Torque topic

[Slartibartfast]

3 minutes ago, Planemo said:

You do indeed cover more ground with a bigger wheel for X amount of rotations. But that 'extra ground' isn't a free lunch.

I'm not saying you "get it for free". In fact I'm saying the exact opposite.

I'm saying more effort is required to cover the extra distance and the amount of extra effort is exactly proportional to that extra ground.

 

3 minutes ago, Planemo said:

No one (except you) has fallen into the trap of adding the extra variable you did (rpm). As soon as you add that you are venturing into talking about power (which we are not).

Sure. I just mention it because many think that a faster spinning motor produces more torque but I am saying that is not the case.

[Planemo]

1 minute ago, Slartibartfast said:

I'm saying more effort is required to cover the extra distance and the amount of extra effort is exactly proportional to that extra ground.

OK, so if more effort is required, wheres it coming from? And if there isn't any extra effort wheres the free extra ground coming from? Do you see where I'm going with this?

1 minute ago, Slartibartfast said:

Sure. I just mention it because many think that a faster spinning motor produces more torque but I am saying that is not the case.

I wasn't aware that anyone had mentioned anything about 'speed', 'rpm' or 'faster spinning motors' so I was a bit confused about why you brought it up. But fair enough.

[Slartibartfast]

52 minutes ago, Planemo said:

If you are not sure then I'm not sure of a better way of explaining it. But I will have a think and try.

The reason I am not sure is not because I don't understand what you're saying, it's because I am not convinced it would actually be slower. Can you also "guarantee" me that 1" wheel would accelerate faster, and a 1cm wheel even faster again? Other than you assuring me that "this is the case" I just don't see any reason for it.

 

52 minutes ago, Planemo said:

OK what is it then?

This is your example. I have no idea why you're so confident that a larger wheel will accelerate more slowly but if it does all I am telling you is that it's not because of a difference in torque. As I have said many times here already, the torque of the motor remains constant.

 

52 minutes ago, Planemo said:

I haven't calculated the reduction you mention but if you are talking about gearing the larger wheeled RC car to match that of the ungeared smaller wheeled RC car then yes, it would accelerate at the same speed (disregarding what would be quite substantial gearing losses for the sake of your example).

Again, I'm not even bringing RPM into the discussion because I have no doubt it will cloud matters even further. Torque measurements are completely devoid of an RPM variable whether it's an electric motor, IC engine or whatever you fancy so it's irrelevant to the discussion.

Well to save you the maths, yes 12:2 is the same as 6:1: 😅 (no offence intended)

Can I ask why it is that you believe offsetting a wheel diameter increase with gearing reduction would achieve the same result?

In my mind the only difference the gearing reduction would make would be to bring the RPM back to it's original range which it seems we both agree has no effect.

 

47 minutes ago, Planemo said:

OK, so if more effort is required, wheres it coming from? And if there isn't any extra effort wheres the free extra ground coming from? Do you see where I'm going with this?

Quite frankly, no. I'm saying the "extra effort" is directly proportional to the "extra ground". As in if you put in more effort you will cover more ground, if you don't wish to cover any extra ground you don't need to put in any extra effort.

If you want to put numbers to it I'm saying the same amount of "effort" is required to turn a 20" wheel 1° 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".

 

47 minutes ago, Planemo said:

I wasn't aware that anyone had mentioned anything about 'speed', 'rpm' or 'faster spinning motors' so I was a bit confused about why you brought it up. But fair enough.

The reason I mentioned it is because the only difference between a large and small wheel is the rate at which they spin and I thought I went to pains to explain that that doesn't make a difference. But perhaps I wasn't clear.

Edited October 21, 2022 by Slartibartfast

[jtm94]

If you take the same hub motor and increase the diameter it will now have less mechanical leverage. This would be referred to in the community as having less acceleration/torque/power. The same motor with a smaller diameter rim would have more mechanical leverage. Call it what you will this is just arguing semantics and not constructive in any way.

The bit about using a larger RC car tire and gearing it down means nothing because on an EUC you DO NOT have gears. The gear ratio is strictly tied to the hub diameter. If you increase the hub diameter to fit a 22in wheel we cannot just gear it down to perform the same, it will be more sluggish, it will accelerate worse at the same current draw, it will have a higher top speed.

[Slartibartfast]

41 minutes ago, jtm94 said:

If you take the same hub motor and increase the diameter it will now have less mechanical leverage. This would be referred to in the community as having less acceleration/torque/pow

The mechanical leverage at the end of the wheel is called "force" and is typically measured in Newtons. Torque, as is the entire topic if this thread, is frequently misunderstood. If you wish to continue to misunderstand it than by all means don't read the thread: 

41 minutes ago, jtm94 said:

Call it what you will this is just arguing semantics and not constructive in any way.

You can call it "arguing semantics" if you wish but these are "real" quantities we are talking about and sure if you inadvertently use the word "power" when you really mean "work" were not going to keel reach you or anything but to say it's all "not constructive in any way" is a bit disingenuous. If anything it sounds like you're in the "smaller wheels accelerate faster" camp and this is what were trying to understand.

Edited October 21, 2022 by Slartibartfast

[Tawpie]

If you want to go, you need 'thrust'. Learned that from the smart chicken in Chicken Run.

Edited October 21, 2022 by Tawpie

[techyiam]

35 minutes ago, Slartibartfast said:

If anything it sounds like you're in the "smaller wheels accelerate faster" camp and this is what were trying to understand.

How is the wheel torque converted to a propulsion force that accelerates the euc? Free body diagram, Newton's Third Law of motion, and friction force, perhaps? 

[Tawpie]

2 minutes ago, techyiam said:

How is the wheel torque converted to a propulsion force that accelerates the euc? Free body diagram, Newton's Third Law of motion, and friction force, perhaps? 

It's the magic of the round wheel... converts rotational force into linear force

[mrelwood]

5 hours ago, Slartibartfast said:

Oh dear, here we go...

If your aim is to educate people, you might want to think for a second about which kind of an attitude would yield the best results. It's really easy to come out as a Dick Knowitall, after which no-one will take you seriously anymore. On the other hand, if you really do know better, there shouldn't be much reason to throw a tantrum and attack others. Pushing others down is only needed when you're not tall enough yourself.

5 hours ago, Slartibartfast said:

'resigning'? I'm not sure what you mean.

Sorry, couldn't come to with a correct English word. I meant, to remove the distance from the equation.

5 hours ago, Slartibartfast said:

What? It stands for meters, as in newton-meters???

Exactly. And where does the meter in the Newton-meter come from if not from the distance?

5 hours ago, Slartibartfast said:

Of course I agree with how Wikipedia defines torque. I mean, that's what torque is!

I'll quote WikiPedia again:

"Torque is defined as the product of the magnitude of the force and the perpendicular distance of the line of action of a force from the axis of rotation."

So by WikiPedia, torque is defined with the distance included. But you said that:

4 hours ago, Slartibartfast said:

torque is a measure of rotational force that is independent of distance

 The SI unit of force is Newton. To get from Newton (N) to Newton-meter (Nm), you need to multiply the Newton (N) with a distance in meters (m) = Nm. Just like speed is distance (m) divided by time (s) = m/s. That was my point.

 

But the earlier comment on semantics could've been more right than any of us realized. From Wikipedia article on "Couple":

"The resultant moment of a couple is called a torque. This is not to be confused with the term torque as it is used in physics, where it is merely a synonym of moment. Instead, torque is a special case of moment. Torque has special properties that moment does not have, in particular the property of being independent of reference point, as described below."

"The moment of a force is only defined with respect to a certain point P (it is said to be the "moment about P") and, in general, when P is changed, the moment changes. However, the moment (torque) of a couple is independent of the reference point P: Any point will give the same moment."

 

It seems that the definition of torque that you use is this moment of a couple that is commonly used in US mechanical engineering, while others use the definition that is generally used in physics, moment of force, ie. magnitude of force multiplied by distance. Sound about right?

 

5 hours ago, Slartibartfast said:

"you don't know what you're talking about" which is simply replied with "yes I do".

I think so far you have been the only one accusing someone else of being wrong or not knowing what they're talking about.

Edited October 21, 2022 by mrelwood

[Eucner]

So much confusion about torque. I hope I'm not confusing even more.

• A BLDC motor torque is not constant. It has maximum value at stall and minimum value at maximum free spin speed.
• A bigger motor diameter will create more torque, because of greater distance from gap between stator and rotor to the center of motor.
• A bigger tire diameter will create less thrust force, because of greater distance from ground contact point to the center of motor.
• If tire diameter is constant, more torque gives better acceleration due to more thrust.
• Linear and rotational inertia opposites acceleration.

What happens if both motor and tire diameter gets bigger? If they get bigger in scale, the thrust force wouldn't be affected. Bigger diameters means more mass and moment of inertia. This leads to less acceleration.

[EUCzero]

7 hours ago, KiwiMark said:

I thought that the benefits of a larger tyre were the greater stability and the significantly better handling of surface imperfections in the road/path.  I doubt anyone thinks much about rolling resistance, wind drag or anything of that nature.

Obviously with cars/motorcycles/bicycles/etc there isn't much of a problem going with larger wheels, because you can adjust the gearing to compensate.  With an e-wheel it is different, we have the fantastic simplicity of a hub motor and no gearing required - but that means that we can't easily compensate for a larger wheel diameter.  Some sort of clever gearing system might fix that, but then we end up with something  complicated that can wear out and cause problems.

Gearing in an electrical motor is done by the number of magnets and poles used. So it is not gears, but how much movement you get per unit of force/power. Same as gearing.

[Slartibartfast]

15 minutes ago, mrelwood said:

If your aim is to educate people, you might want to think for a second about which kind of an attitude would yield the best results. It's really easy to come out as a Dick Knowitall, after which no-one will take you seriously anymore. On the other hand, if you really do know better, there shouldn't be much reason to throw a tantrum and attack others. Pushing others down is only needed when you're not tall enough yourself.

All right, my apologies. I was just getting exasperated by what seemed to be patronising questions.

 

29 minutes ago, mrelwood said:

Exactly. And where does the meter in the Newton-meter come from if not from the distance?

Of course the meter in Newton-meter is a measure of distance (just as the Newton is a measure of force).

As I have said above, when I say "torque is a measure that "normalises" (or "standardises") against a given length" what I mean is that once the torque of a motor has been calculated we don't actually care how long the arm was that was used to calculate it. It could have been calculated as 200N @ 500mm, 25N @ 4m or even 0.1N @ 1km, we really don't care. They all equate to 100Nm and there for have the same torque.

 

16 minutes ago, mrelwood said:

I'll quote WikiPedia again:

"Torque is defined as the product of the magnitude of the force and the perpendicular distance of the line of action of a force from the axis of rotation."

So by WikiPedia, torque is defined with the distance included. But you said that:

Yes, again, I know what torque is.

 

17 minutes ago, mrelwood said:

It seems that the definition of torque that you use is this moment of a couple that is commonly used in US mechanical engineering, while others use the definition that is generally used in physics, moment of force, ie. magnitude of force multiplied by distance. Sound about right?

No, I am referring to torque as Nm, as a regular physicist would.

 

1 hour ago, mrelwood said:

The SI unit of force is Newton. To get from Newton (N) to Newton-meter (Nm), you need to multiply the Newton (N) with a distance in meters (m) = Nm. Just like speed is distance (m) divided by time (s) = m/s. That was my point.

Yes, I know how torque is derived. I'm just saying once you know the torque you no longer care about the length used to calculate it, just like once you know the speed of a vehicle you no longer need to know how long it took to travel the distance over which it was measured. If you measured a vehicle taking 3s to traveling 12m you would say it's speed is 4m/s, you wouldn't say it's speed is 4m/s for 3s. Sure you did measure it's speed over 3 seconds but it's speed is independent of the amount of time it took to take the measurement –as in it's not like as if a vehicle measured as traveling 12m over 3s is any faster than a vehicle traveling 2m over 0.5s. They are both traveling at 4m/s and thus their speeds can be compared independent of how long it took to take the measurement. That is all  I meant.

I'm not sure what it is that you think I've misunderstood, and I keep trying to ask where you believe I've gone wrong because I really think we are talking about the exact same thing. Perhaps it was my use of the word "independent" when I said torque is a measure that can be used to compare rotational force regardless (ie. independent) of their length. What I meant by that is, if two motors are capable of producing the same amount of torque it's fair to say they have the same rotational force (regardless of the length from which the torque was calculated).

 

19 minutes ago, mrelwood said:

I think so far you have been the only one accusing someone else of being wrong or not knowing what they're talking about.

Not at all. The only thing I've been trying to get across is that the torque of a motor is independent of wheel size

True, I said what Hsiang explained in his video is incorrect, but that is the entire point of the discussion. I'm really not trying to accuse anyone else of not understanding, least of all you.

I do seem to find myself pushing back against you, but that's because you seem to keep thinking I have a different understanding of what torque is but I can assure you I don't, however you seem to keep trying to imply that I do, so I keep pushing back. To be clear though, I am not by any means trying to imply that you are wrong. In fact quite the opposite. I'm actually trying to say you are right and that we actually think the same thing!

 

Now back to the actual discussion, which is to say whether torque of a motor is independent of wheel size.
Now this is either the case, or it is not. I can't tell if you're agreeing with me on this or not but I'm starting to get the impression that you disagree, which surprises me. Are you able to clarify?

[Slartibartfast]

45 minutes ago, Eucner said:

So much confusion about torque. I hope I'm not confusing even more.

• A BLDC motor torque is not constant. It has maximum value at stall and minimum value at maximum free spin speed.
• A bigger motor diameter will create more torque, because of greater distance from gap between stator and rotor to the center of motor.
• A bigger tire diameter will create less thrust force, because of greater distance from ground contact point to the center of motor.
• If tire diameter is constant, more torque gives better acceleration due to more thrust.
• Linear and rotational inertia opposites acceleration.

What happens if both motor and tire diameter gets bigger? If they get bigger in scale, the thrust force wouldn't be affected. Bigger diameters means more mass and moment of inertia. This leads to less acceleration.

Very nice @Eucner. I totally agree with everything you say there.

Just to be clear when you say "Bigger diameters means more mass and moment of inertia. This leads to less acceleration." you are just talking about the inertia of the physical wheel itself resisting the acceleration, yeah. As in the inertia felt in a "free-spin" rather than a reluctance to accelerate the "payload" as such.

[Eucner]

3 minutes ago, Slartibartfast said:

Just to be clear when you say "Bigger diameters means more mass and moment of inertia. This leads to less acceleration." you are just talking about the inertia of the physical wheel itself resisting the acceleration, yeah.

Yes

[OldFartRides]

Glad we got that sorted. That’s the most excitement since that political discussion torqued some members right off the board.

[Planemo]

3 hours ago, Slartibartfast said:

Very nice @Eucner. I totally agree with everything you say there.

Just so we're clear does that mean you agree with his quote below (as I do), because if yes I think I am very close to explaining where this discussion has been going wrong (hurahh everyone says!)

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

[YCC]

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.

Edited October 21, 2022 by YCC

[Slartibartfast]

10 hours ago, Planemo said:

Just so we're clear does that mean you agree with his quote below (as I do), because if yes I think I am very close to explaining where this discussion has been going wrong (hurahh everyone says!)

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

Yes, indeed.

In fact I've said the exact same thing myself:

20 hours ago, Slartibartfast said:

Now it is fair to say that a given motor that produces a given amount of torque will result in more force (ie. newtons) when applied to a smaller arm than it will to a larger arm –which I think is what people are trying to say.

To which I had thought you had agreed.

However I then went on to say that that "extra force" is applied over a shorter distance and that the amount "shorter" was exactly the same as the amount of "extra" force that is applied, which essentially means we wind up in the same place... and I suspect this is where we stop agreeing: 

 

[Slartibartfast]

1 hour 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.

That is a very interesting question, and in the absence of anything else I would say they would have the same amount of torque. Of course the Mten4 is by Begode and the V8F is by Inmotion so there could be any number of other discrepancies between these two wheels but yes, if the motors are the same than the amount of torque they produce would likewise be the same.

Note I'm always dubious about the values manufacturers give when they state power values for wheels, not least because some quote "constant draw" and others "peek power" because these values are wildly different. Kingson's S22 for instance is listed as having a "Rated Power" of 3300W and a "Max Power" of 7500W, but I wouldn't be taking either of these values as gospel. They are of course useful as a general guide, I'm just saying always take such values with a pinch of salt: 

 

Another comparison worth considering would be Gotway's (now Begode's) MSX to their Monster V2. One has a 19" wheel while the other has 22", and these both use the exact same motor. As it is I happen to own both these wheels myself and I will confess that the MSX feels more "zippy" (especially when it comes to breaking) however I maintain that it's not because the MSX has more torque, it must be for other reasons. My best guess is it's because the Monster's peddles are kind of short and so far below the centre of the wheel that leaning back just doesn't have as much effect or something rather than exceeding the torque potential of the motor as such. I suspect if I had power pads on this Monster I would be able to extract a lot more performance out of her –which is a clear indication that I'm a long way from meeting it's torque limit.

[Eucner]

7 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.

Torque is a feature of the motor. Tire size is not directly related to it. It just restricts how big motor can be put inside it. Motor power has 2 components, torque and speed. Equal power motors can have different torque.

V8F has larger diameter motor with more torque than Mten4. Due to small tire size Mten4 has more thrust force accelerating you. Even thought both wheels are specified to have same power, V8F has actually little more.

[techyiam]

Regarding acceleration: torque vs power.

Consider two identical motorcycles except for gearing and motor characteristics. 

Bike A has 50 ft-lbs of torque and a redline of 5000 rpm.

Bike B has 25 ft-lbs of torque but a redline 10000 rpm.

The gearing of Bike B is such that when they are traveling at the same speed, the motor of Bike B is revving at twice the rpm as Bike A.

Which motorcycle will accelerate quicker if both can instantaneously run at full torque and at redline?

Even though Bike A has twice the torque, they both would accelerate equally as quick. Hence, if gearing is involved, power dictates acceleration, not torque. 

 

For BLDC motors, if motor current is not limited by the controller, the maximum power occurs roughly at 50% of the free spin speed. 

Hence, for acceleration, the 1000W motor, and the 11" wheel are important factors for the Mten4, since wheel size is equivalent to gearing.

 

[UniVehje]

7 hours ago, Slartibartfast said:

Another comparison worth considering would be Gotway's (now Begode's) MSX to their Monster V2. One has a 19" wheel while the other has 22", and these both use the exact same motor. As it is I happen to own both these wheels myself and I will confess that the MSX feels more "zippy" (especially when it comes to breaking) however I maintain that it's not because the MSX has more torque, it must be for other reasons. My best guess is it's because the Monster's peddles are kind of short and so far below the centre of the wheel that leaning back just doesn't have as much effect or something rather than exceeding the torque potential of the motor as such. I suspect if I had power pads on this Monster I would be able to extract a lot more performance out of her –which is a clear indication that I'm a long way from meeting it's torque limit.

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.

[Eucner]

32 minutes ago, techyiam said:

Even though Bike A has twice the torque, they both would accelerate equally as quick. Hence, if gearing is involved, power dictates acceleration, not torque.

Less torque would let bike B have a lighter engine and less rotational inertia. Due to a higher gear ratio the external inertia would also affect less to the bike B. High gear ratio is less efficient, so bike B would loose some torque here. All in all, I think bike B would accelerate slightly faster than bike A. 

[Planemo]

8 hours ago, Slartibartfast said:

Yes, indeed.

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...

The answer? We are both right. You're right in that its not due to torque, and I'm right in that with any given motor, putting it in a bigger wheel WILL make it accelerate slower, even disregarding the red herrings applied to EUC's such as pedal height, thrust angles etc.

At this point I will say that @techyiam got in before I did and therefore he gets the cigar. Some may say it confuses matters because it introduces gearing but the basic premise is correct.

The answer is indeed POWER and this is where I apologise and admit my error of deliberately trying to leave out of the discussion the one glaring point that would have cleared all this up some time back, and it only clicked when I started thinking about setting off from a dead stop on our big wheel vs small wheel euc's.

Power introduces a time element, rpm. The bigger wheel WILL accelerate more slowly, so its producing less work over time but with the same amount of torque, therefore its power is less.

Bigger wheels will ALWAYS accelerate more slowly given the same motor because of a reduction in power. Thats it.

Got there in the end!

 

[Eucner]

4 minutes ago, Planemo said:

Power introduces a time element, rpm. The bigger wheel WILL accelerate more slowly, so its producing less work over time but with the same amount of torque, therefore its power is less.

Bigger wheels will ALWAYS accelerate more slowly given the same motor because of a reduction in power. Thats it.

Less power is not the reason for less acceleration, both are outcomes from gear change.