I was thinking if bullet vehicle wrapper’s function “applyEngineForce()” takes input as N force insteas of Nm torque. If so, I need to know how to convert torque in Nm to force in N. Who can help me with this?
First off I need to know:
Does the function take in N or Nm?
If N than I must need to know how to convert Nm to N.
I think it’s time to recommend a first-year physics course at your local university (or an introduction to engineering course would be better). The further you go into simulation you go, the harder the maths becomes, and the more high-level thinking you need to be able to do. Looking at your sig, maybe get friendly with your physics teacher. They’ll love to work through the mechanics of a car with an interested pupil. (But beware the label ‘nerd’ from your friends)
It sounds like ‘applyEngineForce’ applies … a force. Forces are in Newtons. How is it applied to the vehicle? No idea, but it isn’t through the wheels. It probably just runs ‘applyForce’ on the cars body. I have not looked at the documentation or the source, so this is just a best guess based on what you said above.
How do you convert Nm into N?
Well, Nm stands for Newtons*meters. So to get from Nm to N, you divide by a distance. Apply some brainpower about where the force relates to torque, and you can figure out what distance it should be.
Well, I found the fact about distance when I typed Nm to N converter, lol, but I just can’t think of distance there. LOL, only relation to distance there I see is the circuit of tire. It is “wheelRadius” * math.pi. Is it the right distance:D
But if I divide torque by ~0.9, I will get even more force, lol:D
Think of a spanner. Where is the force, where is the torque? Draw a diagram. Now replace the spanner with a tire. Is the relevant distance the circumference? (Hint: it’s actually the radius, but please draw the diagrams, they’ll help you understand)
So let’s think about torque and distance. If I apply a torque to a beam, say 10Nm, it makes sense that this beam can support … 1kg at 1m or 10kg at 0.1m. Get out a board of wood and try it.A good rule of thumb for inventing formulae if you don’t know it is:
Make a fraction. On the top, put things that make the output bigger. On the bottom put things that make the output smaller.
Hm… I don’t get this thing. I don’t get also the spanner example. Could you draw a very small preview of how this all works?
Get a 30 centimeter ruler and an erasor.
Hold the ruler by one end, horizontally between your thumb and first finger.
Gravity will apply a force to the ruler, which your thumb/finger exterience as the ruler trying to rotate - essentially applying it as a torque.
Now take the erasor and put it on the ruler close to your fingers. How does this influence the torque?
Slide the erasor to the end of the ruler, away from your fingers. What happened to the torque on your fingers?
In this demonstration, the distance between the erasor and your fingers is the radius, the force is the mass of the erasor, and the torque is applied by your fingers.
OK! Thank’s for explanation. I use SI for everything, so it will be: N = Nm/m, but - it will make it out ~3 times higher. But I don’t think that I need it 3 times more force. It already feels a bit too powerful:D
Stupid question…but isnt an N an nm2,Since i can convert Metric to standard(meters to feet), wouldnt a N become a Slug. Sorry i dont know the abbreviation. Ill try it. but if I convert from metric(newtons) to standard(slugs), wouldnt the 9.8 squared turn into whatever a slug is. Somehow this converts to Ft/lb’s or m/kg…Sorry my head just exploded
Edit:
Sorry im taking physics and we convert weird things that I didnt even know converted, like volume to force. Its neat to do in bullet what we do in class. I didnt even know what a slug was before last week.
And as for the picture. Friction and damping has to come in somewhere. but I dont know exactly what those are as far as forces.
Seems I’m becoming a physics teacher! Anyway, let’s continue.
In the whole universe we know about, there are … 7 units. They are:
These are known as the SI base units, and are measured in (respectively):
Note that these aren’t true base units. With some clever use of the speed of light, planks constant and some other horrible rubbish you can get rid of some of them, but I won’t go there.
There are several rules to follow when working with these units:
So let’s figure out what energy is.
Normally we talk about it in joules, but some basic physics tells us that E = 1/2 mv^2
Because we’re not working with number here, only units, we can discard the half, and energy = m*v^2
Now we know that velocity is meters per second. So energy = m^3 / s^2
Now lets think abotu this. If I take a volume, and divide it by some time, uh, hang on. What? That is a warning: just because the units make sense doesn’t mean the physics is tangible/real. UNIT ANALYSIS CAN SHOW A FORMULA IS GARBAGE, BUT CANNOT PROVE IT IS CORRECT.
So let’s do one that’s more understandable.
You should know that acceleration is measured in … m/(s^2).
And lets’ take the formula a = (v^2)/r This happens to be the acceleration something experiences when travelling in a circle. Let’s see if we can prove that it makes physical sense.
Let’s stick in v = m/s (because velocity is measured in meters per second), and we know that radius is measured in meters. Thus we have:
a = (m/s)^2/m
Expand it:
a = (m^2)/(s^2 * m)
a = m/(s^2)
Hey! So obviously that formula is, at the very least, not too wrong.
So what can we use this for?
Straight up:
N = Nm/m
Yes, if you divide the meters away from torque (Nm), you end up with just the force.
N an nm2
Hmm, a newton equal to a newton-meter squared? A newton meter squared is a measure of pressure, there’s that extra m^2 in there. So unless I’m misreading nm2, nm2 does not equal n.
wouldnt a N become a Slug. Sorry i dont know the abbreviation. Ill try it. but if I convert from metric(newtons) to standard(slugs), wouldnt the 9.8 squared turn into whatever a slug is. Somehow this converts to Ft/lb’s or m/kg…Sorry my head just exploded
So conversion from metric to imperial uses dimensionless numbers. They’re simply ratios. So you can convert from a meter to a foot, or from a pound to a kilogram, but you cannot convert from a foot to a kilogram. Sorry if I’m stating the obvious here.
I think you may be getting mixed up here about gravity.
So gravity will accelerate an object downwards at 9.8m/s (here on earth).
This can simply be proven by the knowledge that the unit for a netwon is … a kilogram-meter per second. (F = m*g)
im taking physics and we convert weird things that I didnt even know converted, like volume to force.
I hope there are some factos in there that you didn’t mention. You can’t convert a volume straight to a force. A meter cubed does not push unless it has mass and is in a force field. (eg gravitational or electrical field)
Friction and damping
Friction and damping has to come in somewhere. but I dont know exactly what those are as far as forces.
I’ve simplified the diagram a lot. If I put every single force on there, I’d be there all day and the page would be a black smudge. If you have sensitive enough equipment, you’ll discover that … light exerts a measurable force on objects.
Damping is always friction, but friction is not always damping. So I’m just going to talk about friction.
Where is there friction? Everywhere:
There are plenty of other forces in the system to:
A final word on torque and unit analysis:
You never actually experience a torque: When you touch a spinnign rod your hand experiences a force. Where in a system is the torque? At the rotation point? no matter how small you make the shaft, when you touch it, you will experience a force. Torque is just a mathermatical contruct that is very useful for comparion.
Hope I gave you some interesting reading…
Come back tomorrow with some more questions.
I don’t think that I need it 3 times more force. It already feels a bit too powerful
You’re probably correct. In all the modelling we’ve been doing for your car system, we’ve assumed perfect efficiency in the transmission. In reality you lose up to about 3% energy per meshed-gear. So in your car’s gearbox where you have several meshing gears, and in the differential, you can easily lost 15% of your power. Take into acount friction in the bearings, and there goes even more. CVD’s in the front wheels (if it’s a front wheel drive) lose another percent or so, the alternator charging the battery takes a little.
Gradually, the energy get’s sucked away.
So the question is:
Well, we have a power / rpm graph for our motor. That doesn’t change. The motor still outputs that much power. But between it and the wheels, some gets lost. The easiest way to model this loss is to treat it as a constant loss (subtract a constant percent of your engine power) and a variable loss (subtract some factor of your velocity) from the engine power.
As to what those values are: good luck.
I’m getting a little tired, so I can’t remember exactly how efficiency applies to gearboxes, something about power equalling torque times rotational velocity. Draw some diagrams if you want to and try figure it out…
Welcome to the world of modeling. The more accurate you want a simulation, the more work it is. But you seem to be sticking at it, and I don’t mind answering the sorts of questions you’re asking.
Just a few closing words:
The material above comes largely from a first-year course I took two years ago, EMTH171. If you can understand it and use it, you’re well ahead of other people. (The modeling I’m doing now in a third-year course is so bizarre I can’t even visualize it. There’s some cool stuff there - though the math is pretty heavy lifting)
I may go through that lot tomorrow and add some diagrams or write out the formulae properly.
I’m also considering creating a resource ‘Math and physics for game developers’
If you can think of stuff I should to put in there, let me know.
I have a 0.7 transmission effiency multiplier already;)
CVD’s in the front wheels (if it’s a front wheel drive) lose another percent or so, the alternator charging the battery takes a little.
What are CVD?
Thank you! You’re actually helping me here to understand physics better!
What are CVD?
Sorry, wasn’t thinking straight when I wrote that, I was meaning Constant Velocity Joints.
Oh… OK! I see… Usually there is just one for car, right? How high power loss is there?
