Bafang G310 geared hub - 11:1 reduction ratio!!!

[neptronix]

Just got back from a 10 mile unpowered ride on my roadbike with the G310 installed as a tester.
This is probably the last day of the year we'll see >45 degrees here in Utah, so this build is stalled until next year. But i had to ride it.

You know, this motor has exceptionally low drag, considering the fact that while the hub spins, you're getting the friction of 1 set of the gears.

I was able to average the usual 14-18mph i ride at on this bike and felt like i was maybe getting docked 1mph at most at high speeds. The MAC i know and love had imperceptible drag, but i don't mind this at all.

One other observation is that that phase wires are a tiny 18 gauge. This is the size you'd see on a 250 watt watt motor. You might see a ~1-3% gain in power delivery with 16 or 14 gauge about 2 inches out of the axle and ditching the higo connector for something bigger.

Best wishes with your builds with this motor in the meantime.

 

[1N4001]

considering the fact that while the hub spins, you're getting the friction of 1 set of the gears.

You don't. The clutch is part of the cover plate, so you're completely disconnected from the gears while running unpowered.

 

[tomtom50]

Adjusting wheel sizes to scale the motors to the same no load speeds

Ah no, you can't do that for a fair comparison because you are then comparing the motors at different rpms and torques. The smaller wheel size almost always has the advantage since it needs to produce less torque for the same thrust.

Whoa...
Power = Force X Velocity (equals Thrust X kph except for unit conversion)
The rotational analog is
Power = Torque X Angular Velocity

A smaller wheel needs less torque to produce the same thrust on the road, but you are going slower, so you only have an advantage if your gearing/winding was too high in the first place! No magic there, you have just figured out the motor is too fast for you. If the smaller wheel almost always has an overall advantage that means you need a slower hub.

Changing the wheel diameter is a completely sound way to find a hub rpm that meets your needs. It changes ratios, that's all. You'd get the same result as if the planetary ratio was changed (provided you've stayed within the practical limits of 2-stage planetary train). I'm a mechanical engineer and I know this part cold. I'm not an EE, so I'm less confident changing windings would give such closely equivalent results. Maybe Bafang found 3000rpm was the lower limit for best performance of this inrunner. Or maybe the gears can't reliably handle more torque.

Too bad for me. I'd buy one if Bafang sold a 220rpm version. But the hills around here would give me a choice of toasting the motor or getting off and pushing.

 

[neptronix]

considering the fact that while the hub spins, you're getting the friction of 1 set of the gears.

You don't. The clutch is part of the cover plate, so you're completely disconnected from the gears while running unpowered.

Really? another member told me that it was like the xiongda ytw-06..



So this is where the clutch is, eh?

 

[neptronix]

Changing the wheel diameter is a completely sound way to find a hub rpm that meets your needs. It changes ratios, that's all. You'd get the same result as if the planetary ratio was changed (provided you've stayed within the practical limits of 2-stage planetary train). I'm a mechanical engineer and I know this part cold. I'm not an EE, so I'm less confident changing windings would give such closely equivalent results. Maybe Bafang found 3000rpm was the lower limit for best performance of this inrunner. Or maybe the gears can't reliably handle more torque.

Changing windings won't help you too much. A given amount of magnet, copper, and iron will still give X power at X RPM, give or take 1-3% if one winding has more or less copper in it because the absolute exact equivalent of copper thickness between windings wasn't available. So one winding is usually better than another, but it will take some testing to find out..

In general, the faster you can spin the motor, the more potential power it can make, both peak and continuous. So if you were to bump up the internal reduction ratio another 15% and change the winding so that it's 15% faster, then we can make something like 15% more torque on the same voltage, but then we need to push more amps to make the additional power, of course.
This would turn it into a better steep hill climber tho. For sure. But not good enough for climbing a mountain.

You can also do this by dropping down to a 20" wheel and boosting the voltage. The results with the G310 are amazing:
on a 26", the continuous power is around 700w for an hour.
on a 24", the continuous power is around 775w for an hour.
on a 20", the continuous power is around 900w for an hour long ride.

But this is a dual reduction motor, so we have two problems in a 20" wheel..
1) the electrical RPM climbs into the stratosphere on a 20" wheel, and you will need an exotic controller to be able to handle such a high RPM. A phaserunner or better is now mandatory.
2) At >450 wheel RPM, ebikes.ca says they've seen the magnets fling off the rotor, therefore, 26mph is the limit in a 20" wheel. This is 4,950 RPM at the rotor because of the 11:1 gear ratio. RC motor speeds.

The best case scenario for maximizing the power out of this motor is such:
24" wheel, 'fast' winding on 48v, ride in an aerodynamic position, pedal, and you will see a hair over 30mph continuously for an hour and can occasionally take a short but steep hill, but you'll need to limit speed before/after so that the motor can cool off and not melt.

https://www.ebikes.ca/tools/simulat...=B4823_AC&frame=road&hp=100&throt=100&grade=0

So yah, on a 700c or 26" wheel, it's not the strongest hill climber. It's not a MAC or big DD.
Justin's oil fill technique nearly doubles the heat dispersion though, making it a competent climber.

On the flats or moderate hills (4% or less grade)? fantastic motor. Best watt per lb you'll find in a hub.

 

[1N4001]

considering the fact that while the hub spins, you're getting the friction of 1 set of the gears.

You don't. The clutch is part of the cover plate, so you're completely disconnected from the gears while running unpowered.

Really? another member told me that it was like the xiongda ytw-06..

2018-11-27-08_01_31-Bafang-G310-Motor-Disassembly-Video---YouTube.jpg

So this is where the clutch is, eh?

It's pretty much exactly where you pointed the arrow at. The clutch mechanism is behind the brown seal. Here's a clearer picture:
https://www.pedelecforum.de/forum/index.php?attachments/g310-11-jpg.216831/

 

[1N4001]

Yo, Grin just hadded the oil-cooled G310 to the motor simulator. Dems some really good performance, I tell ya what.

 

[lightrush]

Is it possible to put a temp sensor in this motor?

There's an easy way to do this if you're willing to forego the internal speedometer sensor. Just open up the motor and remove the white wire from the speed sensor PCB, and instead wire it up to a grounded thermistor or other temperature sensor. Or tap it in right where the original speedo hall sensor is located as I did here:

G310_ThermistorMod.jpg

although in this case IIRC there was also a pull-up resistor on the hall PCB that I had to remove so that the CA3 would report an accurate temperature.

If you have a CA3 device, this signal goes up to the display via a yellow wire to the CA3's speedometer input pad. So you can then desolder it from there and move the yellow wire to the temperature/thermistor input pad instead and have temperature sensing with no extra cables or wires at all, and if you want a speedometer again just hook up a normal spoke magnet wheel sensor to the CA3.

The other possibility is to run the motor sensorless and then repurpose the hall signal wires for your temperature probe, or if you are crafty you can feed additional small gauge signal wires beside the motor cable as I did here with the blue and black wires:

G310_TempWires.jpg

(this was part of an experiment to use statorade for bridging heat from the stator to the motor shell with external magnets on the shell to hold the fluid in place)

Justin, why do you have both ground and signal on the thermistor? Can't it share ground with the main cable? Or is it just harder to connect it to the main cable's ground?

Also when do you expect spare gearsets to be in stock?

 

[qwerkus]

Just discovered the even smaller Bafang G370 hub motor. 1:12.5 Reduction, 42n-m for just 1.7Kg - sounds kind of silly. Did anyone see the actual thing ?

 

[neptronix]

Just discovered the even smaller Bafang G370 hub motor. 1:12.5 Reduction, 42n-m for just 1.7Kg - sounds kind of silly. Did anyone see the actual thing ?

Nice find, fella. A bit porkier than the xiongda ytw-06, but probably better built.
Bigger reduction ratio is a plus!
Maybe like the G310, it's a bit underrated as well?

Kick off a new thread for that baby!

 

[lightrush]

Just discovered the even smaller Bafang G370 hub motor. 1:12.5 Reduction, 42n-m for just 1.7Kg - sounds kind of silly. Did anyone see the actual thing ?

Rear version with a freehub body. 145 OLD though:
https://www.bafang-e.com/en/components/component/motor/rm-g370250dc.html

So any issues spreading an aluminum frame with 132.5 OLD to 145?

 

[Ron Paul's Blimp]

Would the G310 fit an 11 speed SRAM road cassette? Would it fit into a titanium frame with 135mm dropouts?

 

[1N4001]

Would the G310 fit an 11 speed SRAM road cassette?

No, only 11s MTB cassettes for Shimano-style freehubs.

Would it fit into a titanium frame with 135mm dropouts?

You'd likely have to spread the dropouts to around 138-139mm.

 

[Ron Paul's Blimp]

Thanks!

No, only 11s MTB cassettes for Shimano-style freehubs.

If I get a new 11s MTB cassette, will it work with my existing 11s road chain and shifter? Or would an 10s road cassette work?

You'd likely have to spread the dropouts to around 138-139mm.

Is that possible / safe with titanium? And would I be able to just cram it in, or would I need to spread it with tools first?

 

[1N4001]

If I get a new 11s MTB cassette, will it work with my existing 11s road chain and shifter?

Afaik, 11s road cassettes have the same gear spacing as the 11s MTB ones, so I think it should work. No guarantees. Just make sure your road derailler has the capacity for the larger cassette. Note that MTB deraillers need a converter if you intend to use them with road shifters.

Or would an 10s road cassette work?

This might work. 10s road cassettes are 35mm wide, while 11s road are 36.8mm. MTB cassettes are 35mm for both 10s and 11s. The G310 supports 35mm cassettes, but no more.

Is that possible / safe with titanium? And would I be able to just cram it in, or would I need to spread it with tools first?

I think you should be able to cram it in, but I have no personal experience with that. Ebikes based on Ti frames are very rare.

But according to internet lore, spreading 3-4mm should be no problem. Personally, I'm designing my frame around not having to bend anything.

 

[Ron Paul's Blimp]

I think you should be able to cram it in, but I have no personal experience with that. Ebikes based on Ti frames are very rare.

But according to internet lore, spreading 3-4mm should be no problem. Personally, I'm designing my frame around not having to bend anything.

Thanks again. Any reason Ti is rare other than price? They're not less suited for use as ebikes in some way, right? When you say you're designing your frame, do you mean welding your own or speccing it out for someone else to custom build?

 

[Adamlivi]

Fellow ti ebiker. Ti is lovely and sweet. You should have zero issue with a 5 mm spread on your rear dropouts.

 

[lightrush]

Would the G310 fit an 11 speed SRAM road cassette? Would it fit into a titanium frame with 135mm dropouts?

I can confirm that Shimano CS-M8000 can be mounted and works well. Also can confirm that 11s road shifters with road derailleur can operate 11s MTB cassettes, BUT as prev poster mentioned, your road derailleur likely can't take the 42-44t cogs. Most road derailleurs top out at 32-34t. With that in mind you -can- remove cogs from a road cassette and put spacers in order to fit it on the G310. You also -can- remove largest cogs from a mountain cassette that your derailleur isn't compatible with and install spacers. It's fairly trivial to do with a good set of bottom bracket spacers and digital calipers. The possible configurations depend on the exact cassette model. For example if you take a CS-M8000, you can remove the innermost cluster and you'd be left with a 11-13-15-17-19-21-24-27 or a 11-13-15-17-19-21-24-28 8-speed cassette. You'd also need to find a long limiting bolt and dial up the low-end limit of the derailleur to prevent accidental shifts beyond the 8th gear.

 

[Ron Paul's Blimp]

Thank you both. My derailleur can supposedly get out to 42t .. the CS-M8000 11-40 looks perfect.

 

[1N4001]

Thank you both. My derailleur can supposedly get out to 42t .. the CS-M8000 11-40 looks perfect.

There's also the CS-M9000/9001. More expensive, but featuring some lightweight titanium on it. 8) Additionally, the 9000 has two-gear clusters instead of the 8000's three-gear clusters, so you won't lose as much should you end up having to remove the largest ones.

 

[Ron Paul's Blimp]

Er I just realized that since my bike is thru-axle, I can't use this motor at all, can I?

 

[1N4001]

Er I just realized that since my bike is thru-axle, I can't use this motor at all, can I?

Oh damn, yeah, you're SOL unless you have replaceable dropouts.

Your remaining hub options are a Grin All-Axle at the front or a Go Swissdrive in the rear. Both are availabe for thru-axle. There's also the Bafang H800, but I'm certain you'd have to mill your dropouts more deeply to be able to mount it (see here).

edit: or swap out your fork for a quick-release one and you'll be able to mount a G311.

 

[Ron Paul's Blimp]

Your remaining hub options are a Grin All-Axle at the front or a Go Swissdrive in the rear. Both are availabe for thru-axle. There's also the Bafang H800, but I'm certain you'd have to mill your dropouts more deeply to be able to mount it (see here).

Thanks for the leads (and for all your help). Unfortunately those are all quite a bit over my weight budget Hey Justin, could you ask Bafang to make a through-axle G310 without increasing the O.L.D.?

 

[qwerkus]

Anyone tested the g310 against a xiongda YTW-S (the famous 2 speed motor) ?

 

[tomtom50]

Anyone tested the g310 against a xiongda YTW-S (the famous 2 speed motor) ?

What would you test, they are so different?

The xiongda in low is low. 125rpm. Able to climb steep hills without overheating.

The G310 is 300 rpm at 36v / 400rpm at 48v. Good for high speed on the flat, but not safe on a steep hill.

They are built to different purposes, not really comparable.

On the flat the G310 is better. On hills or varied terrain the xiongda is better.

It is a bit like comparing a single speed tack bike with a mountain bike. Both are great in their element.