eBike hub motor rumble / grumble / rattle noise - High torque, low speed

[NDJ]

Hello everyone,

I need some assistance with a noise problem I'm facing with my direct drive ebike motor. The issue occurs when I start off with high torque at low speeds, causing a rattling or rumbling noise. The noise will continue if climbing a hill in say PAS with limited power output. It's worth noting that the noise goes away at higher speeds and when the bike is lifted without any load. This sound is very loud and my bike is usually whisper quiet. My bike is a custom build mtb with KT controller 45A 2000W. I'm not sure on the make of the motor as it has no markings but is the common 2000W DD hub motor included with kits. I have done well over 3000 miles on the bike and have not gone easy on it. Have not had any motor / controller issues until now.

Here is a video that shows the sound its making:

Here's what I've checked so far:

I have checked all connections to the controller and reconnected them. Ensured phase wires are tight etc. Fully charged battery, same issue with lower charged battery..

1. Hall Sensor: I have tested the hall sensors from the connection to the controller using a multimeter, and they appear to be functioning correctly. When rotating the motor, the hall sensors turn on and off as expected, indicating that they are detecting the magnetic field changes accurately. I didn't fully remove the hub motor cover for this test.
2. Bearings and Mounting: I have inspected the bearings and mounting, and they seem to be in good condition without any obvious issues.
3. Controller: The controller doesn't seem to be causing the problem as I haven't noticed any other related issues with it and from what I've researched, common issues related to the controller are usually the mosfets and there is no noticeable loss of power with my bike..
4. Gears: Since it's a direct drive motor, there are no gears involved, eliminating any gear-related problems.

Based on these observations, I'm seeking advice from the community. If any of you have encountered a similar problem or have expertise in this area, I would greatly appreciate your suggestions or insights regarding the possible cause of the noise.

Thank you for your help, and I look forward to hearing your thoughts.

 

[NDJ]

Thanks to all that took the time to read my post. I have found the problem! Something has burned out inside the controller as shown in the images below. Looks like I am going to have to replace the entire controller. It's a shame as I am more than capable of replacing the part if I knew where to purchase it. It's a resistor but is attached to a seperate board which looks to be damaged also. I can see the part number on the chip attached: A1013041. As explained above it is a KT 45A+2A controller. If anyone knows where I can purchase a replacement part to fix this controller it would be strongly appreciated if you could let me know!
I will keep this here in hopes it's able to assist others in the same situation!

 

[harryS]

As shown on the top left corner of this schematic for their S06S controller, KT often uses a 2W 1800-2000W resister in front of the DC-DC converters that drop battery voltage down to 15V and 5V for the controller. If there is an external board, it's probably used to run the light output. I think it's external since users don't use relays and blow out the light circuit.
.
I could be wrong, but don;t think this is necessarily why a direct drive motor would rattle,

 

[NDJ]

As shown on the top left corner of this schematic for their S06S controller, KT often uses a 2W 1800-2000W resister in front of the DC-DC converters that drop battery voltage down to 15V and 5V for the controller. If there is an external board, it's probably used to run the light output. I think it's external since users don't use relays and blow out the light circuit.
.
I could be wrong, but don;t think this is necessarily why a direct drive motor would rattle,








View attachment 157389

Hey harryS, thanks very much for your response.. You are definitely NOT wrong. A while back I did setup an LED light connected directly to the controller and it did not work for long.. I searched online and found that like many others I should have used a relay and subsequently burned out the light output.. I then set the light up directly to battery output via a switch and forgot about it.
In my haste, when I saw the burned part yesterday I assumed it was relating to my current motor issue but what you mentioned makes perfect sense.
With that in mind, I unfortunately still do not know what is causing this issue with the motor noise.
I have since purchased a replacement controller so I hope this it the problem. I would still like to try and fix this one regardless..
I will disassemble the controller further today in hopes I can find some other issue with it..
Thanks very much for your help, it's strongly appreciated!
Any further suggestions welcome

 

[indianajo]

Your rattle could be a loose motor cover. I've found I had to tighten the cover screws at least once a year on my hub motors. Loktite blue on the threads did not help, but KeyTite pipe joint compound did. KeyTite is about $28 a quart at mcmaster.com, so getting a bit is quite a commitment unless you do occasional steel pipe thread home repairs. Use latex gloves, the only thing that removes it is alcohol and that not very well.
Your burnt part in the controller looks to be about a 2 watt carbon film resistor. You can't measure it burnt out, but you could measure half from one end to the track in the middle. Then double that value for a new one. I would go up to 5 W next time, wirewound. I buy such things from newark.com digikey.com or mouser.com . They tend to hammer people that buy one or two parts with a $20 handling fee. There are storefront electronics distributors in mega-cities, I forget the name since I don't live in one.
Wear safety glasses unsoldering & replacing the resistor, solder can splash in the eye. Use rosin core solder, not acid core. My lastest successful soldering iron came from partsexpress.com, which also sells resistors.