Noise while coasting - Bafang Max torque motor

Hey guys, I'm new here. I have a pedelec with the Bafang Max torque sensing motor. Not sure whether it's 250 or 350w, but it's this one: (https://voltonbicycles.com/shop/alation-mid-drive-48v/) I've put about 500 miles on it so far.

I looked through the stickies and didn't see anything specifically about the issue I'm experiencing.

Power delivery is smooth and quiet and I have no issues when I'm pedaling. However, when I find myself coasting at medium to slow speeds - like when approaching a stop sign - I notice a repetitive noise that sounds and feels a bit like the motor is trying to get in gear and accelerate. Sort of like if you're standing on one pedal at nearly a standstill and the bike isn't quite sure whether to deliver power or go into neutral.

If I'm coasting at a high speed, like 25-26 mph going down a hill, it's not noticeable. Only when I'm going 10-18 mph or so in the middle gears (3-6 or so, it's an 8 speed with only one front chainring).

Should I be worried about this? My ride today was the fastest yet - I powered through almost 19 miles in 59 minutes with 1,000 feet of egain, but I noticed the noise a few times. I don't think it's the chain, derailleur, or cassette making the noise.

The only modifications I've made to the bike are adding a rack and unlocking the speed limit (now set to 60 km/h but realistically I can't go higher than 50 km/h without insane cadence) using the stock Bafang passcode. I have not reprogrammed anything.

Thanks in advance for any info!

Nothing, eh? Should I post this in the Non-Hub Motor section?

Rode again today in freezing temps... same behavior. Quiet and smooth while engaging full power, slight whispering/catching noise while coasting or slowing without pedaling.

A lot of people here are doing DIY builds and we don't have much experience with things like this, sorry.

Probably every single possible problem a BBSHD has is known tho..

I wonder if it could be my freehub or freewheel? I'm not sure which I've got...

Example in this thread:

https://endless-sphere.com/forums/viewtopic.php?t=48112

The Ultra motor is pretty different than the BBSHD. Possibly the torque sensing is picking up something even though you aren't pedaling. Just the weight of your feet on the pedals might make a difference. When you hear the noise, try lifting your feet off the pedals and see if it changes. Also try pedaling backward. Another test would be to turn the power off when coasting and see if it changes.

I guess I'm trying to see if it's a controller issue or a simple mechanical clutch/gear issue.

I have tried taking my feet off the pedals and it doesn't really seem to make a difference. Sometimes slow pedaling maybe reduces it a bit?

I just put the bike on a stand and couldn't reproduce the noise with the motor off. Then I tried riding it around the parking lot with the motor off and couldn't reproduce it either.

I turned the motor on and couldn't really reproduce it either . I wonder if the ground was too smooth... Like, maybe when I go over a bumpy bit on the road and I'm coasting, the torque sensor is somewhat fooled and thinks torque is being applied, but then it backs off quickly... could that be the whispery/catchy sensation I'm feeling/hearing?

I didn't get it at ALL pedaling backward on the stand. One interesting thing I noticed, however, is that the chain doesn't move backwards when I pedal backwards on a stand. On my road bike, it does. What's up with that?

Bigger picture, should I even be worried about this?

So it sounds like a controller issue, not a strictly mechanical issue.

It's normal for the chain to not move when you pedal backward. The motor has to be able to drive the chain without driving the pedals.

To me it doesn't really sound like anything to worry about. If the motor is getting small pulses of power when it doesn't need to run, it really won't hurt anything. If the motor was running when you were trying to stop or gave bursts of power unexpectedly, then it would be a safety issue.

gebmebsebwebbandteg said:

It's definitely not running when I try to stop or anything like that. I guess I've been worried that something will strip if it keeps lightly "catching" like that (if that is what's happening), or that it will get worse and eventually form a drag on my coasting momentum.

I guess I'll just keep riding for now and monitor it.

Click to expand...

Oops, somehow I accidentally deleted your last post but copied it in the quote above. Sorry.

Update! The problem seems to have revealed itself. I'm 95% sure it was the freehub, as it completely failed on my ride last night.

I suddenly lost all pedal power whether the bike was turned on or off. I could pedal with the rear wheel firmly on the ground and the chain was just spinning the cassette.

So I had a long walk to the train station. Sometime this week I'll remove the rear wheel and take it to the lbs to get the freehub replaced.

I'm just glad it wasn't the motor, even though the motor is still under warranty.

Did you buy it online ? Contact suppler for replacement. Such a new bike I would think would have a cassette and not a Freewheel on the rear.

999zip999 said:

Did you buy it online ? Contact suppler for replacement. Such a new bike I would think would have a cassette and not a Freewheel on the rear.

Click to expand...

I did buy it online, but the freehub is one of the components that they exempt from their warranty as a consumable, along with brake pads, chain, etc...

And it is a freehub with a cassette, not a freewheel. I'm disappointed that it broke so quickly (I have only 750 miles on the bike), but it sounds like it can happen almost randomly with regular bikes, too.

Just a mid drive problem that is exacerbated the more power you dump through a drivetrain designed for ~100 watts of sustained output and ~500 watts peak.

Any bike manufacturer worth their salt would have fitted it with components suited to the extra load instead of stating that every part of the drivetrain is consumable.

neptronix said:

Just a mid drive problem that is exacerbated the more power you dump through a drivetrain designed for ~100 watts of sustained output and ~500 watts peak.

Any bike manufacturer worth their salt would have fitted it with components suited to the extra load instead of stating that every part of the drivetrain is consumable.

Click to expand...

Definitely true, although I thought I got one with halfway decent components. This one has Novatec Alloy MTB hubs and the wheels are DP20 XC Alex Rims with Stainless Steel Spokes. Shimano Alivio derailleur, etc.

That said, I'm probably pedaling a lot harder than the target market for these bikes. I'm going up hills and pushing hard with max assist turned on, and I'm a reasonably fit cyclist on a regular bike. I'm going to ask the lbs if there's any option to upgrade the freehub to something more robust.

Ah yeah.. strong pedaling plus motor = even more torque = even more probs.

I am a fairly strong pedaler too and have sheared off the freewheel attachments on some motor side covers. Sent the cover back to China for them to look at it. At least one hub motor out there got re-engineered because of me.. i consider it a compliment :lol:

I think that white industries might have an ideal hub for you. They're said to produce some strong stuff with BMXes in mind.

They make a hub designed for tandem bikes. Probably nicely overbuilt and worth a look.

An update. It turns out that it was the hub itself, not the freehub. The attachment may have been slightly loose when the wheel was delivered, as the force of my pedaling eventually sheared the splines, leading to the problem.

The manufacturer has covered the part under warranty, so I'll be rolling again as soon as the weather is decent. The bike is already back together and functional.

FWIW I did a 5 minute power test on a Peloton bike and maintained an average of 339 watts, with a peak of 488, so in conjunction with the Bafang motor, I'm definitely putting some force on this drivetrain when I ride up the hills around here.