Inmotion v8 behaved like "anti-lock" braking system (ABS) and lead to two crashes

[August]

Hey,

I have inmotion v8 more than a year now, drove around ~1000 km. Face planted only once (after 3 months of usage) when I reaches "I'm-too-cool-to-look-at-road" mastery level, hit the pothole in the road, the only real damage was torn clothes as I was with helmet, wrist guards and bikers jacket.

Today I was driving my usual route on a kind of dry day (10^C), battery ~90% full and driver blocked my path with the car on pedestrian walk, I had like ~15 meters to stop from ~25-27ish km/h speed. No bigy, done that before, just lean back, look awesome, reduce speed to put one foot down and turn 90^o. v8 started wobble front/back like ABS (anti-braking system) in cars do, like never before, this intermittent braking shook my feet of the EUC and we were both sliding under the car. Ti's was only a mere scratch - to me, EUC, my self-respect. Shook of the dust, hopped on EUC and continued down my usual route.

Two kilometers later, was doing pathetic sub ~20 km/s and started gently braking before ~80^o angle turn. That son of a b*tch shook me of in same (tilting quickly front/back/front/back) way as few minutes back, EUC ended up driving in car road, got under the car, broke bunch of EUC plastic covers, left me sitting on my ass.

Anyone had this behavior with v8?

P.S. I changed to summer tire few weeks back, not sure if related.

[EUCMania]

One possibility: The battery does not take charge that easily as new, so the braking, which needs battery to dump energy in, does not work well. To test if this is the reason, discharge EUC to 50% or lower battery level, do the brake to see if the anti-lock behavior is gone. If it disappears at low battery level, then the guess is confirmed, then you need a new battery.

[August]

7 hours ago, EUCMania said:

One possibility: The battery does not take charge that easily as new, so the braking, which needs battery to dump energy in, does not work well. To test if this is the reason, discharge EUC to 50% or lower battery level, do the brake to see if the anti-lock behavior is gone. If it disappears at low battery level, then the guess is confirmed, then you need a new battery.

That's actually not a bad idea. EUC was charging for day or two, but battery indicator was still jumping from 4 to 5 bars. Which kind of sound consistent with your assessment.

Is it business as usual that after ~13 months of usage, one needs to replace component which cost ~half of EUC cost, or would this battery be considered a faulty component?

It will take some time to duct-tape plastic covers before I could test this theory, but I was wondering is there some sure way to limit charge let's say 70% (as my daily route is around 10km)

[Marty Backe]

7 minutes ago, August said:

That's actually not a bad idea. EUC was charging for day or two, but battery indicator was still jumping from 4 to 5 bars. Which kind of sound consistent with your assessment.

Is it business as usual that after ~13 months of usage, one needs to replace component which cost ~half of EUC cost, or would this battery be considered a faulty component?

It will take some time to duct-tape plastic covers before I could test this theory, but I was wondering is there some sure way to limit charge let's say 70% (as my daily route is around 10km)

A Charge Doctor will do what you want

[Chriull]

1 hour ago, August said:

That's actually not a bad idea. EUC was charging for day or two, but battery indicator was still jumping from 4 to 5 bars. Which kind of sound consistent with your assessment.

That's something absolutely not normal. After a couple of hours the leds have to show stable full charge!

Quote

Is it business as usual that after ~13 months of usage, one needs to replace component which cost ~half of EUC cost, or would this battery be considered a faulty component?

With something like 17Wh per km you should have used about 17000Wh in total making 48 full charge cycles. That's nowhere near the "normal" lifetime of about 500 full charge cycles li ion cells should need before reaching 80% of their capacity.

But if the pack was not assembled from perfectly matched cells, this can lead to much faster pack deterioation (http://batteryuniversity.com/learn/article/bu_803a_cell_mismatch_balancing)

 

Quote

It will take some time to duct-tape plastic covers before I could test this theory, but I was wondering is there some sure way to limit charge let's say 70% (as my daily route is around 10km)

If it's a balancing/bad cell problem charging it only to ~70% will worsen your prob since the cells in the pack get less/no balancing anymore.

Btw - did you notice a decrease in range over the time?

If i remember right @Cranium had some battery pack probs and recharged the cells individually to get them balanced again - but was just a short time solutuon, the cells drifted apart again and he replaced the pack...

And braking probs at ~90% charge show some real problem.

Best would be if you know another inmotion v8 owner and could swap battery and look if the prob is gone then (eliminate the possibility of other reason for this behaviour)

[EUCMania]

@August Looks like one or more of your battery cells cannot hold charges. Sometimes, a bad cell or two can ruin the whole pack. You can swap a good pack to test the hypothesis as suggested by @Chriull

If you are handy, you can repair it.

Option 1: Eay way, just try to rebalance the cells like what @Chriull said. But it may not work is one cell is bad.

Option2. Identify which cell is bad and replace it, requiring soldering or better: spot welding.Method: Full charge the pack, discharge it by riding to 50 - 60%. Get the pack out, Measure the voltage of each cell. Those cells showing voltage far below average are bad cells. Replace them.

Option 3. Just buy a new pack.

 

[Kuji Rolls]

Ive had a similar experiences (maybe 8 times in 5000km) on my v8 typically after dropping off curbs at 20+kph. What it feels like is violent and quick shaking that lasts a second or two. Like a stepper motor rocking back and forth between detents. The movement isnt enough to force me to eject, but it is quite challenging if im upright and not prepared for it. Ive crashed once and had to bail a couple times, but most of the time i just push my knees in to grip it and wait for it to stop. It might be related to the sudden force causing it to dislodge its rotational location. Then the firmware thinks the wheel rotation is somewhere else and cant control it properly. Then after a second (maybe after the wheel has rotated completely and the hall effect sensors update the location, it corrects itself. Other than that, the v8 has been a very reliable wheel for me. Those pedals stay balanced down stairs better than other wheels ive ridden (and ive ridden them all). 

My recommendation is to just go hard and gradual rather than hard and abrupt... bend the knees and pinch the frame. 

[WARPed1701D]

9 hours ago, August said:

That's actually not a bad idea. EUC was charging for day or two, but battery indicator was still jumping from 4 to 5 bars. Which kind of sound consistent with your assessment.

Is it business as usual that after ~13 months of usage, one needs to replace component which cost ~half of EUC cost, or would this battery be considered a faulty component?

If you consistently leave your wheel charging like this or charge it to max and then let it sit I can fully believe that you can potentially make the cells unusable in 13 months (especially given the demands of an EUC). The nemesis of Li-Ion cells is a full charge especially if left in that state for any period of time.

[August]

On 4/26/2018 at 5:04 PM, WARPed1701D said:

If you consistently leave your wheel charging like this or charge it to max and then let it sit I can fully believe that you can potentially make the cells unusable in 13 months (especially given the demands of an EUC). The nemesis of Li-Ion cells is a full charge especially if left in that state for any period of time.

Based on my usage route I would have EUC with ~55% or ~10% left capacity and I would leave it plugged over night and usually through weekend. In my defense I do disconnect during holidays

It looks as if I was doing all the bad practices? @Marty Backe suggested Charge Doctor, but it's a generic term and could not find something I could easily use to limit charging time. Any  particular good type/model would anyone could recommend? Manually tracking charging duration and then disconnecting is too much overhead

@Chriull it looks as if I'm only guy with any EUC in my city. So no battery swap tests for me.

@EUCMania I will do option 2 as you suggested, dropped my battery pack at local battery repairman - will keep you posted on battery assessment.

Thanks for the tips guys, appreciate it.

[Chriull]

13 minutes ago, August said:

Based on my usage route I would have EUC with ~55% or ~10% left capacity and I would leave it plugged over night and usually through weekend. In my defense I do disconnect during holidays

Maybe i'm a bit paranoid but i'd never charge the wheel unattended or while i'm sleeping - i love my flat and my life.

Maybe if i had a shabby garage with an old car... die

[alcatraz]

I have a v8 and this happened to me only once in 2000km, without accident. At high speed going over bumps it seems this can happen. I don't know why but my guess it has to do with the system reaction time being so short at those speeds that the motor is getting all the funky data from the bouncing gyro and goes into some kind of evil spiral. Acc/brake in quick succession.

Maybe this can be fixed in a firmware update.

Maybe the gyro cirquit isn't perfectly fixed and is allowed to move around a bit when submitted to shocks.

/a

[mrelwood]

Charge Doctor is a special charging tool designed for unicycles. I have the dual input version, and I have found it very useful. You can buy one here for around 30€:

http://hobby16.neowp.fr/buy/

[Cranium]

The limitation of Charge Doctor is that it will not show you the internal resistance of the cells or if there is an out of balance situation in a pack.  This would be, in my opinion, more important to find out rather than showing voltage and current for the entire battery. Especially when the pack viability is in question. 

When I had an issue with my battery, I took my battery heatshrink off and checked then charged pairs of cells individually.  I say pairs of cells since the battery configuration is a 15S2P (15 cells in series and 2 of these in parallel) for the Ninebot so I was only able to isolate a pair of batteries at a time for charging without having to desolder the battery pack.  The charger I used was an RC charger which would also provide the IR (Internal Resistance) of the cells.  While the accuracy of IR value could be questionable and the value of any set of cells may not be actionable alone, the value is great to use to compare to the other cells.  For example, if most of the cells showed an IR of 15 ohms and one cell showed 25 ohms, this would indicate an issue in that pair of cells.

If you have cells with a higher internal resistance, it will affect their charging and discharging characteristics and lead to an out of balance situation more rapidly.  So doing this will allow you to see if your pack is balanced when you check it and allow you to see if you have cells going bad.  

A charge doctor, buying a charger that has an 80% charge function, or modifying a charger to only charge to 80% is a great thing to do if you want to baby your batteries and get longer life out of them.  It also provides a built in buffer if you do have some cells starting to go bad since all cells will never be at 100% or close when you brake or go down a hill right after you take it off the charger.  And with the charge doctor data logging, you can do a trend analysis of charge cycles.  This would give you a peak inside the chemistry of the battery as it's changing over time without having to open up the pack.  So a new battery, for example, may take 1.5 hours to fully charge and only 1 hour to go from constant current to constant voltage mode.  After 6 months, this time would be expected to gradually increase as the internal resistance of the batteries slowly increase.  But if you see a sudden change, you have an issue.

I retired my Ninebot One P after I fried another controller while trying to test out the battery pack to see if it was having issues.  So I didn't get to fully test if my pack had an ongoing issue or if it became out of balance due to my poor charging habits (I would keep it 100% and charge after every ride which didn't give it time to balance properly).  I had even bought some LiPo alarms to use for testing which would alert me if any pair of cells started going low before the BMS shut down.

[Herbas]

On 4/27/2018 at 9:14 PM, August said:

@Marty BackeBased on my usage route I would have EUC with ~55% or ~10% left capacity and I would leave it plugged over night and usually through weekend. In my defense I do disconnect during holidays@Chriull

@EUCMania

 

When I fully charge it (in just a couple of hours), I can get ~20-22km and still have ~50% battery level. If I understand you right, you only have 10% left after 20 km. It seems like your batteries are done Especially considering your mentioned battery charging LED behaviour.

[August]

Apparently, it's not battery's fault, at least not cells fault (current from new 6.6A fell to ~6 A). Attached discharge diagram and two bottom line are a bit out of order because they were on weaker connection.

So BMS or something else in EUC is at fault. - Any tips on this?

I'm a fat man (with clothes ~100kg) most of the way driving at max speed 30km/s so I guess that explains my ~21km range.

That does not help with my lost confidence in v8. I guess I just have to do the unthinkable, drive slower and anticipate wobble during braking. 

Bought charge doctor while waiting for results, thanks @mrelwood for recommendation.