Bafang G3xx series high reduction ratio geared hub motors

[Bequmi]

After much waiting and back and forth I finally got some sort of information from gomax about the windings of the g360... Kind of. They wouldn't tell me anything related to windings or Kv and only asked what speed I wanted to go at each voltage and wheel size, which I think looks right so far in the simulator when converted back to Kv and input that way.

The list they sent me is as follows. I realize I should probably have asked about 26" wheels as well just for the knowledge of others, but my application is either 24" or 29er.

24" wheel as follows

35km/h @ 36v is 304 rpm (8.44 Kv)
40km/h @ 36v is 348 rpm (9.66 Kv)
35km/h @ 48v is 304 rpm (6.33 Kv)
40km/h@ 48v is 348 rpm (7.25 Kv)
45km/h @ 48v is 390 rpm (8.125 Kv)

700c / 29er wheel as follows

35km/h @ 36v is 265 rpm (7.36 Kv)
40km/h @ 36v is 303 rpm (8.41 Kv)
35km/h @ 48v is 265 rpm (5.52 Kv)
40km/h@ 48v is 303 rpm (6.31 Kv)
45km/h @ 48v is 340 rpm (7.08 Kv)

The Kv is an estimation by me of the rpm and voltage.

Looking at all of those specs I'm guessing that they actually only have a few different windings, and that the t11 motor in the simulator is potentially the 340 rpm version (@36v) that we were guessing it was.

 

[justin_le]

After much waiting and back and forth I finally got some sort of information from gomax about the windings of the g360... Kind of. They wouldn't tell me anything related to windings or Kv and only asked what speed I wanted to go at each voltage and wheel size,

That's pretty much how Bafang works. You can never get through to them with KV and they'll mostly refuse to let you call the shot on the specific winding turn count that you want, instead they want you to tell them the wheel size and speed requirement and then their 'experts' will choose the right motor for you. So we're often doing things like saying "We're using this motor with a 24V battery in a 20" rim and need it to do 30 kph" or something like that just in order to get them to supply a specific fast winding.

The good thing is that at least once you have the motor there is usually written in a clear marker the winding count on the stator if you open the hub up, so that you will ultimately be able to know the precise winding you got.

 

[justin_le]

I plotted a ride out the other day

It's a bit of a mess, data is out of Strava visualised over the trip sim of the same route. Trip sim obviously isn't the most accurate representation of real life, as it uses full power where it could not be used in real life etc, but from a temperature perspective it's pretty spot on in this regard.

Top graph I have plotted real speed over the top of simulated speed.
I've combined bottom graph to show both Grade and Shell temp.

After a 2km 4% average grade segment at full power core temp got to 65 C, pretty much bang on the sim.

Thanks Will, I really appreciate you doing a direct comparison here between the beta trip simulator web app and an actual real world bike trip temperature measurements. I really haven't yet made the effort to validate any of the data outside of the controlled wind tunnel experiments and was only hoping/expecting to be within the ballpark of actual road tests. To see that field rides show it being even better than this is encouraging

 

[Bequmi]

That's pretty much how Bafang works. You can never get through to them with KV and they'll mostly refuse to let you call the shot on the specific winding turn count that you want, instead they want you to tell them the wheel size and speed requirement and then their 'experts' will choose the right motor for you. So we're often doing things like saying "We're using this motor with a 24V battery in a 20" rim and need it to do 30 kph" or something like that just in order to get them to supply a specific fast winding.

The good thing is that at least once you have the motor there is usually written in a clear marker the winding count on the stator if you open the hub up, so that you will ultimately be able to know the precise winding you got.

Hey thanks Justin!

That's what I figured out after some back and forth. I ended up ordering two different motors to test. I requested a 40km/h and 45km/h motor at 36v in a 24" wheel. I believe they suggested this was going to be something like 340-380rpm. We'll see what shows up though. Hopefully this will be sufficient for my needs and goals when run at 48/52/60v if necessary. I am actually going to be using it in a 24" wheel, so I'm hoping the voltage jump will make up for the speed difference.

Justin, do you usually refer the winding turns back to the known labeling for the bafang cst, or something else? Is there another way to get an idea of Kv based off of windings?

 

[justin_le]

Justin, do you usually refer the winding turns back to the known labeling for the bafang cst, or something else?

No, not at all. The winding turns would hopefully be written on the actual motor stator when you open it up, at least that's been the case from what I've usually seen. There is no reason for there to be any correlation between turn counts across different motor series. The kV constant for a given winding count depends on the actual flux linkage inside the motor and winding pattern of the stator. A 10 turn wind on one motor model could be 12 rpm/V and on another motor model 10 turns on the stator might correspond to just 5 rpm/V.

But once you do know both the kV and turn count for a _given_ motor series, then it is easy to accurately predict the expected kV for a different winding.

Kv (new) = Kv (old) * Turns(old)/Turns(new)

While the other motor properties like winding resistance and inductance change at the square of the turns count:

R(new) = R(old) * Turns(new)^2 / Turns(old)^2

In general for a given motor series you would have a relationship like
Kv * Turns = Constant. And it would be fantabulous if manufacturers would simply publish what this constant was on each motor series. I could compile a table of that constant for all the Bafang G3x motors that I've tested here if it's of interest.

 

[Bequmi]

But once you do know both the kV and turn count for a _given_ motor series, then it is easy to accurately predict the expected kV for a different winding.

Kv (new) = Kv (old) * Turns(old)/Turns(new)

While the other motor properties like winding resistance and inductance change at the square of the turns count:

R(new) = R(old) * Turns(new)^2 / Turns(old)^2

In general for a given motor series you would have a relationship like
Kv * Turns = Constant. And it would be fantabulous if manufacturers would simply publish what this constant was on each motor series. I could compile a table of that constant for all the Bafang G3x motors that I've tested here if it's of interest.

Ahhh thanks! That's very helpful. I'll definitely let you know what I receive when it shows up and I can see how they have it labeled.

 

[CristianMM]

I also ordered a rm g360 from alibaba Gomax..this supplier was indicated in the first page..i think, and after 2 months of waiting and lots of lies from this GOMax scammer i finally gave up and filed for a refund.

 

[right arm]

I managed to melt / break my gears circled in orange here somehow after 1500mi commuting here in Portland. Anyone know where I'd find some replacements?

 

[wil]

I also ordered a rm g360 from alibaba Gomax..this supplier was indicated in the first page..i think, and after 2 months of waiting and lots of lies from this GOMax scammer i finally gave up and filed for a refund.

They definitely aren't scammers, I did get the correct motor from them, but they were absolutely pathetic/useless at the same time in regards to time and communication and your experience sound similar to mine with them.I got a spare set from Gomax when I ordered my motor, see if they will sell you a set. Supposedly Bafang is cracking down on out of dealer repairs though so parts may be difficult.

Wendy at CNEBikes was also able to source G360s when I was originally trying, they didn't stock them so it was a 40 day lead time. You could try there for gears.

What power levels where you running by the way?

-----------------------
Update! Got sick of the motor hitting thermal limit (I have 85°C limit programmed), and have oil filled it with 100ml ATF, through one of the brake disk holes drilled out.

The same ride I did previously motor temp at the top of the hill was 65°C now 60°C.

More importantly the rate of cooling has substantially increased, previously it would get hot and kind of just stay like that, now at ambient +50 degrees temp drop is about 1 degree every 12 seconds. Case temperatures are also a lot higher, indicating more heat transfer.

One note is, due to the design of the motor I'm not sure how much of that oil has reached the core winding and stator section, and how much is just between the inner and outer case. When assembled the only way in to the core is via a cutout that the speed sensor sits in, and this sits at the top of the motor, so kinda tricky to get oil to when assembled. I filled it with the motor facing brake side up so I am hoping some got in here, + hoping some splashed in.

As a side bonus the motor is even quieter now!

 

[Jil]

But my biggest beef with Bafang, as well as other hub makers, is that they don't seem to have gotten the message that there are many more options for 32h drilling pattern rims available these days than 36h.

Have a look at Ryde Andra rims, dedicated to ebikes and trekking bikes. They are not light, but strong. And all models are available in 32 and 36h.
https://www.ryde.nl/-andra-rims

 

[Bequmi]

I'm just curious if anyone else had order / shipping issues while dealing with gomax?

I ordered and paid for said order eleven weeks ago, and It finally shipped and arrived last week (three days DHL shipping time total which is crazy) but what arrived is not what I originally ordered, and all the motors have a varying level of moderate to major scratches and damage.

Just curious if anyone else has had similar issues with gomax. I'm not sure how to proceed. I notified them on Friday and they said they would look into the details on Monday. So far no response.

Any thoughts on how I should proceed?

This may be the wrong thread, but I figured since it relates to the same motor and supplier it may help future readers as well.

 

[bushido]

@justin_le when you have determined that the 40A phase current limit on the G310 is the limit, was it because 40A created to much heat, or the actual strength of the nylon gears ?

would active cooling allow more torque ?

 

[Bequmi]

Has anyone had a problem with their g360 stuttering? Mine (I have two, both do it) will function okay at the walking speed on the lcd8s / lcd 3 but using a PAS or throttle at any higher speed and they seem to stutter or rev up and down in rpm. Seems to be about every half second or so. I've tested two motors with two different lcd8s and two different sinewave controllers and the results are the same. All other parts besides the motors seem to function normally with a g310. I'm wondering if this is a potential issue with the hall sensors or something similar?

Edit: I was able to test one of them with a cycle analyst and controller today for a minute. The motors are functional there, which seems to leave the only option being the controller and motor not playing nice together.


If anyone has any advice or suggestions on other things try or information to get, please let me know.


Thanks,
Ben

 

[justin_le]

@justin_le when you have determined that the 40A phase current limit on the G310 is the limit, was it because 40A created to much heat, or the actual strength of the nylon gears ?

That was directly related to the strength of the gears. We had several cases of gears stripping with 50A of phase current, so we decided to reduce the limit by another 20% to have some margin. The goal is to limit the torque to about 40 Nm, which is ~40A with a standard motor winding, but for faster windings the phase amps can be higher since they have proportionally lower Nm/A.

would active cooling allow more torque ?

Active cooling definitely increases the continuous torque capability of the motor, which is about 15-18 Nm in this case. But it won't really increase the peak torque that you can do without mechanical damage.

 

[john61ct]

Even with replacing the plastic gears with metal ones?

 

[wil]

Update: Oil fill has started leaking 6 months post fill.
It's leaking from both the wiring side, and from the case closure past the o-ring. Wiring side is worse than the case side.

Good thing is that both these spots mean no oil gets on the disk.

 

[Smileandbeware]

I'm just curious if anyone else had order / shipping issues while dealing with gomax?

I ordered and paid for said order eleven weeks ago, and It finally shipped and arrived last week (three days DHL shipping time total which is crazy) but what arrived is not what I originally ordered, and all the motors have a varying level of moderate to major scratches and damage.

Just curious if anyone else has had similar issues with gomax. I'm not sure how to proceed. I notified them on Friday and they said they would look into the details on Monday. So far no response.

Any thoughts on how I should proceed?

This may be the wrong thread, but I figured since it relates to the same motor and supplier it may help future readers as well.

Mine arrived pretty bashed-up too. The parcel was clearly dropped and the axle pierced the packaging, damaging the thread in process. The nut wasn't going on very easily, but the axle itself was fine. So I forced it through couple of times, now it's OK. I did not file a claim.

 

[beartaco]

I ordered my G360 in a 700C wheel from cnebikes.com. Everything arrived exactly to my specs and in good shape.

 

[Smileandbeware]

Here's a true story for shits and giggles.
So I shredded my original G310 gears, and as I opened the motor to install the replacement - surprise surprise, somebody at the factory forgot to put the third gear in:


Or maybe they did it for weight reduction? Less is more!

 

[CristianMM]

hi .i am stuck here. i don't know how to open this , to reach the internals to change the cable

 

[CristianMM]

i am stuck here.

 

[CristianMM]

Wil, please help me. I saw that you opened this part.

 

[wil]

Wil, please help me. I saw that you opened this part.

They should be already as opened as you need.

Wiring is potted on

Finally at the internals

That piece you are holding is the top piece in the picture here with the wiring. I never got it physically as separated as you appear to have it because
A: The wiring is potted to this top case
B: The wiring is wired to the core wiring, which is stuck in the other half of the case.
So I only angled them apart for the photos.

From where you are though all that should remain would be to remove the potting, and then I THINK the cable will just pull through.

 

[wil]

Looking at your picture closely I can see you still have the speed sensor visible through the cutout in the top case.

On mine this was tied to the stator, and the stator stayed in the more inner half of shell when I separated the two halves of the wiring shell.

Is the thing you are having difficulty with that the stator is instead stuck in the more outer half (with the axle shaft that you are holding in your image?)

 

[CristianMM]

yes, in my case, the top case (with the speed sensor) is stuck with the stator , and i cannot reach the internals. i want to open the two parts in the last picture.mine are stuck together.
Thank for helping me