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Electric Unicycle Terminology

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@esaj

 Excellent post, great for beginners! Thanks for taking the time to write such a comprehensive terminology guide (based on the title, I was only expecting a brief listing of acronyms). 

Personally, I don't think the post needs any pictures or videos, your explanations are very thorough and easy to understand. Plus, after all the work you put into this, it's not that hard for readers to type "EUC over lean" or "BMS" into YouTube (actually writing/using the terminology is another good way to integrate it). 

In short, great post! 

P. S. Tire and tyre are both correct, it just depends on where your live :)

 

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A lot of information. I did not even notice that I spent a lot of time behind her studying additional material. Thank!

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Hi Everyone - I'm a new member and lifelong unicyclist (of the pedaling variety) who is looking forward to going electric sometime soon. I was wondering if the EUC community has any terms that carried over from the traditional unicycling community? One term that immediately comes to mind is UPD, which stands for Unplanned Dismount. The 0:57 mark on the linked video shows a classic example of a UPD.

 

 

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Hi there. As a "real" unicyclist, you'll learn very fast.

12 hours ago, andrew900nyc said:

One term that immediately comes to mind is UPD, which stands for Unplanned Dismount.

Here it's called faceplant, because that's what it eventually ends up to be. There are very few crashes where people fall backwards (or sideways, if that's even possible). In 99% of cases a crash is just the standard superman forwards.

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7 hours ago, meepmeepmayer said:

Hi there. As a "real" unicyclist, you'll learn very fast.

19 hours ago, andrew900nyc said:

One term that immediately comes to mind is UPD, which stands for Unplanned Dismount.

Here it's called faceplant, because that's what it eventually ends up to be. There are very few crashes where people fall backwards (or sideways, if that's even possible). In 99% of cases a crash is just the standard superman forwards.

Hello meepmeepmayer and thanks for the response.

Thanks! I sure hope some of my traditional unicycling skills will carry over so that I can make good progress.

I should have figured that most of the UPD’s in the EUC realm would be faceplants. So even at moderate speeds at which there could be a possibility of running out a UPD (IF you were able to land on your feet), 99% of cases still wind up being superman faceplants? Is that due to the way the UPD occurs, such as getting too close to top speed and losing longitudinal stability due to limitations of the electronics or does that same outcome happen just as easily from hitting a pot hole or bump in the road? And in the case of hitting a pot hole or bump in the road, is the UPD due to a failure of the electronics to react to such a rapid change in orientation?

As a pedal unicyclist, my specialty is riding the big wheel (36” rim) variety. I've also ridden an internally geared 36” unicycle that was capable of speeds at which any UPD would nearly always results in a faceplant, so I learned the importance of watching the road surface and my surroundings like a hawk and always having one or more escape options in case any unexpected obstacles (people, cyclists, cars, etc.) suddenly crossed my path. When travelling at speeds on my geared 36er that were close to the limit of being able to run out a UPD, there were some instances when I was thrown off my wheel and was able to land on my feet and run them out without falling down. On other occasions, I was only able to run them out a little bit before tumbling. I think one main reason why I could sometimes not have a UPD turn into a faceplant on my 36” unicycle was because I was fairly high off the ground, so it gave me more time and a better chance of landing on my feet. On a EUC, the rider’s feet are so close to the ground that it seems nearly impossible for a UPD not to result in a faceplant, if you’re riding at any decent speed. I’d definitely be interested in hearing from any EUC riders who were able to run out their UPD.

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Posted (edited)
1 hour ago, andrew900nyc said:

Hello meepmeepmayer and thanks for the response.

Thanks! I sure hope some of my traditional unicycling skills will carry over so that I can make good progress.

I should have figured that most of the UPD’s in the EUC realm would be faceplants. So even at moderate speeds at which there could be a possibility of running out a UPD (IF you were able to land on your feet), 99% of cases still wind up being superman faceplants?

Depends on the speed, most "falls" are just the wheel falling over, and in slower speed (when it does't happen really suddenly) you can "out run" the crash, just allowing the wheel to fall and take a few running steps before coming to a stop. Although some people claim that they can out run wheel crashing at 30km/h (about 20mph), I seriously doubt that. That's like starting to run at professional athletic speed from a standstill... :P 

 

Quote

Is that due to the way the UPD occurs, such as getting too close to top speed and losing longitudinal stability due to limitations of the electronics or does that same outcome happen just as easily from hitting a pot hole or bump in the road? And in the case of hitting a pot hole or bump in the road, is the UPD due to a failure of the electronics to react to such a rapid change in orientation?

Modern wheels have very high power, so usually a bump won't cause a crash due to electronics, but a less experienced rider might get caught off guard. Then it's up to environmental factors, speed, possible landing if the wheel takes some air etc. (let's call it "dumb luck"). Keeping your knees bent a little helps, if you stand up with your legs "locked" and hit a bump, it might throw you off the pedals.

Still, if you take a high-speed Gotway and hit a big bump at 50km/h ( 32mph or thereabouts), it is possible that the power required to keep the wheel upright would hit so insane numbers that the wheel can't keep up...

I'd claim that most crashes are due to a) inexperience, b) overconfidence and c) too high speed for the situation.

 

Edited by esaj
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Posted (edited)
46 minutes ago, esaj said:

Depends on the speed, most "falls" are just the wheel falling over, and in slower speed (when it does't happen really suddenly) you can "out run" the crash, just allowing the wheel to fall and take a few running steps before coming to a stop. Although some people claim that they can out run wheel crashing at 30km/h (about 20mph), I seriously doubt that. That's like starting to run at professional athletic speed from a standstill... :P 

Personal anecdotes here: I fell riding my Luffy at around 7 to 10 mph because of combination of pothole and incline. I feel the motor shut down and aware that the wheel start dipping forward but I still can't out run it. I only able to take 3 steps before the inertia overwhelm me :crying:

Kinda like this guy only I'm in EUC

 

Edited by Kens
Cannot get YouTube right...
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omg, i felt it a bit.. :-/

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As has already been said, it depends on a variety of factors, but high-speed dismounts are almost guaranteed to end in a faceplant, simply because you can't outrun the wheel. If you can, it depends on the nature of the fall, the angle, how your weight is distributed when you dismount (centered, all to one side because you're turning, etc). 

Electronic failures are extremely rare in modern EUC's, the only thing you need to worry about are cutouts, which are also pretty much guaranteed to end in a faceplant. Cutouts are basically when the wheel switches off the gyroscope due to an excessive power demand, as a safety mechanism to prevent the wheel from being fried. 

This can happen in several different scenarios, but they all boil down to a sudden surge in current :

- Overlean: you accelerate / lean forward too aggressively, asking the wheel for too much power at once

- Accidental overlean: this isn't an issue at low speeds, but if you're near the wheel's max. speed (so it doesn't have much margin to deliver a sudden surge of power), and a) you hit a bump and become airborne for a split second, and land leaning forward, or b) don't become airborne but your weight shifts suddenly forward when you hit the bump (as it tends to happen), the wheel interprets this as a sudden power demand that it can't deliver, and cuts off the power to the gyroscope. Which is why it's important to be very vigilant when near the wheel's top speed, and why it's advisable to buy a wheel whose max. speed is higher than your intended cruising speed. Many such accidents can be prevented by knowing your wheel's limitations and applying common sense: If your wheel's maximum speed is, say, 30 km/h, don't ride near its top speed on roads /paths that are bumpy or you aren't familiar with (potholes, unmarked speed bumps, etc. ) , for instance, or you risk a cutout. 

- Speed-related cutouts: when you simply push your wheel past its limits to the point where torque is near zero and it can't deliver the power you're demanding. 

Cutout related faceplants are the nastiest IMO, as it isn't so much of a forward fall, but a downward, face first fall... Since you're relying on the gyroscope to keep you upright, and leaning forward when it happens, when the gyroscope switches off...you can imagine how it goes... 

Some falls and dismounts are  inevitable (unexpected obstacles, etc), but many others (inattention, lack of spatial awareness, excessive speed, lack of experience and overconfidence, as @esaj pointed out) are completely preventable, and IMHO, cutout related faceplants are at the very top of the list. That's why it's worth taking the time to learn how these machines work and what the limitations of your particular wheel are. :)

 

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Thanks for your responses and for all the helpful information, esaj, Kens, Lefteris, and travsformation. I think I’m starting to gain an appreciation for the nature of these interesting beasts! For those people who ride often and tend to approach top speeds, it sounds like UPD faceplants will inevitably occur at some point. Now I can see why comprehensive safety gear makes a lot of sense. Can’t wait to join the community of 21st century BCers!  

BC comic.jpg

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9 hours ago, travsformation said:

Electronic failures are extremely rare in modern EUC's, the only thing you need to worry about are cutouts, which are also pretty much guaranteed to end in a faceplant. Cutouts are basically when the wheel switches off the gyroscope due to an excessive power demand, as a safety mechanism to prevent the wheel from being fried. 

Cutout related faceplants are the nastiest IMO, as it isn't so much of a forward fall, but a downward, face first fall... Since you're relying on the gyroscope to keep you upright, and leaning forward when it happens, when the gyroscope switches off...you can imagine how it goes... 

I don't think the more modern wheels shutoff at high speed anymore. Older wheels (say, 2015/2016 and before?) did that, either because the BMS cut off the power when the current rises too high, or the mainboard logics did that for whatever reason. It's not the gyroscope switching off as such, either the logics stopping the motor drive altogether and leaving it powerless or entirely losing power to the wheel due to BMS switching off the discharge-side, but like said, I don't think any modern wheels do this anymore. I probably should revise the first post at some point, speed-related cutouts could be nowadays better described as the motor back-EMF (voltage generated by the turning motor itself, it acts as a generator) rising too high and then not having enough voltage on the battery/mainboard-side to drive current through the motor. The motor torque drops linearly with speed because of this, and when the back-EMF equals the battery voltage, the current, and thus torque, becomes zero. Of course on an actual riding situation, it's more complex, as the needed torque changes a lot, and the battery voltage goes up and down depending on how much current is flowing.

bldcfig5.jpg

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Posted (edited)
40 minutes ago, esaj said:

The motor torque drops linearly with speed because of this, and when the back-EMF equals the battery voltage, the current, and thus torque, becomes zero. Of course on an actual riding situation, it's more complex, as the needed torque changes a lot, and the battery voltage goes up and down depending on how much current is flowing.

The maximum possible torque decreasing linear over the speed is already including the internal resistance of battery and motor (ie the battery voltage drop over the internal resistance). Just the additional voltage drop by the cell chemistry, which recovers again after the burden is released, decreases this values tempararily. And the discharge of the cells, of course continousily.

With:

U_battery_0 .... idle voltage of the battery

R_i = R_i_battery + R_i_motor .... internal resistance of the "system"

v_max_no_load .... maximum motor speed, with U_back_emf == U_battery_0 and no current flowing

so kv = U_battery_0 / v_max_no_load

The torque is proportional to the motor current ( M = km * I), so i just consider the max motor current here.

One gets the max stall current I_max_(v=0) = U_battery_0 / R_i = 168A.

For a given speed v U_back_emf(v) = v * kv. So I_max(v) = (U_battery_0 - U_back_emf(v))/R_i = (U_battery_0 - v*kv)/R_i.

This I_max(v) over speed is a straight line regarding already the battery voltage drop over R_i_battery from the flowing current. And with M = km * I one has the maximum torque over speed limit as straight line regarding this, too.

Edit: PS.: What i forgot and what i not to think of in detail is, what happens once one regards the inductance of the motor coils .... . I'd assume then one is at this more complex, about chaotice system you mentioned...:ph34r:

 

Edited by Chriull
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34 minutes ago, esaj said:

I don't think the more modern wheels shutoff at high speed anymore.

Isn't the video "Why we gear up, 40 mph crash" an example of that? Modern wheels have plenty of safety mechanisms to prevent it, but if you disable tiltback and ignore/don't hear the beeps...isn't it still a possibility? I was under the impression, from the thread where that video was originally posted, that there was general consensus that had been speed-related cutout (resulting from pushing the wheel too much by racing a custom-built boosted board). Then again, I clearly don't have the technical knowledge you do, so....I'm happy to learn and hear your opinion on this particular instance :) (I can't recall whether you were in the conversation or not)

As to overlean and accidental/bump-related overlean cutouts...I can attest to having had both on the V8. No such issues with the 18XL, as my cruising speed on bumpy roads is 15-20 km below its max. speed (which is why I bought it, after all. Well, that and the range...and higher cruising speed....and better torque and offroad capabilities...pretty much everything except the price tag :efee612b4b:)

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Posted (edited)
11 minutes ago, travsformation said:

Isn't the video "Why we gear up, 40 mph crash" an example of that? Modern wheels have plenty of safety mechanisms to prevent it, but if you disable tiltback and ignore/don't hear the beeps...isn't it still a possibility? I was under the impression, from the thread where that video was originally posted, that there was general consensus that had been speed-related cutout (resulting from pushing the wheel too much by racing a custom-built boosted board). Then again, I clearly don't have the technical knowledge you do, so....I'm happy to learn and hear your opinion on this particular instance :) (I can't recall whether you were in the conversation or not)

I haven't read that topic, and probably explained it badly and got too much caught up in the details. Yes, if you try to ride "too fast", you will fall. It's just that it seems that modern wheels no longer deliberately cut the power to the motor, rather just plain physics at work. Even while the mainboard logics / battery BMS doesn't cut the power, the motor cannot produce more torque after the speed (motor RPM) goes high enough, due to the voltage produced by the motor itself raising to high enough value to "overcome" the voltage of the battery / mainboard capacitors. The wheel will just fall forwards as it can't keep balancing anymore (cannot accelerate fast enough to "catch" you).

 

Quote

As to overlean and accidental/bump-related overlean cutouts...I can attest to having had both on the V8. No such issues with the 18XL, as my cruising speed on bumpy roads is 15-20 km below its max. speed (which is why I bought it, after all. Well, that and the range...and higher cruising speed....and better torque and offroad capabilities...pretty much everything except the price tag :efee612b4b:)

Overlean and high power spike demands of bumps can still cause a fall. In an overlean, the battery cannot give out enough current to produce high enough torque to pull the wheel back upright. Even if you're running at a steady speed on level ground, if you go fast enough, the sudden bump can similarly need "too much" torque to keep the wheel upright, or if you're already close to the end of the torque-curve and try to demand more speed (acceleration) by leaning forwards. 

Edited by esaj
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21 minutes ago, esaj said:

modern wheels no longer deliberately cut the power to the motor, rather just plain physics at work. Even while the mainboard logics / battery BMS doesn't cut the power, the motor cannot produce more torque after the speed (motor RPM) goes high enough, due to the voltage produced by the motor itself raising to high enough value to "overcome" the voltage of the battery / mainboard capacitors. The wheel will just fall forwards as it can't keep balancing anymore (cannot accelerate fast enough to "catch" you).

That was the wee detail I was missing! Thanks!

22 minutes ago, esaj said:

Overlean and high power spike demands of bumps can still cause a fall. In an overlean, the battery cannot give out enough current to produce high enough torque to pull the wheel back upright. Even if you're running at a steady speed on level ground, if you go fast enough, the sudden bump can similarly need "too much" torque to keep the wheel upright, or if you're already close to the end of the torque-curve and try to demand more speed (acceleration) by leaning forwards. 

Exactly. BTW, thanks for explaining this in layman terms hehe :)

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Doesn't really make a difference why the motor switches off;) It does if you ignore all the warnings.

11 hours ago, andrew900nyc said:

For those people who ride often and tend to approach top speeds, it sounds like UPD faceplants will inevitably occur at some point. Now I can see why comprehensive safety gear makes a lot of sense.

It's simple: always look where you are going. Always as in "every single second, no kidding". The second you don't look, there will be a crazy unlikely obstacle just this moment, that's how it always goes;) Looking will also drive the subconscious process or riding in a matter so possible obstacles are considered or avoided.

Or a car hits you.

Don't expect a crash due to the electronics failing. It can happen, no way around it, a EUC is inherently unstable and only kept upright by the electronics, so any failure there means crash. But it is extremely unlikely, so unlikely it's not worth considering (not that you can see it coming anyways). Your protective gear also covers this fringe case.

Worry about crashes you or someone else causes.

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Thanks for all the information! It sounds like these machines have evolved to the point where the electronics are quite reliable. If ridden according to their operating parameters with a keen eye on avoiding major surface irregularities, it seems like you can depend on these vehicles not having sudden failures. I'm real happy to find out that today's electric unicycles seem to be sophisticated, capable machines.

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15 minutes ago, andrew900nyc said:

Thanks for all the information! It sounds like these machines have evolved to the point where the electronics are quite reliable. If ridden according to their operating parameters with a keen eye on avoiding major surface irregularities, it seems like you can depend on these vehicles not having sudden failures. I'm real happy to find out that today's electric unicycles seem to be sophisticated, capable machines.

Almost - battery managment zechnology is not sophisticated by now :(

https://forum.electricunicycle.org/topic/13590-ks-16s-caused-a-fire/?do=findComment&comment=232810

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Posted (edited)
27 minutes ago, Chriull said:

Almost - battery managment zechnology is not sophisticated by now :(

https://forum.electricunicycle.org/topic/13590-ks-16s-caused-a-fire/?do=findComment&comment=232810

No disrespect intended, but let's not jump to conclusions. If it actually was BMS related, it's a one in a million case. And there are some odd circumstances (and wheel abuse)  surrounding this particular case....

This is in no way representative of 99.9% of users' experience. Personally, I think it would be better to wait until the exact circumstances have been cleared and Jason has further investigated the subject before scaring newcomers with tales like this... 

But as The Dude would say, "That's just, like, my opinion, man" 😉 

Edited by travsformation
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12 hours ago, travsformation said:

No disrespect intended, but let's not jump to conclusions. If it actually was BMS related

I am not concluding that this fire is caused  BMS related, but this is just a worst case example of what can happen by the BMS shortcommings. Mainly that there is no warning of possible bad cells in the pack.

Of course this special incident could be caused by anthing else. And as you already wrote noone knows if there was maybe improper misuse or other design flaws that could cause such hazards with normal (mis)use.

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