Grin AAv3 Chain Slap Issue - Help Needed

[StouteTiago]

Hey All, I have a Grin AAv3 Slow Wind motor with statorade and a Torque Sensing HG freehub, a PhaseRunner controller, a Grin sourced 52v/20A SuperShark Battery and a miniOLED display connected through the SuperHarness. Everything seems spot on with the setup and performance, except I have a weird Chain Slap issue that specifically happens when I stop peddling that I can't seem to get rid of. I have about 200 miles on the system so its not seen many miles. And I'm using a non-clutched Deore M4120 RD shifting a 12-50T 1x10 drivetrain.

I've been fussing with the system for a while in the Phaserunner suite software to try to eliminate the chain slap issue that happens when I stop peddling and at this point I'm fairly certain the issue is Electrical as opposed to Mechanical, meaning there is some ghost current for some reason that continues to turn the motor after i stop pedaling causing the chain to slacken and slap the top of the chainstay, but I've been wrong before so I'm not 100% sure of this. I've thought of trying a clutched RD, like the M5120 that is also compatible with 52T 10spd cassettes, but that would be more like masking the issue rather than fixing it. But it is a last resort option.

The chain slap seems to have no relationship to what assist level I'm in. It also doesn't seem to be related much to bike speed. BUT, it does seems to have a relationship to which gear I'm in. When I'm in the biggest 1/3 of the cogs, the ones closest to the spokes, there's basically no chain slap happening when I stop pedaling. When I'm in the middle range of the cogs, there is a small amount of slap that happens when I stop pedaling. And when I'm in the smallest cogs, the ones on the outside of the cassette, the chain slap is most pronounced. And again, going at speeds where I can use the smallest cogs, but not super fast, or if I'm going as fast as the bike will go, about 32mph, this behavior relative to cog size to be unchanged.

Has anyone experienced anything like this and have either some Phaserunner settings to double check, and maybe adjust. Or thinking about the wheel and freehub, I seem to remember there was one small washer that Grin wanted you to install under an endcap that they shipped in a small ziplock bag at some point, that I'm not 100% sure I in fact did install. Could have forgetting this washer maybe be causing a slight amount of physical binding on the freehub by the endcap? Or is there anything else relating to the the physical setup that I should double check that would be causing the chain to slap more in the small cogs and almost none in the larger cogs?

TIA for any suggestions or solutions for this issue.

 

[lnanek]

Have you tried shortening your chain or moving the hole the derailleur spring is in to a tighter one?

 

[offGridDownUnder]

at this point I'm fairly certain the issue is Mechanical as opposed to Electrical,

Hello. Grin rarely sells bikes - usually their kits are added to an existing bike by someone. Was that you?

1. How was the shifting before the motor was added?
2. Is the derailleur you are using now the same or did you change, and if so from what before?
3. Was the chain length changed if/when the derailleur was changed?
4. Does the current set up shift completely cleanly when the power is off and pedaling on the road or on the bench?
5. Is it obvious where the chain strikes? I'd expect between the rear and front cogs onto the chainstay, but is that so?
6. Can you provide a picture of the set up?

Given the behaviour you report from largest to smallest rear cog, I'd first wonder about the tension from the derailleur, but please answer the other questions above rather than jumping past this. If it's the derailleur vs. chain tension, I'd really like to know about any changes made from the original, and I'd like to see the set up as it is now - perhaps shifted to largest cog and also shifted to smallest cog. Both views would be very helpful.

 

[Apartunis]

Clutched derailleurs are specifically to keep the inertia of a huge cassette like yours from carrying the chain forward when you suddenly stop pedaling. Any drag in the freehub body can exaggerate a tendency to spool chain over the top.

 

[StouteTiago]

Hi All, thanks for the suggestions. Except for the chain slapping issue when I stop pedaling and the chain is in the smaller side cogs, the bike operates stunningly.

To the questions above, the bike is a fresh build using all new MTB or Gravel components from Shimano. No AliExpress bits were used, though I know good options can be found there too. Given the drivetrain is a 1x10 with a 12-50T cassette, chain length is set using the big cog plus 2 links method and the B-screw is set by having 3 to 5 mm of space between the top RD wheel and the largest cog when the chain is in the 2nd largest cog. Both are industry-standard practices, but I'll try to get a pic posted ASAP. The system shifts flawlessly regardless of power on or off. And yes, the chain is slapping the top of the chainstay. There is zero evidence of even the remotest amount of binding in the freehub when I take the chain off and just spin the cassette by hand when the wheel is mounted in the frame. And the Shimano RD I'm using (M4120) is specifically designed for use with up to a 52T cassette, though it doesn't have a clutch like the next model up does for the same tooth range (the M5120). Why would Shimano even put out a RD made for a 52T cassette if all it would lead to is persistent chain slap when using a 50T cassette? It's possible, but definitely doesn't seem logical, LOL.

I like some of the testing suggestions raised. I will double-check and confirm if the chain slap also happens with the system fully powered off as well as with the system powered on. I honestly don't know the answer to that question.

I'll continue to do some testing and troubleshooting on my end and will post an update ASAP.

 

[Apartunis]

Why would Shimano even put out a RD made for a 52T cassette if all it would lead to is persistent chain slap when using a 50T cassette?

Their objective is to sell stuff for as much as the market will bear, not to live with its shortcomings. if the market wants huge cassettes and cheap derailleurs then that is an opportunity for them rather than a conflict.

 

[lnanek]

Yeah, pretty sure they flat out said in interviews that the no-clutch option on cheaper model derailleurs will have chain slap, but that it is there for people who don't want to pay more:

That U4000 rear derailleur works with a 9-speed 11-46 cassette. It's got great chain retention so you don't need a chain catcher up front or anything special, anything high-tech and expensive, basically, in order to save cost. It doesn't have a traditional clutch in it, it just kind of has clever architecture and a stronger spring. So the chain stays on, which is that minimum level of performance for real mountain biking, but it's noisier, and we hope you can accept that, but we've lowered the barrier to entry.

https://www.pinkbike.com/news/the-pinkbike-podcast-shimano-linkglide-cues-explained.html#cablepull

Could just wrap the chain stay with helicopter tape and send it, I guess.

Amusingly, I saw a video today where you can actually just remove a plastic piece and change a 9 speed shifter into an 11 speed. So that's not even the weirdest thing they do to make artificial price points.

 

[glennb]

Can you replicate the slap by grabbing the pedal and flicking the crank anti-clockwise (backwards)?