Torque topic

[Planemo]

Power is the measurable factor though, so its kinda what matters from a data point of view, both to manufacturers and users.

People could also relate to:

"This wheel will feel slower because it has X power less than this wheel which has X"

rather than

"This wheel will feel slower because its effectively being geared differently because of the bigger diameter"

which doesnt tell people much.

 

[Eucner]

52 minutes ago, Planemo said:

Power is the measurable factor though, so its kinda what matters from a data point of view, both to manufacturers and users.

People could also relate to:

"This wheel will feel slower because it has X power less than this wheel which has X"

Power is not measurable by standard user. Spec sheet power alone doesn't tell anything about the zippiness of wheel. Power varies with speed and torque. At the stand still all wheels have zero watts power. It doesn't give any clue how they would accelerate.

52 minutes ago, Planemo said:

rather than

"This wheel will feel slower because its effectively being geared differently because of the bigger diameter"

which doesnt tell people much.

That wouldn't be enough for an explanation. You could say

"This wheel will feel slower because it has less thrust than this other wheel."

[Slartibartfast]

4 hours ago, Planemo said:

Right, we're there then. But this is where we lost direction because when I had applied the exact same scenario to my RC car wheels you didnt agree, but neither could you provide an explanation for it when using the euc example which you did agree with...

Arr, where have we got?

I can't help but think we are constantly treading over the same ground, but yes, given the torque remains constant and given force is inversely proportional to distance (by definition) if you reduce the length you proportionally increase the force. This comes directly from the definition of torque.

In your example of the RC car yes, the force applied at the circumference of the 2" wheel will be 6x that applied at the circumference of the 12" wheel but, even though the larger wheel has 1/6th of the force it travels 6x the distance for every degree of rotation, and these cancel each other out. This is precisely why torque is a useful measure (because, [dare I say it] it essentially eliminates distance as a variable: 😬).

 

@Planemo, you are the one that is "guaranteeing" that the larger wheeled car will accelerate more slowly. I think I have explained, several times now, why I don't believe this would necessarily be the case. Are you able to explain how you are able to "guarantee" that it will accelerate more slowly, because I can't see it and you are the one asserting that it will happen.

As I said before: the amount of "effort" required to turn a 20" wheel 1° is the same as would be required to turn a 10" wheel 2°. What we are talking about here is what is known in physics as "work" and both these examples require the exact same amount of "work". @Planemo, I take it you are saying one would be able to turn the 10" wheel 2° more quickly than they would be able to turn the 20" wheel 1°. To me these both look like the same amount of work and would there for both take the same amount of "effort". Are you able to say which you believe would be eaiser (ie. could be done more quickly)?

[Slartibartfast]

Also, now that we are talking about power it's probably worth explaining that while "work" is defined as force over distance [and also measured in newton-meters], "power" is defined as work per unit time (Nm/s). I also agree that acceleration is a measure of work per second and there for is a product of "power". Rather than defining power as torque X PRM (which I think is what @mrelwood would call a "US engineering" definition of power) I think it would be better to describe it as work per second, which is the way a physicist would define it.

[Planemo]

3 hours ago, Eucner said:

You could say

"This wheel will feel slower because it has less thrust than this other wheel."

Which is pretty much exactly what I said, exchanging your word 'thrust' for my word 'power'. I think its semantics at this point. Either way, I think a buyer would understand either word (or rather, understand it as much as they need to).

[Planemo]

2 hours ago, Slartibartfast said:

 

@Planemo, you are the one that is "guaranteeing" that the larger wheeled car will accelerate more slowly. I think I have explained, several times now, why I don't believe this would necessarily be the case.

I'm not sure I understand your logic when you cannot believe the above but agree that the below is true:

• A bigger tire diameter will create less thrust force, because of greater distance from ground contact point to the center of motor.

Unless you are saying that because the bigger wheel travels further per revolution it 'cancels out' the reduced thrust it has? At least I think thats what you're trying to say.

[blox1130]

Guys with bigger wheels have bigger torques. And bigger torques means more girls. it's simple maths

[mrelwood]

Wow, you guys have been busy! I should visit here more often.

 

18 hours ago, YCC said:

How do you think the torque (Newton -Meter) of Mten4 compared with V8F?Both EUC have 1000W motor power, however, their tire size is 11” and 16” respectively.

In this specific question the nominal power handling figure of the motor is as irrelevant as the manufacturer of the tire.

I think a big problem for many is to understand where the power comes from in an EUC. In a car or motorcycle, motor is the source for the power. On the EUC it is not:
 

Spoiler

The "motor power" is a bad abbreviation from nominal motor power handling, which has caused way more confusion than it has given information:

• "Nominal" refers to the amount of power the motor can handle for "an extended perioid of time". That's really how it's defined. No-one even knows how long this "extended perioid of time" is.
• "Power handling" means the amount of power that can be put in the motor through the cables.

So all that a "1000W motor" in an EUC tells us is that the controller can keep pushing 1000W to the motor continuously, and the motor should be able to keep converting it into torque without damaging itself. Nothing more.

But it gets worse. When GW used the exact same older motor in a newer wheel with a bigger battery and more powerful controller, they had to push up the figure a bit so that it would better relate to the actual difference in the available motor output. So they stamped a bigger wattage value for the exact same motor. And this has been going on ever since, with all manufacturers.

The worst case was when a new wheel got a motor power figure increase from a firmware update. It could've actually been the V11 that got bumped from 2000W to 2200W right at the time of release so it wouldn't look bad next to the then recent 18XL motor upgrade.

The torque that an EUC motor creates is taken from the battery, then lossly converted (and limited) into a suitable PWM waveform in the controller, and then lossly converted to rotary motion by the motor itself. "Motor power" is the crappiest ever figure that tries to describe all this. And most customers buy it at face value.

(V13 is the first ever wheel to advertize the actual measurable amount of torque it's able to create (300Nm). Would be nice to see this become a trend!)

Ps. If you ever buy a music system, amplifier, powered speakers etc, please don't get duped by the power figures! The funniest I've seen is when a small computer speaker set advertized it's 25000W power. And this speaker system was powered by something like a 4.5W power source... So where did the rest of the 25KW come from?? (Answer: The marketing department.)

 

I have to applaud @UniVehje for being the first one here for seeing the big picture, and to be able to condense all these derailing comparisons and symbolic examples and point out why this whole discussion even exists. You beat me to it, again! I can't even get myself to snip anything out from this quote:

9 hours ago, UniVehje said:

You’ve reached to the very core of this discussion on this forum. All the talk of rated power, voltages and torque culminate on this. On non self-balanced vehicles the discussion is straight forward and simple as you have full control of throttle or current. You can just slam vehicles to full throttle and very simply predict the behavior from numbers. Nothing to argue there. 

On self balancing one wheeled vehicles “full throttle” is difficult to achieve and by definition at the very edge of performance. Lean a bit more and it cannot balance any more. The more sluggish feel of the Monster compared to MSX cannot be corrected with more rated torque on the motor. MTen4 will always smoke both of them in zippyness. And that’s what most people talk about when discussing torque here. It’s understandable as on normal vehicles more torque is exactly what you would need if the vehicle feels sluggish to get going and is clearly “geared” higher. So that’s what people ask for. And then we continue have this discussion on torque even when we already have bigger numbers, more voltage, more rated wattage, C38 and C40 motors wound for torque etc. Our wheels still feel the same in comparison with different tire sizes. 
 

We should discuss geometry.

 

And geometry is exactly what @Hsiang tried to explain in the video that provoked this whole discussion, not the technical capabilities of the motor. Because geometry is what causes a larger diameter wheel to feel sluggish. It has nothing to do with the motor's, controller's, or battery's performance. A V8S is hugely (25%) more zippy than any 18" = 19" = 20" = 21" wheel, despite these new monsters having FOUR times the amount of power in the battery, controller, and even in the motor power handling. And even in the actual motor output.

If you'd modify any wheel in a way that the controller would output twice the amount of power for the same amount of rider input, would it accelerate faster?

Spoiler

No, it would not. It would accelerate slower. The wheel would start accelerating faster, but 0.00125 seconds later the gyro would tell the mosfet controllers to back down, because the forward angle that the rider created for acceleration has now been corrected, and the wheel is again horizontal. After 0.5 seconds (reaction time of a human) the rider would notice this and wonder what happened, why can't he accelerate?? He'd try again with practically the same outcome. And so on.

The amount of thrust that the EUC creates must always be in line with the force that tries to tilt the wheel forward. If a controller has bigger losses (or any other reason for a different amount of output power), the rider will fall further forward, which causes the controller to output more power until the system is in balance. The power consumption will be higher, but the thrust of the motor is still the same.

 

In the video, @Hsiang tried to explain how larger wheels are more sluggish. If it's not related to torque, power, thrust, or such, why is it then??

 

@Hsiang's door example was actually pretty clever. It wasn't about the motor's gearing though, it was about the input side of the system.

When a rider sets his CoG at 75% of the front end of the 28cm pedals (10.5cm off center), the amount of acceleration required to counteract the displacement depends on the tire diameter. Imagine an EUC with a 30 feet tire diameter. And when powered on and stationary, the tire is nearly locked. The contact patch of the tire alone would be closer to a metre, so a 0.105m (~1% of the tire diameter) displacement wouldn't require barely any acceleration at all in order to keep the EUC upright. The rate that the wheel with a locked tire would fall forward is very very miniscule.

Then we put the same pedals and the same rider on a 10" Mten3. Now the displacement is ~40% of the tire diameter, so the wheel falls forward fast, and requires a lot of acceleration from the motor to compensate. So the Mten3 accelerates 40 times faster than the 30 feet diameter EUC prototype, which is then discarded and never pushed to market.

For a more practical example, a 20" tire diameter would have a displacement of ~10%, making it four times less zippy than an Mten3. Sound about right?

I'm not good enough in physics to start calculating this any more precisely than this, and pedal height and a few other matters affect the results a bit as well. But be the torque figures and the rest what they may, they are always determined by the firmware, and based only on the forward angle of the wheel. And tire diameter is crucial in determining the forward angle displacement of the wheel that the rider is able to create.

 

Conclusion: People talk about torque, but they are not at all interested in the actual physical torque. They mean zippyness. Just like they talk about a gyroscopic effect as a means to describe EUC steering, when in fact they mean the cone effect of the tire. And these wrong terminologies will forever derail EUC related discussions.

 

35 minutes ago, blox1130 said:

Guys with bigger wheels have bigger torques. And bigger torques means more girls. it's simple maths

Incorrect! I've been running this exact practical experiment for 5.5 years now. The amount of girls remain unchanged. Despite being open and social, for example in this torque thread...

 

Edited October 22, 2022 by mrelwood

[Planemo]

2 minutes ago, blox1130 said:

Guys with bigger wheels have bigger torques. And bigger torques means more girls. it's simple maths

Yes but some girls may see a V5F as 'cute' and see a Sherman as 'compensating'...

As an ex Sherman owner I cant comment 

[Planemo]

@mrelwood, all true of course but without wishing to pi$$ on your cornflakes the discussion is now actually very little do with the specific operating conditions/physics of euc's anymore. And I fully accept the conditions/power application/rider physics for an euc are different to most other applications of a BLDC motor but..

The discussion is this:

Will X motor accelerate a bigger wheel under load as fast as a small wheel under load?

We're disregarding any physical gearboxes or how you tap into the power etc etc.

Lets assume a max set voltage and a max set current (say manufactuer figures) which I think will make it easier.

I'm saying a bigger wheel will take longer to accelerate, @Slartibartfast is saying they will be the same.

I, as always, will be open to being educated 

[Eucner]

2 hours ago, Planemo said:

Which is pretty much exactly what I said, exchanging your word 'thrust' for my word 'power'. I think its semantics at this point. Either way, I think a buyer would understand either word (or rather, understand it as much as they need to).

It is not only semantics when one is correct word and other is not. I think we should prefer the correct one.

22 minutes ago, Planemo said:

The discussion is this:

Will X motor accelerate a bigger wheel under load as fast as a small wheel under load?

We're disregarding any physical gearboxes or how you tap into the power etc etc.

Lets assume a max set voltage and a max set current (say manufactuer figures) which I think will make it easier.

I'm with you. Bigger wheel would take longer to accelerate because of less thrust. Longer tire perimeter is not relevant here.

[mrelwood]

 

1 minute ago, Planemo said:

The discussion is this:

Will X motor accelerate a bigger wheel under load as fast as a small wheel under load?

We're disregarding any physical gearboxes or how you tap into the power etc etc.

So we're past discussing EUCs now? Ok. (Boring...)

I'm not sure how we can disregard the gearbox though, since it is crucial whether the gearbox is the same, or if it has been modified to compensate for the tire change like it would be if the cars were to participate in an actual competition.

But if the gearbox is the same, then yes, the larger wheels will accelerate slower. Even disregarding the increased mass of the larger tire.

@Slartibartfast is correct in that the amount of total work done when moving the car from A to B is the same, but the speed at which it happens is not. After all, the amount of forward force at the tire to ground surface is smaller. If the gearbox is the same, the large tires will have a higher top speed and a slower acceleration. To advance 1 metre, the amount of energy used is again the same, since like @Slartibartfast demonstrated, the larger tire will compensate the smaller amount of force in the larger travelled distance. But again, it will happen at a slower speed.

Disclaimer: I'm pretty freakin' far from being an expert on the subject, and all of the above is just how I think it would be. For a confirmed correct answer, I would hollar someone who actually knows this $h!t.

[blox1130]

Imagine if we could change the wheel diameter on the fly though. Smaller wheel at low speed or when stopped for portability and acceleration/maneuverability. Big wheel when fast for speed and stability. It might be possible with some kind of adjustable spokes and rim that locks together like legos. Tire might need a special kind of rubber.

Edited October 22, 2022 by blox1130

[Tawpie]

1 hour ago, blox1130 said:

Imagine if we could change the wheel diameter on the fly though. Smaller wheel at low speed or when stopped for portability and acceleration/maneuverability. Big wheel when fast for speed and stability. It might be possible with some kind of adjustable spokes and rim that locks together like legos. Tire might need a special kind of rubber.

dragster tires do exactly do that... doesn't do much for portability but talk about THRUST!

 

Edited October 22, 2022 by Tawpie

[blox1130]

@TawpieI thought that was mostly for grip right?

[Tawpie]

27 minutes ago, blox1130 said:

@TawpieI thought that was mostly for grip right?

There's a LOT of flex for grip, but near the end of this run (speed) you can see the diameter is larger...

https://www.bing.com/videos/search?&q=slow+motion+drag+tire&docid=608010461593863347&mid=543F7CE8A9AE30FDC9E9543F7CE8A9AE30FDC9E9&view=detail&form=VDRVRV&ajaxhist=0

 

[blox1130]

@TawpieOh i see what you mean, the rubber is so soft the centrifugal force is stretching it away from the center.

[Tawpie]

tires only last 1.5 miles tho... here's a detailed explanation

https://www.caranddriver.com/features/columns/a26089565/drag-racing-tires-explainer/#:~:text=Each one is expected to last eight runs%2C,the tires' rubber and the full-power run begins.

[Planemo]

On 10/22/2022 at 8:12 PM, Eucner said:

It is not only semantics when one is correct word and other is not. I think we should prefer the correct one.

I've only ever heard the word 'thrust' used when referring to anything not on the ground. Like jets/rockets etc. But whatever you feel. I think we are talking about the same thing though.

On 10/22/2022 at 8:12 PM, Eucner said:

I'm with you. Bigger wheel would take longer to accelerate because of less thrust. Longer tire perimeter is not relevant here.

OK cool.

On 10/22/2022 at 8:13 PM, mrelwood said:

So we're past discussing EUCs now? Ok. (Boring...)

Not at all, the issue we are discussing would still refer to EUC's, we are just removing the additional physics that EUC's involve.

On 10/22/2022 at 8:13 PM, mrelwood said:

I'm not sure how we can disregard the gearbox though, since it is crucial whether the gearbox is the same, or if it has been modified to compensate for the tire change like it would be if the cars were to participate in an actual competition.

We don't really need to involve a gearbox though so it just confuses matters. We are simply talking about X electric motor being fitted to two different sized wheels. It keeps it nice and simple, and EUC's don't use gearboxes or in fact any kind of non-direct drive as you know.

On 10/22/2022 at 8:13 PM, mrelwood said:

But if the gearbox is the same, then yes, the larger wheels will accelerate slower. Even disregarding the increased mass of the larger tire.

So we all seem to be in agreement except Slarti.

On 10/22/2022 at 8:13 PM, mrelwood said:

@Slartibartfast is correct in that the amount of total work done when moving the car from A to B is the same, but the speed at which it happens is not.

This has been my stance all along. Slarti has asked me to 'prove' it and I wish I could in an easy way. My RC cars would do it but I don't have my monster truck wheels any more!

[sunstrong]

I haven’t been able to read the whole discussion but I want to share my understanding after reading the first few posts.

Torque is measured in Nm, that means it is independent of force or distance. 
Just like speed is measured in m/s, meaning it is independent of time or distance.

In other words, knowing the speed, you don’t know the distance traveled or the time. And similarly, knowing torque, you don’t know the diameter of the wheel or the force produced.

I think most people use the term torque to describe the actual force. I.e. we know the diameter of a wheel and the torque of the motor, how zippy it feels. 
 

i think it’s fair to use it this way IF one off the variable is controlled. For example, talking about the same zippiness (acceleration force), I can say a bigger wheel has more torque. Or for the same wheel diameter, more zippiness means more torque.

[Planemo]

1 hour ago, sunstrong said:

In other words, knowing the speed, you don’t know the distance traveled or the time.  And similarly, knowing torque, you don’t know the diameter of the wheel or the force produced.

Correct, but Power introduces the time element. Bigger wheels have less power for the same given motor, therefore accelerate slower over time.

And as we've said, bigger EUC's make it harder to access the available power/torque due to angle changes so bigger EUC's get hit with a double whammy in terms of acceleration - less power AND harder to access (again, for the same given motor compared to a smaller EUC).

[Tawpie]

29 minutes ago, Planemo said:

Bigger wheels have less power for the same given motor

As this is a largely semantic thread, I'm going to say: Bigger wheels cannot convert their motor power/torque to linear thrust as effectively as smaller diameter wheels.

Edited October 29, 2022 by Tawpie

[Planemo]

As you say, we are saying the same thing but as part of maths/physics is all about reducing the amount of text to describe the same thing (how short is E-MC² for such a complicated equation?!) I would argue that the correct statement is 'Bigger wheels = less power for the same motor'. It could get even shorter than that if we resorted to equations but I'm trying to keep it relatively understandable

And if we're being pedantic, adding the word 'power' to your statement is irrelevant because a reduction in power is the outcome. It's the conversion of torque which is the issue.

Edited October 29, 2022 by Planemo

[Tawpie]

6 minutes ago, Planemo said:

adding the word 'power' to your statement is irrelevant because a reduction in power is the outcome

true, so true. edited! 

[Tawpie]

20 minutes ago, Planemo said:

trying to keep it relatively understandable

And that's where using the term "thrust" comes in handy. We're concerned about being able to accelerate out of the way of an impending disaster, or getting across the intersection before our fellow group riders, or climbing that rock... for that we need thrust at the tire to earth interface. But instead we talk about torque as the be-all-end-all metric when torque is just one necessary but insufficient piece of the recipe.

Edited October 29, 2022 by Tawpie