New Goldenmotor MagicPie 5 Vector knocking

[holeshot]

Hello All,

Has anyone experienced knocking issues from within the hub of a new GM motor? I've searched through Endless Sphere and GM's forums and have seen numerous posts regarding spoke tension with new wheels and bearing pretension with older ones, but a lot of these posts lack media attachments that have since expired so it's hard to compare the bearing noises.

I purchased the MP5 Vector 700c rear kit from GM Canada for my urban style raleigh bike (cadent 2). The bike is fitted with standard equipment and aside from the battery mounted on the downtube, and the rider (between 170-200lbs) there is no unusual additional weight or haulage involved.

With a battery cycles worth of riding into operation I noticed a very light knocking sound which seems to echo out of the case. I checked spoke tension and tolerances between bike components. The spokes had worked in and needed to be tensioned lightly but none were severely out of spec. The brake caliper had no issues with clearance and there are no observed markings on the screws for the MP5 cooling cover nor the brake caliper. As the MP5 is new to me and I'm unfamiliar with it's characteristics I wondered if it was the spokes, even though under load, with the heavy motor .. still working themselves in. Over the next week, with careful riding the sound got worse. It will get louder if the riders center of gravity is leaned to either side of the bike, for example when turning.

I removed the wheel from the bike and removed the freewheel, disc brake rotor, cooling fin cover and the controller leaving just the hub intact and installed it into the frames dropouts. I removed the bikes rear derailleur and the freewheel so that the hub could spin freely in the frame with no drivetrain or braking components able to come into contact. As the motor was spun freely in the air by hand, each rotation there was a dull clunk and at the opposite 180 degree position, a loud knock.

https://youtu.be/ulo8g-bsmOY This is the first motor with no controller, brakes or drivetrain on the bike. The bike is upside down with the motor free spinning in the air. This was taken indoors and the sound is much louder in this recording than in person.

I opened a support ticket with GM Canada and didn't want to open the motor covers. As the sound was coming from inside the hub and there were no bike components involved I could only expect this was a manufacturing issue. I was really enjoying the MP5 and as the kit was only a week and a half old, I asked GM canada if we could cross ship the motor and they could assess for warranty refund and the exchange went well. I kept everything from the first kit except the MP5 motor and wheel assembly. I retained the original vector controller and screws, cooling fin cover and screws, freewheel and all associated wiring accessories from the first kit. The first hub motor was taken to GM Canada. I included the video of the hub knocking in my support ticket correspondence with them but they determined it had "no issues" and that I needed to keep my spoke tension in check. They issued a full refund for the cross-shipped motor replacement. The new hub worked well to start but sadly experienced the same decline.

The new hub suffers the same knock and bump sound as the first motor after only about a week. I've been the only rider of the bike and neither of the 2 hubs experienced any potholes in the time on the road. The tires are 700x32c and I kept them between 30-40psi to keep the shock of the road off the motor and myself. Upon removal of the motor cover I found that the stator, winding, magnets and wiring all looked to be in expected condition and are not causing any issues. There is no visible scoring on any. The side covers, bearings and axle align to hold everything together in spec. I believe that either the side covers, which don't appear to have any keying to keep them in place other than torque from the screws are allowing one of the bearings to sit loose on the axle or in the cover or the stator is finding itself free movement on the axle. It sounds like the magnets are pulling the stator around within some tight tolerances that the bearings or covers are allowing through the rotation and one of the three are knocking.

The motor still felt "tight" on the axle with respect to free movement from side to side and in any unintended direction. It is important to note that there has not been a discernible change to this with either of the 2 wheels and motors. The one I currently have still feels true and tight which leads me to believe maybe the stator is moving on the axle.

https://youtu.be/eNyXze2GE3Q
This is the second motor, today, as fitted on the bike. I removed the brake caliper to eliminate question of it's spacing with the hub. I have checked and tested with no caliper or cooling cover installed and still, the same noise. The noise is present whether under human power, electric power, or no power just rolling, even in free air as shown in the last video.


Installation information and other details:
Two torque arms were installed, one on each side of the frame. The frame would not accommodate the correct orientation of the torquearm on one side so it had to be installed in the opposite orientation, while the other torque arm is installed as descibed in grin's installation diagram. Neither of the torquearms come within less than a centimeter of any moving parts and have no contact with anything unintended during operation.

Equivalent washers (one inside and one outside of the dropout) and torque arms are installed on both sides of the axle and the wheel appears centered and true upon installation in this manner. There were no fitment issues regarding the drivetrain components and the freewheel was supplied by the kit.

The rear was fitted with a 160mm tekro novela brake disc and the associated caliper. The spacing between the caliper housing and the MP5 cooling fin cover is tight (between 3-6mm) but even with the frame loaded with the rider the caliper remained the same distance from the MP5. Also, the disc brake rotor screws are not making contact with the vector controller and both hubs have been tested with the rotor, cooling cover and controller removed entirely.


The kit installed with
LCD display,
PAS sensor (not installed)
Thumb throttle
MP5 with Vector controller
7 speed shimano freewheel
2x grin torqarm v4
52V 11.6AH Shark Pack

Has anyone experienced issues like this with new hubs?

Thanks for your help!
-BCC

 

[amberwolf]

If the clicking is definitely coming from the hub itself, then cover bearings would be my first suspect.

As you say, you've already found a number of the potential issues, but I"ll detail them in case they're helpful:

Usually such sounds, when in a new wheel, where the sound doesn't start until it's been ridden a little bit, are from spoke problems. Simply retensioning the wheel will correct the sound, as long as the rim's nipple holes haven't cracked from the too-high tensions required for the too-thick spokes typically used on OEM ebike wheels.

Rarely but occasionally the problem is that the high tension caused the flange of the nipple to actually break off inside the rim and is floating around in there, but that dosn't usually have a periodicity to the sound.. If the flange breaks off, it usually leaves the spoke loose...but not always. However, further tensioning of that does usually pull the nipple remains thru the rim hole, often damaging the hole.

Sometimes loose spokes will break at the J-bend (elbow) at the hub flange, and click as the wheel spins as the remainder moves around in or near the hole.


Another problem that can happen (but doesn't alway sound like yours) is the outer bearing races (in teh covers) can crack, so that they click as each bearing rolls over the crack, and as the load shifts on the race during rotation, it can make a louder click on one side and a lesser one half a rotation later.

Alternately, a ball can break inside the bearing and leave bits that other bearings rollthru, but that dosn't usually have a periodicity to the sound.

 

[holeshot]

Thanks for your thoughts on the issue, Amberwolf. Unfortunately the sound is most definitely coming from inside the hub and not from the wheel assembly or spokes. These were less than 2 week old GM motors both with the same noise coming from inside the hub. A member on the GM forum also believes the noise is bearing related based on the videos.

 

[amberwolf]

AFAICT from the images I found online, and your first video, at least one side of the hub is using a large-diameter bearing. It is likely this is a very "narrow" and "thin" bearing, becuase large-diameter bearings can be a lot more expensive than the typical small ones used on most hubmotors, so the smaller in other dimensions you make it, the cheaper it might be (especially if there is a bunch of common devices this particular bearing is used for, dropping it's cost a lot because of so many being made).

If the races are thin, and narrow, they are more likely to crack under load, especially if the cover or mount they are in is not stiff enough and allows them to repeatedly flex.

If this is something happening to a number of the same version of the motor, especially if they were made / shipped around the same time, they might've gotten a bad batch of bearings, or changed suppliers to make them cheaper (which never goes well), etc.


Unfortunately the only way to find out is to take the covers off to check.

 

[holeshot]

I think you were looking at the right photos online.. Sorry to not have any of this motor disassembled from earlier this week.

This is the model that has a small bearing on one side and a very large diameter bearing on the integrated controller side. A well respected user, BikeMad, on the GM forums thinks that the sound is most likely the bearings as well (see below). The sound seems to be coming from the freewheel side of the motor and the knocking sound is reduced significantly when ambient temperature drops from 70f to 60f.

I'm waiting to hear back on the support ticket from GM Canada regarding next steps and will update with photos of what we find.

Again, thanks for your help

I have been carefully studying both videos, and I would say that neither of the noises are being caused by something binding or catching either inside or outside of the motor.

It is also unlikely to be a loose stator, as this would only produce a single clunk each time either power or regen was applied as any play in the keyway slot was initially taken up as the torque direction changed.
A loose stator would not clunk every single turn of the wheel, especially when there was no torsional load being applied to it in either direction.

If there is no discernible end float movement between the hub and the axle, then this leaves only two moving parts, the two wheel bearings.
If one of the bearings is not fully seated into the side cover correctly, this could cause the bearing to be slightly out of true, resulting in slight flexing of the side cover.
The slight flexing of the cover could cause the inner part of the bearing to move slightly on the axle (or stator/controller housing), which could produce the noise that I was hearing, bearing in mind that any noise produced by any movement of the bearing on the axle/stator would be noticeably amplified by the large side cover (no pun intended).

Are you able to determine which side of the motor the noise is coming from?

Alan