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Going from a 14in to 18in wheel, suggestions?


NylahTay

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You got it.

Its possible that software needs adjustment depending on the footplate distance from the axle, but this is obviously no big deal.

So we still dont have an answer why 20" wheels cannot be made to be as zippy off the line as an Mten. Wheel radius should not be a factor.

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Thank you all, very useful. I'm excited to see the difference and will be careful as far as leaning and tiltback.  So I had heard that the 18in wheels are more stable at higher speeds, is that true in your experience? Of course, I won't be able to compare that, as the S1 maxes out at 15kph.

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17 hours ago, UniVehje said:

I started with the Ninebot S2 1,5 years ago and also have the 18XL arriving in a few days. Meanwhile I’ve been riding the V10F, which is pretty similar. 

I almost bought the V10F but waited too long and ewheels.com went out of stock.  I'd be interested to hear how you will like your 18XL compared to the V10F. 

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1 hour ago, Planemo said:

Its not! You are the one saying it is, and that the bigger the wheel the more the rider needs to be ahead of the axle line CoG.

We do not need more weight to make bigger EUCs move, nor do we need to move our weight any further foward. The wheels job is to simply read tilt and apply as much power as is required to zero it. As long as there is enough power available this concept should work on any size wheel, in exactly the same way.

As @eddiemoy stated the 18" wheel has a 16" motor so it is applying its torque to a higher ratio tyre diameter relative to say a 16" wheel with a 16" motor.   If that doesn't make sense to a reader.  Imagine a lever welded to the motor case, that is 30 feet long.  One could easily prevent the wheel from spinning by holding the end of that lever; because the motor is applying its force only 6" from the axle but you have 60 times more leverage (6 inches vs 30 feet) to counteract it. I believe the physical term is "moments".  So the further out the resistance is (think tyre meets road) from the axle the more force is required to overcome resistance but the motor and tyre on an 18" have different ratios to each other compared to 16" or 14" wheels that do not use spokes to extend the rim away from the motor

There's also a bunch of physics involved concerning the distance from the axle to the pedal

1 hour ago, meepmeepmayer said:

But maybe the same weight displacement leads to a smaller pedal tilt for some geometric reason. Could be that the pedals have to travel further as they are not on axle height, but below, so they trace part of a circle which gets bigger the further the pedals are away from the axle (like on the usual bigger tire wheels). Maybe that makes a difference? The wheel could still compensate that by having a harder ride mode which means only a smaller part of the circle is traced.

Basically this (above) the further the pedal hangs down below the axle the harder it is to influence the axle by leaning.  This is hard to visualize too.   Imagine this: you have a free rotating axle with a pedal welded directly to it (no pedal hanger).  If you attach a weight on the tow of the pedal it will rotate all the way to a vertical position (the weight all the way at the bottom). Lets call that 100% of the action (what the action is doesn't matter, lets call it 100% because you can't achieve any more movement than that , other than oscillation around bottom dead centre, which is not germane to the example)

NOW. lets take that same free spinning axle and suspend the pedal 6 inches (16cm) below the axle on a hanger.  Attach the weight and the weight falls to the bottom, directly below the axle (give or take the weight of the pedal- also not germane to the discussion).  But can we call this vertical? NO.  Because it is the toe of the pedal directly below the axle (where the weight is attached), the pedal itself is angled up behind the toe weight at something like 45 degrees (no live calculations were harmed in the making of this example) So, seeing at the pedal has only rotated half the distance of the original experiment, I'm calling this 50%. So if the same weight can have its effective rotational force reduced by 50% simply by adding a pedal hanger then I don't think its too much of a stretch to assume that the longer pedal hangers of an 18" wheel (1" longer, or about 20% ) will impart a somewhat less rotational force for any given input.

Now if you combine the less acceleration due to the 18" wheel having a smaller motor, AND the estimated 20% extra force required to impart the same amount of rotation to the axle, due to a longer pedal hanger....somewhere in there are the correct numbers for why an 18" wheel feels the way it does.

That's just my understanding of it.  I may be way off.  It's happened before.:(

Edited by Smoother
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You're correct Smoother. I was just pointing out that wheel diameter doesnt make the difference, other factors do. If you had a 20" wheel with a motor that filled the wheel, and footplates that were the same distance from the axle as an Mten, theres no reason why the big wheel shouldnt accelerate as fast.

Taking it further, I actually see no reason why hanger length even has to make a difference. You would have to tighten up the software to accomodate the fact that the plates will not have the same range of movement (making for a 'hard' ride mode) and the rider would have to adjust their skills accordingly as a tiny weight shift could result in dramatic acceleration.

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1 hour ago, Planemo said:

If you had a 20" wheel with a motor that filled the wheel, and footplates that were the same distance from the axle as an Mten, theres no reason why the big wheel shouldnt accelerate as fast.

Bigger diameter will always require more torque to accelerate from standstill. You can try it out on a normal unicycle with pedals. Try out different sizes and you’ll know. I’m not sure that just placing the magnets on the outer diameter on bigger wheels would increase the torque linearly. The 14” wheels have the motor filled all the way, same with 16” wheels. There is still a big difference in how they feel. 

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@Planemo, I truly wish I was able to explain it better. Hopefully someone will help you get it.

One thing missing from all ponderings in this thread up till now is time. Acceleration is not about the amount of force at a frozen moment in time, but the total speed increase of the rider and the wheel.

Force is applied, wheel accelerates. Then what? How much does the wheel need to accelerate to achieve the balance it is after?

Hold a pen vertically on your fingertip. You need fast movements to keep the balance. Now take a 3 feet long wooden rod and do the same. Much easier, the balance can be kept with much smaller accelerations.

Why is that?

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1 hour ago, mrelwood said:

 

Hold a pen vertically on your fingertip. You need fast movements to keep the balance. Now take a 3 feet long wooden rod and do the same. Much easier, the balance can be kept with much smaller accelerations.

Why is that?

I know why, but I wont go into it as its irrelevant to my point, which is, there is no reason why a bigger diameter wheel should be any slower to accelerate than a small one, assuming you increase the available power and motor wattage accordingly.

With the greatest respect, you appear a little uncertain ever since your apparant claim that one would need to step off a 100" wheel in order to get your CoG to a point where you could get the wheel to move.

So with that, I'm out. All the best.

 

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1 hour ago, Planemo said:

I know why, but I wont go into it as its irrelevant to my point, which is, there is no reason why a bigger diameter wheel should be any slower to accelerate than a small one, assuming you increase the available power and motor wattage accordingly.

You are correct and you also answer the original question of why Wheel makers "don't" make large wheels as zippy as small ones. You have to provide more power, which is probably seen as a waste of resources.  Once the large wheel gets moving it's going to leave the little wheel in the dust. Please note that more power only relates to straight line acceleration and not nimbleness. You can't make a large wheel as nimble as a small wheel. 

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5 hours ago, Planemo said:

there is no reason why a bigger diameter wheel should be any slower to accelerate than a small one, assuming you increase the available power and motor wattage accordingly.

We seem to be talking about different things. Perhaps my English hasn’t been precise enough, as you have repeatedly referred to my point as being that a large wheel wouldn’t ”move” unless CoG reaches the front end of the wheel. And here you say ”slower to accelerate”. Neither of which happens, nor did I mean, nor is the point of discussion. 

5 hours ago, Planemo said:

your apparant claim that one would need to step off a 100" wheel in order to get your CoG to a point where you could get the wheel to move.

”Step off”? Never said that. And here again, in order ”to move”? No.

The point is that for the same rate of acceleration, a larger wheel requires more physical labour/input from the rider.

Often worded as larger wheel being less ”zippy” or feeling ”lazy”.

That is a fact which every rider knows to be true after the first acceleration on a different size wheel. I was trying to discuss the reason why it is so.

5 hours ago, Planemo said:

So with that, I'm out. All the best.

I agree, this discussion isn’t taking us anywhere.

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8 hours ago, Jerome said:

You are correct and you also answer the original question of why Wheel makers "don't" make large wheels as zippy as small ones. You have to provide more power, which is probably seen as a waste of resources.  Once the large wheel gets moving it's going to leave the little wheel in the dust. Please note that more power only relates to straight line acceleration and not nimbleness. You can't make a large wheel as nimble as a small wheel. 

Ok, I think we maybe right, maybe its just a case that there isnt the available power nor the strong motor to give the acceleration we are discussing. Yet ;)

Totally agree with bigger wheels not being as nimble, (left to right movements) due to the fact that we dont have G sensors, batteries and motors to amplify our little movements into additional power in the left to right plane. Maybe one day we will. That could be quite exciting. I remember flying model helicopters years ago with single axis gyros to keep the tail steady in crosswinds. Then we went to 'heading hold' types which used a compass to fix the bearing from the last stick input (which was a game changer) and now we have full 3 axis gyros on the little drones which makes them incredibly stable without flyer input. Not sure how we would ever package it into an euc, nor how the additional assistance we need would be applied (we cant really fill our wheels with gyroscopic weights) but it would be fun to be able to ride a big wheel with the nimbleness of a tiny one, and be stable to boot. A bit like how a tiny drone is now as stable to fly as a Chinook. Amazing stuff tbh!

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2 hours ago, Planemo said:

maybe its just a case that there isnt the available power nor the strong motor to give the acceleration we are discussing.

If the wheel doesn’t have the power to accelerate as fast as the rider asks for, it is called an overlean and a face-plant. Not ”unzippyness”.

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We are not talking about overlean. We are talking about why the batteries and motors are not available to make an 18" wheel accelerate off the mark as fast as a 14".

As I said earlier, we are not going to agree on your viewpoint (although I am not even sure it is the same as mine anymore) which is why I am out with you. Regards.

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2 hours ago, Planemo said:

We are not talking about overlean. We are talking about why the batteries and motors are not available to make an 18" wheel accelerate off the mark as fast as a 14".

Just a heads up, that is an overlean to the rest of us.

Good luck.

 

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Its no beef bud, it just started out as a question! Its common knowledge that bigger wheels dont accelerate as quickly as small ones, and all I was doing was trying to find out was why, as I suspect that motors and batteries are available to do it. I dont believe its a physics issue, thats all. It just seems that none of the manufacturers have upgraded power with size. Maybe theres just no call for it, and folks on bigger wheels are fine with them. Its all cool with me.

 

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20 minutes ago, Planemo said:

Its no beef bud, it just started out as a question! Its common knowledge that bigger wheels dont accelerate as quickly as small ones, and all I was doing was trying to find out was why, as I suspect that motors and batteries are available to do it. I dont believe its a physics issue, thats all. It just seems that none of the manufacturers have upgraded power with size. Maybe theres just no call for it, and folks on bigger wheels are fine with them. Its all cool with me.

The manufacturers develop their mainboards/battery packs/used motors iteratively. And make one wheel after another - like KS had as last wheel the 18XL and now announces the 16X. So presumably more or less same mainboard/batteries and motor - just no spokes between the motor and the rim to reach the 16 inch. A little bit adopted firmware ...

Inbetween, like GW the new motherboard revisions are also reused for their old, still active wheels.

If they have some new stronger motor and/or motherboard developed the next wheel generation is started. And/or some new features/lights/design etc...

So there is in most cases just the leverage of the same torque of the 16 inch motor to the 18 inch wheel as difference. And sometimes more batteries in the 18 inch model which offers more space...

Imo.

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I'll respond too since I just upgraded from an S1 to a KS16S, so not quite a big, but @Rama Douglas let me try his 18XL. The biggest difference I noticed going from the S1 to either the 16 or 18 was how much sturdier they felt. The S1 has a very "soft" ride by comparison and the wheel leans way more than either the 16 or 18, but we both had our wheel setting to "experienced" whereas intermediate/beginner give more of that soft ride you get from the S1 (after riding for a few minutes you'll probably prefer the experienced mode as well). I had the S1 for about 6 months before upgrading, the thing I found surprising is that I didn't think the wheel was under powered until I rode the K16S for an hour and then went back to the S1 and all the sudden I felt how easily I could overpower it. In terms of control, the 18 takes a little longer to accelerate/slow down, it reaches further up between your legs so you will not be able to tilt the euc between your legs to turn as steeply as you can on the S1, instead you'll need to use a little more body motion. Overall the 18 was a ton of fun and for distance rides I can easily see it's appeal, just give it a day or two of riding before you make your judgments. Coming from the S1 to the K16S at first I really questioned if I made the right choice, but a day or two later I fully adjusted and just love the wheel now.

Edited by Austin
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17 minutes ago, Austin said:

the 18 takes a little longer to accelerate/slow down,

That's imho mainly a firmware/"calves grip" problem? The 18Xl is reported to have a insensitive firmware and needs much leaning to perform?

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1 hour ago, Chriull said:

The manufacturers develop their mainboards/battery packs/used motors iteratively. And make one wheel after another - like KS had as last wheel the 18XL and now announces the 16X. So presumably more or less same mainboard/batteries and motor - just no spokes between the motor and the rim to reach the 16 inch. A little bit adopted firmware ...

Inbetween, like GW the new motherboard revisions are also reused for their old, still active wheels.

If they have some new stronger motor and/or motherboard developed the next wheel generation is started. And/or some new features/lights/design etc...

So there is in most cases just the leverage of the same torque of the 16 inch motor to the 18 inch wheel as difference. And sometimes more batteries in the 18 inch model which offers more space...

Imo.

Totally agree with you. I think that it just needs a new generation motor, maybe specifically designed for an 18" before we see any real increase in 18" acceleration. I think we probably already have the battery power we need though tbh. Using the same small wheel motor in bigger wheels is just going to give a reduction in torque as we have all agreed on. I appreciate that designing and building a new motor from scratch is big money though. I am surprised that there is nothing from the Ebike world that could be used, there have been many generations and a lot of advances in the area, way more development than the euc industry I feel. It really doesnt bother me personally, and I am sure lots of folks love their 18"+ wheels, but given I see so much talk of people constantly wanting more, I was suprised to see it wasnt being done on the bigger stuff. I think you have answered the question - its just that none of the big players have decided to invest in a dedicated 'big wheel' motor yet.

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Skateboards with smaller wheels accelerate faster than skateboards with larger wheels. Larger wheels have a higher top speed. This is indeed physics. Making an “18inch motor” is all fine and good, but there’s no reason why you wouldn’t also put that stronger motor on a 14 inch wheel and leave the 18 incher in the dust, again.

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When we are talking about an '18" motor' what we mean is a motor that takes up all the available space inside the diameter of an 18" wheel. A big motor, with lots of windings, coils and magnets.

IE one that wont fit in a 14" wheel...

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15 minutes ago, Planemo said:

When we are talking about an '18" motor' what we mean is a motor that takes up all the available space inside the diameter of an 18" wheel. A big motor, with lots of windings, coils and magnets.

IE one that wont fit in a 14" wheel...

For beefing up a motor a stronger motherboard will be needed, too to provide the higher power requirements.

I'd assume the handling of the power dissipation of the mosfets is by now the bigger problem to solve/design. Beefing up the motor could be in comparison quite easy - if it's not only filling out an order form with the needed specifications :)

If one watches @Marty BackeBacke's hill climbing videos, the new wheels perform really great - but the power dissipation of the mosfets (heatsinks) is still the limiting factor by now.

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1) A larger wheel turns differently due to physics.  For leaning turns, larger wheel radius means that the required leaning angle is different to achieve the same turning radius.  For "hip-twisting" turns, greater mass means more inertia must be overcome and more overall energy must be expended to achieve the same rotation angle on the turn.

2) A larger wheel accelerates and decelerates more slowly due to physics.  Per I=(1/2)*M*R^2 it has more inertia, not only due to more mass M, but also due to greater wheel radius R.

Increasing motor torque cannot compensate for 1) at all, and it can only compensate for 2) up to a point, as the static coefficient of friction of the contact patch with the ground is only slightly affected by the greater overall mass of larger wheel plus rider, and a super-upscaled torque motor would cause a wheel to lose traction and dump the rider as balance is lost. Not to mention that attempting this feat would require rotating the EUC chassis quite far forward, to entice the gyro/electronics/motor system to try to spin up to the point of attempting an acceleration that feels the same as it might have on a smaller wheel.  An analogy for the inertial vs. power problem is a monster truck.  Put all the power in it you want, but it will never be as "nimble" as a Miata, period.  Instead the power eventually gets to the point where this heavy high-inertia machine just wallows around and spins its wheels uselessly.

Also, while the physics of a unicycle are conceptually simple and don't change with different size wheels (rotate the chassis and the motor is spun to try to return to "level," either successfully or unsuccessfully...that's it, that's all an EUC ultimately does), what makes a large wheel different is that due to the pedals hanging below the rotational axis, the moment required to achieve the same leaning angle is increased.  Moment can be increased by increasing mass or increasing length of arm.  Therefore, a larger wheel requires "more lean" from the rider's perspective to get the same leaning angle on the chassis, and therefore the same acceleration response from the motor/wheel.

I think one common misconception with EUCs is that leaning is just a cue for the eletronics to "make it go," but in fact the leaning causes an imbalance that the electronics desperately try to counteract, always trying to return to the calibrated level plane.  How much the wheel accelerates or decelerates to achieve this is not a function of settings, or manufacturer decisions, but simply of physics.  Either the wheel manages to stay under you as you lean it out of level, or it doesn't (and you fall).  In this respect all wheels, of all sizes and all mannufacturers, must be identical because they don't get to cheat gravity, inertia, and acceleration forces.

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