Fork vibration with Mac hub motor

J

Jatem

100 mW
Joined
Jun 3, 2019
Messages
48
Is it normal for a front hub motor to cause the forks to oscillate/vibrate?

I have just installed a Mac front hub motor with a KT 36/48V sine wave 20a pswpower controller, and a em3ev battery. I'm using Surly Troll cro-mo forks. It pulls well at different levels of PAS, and generally rides as I'd expect. However, I'm concerned that it causes some vibration/oscillation in the forks. It sounds similar to this video ... https://youtu.be/aITlPe3-5SI?t=26

I was expecting a smooth motor sound, not the pulsing that causes vibration. The forks oscillate worst at low to mid current levels, and smooth out at high power/speed.
 
Sound like a controller issue. Mac hub are known to work only with certain types of controllers because of the high pole number. What wheelsize/speed are you riding? Are you using the open source kt firmware?
 
I installed a 10t Mac on 26" and another Mac on a 29er. The resonance/vibration is worst at lower amperage when accelerating around 15-25 km/hr. The motors accelerate well and reach speeds of 40-45 km/hr, power usage seems ok. It's just this chuff chuff chuff noise that causes the tips of the fork to visibly vibrate back and forth, which I'm concerned will fatigue the fork or cause the axle nuts to loosen.
 
If it's sensorless, then it's not uncommon to get a pretty severe shudder at startup from a stop, especially with significant weight vs the torque the motor has via the wheelsize it's in.

My SB Cruiser with a pair of Grinfineons presently in sensorless mode is horribly loud, almost like a really big truck that missed the gear change and the transmission is grinding gears ripping teeth off. :shock: Shakes the whole trike. Once it gets rolling it gets much quieter, and is just a normal trapezoid-controller sound.



The other possibility is there is a wrong phase/hall combination, if it's a sensored setup. It could be a false positive, where it spins forward like it should, but current draw is much higher than it should be. Test it offground and see what current draw is. Should be an amp or so. A false positive may show several times that.
 
I just set up a Mac 10t on a KT controller with sensors. It's smooth as silk right from a stop.

PSWpower does sell sensorless KT controllers, so I'm curious what you are running. With or without sensors?
 
AHicks said:
I just set up a Mac 10t on a KT controller with sensors. It's smooth as silk right from a stop.

PSWpower does sell sensorless KT controllers, so I'm curious what you are running. With or without sensors?
Click to expand...

Great to hear you have a similar setup working well. Any settings you had to change to get it working well?

I'm using the KT36/48SVPR-20A controllers on both bikes. I can check the current draw, but they start and accelerate like I'd expect. It goes well, there's just a major resonance in the hub/wheel on both bikes at middle PAS levels and middle speeds under load.

It's in torque simulation mode, max current reduced to 13A.
I do only have one torque arm, wonder if that could affect it.
 
Have you checked your rim to verify that it's trued? My wheel had that slight pulsating sound and the wheel needed truing, which smoothed things out once I tweaked to spokes. Tire being out of balance could also contribute, so maybe trying the motor with only the rim may provide some insights.
 
I built the wheels from scratch, nice and true, used a spoke tension meter. It could be the tyres/balance, but it's a noticeable chuf chuf oscillation.

I tried swapping the 6 combinations of phase leads, and the combo I was using is the only good one. I swapped two leads on the hall sensors, and I found the best phase lead combo was running in reverse, with a similar vibration to my current forwards setup. I think this means I don't have a false positive.
 
Here's a recording of the hub with increasing throttle (and a bit of brake rotor rubbing)...
https://vocaroo.com/i/s118Pq576Ogs
 
It's very normal to get some oscillation through the front fork with a front hub. Moreso when aluminum is involved.
 
Jatem said:
I installed a 10t Mac on 26" and another Mac on a 29er. The resonance/vibration is worst at lower amperage when accelerating around 15-25 km/hr. The motors accelerate well and reach speeds of 40-45 km/hr, power usage seems ok. It's just this chuff chuff chuff noise that causes the tips of the fork to visibly vibrate back and forth, which I'm concerned will fatigue the fork or cause the axle nuts to loosen.
Click to expand...

The axle nuts will loosen if you let them, by not using a torque arm.
Watching a front fork twist while i applied the throttle from a stall on my first front motor build spooked me out of using front motors forever. That and the lack of traction from putting the drive mechanism on the wheel that has the least weight on it.
 
I'm using a heavier KT controller with the MAC 12t. It's a 12 mosfet rated for 35a max. I have it limited to about 1300w (+-) using the parameters over concern for the battery. Plenty of grunt available with that for my purposes.

It sounds like you have the color sequence figure out, but I'll show what I used so you can confirm.

Phase Firing order    Motor    Controller     
A                    Blue          Yellow           
B                    Green        Blue           
C                    Yellow       Green 

Hall sensors fire in the same order, so they match the phase motor/controller color sequence.

After listening to the sound recording, wondering if you're getting that same resonance when actually out riding?
 
Jatem said:
Here's a recording of the hub with increasing throttle (and a bit of brake rotor rubbing)...
https://vocaroo.com/i/s118Pq576Ogs
Click to expand...

Wow. The tail end of that recording sounds like there's something mechanical going on, versus electrical.
 
AHicks said:
I'm using a heavier KT controller with the MAC 12t. It's a 12 mosfet rated for 35a max. I have it limited to about 1300w (+-) using the parameters over concern for the battery. Plenty of grunt available with that for my purposes.

It sounds like you have the color sequence figure out, but I'll show what I used so you can confirm.

Phase Firing order    Motor    Controller     
A                    Blue          Yellow           
B                    Green        Blue           
C                    Yellow       Green 

Hall sensors fire in the same order, so they match the phase motor/controller color sequence.

After listening to the sound recording, wondering if you're getting that same resonance when actually out riding?
Click to expand...

I used matching colours for the motor and controller, on all phase and halls. PSWpower have a diagram for my 20a sine wave controller showing the controller pins as A blue, B green, C yellow which matches the em3ev documentation.

The resonance is mostly there when riding PAS 1, 2 or 3 and at speeds up to about 25kmhr. At high power and speed it's much better.

There is a setting on the controller C2 which related to hall phase, with two settings 0 or 1. It isn't documented well, but if I turn that on it makes a grinding noise. I wonder if I should turn that on, and then test the 6 motor phase combinations?
 
All the notes I have are showing C2=0, but 1-6 are available. I've always used 0.

Odd that KT would use different firing orders on their colors from one controller to the next.
 
AHicks said:
All the notes I have are showing C2=0, but 1-6 are available. I've always used 0.

Odd that KT would use different firing orders on their colors from one controller to the next.
Click to expand...

Does your Mac have any oscillation, or is it completely smooth sounding?

I noticed that your wiring order is in the same sequence at as mine, just moved forward one step in the cycle. Eg. Bgybgybgy. They are probably just two of the three valid forward combinations, still in the same firing order as mine.
 
As mentioned, my Mac is smooth as silk right from a stop! It replaced a 1500w direct drive, and is no noisier than that was. Barely audible. Able to do an "all else being equal" 1500w direct drive vs. Mac 12t comparison, because that's literally all that was changed - if I don't count the added speed sensor and parameter settings.

Mac seems to be using less power as I don't find it necessary to switch to a higher PAS level as often. The torque of the gear driven MAC just kinda pushes right through the stuff the direct drive struggled with at low speeds - which is where I spend most of my time. Bottom line seems to be I have more torque available, while using less power. A real win-win.
 
AHicks said:
As mentioned, my Mac is smooth as silk right from a stop! It replaced a 1500w direct drive, and is no noisier than that was. Barely audible. Able to do an "all else being equal" 1500w direct drive vs. Mac 12t comparison, because that's literally all that was changed - if I don't count the added speed sensor and parameter settings.

Mac seems to be using less power as I don't find it necessary to switch to a higher PAS level as often. The torque of the gear driven MAC just kinda pushes right through the stuff the direct drive struggled with at low speeds - which is where I spend most of my time. Bottom line seems to be I have more torque available, while using less power. A real win-win.
Click to expand...
Is your KT 35A a sine wave controller? I wish my Macs would run as smooth as silk.
 
Yes, Sine wave no doubt. Square runs with kind of a ring that would have been very noticeable when the direct drive was installed.
 
AHicks said:
Yes, Sine wave no doubt. Square runs with kind of a ring that would have been very noticeable when the direct drive was installed.
Click to expand...

My Macs are using about 200w on the display with WOT and no load, around 40+km/hr, which suggests I don't have a false positive wiring combo. Might just be noisy motors, or noisy controllers.
 
Just went out and checked mine. It's floating between 50 and 60w at WOT. Noteworthy possibly, is that the max amperage has been limited to 1300w or so in the parameters.
 
AHicks said:
I'm using a heavier KT controller with the MAC 12t. It's a 12 mosfet rated for 35a max. I have it limited to about 1300w (+-) using the parameters over concern for the battery. Plenty of grunt available with that for my purposes.

It sounds like you have the color sequence figure out, but I'll show what I used so you can confirm.

Phase Firing order    Motor    Controller     
A                    Blue          Yellow           
B                    Green        Blue           
C                    Yellow       Green 

Hall sensors fire in the same order, so they match the phase motor/controller color sequence.

After listening to the sound recording, wondering if you're getting that same resonance when actually out riding?
Click to expand...
Changed to your wiring order, and it's using about 60-110w according to the LCD8 at WOT no load. It seems a bit smoother.

I think there's some resonance happening around 20-25km/hr with the fork, mudguard, tyres. Might try balancing the tyre with some weights, see if that makes a difference.

Thanks for the suggestions!
 
My tire seemed way out of balance while running it to check the wattage for you last night. It's not something I notice while riding though. I'm running some sort of snot in the tube for flat prevention, am figuring that's what was causing the seemingly way out of balance while spinning it up.

Point being, wondering if you notice any difference in the resonance while actually riding it?
 
On the 26" cargo bike, it's really wobbling the fork tips back and forth at 20-25kmhr while riding along. It smooths out after 30kmhr. I'd rather not have the vibration causing the wheel to come loose or the forks to fail.
 
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