Motor noise issues

[rocketman58]

I have posted about this problem a few times, but I thought I would try once more.

I acquired a used Bafang CTS 500w/48v geared hub motor. It is marked for use with a 26” wheel. I built it up in a 20” wheel. I chose this standard wind motor as opposed to a fast wind motor because the tadpole trike will be used for riding hills and off road. The motor does very well in this type of riding. As expected it has great low end power but tops out around 17mph. While that top speed is still fine for this type of riding, it is lower than I expected.

However, the big issue I have with this setup is noise. Up to 7mph the motor is very quiet, only emitting an electrical hum. It is almost sounds like a direct drive motor. But past 7mph the noise becomes much louder. The whining of the hubs gears becomes increasingly louder, and I start getting what I assume is electrical pulse noise from the controller. The noise is loud enough that I no longer need a bell when I come up behind pedestrian as they can hear me coming from a block away.

In comparison I have a Bafang G020 500w geared hub motor on another trike that is set up the exact same way. While I still get similar gear and electrical noise, it is noticeably quieter. Also unlike the CST motor the noise is there at any speed, only increasing a little as you gain speed. Top speed on this motor is just over 20mph. Based on this I can only assume it is an issue with the CST motor.

I am using a KT 22A square wave controller on both trikes. I experimented with a KT sine wave controller as they are supposed to be quieter. I really did not notice any difference. Since the CST was a used motor I don’t know if it was abused or maybe it works differently than the G020 motor. While I like the CST’s low speed performance, the noise at typical riding speed is annoying. If I can’t resolve this I may replace the CST motor with a new G020.

I would appreciate any thoughts or insights.

 

[Dui ni shuo de dui]

I have posted about this problem a few times, but I thought I would try once more.

I acquired a used Bafang CTS 500w/48v geared hub motor. It is marked for use with a 26” wheel. I built it up in a 20” wheel. I chose this standard wind motor as opposed to a fast wind motor because the tadpole trike will be used for riding hills and off road. The motor does very well in this type of riding. As expected it has great low end power but tops out around 17mph. While that top speed is still fine for this type of riding, it is lower than I expected.

However, the big issue I have with this setup is noise. Up to 7mph the motor is very quiet, only emitting an electrical hum. It is almost sounds like a direct drive motor. But past 7mph the noise becomes much louder. The whining of the hubs gears becomes increasingly louder, and I start getting what I assume is electrical pulse noise from the controller. The noise is loud enough that I no longer need a bell when I come up behind pedestrian as they can hear me coming from a block away.

In comparison I have a Bafang G020 500w geared hub motor on another trike that is set up the exact same way. While I still get similar gear and electrical noise, it is noticeably quieter. Also unlike the CST motor the noise is there at any speed, only increasing a little as you gain speed. Top speed on this motor is just over 20mph. Based on this I can only assume it is an issue with the CST motor.

I am using a KT 22A square wave controller on both trikes. I experimented with a KT sine wave controller as they are supposed to be quieter. I really did not notice any difference. Since the CST was a used motor I don’t know if it was abused or maybe it works differently than the G020 motor. While I like the CST’s low speed performance, the noise at typical riding speed is annoying. If I can’t resolve this I may replace the CST motor with a new G020.

I would appreciate any thoughts or insights.

Noise issues are difficult to troubleshoot remotely especially since we can't hear the noise you're talking about.
It could be either the gears themselves, or electrical resonnance.

I'm not an expert, but from my experience resonnance comes from the motor laminations/its physical configuration (number of poles and magnets, etc). It can't really be changed and it will be more or less exacerbated by some controllers. From my experience, it always happen at a specific range of rpm, if you go slower then no noise, if you go faster then no noise as well.

In your case, you have a geared motor, so the first thing I would check is the actual gears. In what condition are they? are you sure they still have enough lubrification? I'd open the motor assess its condition and add grease, just to be sure.
It could also be a dead bearing, but it is less likely.

 

[neptronix]

It would be helpful to hear this on the road.. how about a youtube video?

In general geared hubs are designed for larger wheels and will be a lot louder in a 20" due to a higher pitch noise ( human hearing perceives higher pitch noises up to a point to be louder )

They also tend to lose efficiency on the flats due to the gear friction being higher than before.

I almost always recommend DDs for such small wheels

 

[rocketman58]

It would be helpful to hear this on the road.. how about a youtube video?

In general geared hubs are designed for larger wheels and will be a lot louder in a 20" due to a higher pitch noise ( human hearing perceives higher pitch noises up to a point to be louder )

They also tend to lose efficiency on the flats due to the gear friction being higher than before.

I almost always recommend DDs for such small wheels

It's interesting about higher pitch noise being perceived as louder. On the G020 motor I do notice it is louder in the 20" wheel vs the original 26", but not overly so. The problem I had with the 26" wheel was that the trike had rear suspension. With the weight of the hub motor out on the end of the log swing arm it effected the suspension operation. But even more so, it introduced too much flex in the rear, especially when cornering. So much so it became dangerous at higher speeds. I don't have that problem with the shorter more rigid 20" wheeled trike.

A DD hub motor is even heavier than a geared hub motor. Adding more weight to the rear suspension would not be a good idea. I was also under the impression that a DD hub motor is not as good for hill climbing. Would the DD provide more range than a geared hub drive on long flat rides?

From everything I have learned form the various posts, it sounds like the better option would be to switch from a hub drive to a mid drive. No suspension issues, quieter operation, more power on climbs. Possibly a higher top speed as well?

 

[rocketman58]

Noise issues are difficult to troubleshoot remotely especially since we can't hear the noise you're talking about.
It could be either the gears themselves, or electrical resonnance.

I'm not an expert, but from my experience resonnance comes from the motor laminations/its physical configuration (number of poles and magnets, etc). It can't really be changed and it will be more or less exacerbated by some controllers. From my experience, it always happen at a specific range of rpm, if you go slower then no noise, if you go faster then no noise as well.

In your case, you have a geared motor, so the first thing I would check is the actual gears. In what condition are they? are you sure they still have enough lubrification? I'd open the motor assess its condition and add grease, just to be sure.
It could also be a dead bearing, but it is less likely.

Thank you for the info.

The whine from the gears is pretty consistent and increases with speed. The noise I am complaining about seems to be more electrical. My non educated guess would be the square wave controller. Since both motors are older, it would be wise to check and grease the gears as well.

 

[Dui ni shuo de dui]

From everything I have learned form the various posts, it sounds like the better option would be to switch from a hub drive to a mid drive. No suspension issues, quieter operation, more power on climbs. Possibly a higher top speed as well?

Suspension issues is a thing if you go offroad, like for a dirt bike. There is no issue at all for road use.
Quieter operation? a mid drive? no, definitely not.
Power on climbs would be the same unless you have a gearbox or a way to change gear ratios while riding. With a fixed gear ratio you will either get more power on climb or more top speed, but not both. There is no free lunch.
Usually hubs are more powerful and have better starting torque They have a much greater mass so they can tolerate way higher current peaks. Also their top speed is not fixed, you can go at much higher speeds with a proper controller that does field weakening. That is also possible for mid drivves, but then the RPM are very high so that creates a lot of constraints.

Changing controller for a better unit is always a good idea, sometimes it makes the vibrations a lot less significant, but these vibrations at a specific rpm range are usually coming from the motor structure itself. I have a motor that vibrates like that no matter what controller I connect to it. I got used to it, the motor works fine despite that.

 

[docw009]

I have a Bafang front motor that makes so much noise, I don't like riding it. Sine wave controller. I think a lot of it comes from resonance with the fork/frame. Removing the front fender helped a lot, Earlier this year, I filled the steel forks with foam which helped, but will likely lead to rust, I still plan to fill the alloy frame with foam, as I think I can feel the vibrations in it.

I have bafang rear motor bikes., Very quiet,

 

[neptronix]

It's interesting about higher pitch noise being perceived as louder.

Human hearing is funny like that!

 

[Chalo]

On a related note, I recently started using cheap "three mode" controllers on a couple of my bikes. Subjectively, the bikes' being able to push silently makes them feel faster to me, even though they aren't.

 

[99t4]

Suspension issues is a thing if you go offroad, like for a dirt bike. There is no issue at all for road use.
Quieter operation? a mid drive? no, definitely not.

One undesirable effect I have found with rear hubmotor in a FS frame ridden onroad: Encountering a bump in a turn can cause rear wheel hop to the outside as the extra unsuspended weight of the motor launches the wheel higher and longer, breaking traction in the turn.

 

[rocketman58]

One undesirable effect I have found with rear hubmotor in a FS frame ridden onroad: Encountering a bump in a turn can cause rear wheel hop to the outside as the extra unsuspended weight of the motor launches the wheel higher and longer, breaking traction in the turn.

I'm not having that issue with the 20' wheel. The 26 was a different story. Worse was changing direction at higher speeds. The rear swing arm would flex and then snap back. When it did the trike wanted to go in that direction.

 

[Dui ni shuo de dui]

One undesirable effect I have found with rear hubmotor in a FS frame ridden onroad: Encountering a bump in a turn can cause rear wheel hop to the outside as the extra unsuspended weight of the motor launches the wheel higher and longer, breaking traction in the turn.

Get a better shock and the problem will be a lot less noticeable.
All my electric bikes are hubs, and I never really felt that was an issue. I do have a gas bike with a light rear wheel to compare and honestly it doesn't make much of a difference. I felt that the tire width made a lot more difference than the wheel weight.
Maybe that would be an issue on a racetrack, but for city riding honestly it doesn't matter all that much.

Anyway, your build, your rules.

 

[99t4]

Thanks. It's a Fox DHX 3.0 Coil, 6.75" travel. Works smoothly, holds air pressure well, doesn't leak oil. Most likely it could be tuned better for my conditions. It has coil spring preload, air pressure, and rebound adjustments. Do you have any suggestions? I'm trying to reduce wheelhop in turns. It's not constant but it will surprise me from time to time.

 

[E-HP]

A DD hub motor is even heavier than a geared hub motor. Adding more weight to the rear suspension would not be a good idea. I was also under the impression that a DD hub motor is not as good for hill climbing.

i agree a lighter geared motor may work better for suspension, but it can’t climb a long steep hill, at least not the hills bin my area. Since the DD hub can be cooled with statorade, it can keep climbing while the geared hub melts. That said, I did see a guy chugging up the 17% section of one route at about 8-10mph but he turned off before hitting the 22% section. That motor isn’t going to cut it once summer hits.

 

[rocketman58]

On my ICE trikes the 500w geared hub motor was heavy enough. While ok for the 20" wheel, it was too heavy for the 26" wheel due to flexing of the long rear swing arm. ICE uses elastomers for the rear suspension so you cannot change the "shock". A DD motor would be out of the question for either size drive wheel due to the additional weight.

I have never had any issues with my hub drive on long steep hills. I have a three mile long climb with an average 10% grade and it does just fine. Of course I am pedaling along with it, not using the throttle. I also do not tend to ride when it is above 90 degrees.

 

[E-HP]

10% shouldn’t be an issue. I’m biased because a silent bike is one of my priorities (I like to be able to get up close to the deer and other animals along the trails without spooking them).