Terrible accident on Ninebot Z10

[Rywokast]

7 minutes ago, meepmeepmayer said:

No idea. I guess there is something (overcurrent for the individual cells?), but the standard low voltage thing like any standard BMS has is usually disabled for EUCs as far as I read. Maybe a battery related cut-off can even be plain physical? @esaj @Chriull

In this case it might not be battery related. Speed (motor) or something protecting the electronics over the rider.

what choice does a wheel have but to cut off? you cant give what you dont have lol.. that being said, for safety reasons i believe every wheel should maintain an either separate, or reserved battery percentage for emergencies like that that would step up to deliver the power when absolutely needed.. and then not allow you to ride the wheel again until charged.. seems to me its a case of somebody who either doesnt understand how it works, or was too busy showing off to bother heeding any warnings.. i seriously doubt it just suddenly cut out with zero warning

[Rehab1]

 @Igor Rz can you communicate with your friend what he observed leading up to his fall? 

[Marty Backe]

2 hours ago, meepmeepmayer said:

@Igor Rz At what speed was this?

Doesn't look like the Z10's speed limit (45?) to me. Then he should not have been able to overlean the wheel that easily! That looks like a normal sporty acceleration at a still reasonable speed. It should have worked!

Maybe it was some stupid current/whatever limiter throwing the rider off?

I believe EUC BMSes have this disabled specifically so you won't just fall after a millisecond of undervoltage. Early EUCs had hat problem.

Maybe you know something that we don't. Mainly, the battery level of the wheel in question. And I still think that looked like a borderline aggressive lean maneuver. 

[svenomous]

KingSong does a pretty good job of keeping riders safe, from what I've read, by using speed tilt-back and emergency tilt-back in a manner that cannot be overridden.  To have enough margin that no maneuver, no matter how ill-advised, could possibly cause a failure, would require the wheel to have a lot of excess (and unused) battery and motor capacity.  Maybe an emergency reserve via large capacitors?  A separate "reserve" battery pack?  It's a difficult engineering problem, and whatever margins are added, users will then ask why they can't use the additional capability, while promising to use it wisely.

[Marty Backe]

1 minute ago, svenomous said:

KingSong does a pretty good job of keeping riders safe, from what I've read, by using speed tilt-back and emergency tilt-back in a manner that cannot be overridden.  To have enough margin that no maneuver, no matter how ill-advised, could possibly cause a failure, would require the wheel to have a lot of excess (and unused) battery and motor capacity.  Maybe an emergency reserve via large capacitors?  A separate "reserve" battery pack?  It's a difficult engineering problem, and whatever margins are added, users will then ask why they can't use the additional capability, while promising to use it wisely.

I assure you, it's possible to overlean a KingSong wheel.

The Z10 implements tilt-back just like KingSong. When you reach the max speed it starts to tilt-back to slow you down. You can't turn it off like on Gotway. But if you aggressively lean into the wheel, it only takes a split second to over power the motor.

So just like this Z10 episode, the KingSong wheels will also cutout.

Maybe this is a bit of stereotyping, but I think the typical KingSong owner does not ride their wheel as aggressively as a Gotway or Z10 rider. And this is why cutouts are not reported much for those wheels.

[svenomous]

@Marty Backe, while I do buy the theory that KS riders as a population are statistically less likely to ride aggressively, the problem with forums and YouTube, etc. is that statistics go out the window since it's the outliers who're more likely to be present and reporting their woes.  It would only take a few anomalously aggressive KS riders who suffer a cut-out and post their videos or discussions before the number of reports of such cut-outs would seem just as high as it is for Gotway and others.  So, isn't it also possible that KS is allowing for a larger safety margin that gives more time/torque/power for tilt-back to "succeed" before cutout, thereby contributing to the fact that we see a lot fewer cut-out reports for these wheels?

[Marty Backe]

27 minutes ago, svenomous said:

@Marty Backe, while I do buy the theory that KS riders as a population are statistically less likely to ride aggressively, the problem with forums and YouTube, etc. is that statistics go out the window since it's the outliers who're more likely to be present and reporting their woes.  It would only take a few anomalously aggressive KS riders who suffer a cut-out and post their videos or discussions before the number of reports of such cut-outs would seem just as high as it is for Gotway and others.  So, isn't it also possible that KS is allowing for a larger safety margin that gives more time/torque/power for tilt-back to "succeed" before cutout, thereby contributing to the fact that we see a lot fewer cut-out reports for these wheels?

Sure, it's possible. I have no hard evidence either way.

But I can tell you that whether I'm riding my MSX or KS18XL, I'm not going to aggressively accelerate while at speed.

[Michael Tucker]

I ride in the hills a lot, and I accelerate while going up hills from 18mph to 25mph, sometimes with bumps. I have owned all the modern wheels. The MSX-84v feels the most robust doing this. No hint of any fatigue. I do it on my Monster 100v more cautiously because it doesn't feel as torquey and allows too much lean. I do this ride on my KS18XL as well with no problems. Even my MCM5 hands the hills like a champ, just a little slower, but still with incredible control. I tried to bring my Ninebot Z10 on this ride and it felt terrible. Felt very out of control and on the edge of dumping me going up, coming down and maintaining high speed (24mph-100%battery-riding tiltback) on rough streets. I took that Z10 everywhere to test it because I really loved the way it looked and just couldn't believe how terrible it felt, nothing to do with the tire as everyone talks about. 

The MSX, Monster100v, MCM5 and KS18XL have excellent track records of keeping the rider safe with aggressive riding, foolish riding aside. The Z10 has a terrible track record with aggressive handling with many riders falling on video and many people trying to explain away an under-performing wheel as rider error. I think the problem is expectation. If you buy a Z10 and think you can ride it like an MSX or KS18XL, you'll fall. If you ride the Z10 with caution and care, you'll be in for a unique riding experience that's not aggressive, but still quite fun. Ultimately I sold my Z10 because it never felt safe for my style of riding, even at low speed. This video is just another example of how easy it is to overpower a Z10.

[Chriull]

6 hours ago, meepmeepmayer said:

@Igor Rz At what speed was this?

Doesn't look like the Z10's speed limit (45?) to me. Then he should not have been able to overlean the wheel that easily! That looks like a normal sporty acceleration at a still reasonable speed. It should have worked!

Looking at the video in slowmotion it's something about 2 seconds of very sporty acceleration _from_ some reasonable speed. That should be enough to overlean every wheel...

Quote

Maybe it was some stupid current/whatever limiter throwing the rider off?

I believe EUC BMSes have this disabled specifically so you won't just fall after a millisecond of undervoltage. Early EUCs had hat problem.

 

6 hours ago, svenomous said:

Oh, I thought that EUC BMS still does low-volt cut-off.  So what causes low-battery type failure, then, if not a cut-off?  Is it just that the motor can't get enough amps, but the wheel is actually still powered?

This accident was for sure no cut-off. Once the BMS cuts off, the mainboard would have no power supply anymore and so no lights could be on anymore.

6 hours ago, meepmeepmayer said:

No idea. I guess there is something (overcurrent for the individual cells?), but the standard low voltage thing like any standard BMS has is usually disabled for EUCs as far as I read. Maybe a battery related cut-off can even be plain physical? @esaj @Chriull

In the beginning wheels had overcurrent (total output current) protection, which was triggered from time to time while riding. But this was not reported/seen/experienced anymore for some long time. Either they set the limit high enough and/or with enough time delay. Or turned it off completely like GW did (at least with some of their last generation wheels - don't know if they still have no overcurrent/short circuit protection in their BMSs)

Voltage sag just by high current is very unlikely - the wheels have all kind of beeping/tiltback/speed limiting once one comes in the low voltage area around 3.3V (or does the Z10 stop at 3.0V as the KS18XL?). A sound lower cell voltage limit would be around 2.5 V (as specified by the manufacturer), but imho for critical task should be set somewhere as low as ~2V to not accidently cut off while riding in high burden situations. So there should be always around almost 1V for sudden voltage sags. One single cell with around 50mOhm would need to deliver 20A for this 1V voltage sag - so the 6 cells in parallel of the Z10 would need to deliver ~100A. Such burdens are not sanely possible with a wheel already at low to zero battery charge...

And again such protective cut-offs would have time delays again.

But not really much is known about the BMS details, especially the Z10s.

Quote

In this case it might not be battery related. Speed (motor) or something protecting the electronics over the rider.

Imho still everything here looks like an absolut normal overlean. At higher speeds one gets no "real" high currents anymore - the motor already generates enough back emv so there is not enough voltage difference between motor and battery so that any huge current could flow for some limiting taking place. And this not so high current is exactly the reason for the not so high torque available anymore -> normal overlean.

The only battery related reason here could be that his battery maybe was not "full and fresh" anymore - so the torque limits are lower and easier reached.

It's nicely seen in slowmotion that he got some "lean back" while riding over the gras part, the wheel almost overtook him underneath. So he lost "much speed" and reacted be leaning forward and accelerating (at least very sportive) for too long to catch up again...

Edit: PS.: Some crazy mainboard/BMS firmware behaviour/failure is possible everytime and not to be excluded without closer examination of "real data", but as it looks chances are extremely high that here it's just riding over the "normal" wheels limits.

Edited May 28, 2019 by Chriull

[Seba]

4 hours ago, Marty Backe said:

I assure you, it's possible to overlean a KingSong wheel.

It's not only possible but it happens  I overleaned KS-16C on my fourth day of EUC riding and this was a humility lesson I learned for the rest of my EUC rider career  And the situation was almost identical to what we seen on the video. I was trying to accelerate at speed, trying to chase skater on speed roller skates.

Second time I overleaned KS-18L when trying to accelerate agressively from standstil. This time it was intentional and I was prepared. I did it just to confirm that you can overlean every wheel under some conditions. One of such demanding conditions is very hard acceleration from complete stop on a uphill slope.

In general - it's quite easy to overlean wheel when conditions require more power than wheel remaining reserve. Wheel power reserve decreases with speed, so riding with speeds near to maximum is conducive to overlean. But it's also possible to overlean the wheel on start, when there is highest inertia to overcome. You just need curb, hole or something similar tha will cause another, momentary power spike that adds to already high wheel engine load and you have a recipe for a tasty faceplant 

[Chriull]

6 hours ago, Rywokast said:

what choice does a wheel have but to cut off? you cant give what you dont have lol..

It's just "fusspoting" - but going on the limits a wheel is not cutting off, it's still delivering torque and trying to do what's possible - but if this torque is not enough anymore the lean of the rider cannot be balanced anymore and he overleans.

Quote

that being said, for safety reasons i believe every wheel should maintain an either separate, or reserved battery percentage for emergencies like that that would step up to deliver the power when absolutely needed.. and then not allow you to ride the wheel again until charged.. seems to me its a case of somebody who either doesnt understand how it works, or was too busy showing off to bother heeding any warnings.. i seriously doubt it just suddenly cut out with zero warning

A battery reserve would not really change anything. The a bit higher voltage of a fresh and full battery just sets the limit a bit higher, but still with enough burden (acceleration) at high enough speed there is no torque available anymore - that's no matter of power a battery could still deliver.

4 hours ago, svenomous said:

KingSong does a pretty good job of keeping riders safe, from what I've read, by using speed tilt-back and emergency tilt-back in a manner that cannot be overridden.  To have enough margin that no maneuver, no matter how ill-advised, could possibly cause a failure, would require the wheel to have a lot of excess (and unused) battery and motor capacity.  Maybe an emergency reserve via large capacitors?  A separate "reserve" battery pack?  It's a difficult engineering problem, and whatever margins are added, users will then ask why they can't use the additional capability, while promising to use it wisely.

 

4 hours ago, svenomous said:

@Marty Backe, while I do buy the theory that KS riders as a population are statistically less likely to ride aggressively, the problem with forums and YouTube, etc. is that statistics go out the window since it's the outliers who're more likely to be present and reporting their woes.  It would only take a few anomalously aggressive KS riders who suffer a cut-out and post their videos or discussions before the number of reports of such cut-outs would seem just as high as it is for Gotway and others.  So, isn't it also possible that KS is allowing for a larger safety margin that gives more time/torque/power for tilt-back to "succeed" before cutout, thereby contributing to the fact that we see a lot fewer cut-out reports for these wheels?

Don't know the average KS rider, but imho the wheels are strong enough to need real accelerations for overleaning. In combination with the mandatory max speed tiltback that "chatches" many to most overleans. 

GWs with tilt back disabled just "motivates" too much riders to try to get up to max speed, until they learn that this is no constant and has to lead to an overlean...

And Z10 are maybe just the weakest of the actual top wheels, as @Michael Tucker wrote?

Edited May 28, 2019 by Chriull

[Planemo]

7 hours ago, Rywokast said:

what choice does a wheel have but to cut off?

Continue to provide the maximum it can give.

This is the point I was trying to make. I understand batteries, BMS's, motors and how a wheel fundamentally works. What I couldn't (and still cant) grasp is why people keep referring to wheels 'cutting out'. It seems like an easy get-out to try and explain every fall there has ever been.

What I think is actually happening in many cases is that a wheel is asking to be accelerated past the point it can maintain balance. Thus, the rider literally falls off the front because they are leaning foward. A bit like standing still on your feet and falling fowards. So I can accept people referring to this situation as 'overlean' as that is exactly what is happening. What I struggle with is people using the term 'cut out' as I am not convinced that is what is actually happening. That said, if it is then I dont feel this is a safe method to deal with an overlean situation. No wheel should just cut out unless there is a catastrophic battery failure/fire risk and the best remedy is to shut down all and every system.

[svenomous]

@Planemo, I think you're right that in most cases where people overlean, a "cut-out" is not what's happening.  It's what it looks like, because of how fast it happens, but you're right that in most cases the motor is probably still making power at the moment of the fall.  The end result is more or less the same, though, isn't it?  I stand corrected on the cut-off remarks I made.  I assumed that cut-offs can and do happen but if it's true that cut-off voltage is somewhere around 2.0V (40V for a 72/84V wheel), that leaves a very large safety margin for unexpected power demands, even with a very depleted battery pack.  Let's not forget, though, that 1.0V per cell safety margin isn't as much as it seems, given that at 40V it takes twice as many amps to produce the same watts of power than it does at 80V when the pack is nearly full.

[Mono]

8 hours ago, svenomous said:

Oh, I thought that EUC BMS still does low-volt cut-off.  So what causes low-battery type failure, then, if not a cut-off?  Is it just that the motor can't get enough amps, but the wheel is actually still powered?

Why do you think it must be different from a high-battery type failure? The charge status changes the tiltback (or failure) speed, but what else do you need or want?

[Seba]

8 minutes ago, svenomous said:

I think you're right that in most cases where people overlean, a "cut-out" is not what's happening.

Actually, it's a cut out  When you overlean (mostly by overloading power stage but sometimes also if you exceed max permissible tilt angle), controller cuts off power delivery to the motor. That's all. It just detects overload condition that could cause catastrophic failure to the controller power stage, so as a countermeasure it turns off all the transistors. There is no "soft" power limit, it's rather 0-1 situation.

[Rywokast]

31 minutes ago, Planemo said:

Continue to provide the maximum it can give.

This is the point I was trying to make. I understand batteries, BMS's, motors and how a wheel fundamentally works. What I couldn't (and still cant) grasp is why people keep referring to wheels 'cutting out'. It seems like an easy get-out to try and explain every fall there has ever been.

What I think is actually happening in many cases is that a wheel is asking to be accelerated past the point it can maintain balance. Thus, the rider literally falls off the front because they are leaning foward. A bit like standing still on your feet and falling fowards. So I can accept people referring to this situation as 'overlean' as that is exactly what is happening. What I struggle with is people using the term 'cut out' as I am not convinced that is what is actually happening. That said, if it is then I dont feel this is a safe method to deal with an overlean situation. No wheel should just cut out unless there is a catastrophic battery failure/fire risk and the best remedy is to shut down all and every system.

i like to think of it as bending a popsicle stick... you bend it a little and it can spring back, but once you get to a certain point it will just snap.. same with if you have a cut out, which absolutely does happen.. the terminology however is a bit confusing, for instance if you were to hop on a ninebot one and lean hard you would simply push beyond the motors capacity to keep you upright, it just doesnt physically have the ability.. on the most powerful of modern wheels this is basically impossible to do unless you are very heavy and literally trying to make it happen, but me at 120 lbs for instance no matter how hard i tried, could never cause a powerful modern wheel to truly cut-off.. thats why cutouts are virtually unheard of now, what instead happens is the battery, not the motor, is unable to provide the required energy to the motor that it is requesting.. which is why situations like this are much more common when you have a low battery, and why everyone always asks first what the battery level was.. so as you said, the rider literally just falls off the front which is correctly referred to as an overlean... where this gets mixed up is because actual cutouts used to be fairly common and the easiest way to cause a wheel to cutout (where it would literally just go dead in a split second) was to lean too hard, aka overlean. its similar, but not interchangeable terms.. yes, the wheel does continue to give the maximum it can give and will do so indefinitely, but as we all know how batteries work, in certain situations it would be literally impossible for it to do so even if it does want to... once the battery spikes and can give no more, it will cease and you will continue on at your current speed sans unicycle lol.. its easy to see this happening in real time when you watch the app on your phone.. with a 30% or less battery you can frequently see your battery dipping extremely low, sometimes even showing 0% charge.. this is not the true charge level but the calculated charge level according to your real time energy requirements.. basically, maintain this requirement and you are asking for an overlean situation.. safeguards are of course in place, but there is no safeguard stopping your body from physically leaning as hard as you please and overcoming these safeguards  as you know most of these situations happen extremely quick and without warning, and thats how it is because of a sudden large spike in energy, like gunning it as hard as you can, or pushing the limits and then hitting a bump in the road and boom the battery cuts energy to the motor to save itself. nothing is perfect but a spare, reserve only battery could be a way to overcome a lot of these overlean situations where you are skating that line and then hit an obstacle and suddenly and immediately require additional energy not available from the main battery... im not saying its a perfect solution but it would certainly prevent a lot of these overlean situations.. it would be like a one off thing wherein the wheel then tilts back and does not allow you to ride again until you charge it, i would take that over a face plant any day

[Planemo]

11 minutes ago, Seba said:

Actually, it's a cut out  When you overlean (mostly by overloading power stage but sometimes also if you exceed max permissible tilt angle), controller cuts off power delivery to the motor. That's all. It just detects overload condition that could cause catastrophic failure to the controller power stage, so as a countermeasure it turns off all the transistors. There is no "soft" power limit, it's rather 0-1 situation.

This sounds like poor engineering to me.

Why cant the manufacturers build in a system similar to a rev limiter like a car uses to avoid destruction? To avoid your 0-1 situation. In a wheels case, max power draw to be below that in which the fets etc will fry so that a total shutdown is never reached.

[Chriull]

27 minutes ago, Seba said:

Actually, it's a cut out  

Actually not.

Quote

When you overlean (mostly by overloading power stage but sometimes also if you exceed max permissible tilt angle), controller cuts off power delivery to the motor.

One has to differentiate two situations here. First, what you already mentioned in your post before, accelerations from standstill or just high burdens at low speeds. Here the current through the motor could get way too high (would destroy the wheel), so the firmware limits the max current and by this the torque.

The second ("normal", like shown in this video here) case is just hitting the max torque over speed limit of the motor. Here no limiting or cutting off is happening - its just the motor not beeing able to deliver more torque, because no higher current can flow (its limited by (battery voltage - motor back emv(generated voltage))/internal resistances).

As nicely seen in 

 

Quote

That's all. It just detects overload condition that could cause catastrophic failure to the controller power stage, so as a countermeasure it turns off all the transistors. There is no "soft" power limit, it's rather 0-1 situation.

As said, that's only true at standstill and low speeds and the current limiting is afaik realized as "soft" limit, by changing the pwm duty cycle.

Edited May 28, 2019 by Chriull

[Rywokast]

18 minutes ago, Seba said:

Actually, it's a cut out  When you overlean (mostly by overloading power stage but sometimes also if you exceed max permissible tilt angle), controller cuts off power delivery to the motor. That's all. It just detects overload condition that could cause catastrophic failure to the controller power stage, so as a countermeasure it turns off all the transistors. There is no "soft" power limit, it's rather 0-1 situation.

yup, electronic devices generally will do everything in their power to preserve themselves... after all, your sales numbers would plummet if every time someone over leaned one of your wheels you blew the board or some connectors and had to replace parts/send it in to be serviced lol.. also truly depleting a lithium battery can be catastrophic to it.. and if youve ever checked, the batteries are by far the most expensive part of the machine.. they will never allow themselves to be truly depleted so they will simply say no more, and cut themselves off to prevent catastrophic damage to themselves

[Rywokast]

10 minutes ago, Planemo said:

This sounds like poor engineering to me.

Why cant the manufacturers build in a system similar to a rev limiter like a car uses to avoid destruction? To avoid your 0-1 situation. In a wheels case, max power draw to be below that in which the fets etc will fry so that a total shutdown is never reached.

because its what people want lol.. if youre comparing to cars then you would have a $2,000.00+ top end EUC have a max speed of 25 kmph.. you wouldnt be selling many xD cars have a much, much higher top end so they have the ability to do this while still allowing you to go ridiculously high speeds safely. also youre comparing to something thats been mass produced for a hundred years.. there is billions of dollars and man hours of research behind them.. EUC's are made mostly by hand from people making 2 dollars an hour in a chinese factory, pushing the limits of the current technology.. i think its not a fair comparison

Edited May 28, 2019 by Rywokast

[Seba]

Just now, Planemo said:

This sounds like poor engineering to me.

I would rather say that this way of EUC handling is a bad practice: pushing self-balancing vehicle beyond its capabilities.

1 minute ago, Planemo said:

Why cant the manufacturers build in a system similar to a rev limiter like a car uses to avoid destruction? To avoid your 0-1 situation. In a wheels case, max power draw to be below that in which the fets etc will fry so that a total shutdown is never reached.

Rev limiter is completely different thing. We are talking about something that is called "inverted pendulum" - something that is unstable by default and needs constant control and power to keep in balance. This is how all self-balancing vehicles works. This is why electric bike needs only 250 W motor to go with speeds about 20 km/h on a flat surface without pedaling, and the same motor power won't even be able to keep heavier person in balance for a longer time on the same, level surface.

It's crucial to learn how EUC balancing works. In its stable position it needs virtually no power. But this rapidly changes as EUC get tilted. More tilt, more torque needed to counteract and regain stability. So there is some critical tilt angle at which torque needed is larger than possible to deliver by controller+motor circuit. Adding "soft" power limiting won't be beneficial at all - there still be torque deficit as wheel tilts faster and faster.

[stephen]

The engineering is our brain, know the limits keep to them or risk failure if pushed beyond 👍 

Everyone should know the limits of there wheel they all differ and in different situations 😊

[Mono]

14 minutes ago, Planemo said:

This sounds like poor engineering to me.

True, wheels that cut out at high speed is poor engineering. However, I think, most of us believe that modern wheels don't do that anymore.

[Rywokast]

Just now, stephen said:

The engineering is our brain, know the limits keep to them or risk failure if pushed beyond 👍 

Everyone should know the limits of there wheel they all differ and in different situations 😊

exactly.. pretty much dont be foolish, mind your speed and monitor your battery.. in close to 20,000 km ive yet to have an accident on an euc because i never push the limits of what i know they are easily capable of

[Rywokast]

2 minutes ago, Mono said:

True, wheels that cut out at high speed is poor engineering. However, I think, most of us believe that modern wheels don't do that anymore.

not a cut-out per se, not really anymore.. just arent able to be given the requested energy from the battery and so cannot keep you balanced at your current speed/energy requirements, the battery 99% of the time is the limiting factor nowadays, or someone who is foolish enough to push beyond the manufacturer firmware limits put in place in order to preserve the electronics.. to truly make a 2000 watt motor cut out would be a task