Backwards Tiltback Crash?

[winterwheel]

We had a pretty serious crash today which happened at tiltback speed, except that it appeared to tilt the rider forward, basically accelerating the rider into a damaging faceplant. We have been speculating that maybe the wheel was being inadvertently ridden backwards so tilt back became tilt forward. I'm wondering if anyone has experienced tiltback while riding a wheel backwards and can say whether it tilts the rider forward or backwards. I'd like to know for any make/models.

Edited May 5, 2019 by winterwheel

[kasenutty]

Overlean or a slow controlled dumping?

[meepmeepmayer]

Sounds like a classic overlean. No need for theories. I hope nobody was hurt.

Just tested the tiltback on my ACM and the pedals always tilt back against the riding direction (set the tiltback speed to 3kph), no matter how you step on it. So it looks like you can't ride a wheel backwards, that's just the new forwards then.

[winterwheel]

14 minutes ago, meepmeepmayer said:

Sounds like a classic overlean. No need for theories. I hope nobody was hurt.

Just tested the tiltback on my ACM and the pedals always tilt back against the riding direction (set the tiltback speed to 3kph), no matter how you step on it. So it looks like you can't ride a wheel backwards, that's just the new forwards then.

That's what I thought, but it just seemed odd the way it all happened and his description of the way the wheel behaved in the moment.  I'm going to run the same test (low-speed tiltback in reverse) on all my wheels and see how they behave.

[winterwheel]

29 minutes ago, kasenutty said:

Overlean or a slow controlled dumping?

Not sure if I know how to tell one from the other from a distance. He described as the wheel basically threw him off, which is why we thought maybe it had tilted backwards and accelerated him into the fall.

[Chriull]

6 hours ago, winterwheel said:

Not sure if I know how to tell one from the other from a distance. He described as the wheel basically threw him off, which is why we thought maybe it had tilted backwards and accelerated him into the fall.

If one gets surprised by the tiltback and regains balance by balancing on the forward end on the pedal one will keep accelerating! And this until one overleans, if one cannot "shift" the weight back for braking...

Then one "drops" from the tiltback directly into an overlean...

... Could be a possible explanation...

But for sure tiltback works the same in both directions - wheels are not unidirectional.

So high(er) accelerations at high(er) speeds are inherently dangerous! Nearing tiltback speed too fast results in the tiltback kicking in very harsh (tilt back of death ) and secondly the higher the acceleration(burden) is the lower the speed for an overlean gets.. 

[Smoother]

14 hours ago, winterwheel said:

Not sure if I know how to tell one from the other from a distance. He described as the wheel basically threw him off, which is why we thought maybe it had tilted backwards and accelerated him into the fall.

Battery size, battery age, battery charge, rider weight, terrain, terrain inclination, change in terrain inclination, loosness of surface, speed, change  in speed, bumps. dips, obstructions, ambient temp, battery temp, control board temp, make model of wheel.... So much to know before useful analysis/speculation can begin.

But one thing is known already as @meepmeepmayer stated, turn a wheel around and "backwards is the new forwards".

[FlyboyEUC]

Sometimes when I am going fast up a hill and hit a crack in the road, my KS wheels dip forward dramatically then level out again in the blink of an eye. Never fallen but it has surely scared me from going up hill fast. This has happened maybe 5 times in the past 6 months. 

[winterwheel]

22 hours ago, Flyboy10 said:

Sometimes when I am going fast up a hill and hit a crack in the road, my KS wheels dip forward dramatically then level out again in the blink of an eye. Never fallen but it has surely scared me from going up hill fast. This has happened maybe 5 times in the past 6 months. 

Except for the hill and the crack part, that matches with what we saw. Small wheel (14D), 190lb rider, riding at about 30km/h (the official max speed for that wheel) may be a similar trigger as riding up a hill. Odd that it would tilt forward, maybe a mode thing? Do you have it on soft, medium, or hard?

[winterwheel]

23 hours ago, Smoother said:

Battery size, battery age, battery charge, rider weight, terrain, terrain inclination, change in terrain inclination, loosness of surface, speed, change  in speed, bumps. dips, obstructions, ambient temp, battery temp, control board temp, make model of wheel.... So much to know before useful analysis/speculation can begin.

But one thing is known already as @meepmeepmayer stated, turn a wheel around and "backwards is the new forwards".

Brand new 14D. Rider weight less that 190lb. Riding on a smooth tennis court (we were trying out the new wheels). No bumps, dips, obstructions. Wheel had only been operating for about five minutes, so temp would be 20 and 30 just a few quick runs back and forth across the tennis courts as we took turns testing it.  Ambient temp 10c.

I'd assumed backwards is the new forwards, but then we wondered if anyone had actually tried these things backwards all they way to tiltback speed.

[FlyboyEUC]

48 minutes ago, winterwheel said:

Odd that it would tilt forward, maybe a mode thing? Do you have it on soft, medium, or hard?

It tilts forward for me because I'm learning forward. And I do prefer the soft and medium because I can point the head light down so I can see

[Chriull]

5 minutes ago, winterwheel said:

I'd assumed backwards is the new forwards, but then we wondered if anyone had actually tried these things backwards all they way to tiltback speed.

Yes, afair there was a youtube video. But how shall the wheel know which way around you are standing on it? Just turning the wheel and driving forward is enough for a check!

22 hours ago, Flyboy10 said:

Sometimes when I am going fast up a hill and hit a crack in the road, my KS wheels dip forward dramatically then level out again in the blink of an eye. Never fallen but it has surely scared me from going up hill fast. This has happened maybe 5 times in the past 6 months. 

I had the same once accelerating from more or less standstill over some "milled" of part of the pavement. Were just about a couple of centimeters missing - but on the upgoing "corner" the wheel stayed behind, too and getting some fearsome forward tilt. I was quite sure this will be my first faceplant - but my 16s came back under me

This imo comes because the wheel has to go some longer way then i did and additionally it was maybe bouncing a bit at the small corner and jumping over it (so some times without traction and by this no acceleration). So i moved forward, the wheel did not or less -> since my feet stayed on the pedals i tilted forward... Once the wheel had traction again and "noticed" the pedal tilt it accelerated thankfully. This should have happened without an overlean - or the wheel would not have come after me...

[Smoother]

1 hour ago, winterwheel said:

Except for the hill and the crack part, that matches with what we saw. Small wheel (14D), 190lb rider, riding at about 30km/h (the official max speed for that wheel) may be a similar trigger as riding up a hill. Odd that it would tilt forward, maybe a mode thing? Do you have it on soft, medium, or hard?

That's the critical information for me.  Riding right up at max speed but just under tilt back and I assume 3rd alarm set at tilback speed.  When riding this close to the edge (you didn't mention the size of the battery pack-important for amp surge cut outs) then any number of scenarios could come up.  It happens so fast the rider is really not sure what he felt (I know this from personal experience). Its possible that the wheel tried to accelerate to tilt back but half way there, another routine recognized the excess power demand and implemented a shut off.  One must not assume the routines in the programming talk to each other.  Speed controller says "initiate tilt back" BMS says "whoa! too high a current demand (from somewhere) initiate shut down".

Some people here say that tilt back takes no additional power.  I strongly disagree from personal experience, and from logic.  At speed if tilt back merely changed the pedal angles the rider would topple off the front immediately, because at speed, the rider is usually leaning forward to fight wind resistance, and also possible because he is still accelerating.  The writers of the algorithms know this, probably through trial and error, so they wrote the code to make the wheel get in front of the rider before tilting the pedals back.  This strong burst of acceleration can be felt, right before a high speed tilt back.  I have felt it a few times.  It is alarming, it takes one by surprise and it often, in conjunction with the tilt back, lead to a face or butt plant anyway.  I have also felt it lead to a cut out before the tilt back could go into effect.  That was my worst face plant with actual bleeding from my chin (the only real face plant I have had)

[Smoother]

38 minutes ago, Chriull said:

This imo comes because the wheel has to go some longer way then i did and additionally it was maybe bouncing a bit at the small corner and jumping over it (so some times without traction and by this no acceleration). So i moved forward, the wheel did not or less -> since my feet stayed on the pedals i tilted forward... Once the wheel had traction again and "noticed" the pedal tilt it accelerated thankfully. This should have happened without an overlean - or the wheel would not have come after me...

This is a very accurate description of what I have sometime felt on my 16S.  I agree I think that when the wheel loses traction over a bump, when the rider is accelerating or otherwise leaning into it, it gets behind the rider, and because it has no grip (because it is temporarily in the air), as the riders body continues forward, due to momentum, the whole wheel tilts forward; not because the batteries have lost power but because the wheel has lost grip and cannot physically do anything to correct the lean..It is at this time that the wheel speed shoots up rapidly, in a response to the control board trying to accelerate to correct the lean.  When the wheel gets grip again the wheel is spinning very fast and there is a sudden surge forward.  Of course if the wheel accelerated to max then you are going to fall because the wheel has gone into the max speed spas out routine (who wrote that routine anyway?) and it will no longer respond to rider input until it has finished spasing out. I've experienced this a few times.  It's not fun. One time it was up hill on rough grass, at speed.  When the fast spinning wheel hit the other side of the rabbit hole I had just ridden through, all the spinning went into throwing up a rooster tail of dry mud, because it could get no grip on dry mud, and nothing went into accelerating to keep up with my, now rapidly falling, body.  I fell. again. And the wheel ran off in a 20 foot circle beeping angrily at me, until it fell over in a bush. And no, there was no time to "step off". It was a full Superman for all of 0.4 seconds.

[mrelwood]

2 hours ago, winterwheel said:

(we were trying out the new wheels)

Did you charge the wheels to full and pump the tires before the ride? The 14D is a lowishly powered wheel for a 190lbs rider. Add factory tire pressure and factory battery level and you surely have a dangerous combination.

If you accelerate hard with a low battery, there is not enough power in the battery to accelerate the wheel in front of (or under) you, so the wheel will just desperately keep trying as the rider falls forward. This event does sound like a rather typical overlean.

Quote

I'd assumed backwards is the new forwards

I’m pretty sure the Segway/Ninebot MiniPro is the only self-balancing vehicle that initiates tilt-back to the riding direction when riding in reverse. Even that is not an issue since the vehicle can’t be steered when reversing, so no-one will reach tilt-back speed in reverse without modifying the vehicle.

18 minutes ago, Smoother said:

over a bump, when the rider is accelerating or otherwise leaning into it, it gets behind the rider 

In addition, the wheel can also be left behind even if the wheel doesn’t get airborne. If I rode the 16S very slowly to a low curb and not prepare, the wheel would stop, and only once the pedals tilt forward from my feet trying to regain balance, would the power to the motor be increased enough to climb the curb. The same thing happens when riding into small obstacles at speed. It all takes a bit of time, at which point the wheel can be a good bit behind the rider. 

Whenever the wheel hits an obstacle, the forces that gets applied to the wheel slow it down. As does soft sand.

Edited May 7, 2019 by mrelwood

[NylahTay]

I've had this same thing a few times before, once was on an extremely low battery, the other times I hit something slick in the road. Ice, mud, leaves. It seemed to me that it was due to not getting enough traction so gravity and center of mass (which was forward at the time) came into play. 

[winterwheel]

3 hours ago, mrelwood said:

Did you charge the wheels to full and pump the tires before the ride? The 14D is a lowishly powered wheel for a 190lbs rider. Add factory tire pressure and factory battery level and you surely have a dangerous combination.

I (at 240lbs) had ridden it just before without issue, but I didn't have the nerve to quite get it up all the way to tiltback speed. I've been riding the same wheel around for the past couple of days now since the incident to try and get a sense of how it is going to behave in normal use, see if there are any issues with it, so  far without any further problems.

I guess this discussion leads to the corollary, what does KS mean by maximum speed (30kmh  for that wheel); is that the cutout speed? In that case, the real maximum speed from the rider's perspective would be considerably less.

Edited May 7, 2019 by winterwheel

[winterwheel]

3 hours ago, mrelwood said:

Did you charge the wheels to full and pump the tires before the ride? The 14D is a lowishly powered wheel for a 190lbs rider. Add factory tire pressure and factory battery level and you surely have a dangerous combination.

Fully charged, tire pressure was good.

[winterwheel]

3 hours ago, mrelwood said:

I’m pretty sure the Segway/Ninebot MiniPro is the only self-balancing vehicle that initiates tilt-back to the riding direction when riding in reverse. Even that is not an issue since the vehicle can’t be steered when reversing, so no-one will reach tilt-back speed in reverse without modifying the vehicle.

To clarify, the rider was riding forwards, the conjecture was maybe the wheel was reversed and whether it might behave differently when approaching speed limits when riding forwards on a reversed wheel, so steering etc. isn't part of the equation.

[meepmeepmayer]

I really don't think the tiltback will become a tiltforward under any circumstances. The regular speed tiltbacks are going to be the same mechanism, and you can test (or did test) that the pedals will always tilt back (against the riding direction) for the regular speed tiltback.

What you describe sounds just like a standard overlean, I don't see anything special indicating otherwise.

You could do a lift test and see if the jolt you feel when the tiltback kicks in is different or the same in both directions. Or try it on a treadmill. Or lying in a car trunk and dragging the wheel behind you on the road. Something like that.

[winterwheel]

12 minutes ago, meepmeepmayer said:

I really don't think the tiltback will become a tiltforward under any circumstances. The regular speed tiltbacks are going to be the same mechanism, and you can test (or did test) that the pedals will always tilt back (against the riding direction) for the regular speed tiltback.

What you describe sounds just like a standard overlean, I don't see anything special indicating otherwise.

You could do a lift test and see if the jolt you feel when the tiltback kicks in is different or the same in both directions. Or try it on a treadmill. Or lying in a car trunk and dragging the wheel behind you on the road. Something like that.

I think we'll plan to do some tests in that vein next weekend. If nothing else, maybe we get some good video out of it.

[Issah]

Keep in mind, that if the rider was driving at top-speed, the motor has a maximum RPM, beyond which the wheel will become incapable of "keeping up" with itself. The reason why riders who turn off tiltback faceplant sometimes, is because they reach this limit, and the wheel becomes unable to stay upright against the power being asked of it. Think of it like running so fast that you can't keep your own legs underneath yourself.

Feeling the wheel dip as you go over cracks or severe bumps in the road is related to the gyro getting kicked out of whack and takes a split second to figure out where it's at.

[mrelwood]

1 hour ago, winterwheel said:

To clarify, the rider was riding forwards, the conjecture was maybe the wheel was reversed and whether it might behave differently when approaching speed limits when riding forwards on a reversed wheel, so steering etc. isn't part of the equation.

Yes, I got that. The MiniPro I mentioned is a 2-wheeler that has a steering pole between the rider's legs. It behaves the way you suspected the KingSong to behave, but due to the steering behaviour it can't be ridden backwards that fast. There have been multiple threads wondering which way is forward on various KingSong wheels. The answer indeed is that it doesn't matter.

1 hour ago, winterwheel said:

what does KS mean by maximum speed (30kmh  for that wheel); is that the cutout speed?

Not at all. 16S has a top speed of 35km/h, so tilt-back starts at 33km/h, and theoretical max speed (free air speed) was something like 47km/h. I'm positive the free air speed on the 14D is close to or more than 40km/h. But one has to remember that that speed is indeed only reachable in free air. The wheel can't reach that speed on the ground even without a rider, because of the wheel's weight and wind resistance. Add a rider and the actual top speed drops even more.