over the bht threads or take apart my spare to count poles etc. It has done excellent with my style build as noted.
I'd prefer a sealed motor, and mounting doesn't matter (needs customized anyway).
Size also is somewhat flexible.
Reduction is the biggest issue with this build. 11/55 is pretty much max.
And if dropping pack voltage I'd have to change to huge 24fet controller and diff charge setup.

It was a simple enough motor and nothing crazy costing- I'm willing to take a shot on something similar if it weighs 11-15lb and has similar or lower volts/watt. If anyone can recommend specifics, what is out there that even comes close??

 

[scianiac]

I mean there are tons of electric trike motors out there and many have reasonable Kv just not that low. What type of power or phase current levels are you looking for? Sounds like 6-8kw assuming that current you listed it batter and not phase?

Also controllers that use modern FETs are way way smaller, an old 24 fet is equal to a modern 12 or even 6 FET.

You can run a slightly higher Kv motor but only at it's lower RPM like a LR motor at 67Kv which I think are mostly used for electric trikes, they are made by top power who has better quality and design than many, in the same range has QS from what I've seen, there are a lot no name motors out there with the same frame style that have questionable quality.

 

[nutnspecial]

Thanks yes 60 to 80a into controller.
IIRC my previous em3 controller u could set the phases up to 200 or so. This cheapy is whatever its set at.

Had no idea there is newer fet design in the past couple years. Maybe that's a consideration to balance the system back out.

And maybe a more programmable controller for throttle would be nice. Not a golf cart slow one like the Kellys used to have, but just enough ramp up setting for speed type throttle, simulating some battery volt sag would be slightly more friendly than current one.

I had compared LR 'big block' way back and wasn't impressed but will recheck. And will look further into aliexpress and QS, but all of their stuff seems massive over 20lbs. I'll send some emails etc and report back, thanks!

 

[nutnspecial]

that many companies make "GNG" and "GNG Big Block" motors, including David Lida, Unite etc etc.....
For example, this "Easy Tao" webpage shows these "GNG" motors from 400W to 1100W : http://www.easy-taobao.com/item/35592583839

The "GNG Big Block Alternative motor" that is the subject of this thread is the one sold by BHT, which is different to the "GNG" motors, and I believe that it is manufactured by YK Success / YongKang. (Possibly manufactured by others as well, but I have not seen any others yet).

If you look at this page from "Made in China" website Self Balancing Bike, Self Balancing Scooters from China Manufacturers - Yongkang Jojo Technology Co., Ltd. page 5. and scroll down, I believe item 133 is the 1000W 48V motor sold by BHT.
These motors have a significantly lower kV than the "GNG" motor, but are heavier and larger diameter.
Item 135 is the shorter, lighter "500W 48V" version. I assume this would be significantly lighter than the 1000W version but share the kV of around 36. I think it would still be heavier than the GNG motor but would need less reduction ratio to give a sensible pedalling cadence on a mid drive system.

BIG BLOCK alternative Motor

Golden motor (at least 5kw model) is of really low quality, it's just a matter of time when you are going to have a problem with it. It also cant do 5 kw continuous (tested by luke), and when you look at it better, it has low power to weight ratio. One good thing about it is that it can do great...

endless-sphere.com

From 'big block alternative motor' thread, circa 2015. Pretty good read, though there are like at least >6 of us that were doing builds and I'm not sure how almost any of the other guys made out with the motor.

Seems what helped make 'BHT' special is the 6 pair poles VS most being 4 or 5 that I'm seeing now.
I have to go reread the first 7 pages

 

[nutnspecial]

i guess the LMX is one of the few like mine with parallel bike gears, and I love the bikes and the idea of belt drive on brake side, but they obviously used a much higher wound motor, look at the reduction!

QS motor was very helpful and quick to reply, they have two perhaps, mid sized motors but IMO either too small or too large 11.5lb and 18lb. Both a reasonable ~40-50kV (unloaded). The 11lb would be a consideration but is another 1.5" longer than their 5kw 18lb motor (and also bht, and I assume big block too. Too long.)

From the table above BHT has about 35kV unloaded, and closer to 20 loaded which is how I was calculating.

 

[nutnspecial]

I've been pressing one of sellers of a promising form factor 5 pole pair motor for more data on kv/rpm or a graph like from the bht.
After saying no twice, they sent these . . . .

Lol WTF. They do sell BT controllers too- but this doesn't even seem pertinent to that lol.

 

[amberwolf]

The images aren't showing, just the filenames, so I don't understand what the post is trying to say. If you're linking to images hosted elsewhere, try copying and pasting the actual image into your post instead of the link to it; then it will be hosted here with your text and everyone can see them.

I've been pressing one of sellers of a promising form factor 5 pole pair motor for more data on kv/rpm or a graph like from the bht.
After saying no twice, they sent these . . . . kf/Sdeee3b2999ac4aaabaa948e271b608aeg.png S64176f2a071e48088bf515acc5519902J.png

Lol WTF. They do sell BT controllers too- but this doesn't even seem pertinent to that lol.

 

[nutnspecial]

Thanks - I can see those last two, and when I click edit they remain populated.
Still not showing for you? I noticed someone did a laughy face emoji on the post so assumed it showed at least 4 them 2?

 

[nutnspecial]

No luck yet BTW for an 11 - 16lb motor roughly <6"x6" that spins anywhere near 3k rpm @ 24s.
Crazy how there is really only 2 or 3 options widely available (that I've found) in that physical form, in the WORLD.