Torque topic

[Planemo]

28 minutes ago, Tawpie said:

And that's where using the term "thrust" comes in.

...only if the readers interpretation of the word 'thrust' is more understandable than the word 'power'  . to say one is correct and the other isn't is...incorrect. They are both correct.

But I agree with you, there may well be more people who can relate to thrust better than power, despite thrust being a lesser-known term outside of aeronautics.

I found a good quote:

"Thrust is a force. When a force is applied over a distance, it does work. Work is the transfer of energy. The rate at which energy is transferred (i.e. - the rate at which work is done) is power. So you can convert back and forth between power and thrust by accounting for the rate at which distance is covered: Power is force times velocity, P= FV."

 

[mrelwood]

9 hours ago, sunstrong said:

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

I would often like to discredit any post that introduces itself into a conversation this way, BUT:

9 hours ago, sunstrong said:

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 must admit that this was sort of an eye opener for me, as this finally helped me understand what @Slartibartfast was saying all along!

9 hours ago, sunstrong said:

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.

I don't equate zippyness to thrust (= acceleration force) alone. Any modern wheel can create huge amounts of thrust, but some of them are clearly zippyer than others. In my experience the word zippyness is used to describe how little effort is required to create the thrust force.

The Mten accelerates pretty rapidly by just hinting the wheel that you might want to go forward, while you have to have high quality pads precisely positioned and hang off them for dear life (or to have a Kuji level death wish) to get the Master Pro to accelerate fast.

In a sense zippyness is the efficiency of the whole rider-wheel complex.

 

6 hours ago, Planemo said:

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?!)

Z = F / A

Where Z = zippyness, F = thrust force, and A = lean angle.

I don't think anyone has measured this on any wheel just yet though...

 

6 hours ago, Planemo said:

I would argue that the correct statement is 'Bigger wheels = less power for the same motor'.

I agree, but I don't think it's relevant. Nobody over leans the modern wheels anymore unless specifically aiming for the top speed. So the max power, thrust or torque doesn't matter. And if only doing a mid lean, the wheel will balance the equation by using only as much power as is required to stay upright. So all this is purely for calculations, that have no relation to the riding experience. Hence, I prefer zippyness.

[Planemo]

22 minutes ago, mrelwood said:

I must admit that this was sort of an eye opener for me, as this finally helped me understand what @Slartibartfast was saying all along!

It doesn't for me, as I think all of us apart from Slarti is agreeing that bigger wheels will accelerate slower, even taking away the specifics of EUC use (say using an RC car or even a hub drive ebike as an example). My point is that putting say a 250w hub drive in a 10" bike wheel would make the bike accelerate far quicker than putting it into a penny farthing.

Regarding @sunstrongs comment 'Torque is measured in Nm, that means it is independent of force or distance. ' lets not forget that the 'm' in Nm means metre so start changing that length and different things will happen. Put that 'force generator' into anything that actually moves and the more leverage you apply to the axis of that generator the less power it will make (ie less work over time). After all thats why gearboxes were invented in the first place - to provide a useable range of power, particularly at low rpm. Whilst we have enough power to not have to worry about gearboxes in EUC's, it doesn't mean the reduction of power due to increased distance from the axis magically disappears.

I do hear you with regards to many people not being able to tap into the huge power of current EUC's though. Tbf, thats not really what this discussion was about though (which I think you know;)

22 minutes ago, mrelwood said:

Hence, I prefer zippyness.

Very technical 

[Paul A]

If there are two identical motors:

One with a 10 (ten) inch wheel attached

One with a 1000 (thousand) inch wheel attached

Is the torque the same on both?

Will the smaller wheel accelerate faster?

[techyiam]

A force tells you how strong a push or pull will be.

Analogously, a torque tells you how strong a twist will be.

To know how much force or thrust you can generate from a torque, you will need to know the length of the moment arm.

The outer tire radius will give you the length of the moment arm.

Edited October 29, 2022 by techyiam

[Slartibartfast]

9 hours ago, Paul A said:

If there are two identical motors:

One with a 10 (ten) inch wheel attached

One with a 1000 (thousand) inch wheel attached

Wow, you're really stretching the concept beyond all reasonable means but I'm with you...

 

9 hours ago, Paul A said:

Is the torque the same on both?

Yes, the torque is the same.

 

9 hours ago, Paul A said:

Will the smaller wheel accelerate faster?

That is still an open question. It seems most in this discussion believe it would but we don't have a concrete reason as to why.

 

You're kind of putting you thumb on the scale by comparing a "reasonable" wheel to a ridiculously fictitious wheel but theoretically, yes, they would both have the same torque. While I maintained it's not clear which would actually be capable of greater acceleration most here will tell you the larger wheel will accelerate more slowly, and if we continue the same fictitious example the other way I can only assume most here will also say that if you made a 1/100th inch wheel it would accelerate blisteringly fast.

Edited October 29, 2022 by Slartibartfast

[Slartibartfast]

On 10/23/2022 at 3:51 AM, Planemo said:

• 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?

Yes, that is exactly what I am saying.

 

 

16 hours ago, Planemo said:

I found a good quote:

"Thrust is a force. When a force is applied over a distance, it does work. Work is the transfer of energy. The rate at which energy is transferred (i.e. - the rate at which work is done) is power. So you can convert back and forth between power and thrust by accounting for the rate at which distance is covered: Power is force times velocity, P= FV."

Umm, why don't we just call it "force" than? Seems we're introducing a different word with exactly the same meaning as force, or have I missed something: 🤷‍♂️

 

Edited October 29, 2022 by Slartibartfast

[Tawpie]

51 minutes ago, Slartibartfast said:

Umm, why don't we just call it "force" than?

(can't help it...)

May the force be with us

[NSFW]

10 hours ago, Paul A said:

If there are two identical motors:

One with a 10 (ten) inch wheel attached

One with a 1000 (thousand) inch wheel attached

Is the torque the same on both?

Will the smaller wheel accelerate faster?

There are a couple of missing parameters in the scenario, and I want to be explicit about them: let's postulate that the weight of both vehicles is the same, and the moment of inertia of both wheels is the same. Yes, there are real-world considerations that make that unlikely in practice, but the whole point of these kinds of thought experiments is to isolate variables so that we can understand the effects of changing a single parameter.

Consider a slightly different question: which vehicle would win a drag race?

They would cross the finish line at the same time. Because the power is the same, and the weight is the same, and the rest doesn't matter. 

That's why quarter-mile calculators like this one don't need to know engine torque or gear ratios: Quarter Mile Calculator - Good Calculators

[techyiam]

2 hours ago, Slartibartfast said:

Umm, why don't we just call it "force" than? Seems we're introducing a different word with exactly the same meaning as force, or have I missed something:

Weight is a force. Do you ask other people how much force they exert  on the ground vertically, or do you ask them how much they weigh?

Thrust is a force. It is a force that propels an object.

Although, both thrust and weight are forces, people don't use them interchangeably. 

[techyiam]

2 hours ago, Slartibartfast said:

That is still an open question. It seems most in this discussion believe it would but we don't have a concrete reason as to why.

Do you agree that if the tire is not on the ground, then there will be no thrust?

Additionally, do you agree that the thrust is equal to the friction force acting on the tread of the tire?

[Paul A]

https://www.carthrottle.com/post/how-does-wheel-size-affect-performance/

 

How does wheel size affect performance?

 

So, increasing your wheel size will decrease the driving force from your wheels which will culminate in a decrease in acceleration of said wheels.

To summarise, a car’s engine finds it more difficult to rotate larger wheels, making for a decrease in overall acceleration.

[Planemo]

5 hours ago, NSFW said:

That's why quarter-mile calculators like this one don't need to know engine torque or gear ratios: Quarter Mile Calculator - Good Calculators

I would postulate the calculator doesn't need to know torque because its already been catered for in the Power section of the calculator.

Power = torque x rpm / 5252

Dynos only ever measure torque and then calculate the power, depending on how quickly the load they apply is accelerated.

On a dyno, a bigger wheel will reduce the torque, hence power.

So yes, your calculator only needs (or indeed wants) to know power. Once the required trap speed is ascertained by the team it's then down to the car builder to get the car down to the weight required by the calculator and the mechanics to ensure that the power level is maintained throughout the run by using the correct gearing otherwise the engine drops out of it's max power rpm. It makes total sense that the calculator doesn't want to know about gearing, it's just giving raw figures about what power is required to move a weight a certain distance. The rest is down to the team.

[Slartibartfast]

11 hours ago, techyiam said:

Do you ask other people how much force they exert  on the ground vertically, or do you ask them how much they weigh?

I don't even know how to answer that, it seems an absurd question. What point are you trying to make?

 

11 hours ago, techyiam said:

Do you agree that if the tire is not on the ground, then there will be no thrust?

I struggle to follow your train but it seems your trying to lead me to say there wouldn't be; which is kind of ironic given that usually when one talks about "thrust" they are generally talking about a propulsive force that is not connected to the ground (such as a rocket or jet engine). As in the ThrustSSC (Thrust SuperSonic Car) which is a car that competed in the "propulsion" class of the Land Speed Record rather than the "wheel-driven" class because, well, it was a thrust propelled vehicle.

 

11 hours ago, techyiam said:

Additionally, do you agree that the thrust is equal to the friction force acting on the tread of the tire?

What on Earth are you asking? Yes, a "wheel-driven" vehicle requires traction.

I have to say though when you specifically invoke the word "thrust" it really makes me thing of "propulsion" vehicles (which don't really require traction). Setting that aside though, are you trying to say something about "equal and opposite reactions"?

[techyiam]

3 minutes ago, Slartibartfast said:

the word "thrust" it really makes me thing of "propulsion" vehicles (which don't really require traction).

In Physics, a force that propels an object is known as thrust. 

Both rockets and cars get their thrust from pushing against mass in the opposite direction of travel.

Since the mass of rocket fuel is so light compared to mass of the rocket, the mass has to be ejected at very velocities. On the other hand, because the mass of the earth is so much greater than the car, you won't be able to detect the movement of earth going in the opposite direction. 

In the case of the car, the car pushes against the earth via friction force made possible because of traction.

 

[Slartibartfast]

Sure, I get all that, but it's not like it's incorrect to say "a given amount of force is required to accelerate a vehicle".

If anything "thrust" is generally reserved for propulsion via expulsion of exhaust gas. In fact Ms Wiki actually describes "Thrust" as:

Quote

When a system expels or accelerates mass in one direction, the accelerated mass will cause a force of equal magnitude but opposite direction to be applied to that system.

I get it that you're saying "thrust" can be used to mean "pushing against the earth with traction" but it's a somewhat unusual usage of the term.

If you wish to keep using it then by all means knock yourself out, I'm just saying "force" was a perfectly fine term to use to begin with and to me "thrust" seems slightly out of context... but each to their own.

[techyiam]

14 minutes ago, Slartibartfast said:

If anything "thrust" is generally reserved for propulsion via expulsion of exhaust gas.

Nope. Wiki got it right, but you interpret it incorrectly. 

Wiki said "expel" or "accelerate mass".

The "expel" applies in the rocket case, and the "accelerate mass" applies in the car case.

19 minutes ago, Slartibartfast said:

If you wish to keep using it then by all means knock yourself out,

Then the same can applies to you. Hsiang and most layman would use the term torque to mean "perceived torque".

 

Now getting back on topic, you wanted to understand whether a smaller wheel with the same torque would allow the wheel to accelerate quicker.

So, do you agree that a friction force is acting on the tread of the tire when the wheel accelerates? 

[Slartibartfast]

2 minutes ago, techyiam said:

So, do you agree that a friction force is acting on the tread of the tire when the wheel accelerates? 

Sure.

[Paul A]

How wheel size affect the Acceleration

Untangle Club

29.4K subscribers

75,371 views

Premiered Feb 9, 2020

 

In this video, we have explained how does the wheel size affect the acceleration of the vehicle.

 

[techyiam]

4 minutes ago, Slartibartfast said:

Sure.

A force is a vector; it has both a magnitude and a direction. 

And hence, the friction force would have a direction, and its direction is tangential to the round tire. When a tangential force act on a moment arm, it will generate a torque about the axis of rotation. In our case, the moment arm is the wheel, with the length of the moment arm equal to the outer radius of the tire.

Torque is equal to force times the length of the moment arm.  Torque = Force x L

For the torque to be constant, if the moment arm becomes shorter, the tangential force has to increase.

Going back to our case, with  a smaller diameter wheel, the moment arm becomes shorter, and hence the tangential force, or friction force has to be greater. But the friction force is equal to thrust. Therefore, with greater thrust, the smaller wheel with the same torque will accelerate quicker. 

[Slartibartfast]

12 hours ago, Paul A said:

https://www.carthrottle.com/post/how-does-wheel-size-affect-performance/

 

How does wheel size affect performance?

 

So, increasing your wheel size will decrease the driving force from your wheels which will culminate in a decrease in acceleration of said wheels.

To summarise, a car’s engine finds it more difficult to rotate larger wheels, making for a decrease in overall acceleration.

Yes, I had read that article myself.

Sure it's true that changing the size of the wheels will change the final drive ratio, but that is all. If this change were accounted for by re-gearing another part of the drive train would that not "undo" the change?

So really, when the article is talking about swapping out 15" rims for 19" all it's really talking about is changing the drive ratios, right? I grant you gear ratios are important but when you say "a car’s engine finds it more difficult to rotate larger wheels" that is equivalent to saying "a car’s engine finds it more difficult to operate at a lower gear ratio", no?

I'm also curious as to how the 460:360 Newtons is calculated. By my thinking 15:19 is more 460:390. The article is probably right about it being 360 Newtons but I wish they would explain how.

 

By the way, it's interesting to note that that article makes a point of mentioning the engine is capable of producing 350 Nm of torque then goes on to discuss the force at the wheels as XXX Newtons for the different wheel sizes and doesn't mention torque (or Nm) again, implying that the torque stays the same. This was actually my original point in this thread, that is the diameter of the wheel doesn't actually change the amount of torque it has.

[Tawpie]

17 minutes ago, Slartibartfast said:

my original point in this thread, that is the diameter of the wheel doesn't actually change the amount of torque it has.

Ah. That is true. I was assuming that we cared about what was happening to the entire unicycle's ability to accelerate/climb, not just what's happening at the motor axel.

[techyiam]

13 minutes ago, Slartibartfast said:

that is the diameter of the wheel doesn't actually change the amount of torque it has.

True.

But to the layman, it would change the amount of "perceived torque", because the layman associates acceleration with "perceived torque", but what this person is really thinking is thrust.

 

For example, after driving a car, the driver comments: 

"Man, this thing has torque!"

Do you think the driver had measured the torque produced?

 

[Slartibartfast]

4 minutes ago, techyiam said:

For the torque to be constant, if the moment arm becomes shorter, the tangential force has to increase.

Going back to our case, with  a smaller diameter wheel, the moment arm becomes shorter, and hence the tangential force, or friction force has to be greater. But the friction force is equal to thrust. Therefore, with greater thrust, the smaller wheel with the same torque will accelerate quicker. 

Yes, I grant that a smaller wheel will produce more force at it's circumference (this I have now said several times myself). The thing I am not convinced of is that this extra force necessarily translates into greater acceleration. I know most others seem to think this step is a "no brainer" but this I actually don't see.

I am willing to be convinced but simply stating "more force = more acceleration" doesn't actually convince me. The main issue I have is how people are insistent of the fact that "bigger is slower" but if you believe that than you must also believe that "smaller is quicker", and that's the part that gets me. If you could just make smaller and smaller wheels and get more and more acceleration accordingly than why even make wheels as large as they are now? I mean, do we all think those e-skate boards would all burn us off the line given half a chance?

[techyiam]

11 minutes ago, Slartibartfast said:

The thing I am not convinced of is that this extra force necessarily translates into greater acceleration.

Would you agree that a greater force applied directly on the axle would accelerate the wheel quicker?