Non-drag hub motors

[shemozzle999]

Andrew has already changed to Dapu motors. The one we tried was a normal production one like he uses on his bikes. you can't change the ratios. The gears in each motor are fixed for that type, although there's big and small motors that probably have different ratios from each other. You can often get different speed motors of the same type because they have different coil-windings - nothing to do with gear-ratios. I don't know the winding speed of the Oxygen bikes' motors. I guess the same as the previous motors at about 270rpm.

The noise of geared hub-motors (IMHO) comes partly from the design of the motor, but mainly from the controller. You can change controllers and often get a different noise level.

The main noise factor for normal hub motors is related to the amount of current you run. You can see/hear it by using high or low throttle. If you solder your shunt to get more current, you can hear the increase in noise.

The speed you set on the panel has nothing to do with noise. It doesn't affect current in any way, but the faster you go, the less current you get, so the motor will be quieter the faster you go. I don't know if the new Oxygen bikes will be able to reach 24mph like the old ones. It depends on the winding speed of the motor, but I think it was the same when we setup Geoff9's new Oxydrive kit. I know you can adjust the speed limit, like the old one, because we tried it on Geoff's.

The sine-wave controllers I'm getting are for my own bikes - nothing to do with Oxygen. In case you're implying that my mention of them was for commercial reasons, your completely wrong. I only want to try them in the quest for shared knowledge, and I'll publish the results here for the benefit of everyone.

The motor you linked to is a direct drive motor. The ratios are the assist level - nothing to do with gears.

As a general point, I could see that hub-motor technology is moving on all the time. Many now have the spline for cassette gears. I was also shown computer models of one with its own internal 2-speed gearbox. My own opinion is that some hub-motors are better than all the currently available crank-drives. The control systems that most commercially available hub-motored bikes use are fairly rudimentary and could be improved a lot to give much better comfort and dynamics, while as some of the crank-drives have much more sophisticated systems. People should keep an open mind about which type of motor is best and think about the overall system and it's characteristics, and not just try and compare one characteristic to pronounce judgement.

Please see the revised link as to why the motor is quieter.

 

[flecc]

I would agree with your statement if the motor was unloaded but in the real use gear/bearing noise is self evident.

Only to a small degree, but the primary noise in the majority of hub motors is electrically stimulated and that increases with load. Gear noise does become a major factor with steel geared hub motors like the higher power Heinzmanns, and with those and the old Powabyke motor which both have asymmetric gear drives, the gear noise contribution increases due to the unbalanced mechanical drive loading.

 

[shemozzle999]

Only to a small degree, but the primary noise in the majority of hub motors is electrically stimulated and that increases with load. Gear noise does become a major factor with steel geared hub motors like the higher power Heinzmanns, and with those and the old Powabyke motor which both have asymmetric gear drives, the gear noise contribution increases due to the unbalanced mechanical drive loading.

I am talking about my experience of current standard nylon geared motors that adhere to current restrictions. I am not against efficiency improvements to maximise what we are allowed to have, far from it.

Agreed a perfectly balanced system delivering the right matching pulses at the right time through all the rev range over different varying loading schemes would inherently be quieter but in the real world with all different motors having their own unique characteristics, different gearing it would be very difficult and expensive to design and be bespoke for each motor to reap any serious benefit . With a generic matched controller sine or otherwise it is hit or miss as to weather if any improvement would be obtained.
Until a universal system with a programmable power mapping along the lines of a car ECU system can be designed I don't see much improvement but I will wait with an open mind and wait to see if d8veh's noise test results can persuade me otherwise, in the absence of any other evidence being available.

p.s. sorry to eHomer for invading your thread

 

[Deleted member 4366]

There aren't really a lot of different hub-motors and those that there are often share the same components like clutches gears, and bearings. The noise that you hear that you think is the noise of gears engaging isn't. It comes from the force pulses of commutation, like someone knocking it round with lots of frequent blows from a hammer.

The sine-wave controllers are indeed made to match a particular model motor, so you can't use one for a Bafang CST one on an Ananda 350w motor.

People have gone to all the trouble of designing and making sine-wave controllers because they know there's a theoretical advantage, which should create a demand. Now's the time to see if it worked.

 

[trex]

shemmoz may not have to wait long for a programmable controller with Fairchild 8201 - sine wave controller on a chip for about £1.20p each. There is a thread about this here
Endless-sphere.com • View topic - FCM 8201 - Over voltage protection of motor driver
In the application notes, http://www.fairchildsemi.com/an/AN/AN-8201.pdf, the issue of commutation noise and back EMF killing battery BMS and controllers are also very well explained.

 

[eHomer]

p.s. sorry to eHomer for invading your thread

No problem Shemoz, I'm interested in everything that has turned up...

 

[flecc]

The noise that you hear that you think is the noise of gears engaging isn't. It comes from the force pulses of commutation, like someone knocking it round with lots of frequent blows from a hammer.

Indeed, and the magnetic forces are as much radial as circumferential, amplifying the noise production. Square wave controllers generating odd harmonics accentuate the annoyance factor of the noise produced in the way you described earlier, so sine wave controllers won't only reduce the noise level, they're likely to improve it's aural acceptability as well.

A dual sided pancake motor could well be the best way to get the minimum noise level by balancing the forces with synchronised lateral pole pulses, sine wave driven.

 

[shemozzle999]

Indeed, and the magnetic forces are as much radial as circumferential, amplifying the noise production. Square wave controllers generating odd harmonics accentuate the annoyance factor of the noise produced in the way you described earlier, so sine wave controllers won't only reduce the noise level, they're likely to improve it's aural acceptability as well.

A dual sided pancake motor could well be the best way to get the minimum noise level by balancing the forces with synchronised lateral pole pulses, sine wave driven.

Or even a direct drive with a free wheel

 

[flecc]

Or even a direct drive with a free wheel

Yes, but I was thinking in terms of silencing high revving internally geared hub motors. DDs with their larger diameter and low revs are mostly already relatively silent.

 

[jhruk]

The Tongxin is considered to be a very quiet motor, not much noisier than DD ones. Although normally run at low powers this quietness is usually attributed to its unusual roller gearing system, as its core and control system must be very similar to louder toothed gear motors.

This would lead me to think that quite a lot of noise must come from the toothed gearing.

 

[amigafan2003]

The Tongxin is considered to be a very quiet motor, not much noisier than DD ones. Although normally run at low powers this quietness is usually attributed to its unusual roller gearing system, as its core and control system must be very similar to louder toothed gear motors.

This would lead me to think that quite a lot of noise must come from the toothed gearing.

Actually when I ran my Tongxin @ 700 watts it was nearly as loud as my Q100 @ the same wattage.

And it was a LOT louder when the clutch slipped on harsh take offs!

 

[jhruk]

Actually when I ran my Tongxin @ 700 watts it was nearly as loud as my Q100 @ the same wattage.

And it was a LOT louder when the clutch slipped on harsh take offs!

Interesting. I’ve always found the Tongxin much quieter than my Q85, but at lower powers than you were running. Which motor did you prefer?

 

[Deleted member 4366]

If you run a Bafang at low power like a Tongxin, it also becomes quiet. I've got several Q100s, and some are very quiet, and some are relatively noisy. I put that down to quality control rather than the design. One thing I learnt in Shanghai is that there are good factories and bad factories making the same motors. I counted four different manufacturers of the Bafang CST. The motors can be identical on the outside, but slightly different inside. I know one manufacturer of it has a problem with noise. My CST is relatively quiet.

 

[flecc]

If you run a Bafang at low power like a Tongxin, it also becomes quiet. I've got several Q100s, and some are very quiet, and some are relatively noisy. I put that down to quality control rather than the design. One thing I learnt in Shanghai is that there are good factories and bad factories making the same motors. I counted four different manufacturers of the Bafang CST. The motors can be identical on the outside, but slightly different inside. I know one manufacturer of it has a problem with noise. My CST is relatively quiet.

The tolerances are indeed important. Here's an extract from an article I wrote some while ago on the subject of the Bafang motor noise:

"The motor drum is exposed to a series of in/out jerks all around it's circumference as magnets pass poles. These are rapidly rocking the drum about it's bearing, vibrating it, and transmitting the rocking vibration to the gears and then the hub. Because there are many magnet and pole interactions per revolution, the minute knocks are at high frequency and therefore produce a form of whine with an odd vibrating component in the sound. The exact note and the quantity of it depends on all the slight dimensional variations and relationships I've mentioned. Just turning off the throttle and opening it again can slightly change the sound as the twitch produced by that action changes the internal dimensional relationships.

As a bike goes faster and the drum rotates more quickly, there's less time for current to go into each pole winding so the consumption reduces. This means less magnetic push pull, therefore less vibration in each pulse from a pole. In turn, the centrifugal force of the faster spinning magnet drum starts to overcome the now weaker inward push/pulls of the poles, so the operation is smoother and the noise reduces to a minimum at maximum speed.

It might seem that a motor assembly with minimal clearances would be best for the least noise, but that's not necessarily true, minimising the clearances initially just increases the frequency or pitch of the sound, the harmonic energy of which can set up worse vibrational noise elsewhere in the assembly. That's why an assembly can get quieter as it wears, and also why it's so difficult to manufacture this type of motor with an absolutely consistent pitch and quantity of noise."
.

 

[flecc]

This would lead me to think that quite a lot of noise must come from the toothed gearing.

But as I remarked earlier, if the primary noise was gear related, it would increase with speed, but all our internally geared hub motors get quieter with speed, my post just above giving the reasons for that.

 

[amigafan2003]

Interesting. I’ve always found the Tongxin much quieter than my Q85, but at lower powers than you were running. Which motor did you prefer?

The Q100 deffinately.

 

[jhruk]

The Q100 deffinately.

Thanks. I was considering trying a Tongxin in place of the Q85, just to get a direct comparison. Perhaps I won’t bother.

 

[amigafan2003]

The Tongxin is quieter than the q100 but ninot by much and its fine for low power low speed applications. That's not what I'm interested in though.

So the tongxin might still be what you want, depending on what you want ;-)

 

[eHomer]

Could I ask if there's been any further developments in availability of sine wave controllers ?

My limited understanding from many of the replies to this thread was that the noise from geared motors is primarily caused by the square wave controller "blips" rather than the gearing itself.

The point about the noise reducing with speed does indeed make that theory very plausible to me.

Now that the UK's glorious Summer has at last made an appearance, my 250w 36v geared brushless motor is getting much more use, and the "milkfloat" noise is the only downside of my really enjoyable 25 mile rides through the countryside.

I'd be quite happy to give the sinewave controller a shot, if it even only reduced the noise, it would be worth it.

If they are now available, I'd like to buy a higher wattage controller (but still at 36v), so that I'd be free to upgrade the motor at a later date. I assume that would still work with the 250w motor ok ?

thanks,

 

[Deleted member 4366]

You're in luck. They're available from BMSBattery in a range of powers. I tried one in China, and it was nice and quiet, ans smooth. Most motors these days are fairly quiet anyway, so not enough difference to get me too interested. The guy in China said he had one for the Bafang CST, but not a MXUS motor, so their might be some compatibility issues, although I've not heard of any yet.
sine wave controller