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[Pard]

2023 Ribelle, 6K miles.

Past two rides I noticed and odd groaning type of sensation from the motor felt through the bars when in traffic at a steady speed of around 40 mph.  Smooth as silk at other speeds.

Theories on what it might be?

I will inspect the chain to see if it is getting stiff, then will look closely at the motor bearings.

It could just be the motor hunting for a stable RPM at that spot.

Not sure.

What do you folks think?

[MVetter]

I want to say that's something I've noted has a real nice round RPM number like 2500 or something. And I remember thinking the motor sounded the loudest at that RPM. Like maybe some sort of harmonic resonance thing.

[Pard]

^+1 Yep, that may be it, a harmonic resonance.  Never noticed it before.

[jotjotde]

Same here at approx. 46-48 km/h whatever the rpm is at that speed.
In my case it gets less prominent when the chain is freshly lubed. Installation of a rubber-cushioned sprocket (ESJOT 50-29020-15P or JT JTF-704RB) did not change anything, so you can save that money.

[SBK74]

Same here, mostly noticeable when filtering through traffic, typically around 40 km/h there is a roughness in the drive, like you feel resistance of rotating magnets.  Let’s call it character 😃.

[Pard]

Appreciate all the responses!

[Specter]

I get the same thing too, you can feel it like it's pulsing with every pole going by, even though that is not really it, im pretty sure it's some harmonic somewhere.  You will also find it at very slow speeds too if you feel for it.  It seems a bit more noticeable when the chain is on the tighter side than the looser side.  In fact this is what I use after making chain adjustments to say, ooh, maybe this is a bit tight, I better loosen it up a flat or two.

Aaron

[PWM]

Friday opinion time...me thinks speed hunting as OP first alluded to is likely cause because of the motion mapping for our bikes is a mix of torque / speed control and when lightly loaded there's a deadband in terms of feedback resolution (current sense).

Nothing of this sort occurs with the first generation motor w/ Rinehart (Cascadia) drive...the torque / speed (throttle) mapping is spot on.

Try road mode versus sport mode and rain mode over exact speed conditions w/ and w/o regen at extremes to validate the deadband theory.  This resonant / speed hunting event should subside proportional to performance setting reduction.

[Pard]

Friday opinion time...me thinks speed hunting as OP first alluded to is likely cause because of the motion mapping for our bikes is a mix of torque / speed control and when lightly loaded there's a deadband in terms of feedback resolution (current sense).

Nothing of this sort occurs with the first generation motor w/ Rinehart (Cascadia) drive...the torque / speed (throttle) mapping is spot on.

Try road mode versus sport mode and rain mode over exact speed conditions w/ and w/o regen at extremes to validate the deadband theory.  This resonant / speed hunting event should subside proportional to performance setting reduction.

Interesting!  I will perform the tests you outlined.

[MVetter]

Or, again, try and hit that 2500 RPM mark and hold it. I think the speed values are going to be different at 2500 between RS and standard models because of the sprocket difference, but this is all theory in my head at the moment.

[PWM]

Agreed if issue is uneffected by electronic tuning then its mechanical resonance...hmmm, can't see it from a fundamental design unless it's EMC rotor balance...

[MVetter]

Or the number of teeth in the gear reduction and how that plays out. Could be any number of things.

[Pard]

Interesting update on this.  Just changed my chain and sprockets and this phenomenon has been nearly if not entirely eliminated.  Seems to be related to the drivetrain, in my case at least. 

Perhaps the motor controller is hunting for a setting with the chain spinning at that RPM range if the chain is less than consistent in tension.

[jotjotde]

Thanks for the feedback, that will help others with similar issues.

Sounds (pun intended  ) as this really was some harmonic frequency. If you change even a bit in the system, the HF usually shifts to somewhere else.