Thread: RE: [Algorithms] Car engine behaviour
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From: <ms...@co...> - 2006-04-26 23:37:44
|
I'm no expert on vehicle physics, but I find Brian Beckman's "The Physics of Racing" series to be be exceptionally helpful. http://phors.locost7.info/contents.htm -Michael -----Original Message----- From: gda...@li... [mailto:gda...@li...] On Behalf Of Madoc Evans Sent: Wednesday, April 26, 2006 4:24 PM To: gda...@li... Subject: [Algorithms] Car engine behaviour Hello everyone, I'm implementing some vehicle physics and I'm not sure how to simulate the behaviour of an engine. I'm completely ignorant in that I don't really understand the difference between horsepower and torque and how RPM affect engine power etc. What I've done so is translate engine revs into velocity of the tire tread which by means of friction induces movement, and viceversa, friction on the tires affects the wheel velocity which affects engine revs. Here I'm thinking that so far this is quite good but I'm missing the bit that determines how much feedback should be given by the wheel velocity, I have a scalar for this I can set between 0, giving the engine infinite power, and 1, giving the engine no power. I'm hoping that I can now procede by adjusting this value. I could probably fudge something up that behaves believably and I have some ideas but I would like to introduce values like horsepower and torque, and obviously vehicle mass, which also act as expected. I don't need the kind of accuracy that would allow me actually reproduce the behaviour real-world vehicles. Some pointers from someone with experience with this would be really nice. Even other issues like traction or perhaps things I haven't even considered yet. Thanks, Madoc ------------------------------------------------------- Using Tomcat but need to do more? Need to support web services, security? Get stuff done quickly with pre-integrated technology to make your job easier Download IBM WebSphere Application Server v.1.0.1 based on Apache Geronimo http://sel.as-us.falkag.net/sel?cmd=lnk&kid=120709&bid=263057&dat=121642 _______________________________________________ GDAlgorithms-list mailing list GDA...@li... https://lists.sourceforge.net/lists/listinfo/gdalgorithms-list Archives: http://sourceforge.net/mailarchive/forum.php?forum_id=6188 |
From: Madoc E. <tm...@ti...> - 2006-04-27 10:12:04
|
Hey guys, Thanks for all the replies (except for Tom's 'cos he's just bragging about his cars - another Brit boy racer :)). Damn, I've always wanted a skyline. So, most of the replies talk about advanced considerations that I would likely experiment with once I've got the basics in place. For the time being my problem is more basic. This isn't to say your replies were not useful, they have clarified a number of things and are great help. I'm at the prototyping stage for a game that still has a lot of development ahead of it. It is not a racing game, and as such I don't believe it will be subject to quite so much scrutiny but we want stats like HP and so on that reflect in the behaviour of the vehicle so that someone who knows his stuff won't say "this is c**p". I don't know if my original post did a very good job of explaining what my current setup is. No one has commented but I'm still inclined to think that my basic wheel-engine feedback setup is good. From what I can tell, it's pretty much exactly what Jon described without the RPM-dependant torque (which Tom seems to suggest that it could be mostly negligeable). The unfortunate result of it however is that high gears are not really much worse at accellerating from a stand- still than low gears, and in fact the feed-back from the wheels acts more as break limiting top-speed rather than accelleration. I can see that this might be a result of drag at higher velocities resulting in a greater shift in velocity at each integration step. Out of my ignorance, I'm thinking that this could be the lack of consideration of the vehicle's mass and momentum. Something along the lines of: accellerating a mass from 4 to 5 kph takes far more torque than accellerating it from 40 to 41 (bare with me for the simplication). But this isn't coming into play anywhere. When calculating wheel-engine feedback, I only consider the difference in velocity between what the engine revs "want" and what the actual wheel velocity is, and this difference tends to be greater at higher velocities. So, to narrow my most immediate problem down: How should I describe the fact that higher gears will have a harder time at accellerating at lower velocities while they fair pretty well at higher velocities? I get the idea that this is simple dynamics and I'm just being dumb by not just working it out but I don't feel confident with basing it on my own assumptions. I'll have too look at some dyno charts and see if I can generate some suitable curves or get away with some constants. I won't be simulating any real-world models and the vehicles will be subject to a lot of (probably unpredicted) variation. As for traction, I'm thinking the problem is similar to static vs dynamic friction which so far I've only confronted in terms of hard thresholding and contact forces which I guess isn't very suitable for this kind of simulation. From my experience with wheel spins and hard braking it seems almost right but hard thresholding is usually evil... Thanks again, Madoc |
From: david p. <da...@zo...> - 2006-04-27 10:48:39
|
Hi, The difference between acceleration from 5 to 6 kph or 50 to 51 kph is air friction (on earth, in vacuum there is no difference). Air friction is <velocity>^2*<front_surface>*<factor>. I hope that helps, DAVID Madoc Evans wrote: >Hey guys, > >Thanks for all the replies (except for Tom's 'cos he's just >bragging about his cars - another Brit boy racer :)). Damn, I've always >wanted a skyline. > >So, most of the replies talk about advanced >considerations that I would likely experiment with once I've got the >basics in place. For the time being my problem is more basic. This >isn't to say your replies were not useful, they have clarified a number >of things and are great help. I'm at the prototyping stage for a game >that still has a lot of development ahead of it. It is not a racing >game, and as such I don't believe it will be subject to quite so much >scrutiny but we want stats like HP and so on that reflect in the >behaviour of the vehicle so that someone who knows his stuff won't say >"this is c**p". > >I don't know if my original post did a very good job >of explaining what my current setup is. No one has commented but I'm >still inclined to think that my basic wheel-engine feedback setup is >good. From what I can tell, it's pretty much exactly what Jon described >without the RPM-dependant torque (which Tom seems to suggest that it >could be mostly negligeable). > >The unfortunate result of it however is >that high gears are not really much worse at accellerating from a stand- >still than low gears, and in fact the feed-back from the wheels acts >more as break limiting top-speed rather than accelleration. I can see >that this might be a result of drag at higher velocities resulting in a >greater shift in velocity at each integration step. > >Out of my >ignorance, I'm thinking that this could be the lack of consideration of >the vehicle's mass and momentum. Something along the lines of: >accellerating a mass from 4 to 5 kph takes far more torque than >accellerating it from 40 to 41 (bare with me for the simplication). But >this isn't coming into play anywhere. When calculating wheel-engine >feedback, I only consider the difference in velocity between what the >engine revs "want" and what the actual wheel velocity is, and this >difference tends to be greater at higher velocities. > >So, to narrow my >most immediate problem down: How should I describe the fact that higher >gears will have a harder time at accellerating at lower velocities >while they fair pretty well at higher velocities? I get the idea that >this is simple dynamics and I'm just being dumb by not just working it >out but I don't feel confident with basing it on my own assumptions. > > >I'll have too look at some dyno charts and see if I can generate some >suitable curves or get away with some constants. I won't be simulating >any real-world models and the vehicles will be subject to a lot of >(probably unpredicted) variation. > >As for traction, I'm thinking the >problem is similar to static vs dynamic friction which so far I've only >confronted in terms of hard thresholding and contact forces which I >guess isn't very suitable for this kind of simulation. From my >experience with wheel spins and hard braking it seems almost right but >hard thresholding is usually evil... > > >Thanks again, >Madoc > > > > >------------------------------------------------------- >Using Tomcat but need to do more? Need to support web services, security? >Get stuff done quickly with pre-integrated technology to make your job easier >Download IBM WebSphere Application Server v.1.0.1 based on Apache Geronimo >http://sel.as-us.falkag.net/sel?cmd=lnk&kid=120709&bid=263057&dat=121642 >_______________________________________________ >GDAlgorithms-list mailing list >GDA...@li... >https://lists.sourceforge.net/lists/listinfo/gdalgorithms-list >Archives: >http://sourceforge.net/mailarchive/forum.php?forum_id=6188 > > > > |
From: Willem de B. <wd...@mi...> - 2006-04-27 12:24:15
|
David Pangerl wrote: "The difference between acceleration from 5 to 6 kph or=20 50 to 51 kph is air friction (on earth, in vacuum there=20 is no difference). Air friction is=20 <velocity>^2*<front_surface>*<factor>." There are many air-resistance models; the one given above is just one of them. Graeme Harkness wrote: "In terms of pure dynamics, not considering aerodynamic drag,=20 it is just as easy to accelerate a car from 40 to 41 kph as=20 it is from 4 to 5 kph!! " This all gets very confusing. Yes, it is just as easy to accelerate a car from 40 to 41 as it is from 4 to 5, because (neglecting friction as a function of speed) it takes the same FORCE to do so given that the times in which the acceleration takes place remains constant.=20 However, in a typical car, accelerating from 4 to 5 takes less TORQUE than accelerating from 40 to 41 due to the (presumably) different gears one is in when doing so. (4 to 5 in first gear, 40 to 41 in second). This discrepency between torque and eventual force exerted at the wheels is a direct consequence of the number of teeth on a gear. ________________________________________ From: gda...@li... [mailto:gda...@li...] On Behalf Of david pangerl Sent: 27 April 2006 11:48 To: gda...@li... Subject: Re: [Algorithms] Car engine behaviour Hi, The difference between acceleration from 5 to 6 kph or 50 to 51 kph is air friction (on earth, in vacuum there is no difference). Air friction is <velocity>^2*<front_surface>*<factor>. I hope that helps, DAVID Madoc Evans wrote:=20 Hey guys, Thanks for all the replies (except for Tom's 'cos he's just=20 bragging about his cars - another Brit boy racer :)). Damn, I've always=20 wanted a skyline. So, most of the replies talk about advanced=20 considerations that I would likely experiment with once I've got the=20 basics in place. For the time being my problem is more basic. This=20 isn't to say your replies were not useful, they have clarified a number=20 of things and are great help. I'm at the prototyping stage for a game=20 that still has a lot of development ahead of it. It is not a racing=20 game, and as such I don't believe it will be subject to quite so much=20 scrutiny but we want stats like HP and so on that reflect in the=20 behaviour of the vehicle so that someone who knows his stuff won't say=20 "this is c**p". I don't know if my original post did a very good job=20 of explaining what my current setup is. No one has commented but I'm=20 still inclined to think that my basic wheel-engine feedback setup is=20 good. From what I can tell, it's pretty much exactly what Jon described=20 without the RPM-dependant torque (which Tom seems to suggest that it=20 could be mostly negligeable).=20 The unfortunate result of it however is=20 that high gears are not really much worse at accellerating from a stand- still than low gears, and in fact the feed-back from the wheels acts=20 more as break limiting top-speed rather than accelleration. I can see=20 that this might be a result of drag at higher velocities resulting in a=20 greater shift in velocity at each integration step. Out of my=20 ignorance, I'm thinking that this could be the lack of consideration of=20 the vehicle's mass and momentum. Something along the lines of:=20 accellerating a mass from 4 to 5 kph takes far more torque than=20 accellerating it from 40 to 41 (bare with me for the simplication). But=20 this isn't coming into play anywhere. When calculating wheel-engine=20 feedback, I only consider the difference in velocity between what the=20 engine revs "want" and what the actual wheel velocity is, and this=20 difference tends to be greater at higher velocities. So, to narrow my=20 most immediate problem down: How should I describe the fact that higher=20 gears will have a harder time at accellerating at lower velocities=20 while they fair pretty well at higher velocities? I get the idea that=20 this is simple dynamics and I'm just being dumb by not just working it=20 out but I don't feel confident with basing it on my own assumptions. I'll have too look at some dyno charts and see if I can generate some=20 suitable curves or get away with some constants. I won't be simulating=20 any real-world models and the vehicles will be subject to a lot of=20 (probably unpredicted) variation. As for traction, I'm thinking the=20 problem is similar to static vs dynamic friction which so far I've only=20 confronted in terms of hard thresholding and contact forces which I=20 guess isn't very suitable for this kind of simulation. From my=20 experience with wheel spins and hard braking it seems almost right but=20 hard thresholding is usually evil... Thanks again, Madoc ------------------------------------------------------- Using Tomcat but need to do more? Need to support web services, security? Get stuff done quickly with pre-integrated technology to make your job easier Download IBM WebSphere Application Server v.1.0.1 based on Apache Geronimo http://sel.as-us.falkag.net/sel?cmd=3Dlnk&kid=3D120709&bid=3D263057&dat=3D= 121642 _______________________________________________ GDAlgorithms-list mailing list GDA...@li... https://lists.sourceforge.net/lists/listinfo/gdalgorithms-list Archives: http://sourceforge.net/mailarchive/forum.php?forum_id=3D6188 =20 |
From: Graeme H. <alg...@ha...> - 2006-04-27 10:48:45
|
Madoc, > The unfortunate result of it however is > that high gears are not really much worse at accellerating from a stand- > still than low gears, and in fact the feed-back from the wheels acts > more as break limiting top-speed rather than accelleration. I can see > that this might be a result of drag at higher velocities resulting in a > greater shift in velocity at each integration step. You might be missing one important point. It's not the torque that accelerates the car, its the LINEAR force that is applied at the contact between the tyre and the road. These are related through the *effective* radius of the wheel (which is affected by the current gear ratio). Therefore, if you are in a high gear that has twice the gear ratio of first gear, then at 2000rpm (for example) you will be applying half the force at the wheel. This is why it is much easier to accelerate in low gears. Of course, as the speed of the car increases, aerodynamic drag *will* become important, but you probably don't need that in your code immediately. > Out of my > ignorance, I'm thinking that this could be the lack of consideration of > the vehicle's mass and momentum. Something along the lines of: > accellerating a mass from 4 to 5 kph takes far more torque than > accellerating it from 40 to 41 (bare with me for the simplication). I don't think this is true :-| In terms of pure dynamics, not considering aerodynamic drag, it is just as easy to accelerate a car from 40 to 41 kph as it is from 4 to 5 kph!! The laws of physics are the same in any inertial frame after all !! :-) The difference you want is related to the gears I think. Another thing you might need is that forces applied to the car wheels also cause a feedback to the engine (again through the gearbox). You might need that, but I've done plenty of simulations that just fudge that. > So, to narrow my > most immediate problem down: How should I describe the fact that higher > gears will have a harder time at accellerating at lower velocities > while they fair pretty well at higher velocities? I get the idea that > this is simple dynamics and I'm just being dumb by not just working it > out but I don't feel confident with basing it on my own assumptions. HTH, G |
From: Madoc E. <tm...@ti...> - 2006-04-27 12:35:15
|
This is built on top of my rigid body dynamics and so things like aerodynamic drag are implicitly present (and necessary). My vehicles are articulated bodies, wheels are rigid bodies constrained to the chassis in more or less complex ways depending on the vehicle. Wheel traction is based on collision with other surfaces (and here I think I might want to use a different friction model from what I normally use with rigid bodies). My model is based RPM * gear ratio * (differential * tire circumference) = tire tread velocity. This velocity (at this point in "world-space) is then compared to the velocity of the surface it makes contact with and through friction results in forces being applied to the wheel and the other body involved. This all works though my rigid body model, the basic difference being that I don't rely on the standard path for computing the tangential velocity and friction coefficient because I don't expect it to be accurate with the velocities involved. So, not only are these factors considered but they are also localised with notable precision. Gears are present (including reverse and neutral), there is a kind of clutch and RPMs do adjust themselves to the wheel RPMs when switching gears, partly as a function of the clutch behaviour and feedback from the wheels. Within this model, engine power is a function of how much the engine is able to resist the feedback from the wheels, again, much as Jon described. However, the implicit result of this is quite unlike what I observe in real-world vehicles, low gears are more effective up-hill and perhaps do accellerate more effectively than high gears but high gears are perfectly capable of accellerating at low speeds also. Feedback acts by limiting accelleration at high velocities more than at low velocities. Mathematically this make sense to me as a result of increased aerodynamic drag: an increasing difference between what the engine is trying to output and what it is actually achieving. This is not really noticeable unless I grossly underpower the engine, though. Now, if it is just as easy to accellerare from 4 to 5 kph as 40 to 41, then why can high gears do the latter and not the former? Even if it's not from a stand-still, accellerating in 5th gear from 20mph is not very effective, to the point that I don't think I've ever even attempted it, I expect that commonly the RPM would drop to the point of stalling. Basically, that's the question I'm trying to answer. If the momentum of the vehicle is not pertinent to the force required to accellerate, then why can I not accellerate from a stand-still in 4th gear unless I have a 1000hp or so car? Or how can a car accellerate at all in 4th gear if it can't at low speeds and there is no difference there? Thanks, Madoc ----Messaggio originale---- Da: alg...@ha... Data: 27- apr-2006 12.48 PM A: <gda...@li...> Ogg: Re: [Algorithms] Car engine behaviour Madoc, > The unfortunate result of it however is > that high gears are not really much worse at accellerating from a stand- > still than low gears, and in fact the feed-back from the wheels acts > more as break limiting top-speed rather than accelleration. I can see > that this might be a result of drag at higher velocities resulting in a > greater shift in velocity at each integration step. You might be missing one important point. It's not the torque that accelerates the car, its the LINEAR force that is applied at the contact between the tyre and the road. These are related through the *effective* radius of the wheel (which is affected by the current gear ratio). Therefore, if you are in a high gear that has twice the gear ratio of first gear, then at 2000rpm (for example) you will be applying half the force at the wheel. This is why it is much easier to accelerate in low gears. Of course, as the speed of the car increases, aerodynamic drag *will* become important, but you probably don't need that in your code immediately. > Out of my > ignorance, I'm thinking that this could be the lack of consideration of > the vehicle's mass and momentum. Something along the lines of: > accellerating a mass from 4 to 5 kph takes far more torque than > accellerating it from 40 to 41 (bare with me for the simplication). I don't think this is true :-| In terms of pure dynamics, not considering aerodynamic drag, it is just as easy to accelerate a car from 40 to 41 kph as it is from 4 to 5 kph!! The laws of physics are the same in any inertial frame after all !! :-) The difference you want is related to the gears I think. Another thing you might need is that forces applied to the car wheels also cause a feedback to the engine (again through the gearbox). You might need that, but I've done plenty of simulations that just fudge that. > So, to narrow my > most immediate problem down: How should I describe the fact that higher > gears will have a harder time at accellerating at lower velocities > while they fair pretty well at higher velocities? I get the idea that > this is simple dynamics and I'm just being dumb by not just working it > out but I don't feel confident with basing it on my own assumptions. HTH, G |
From: Robert D. <bli...@go...> - 2006-04-27 13:18:29
|
> Now, if it > is just as easy to accellerare from 4 to 5 kph as 40 to 41, then why > can high gears do the latter and not the former? Even if it's not from > a stand-still, accellerating in 5th gear from 20mph is not very > effective, to the point that I don't think I've ever even attempted it, > I expect that commonly the RPM would drop to the point of stalling. Take a look at a torque curve and you will see why. Put a car in 1st gear at 10 mph, and it may well require 2000rpm, which is certainly well into the part of the torque curve where you actually get some power, and probably quite a decent amount of it on most cars. Now put it in 5th gear and it would require 400rpm (it would on my car anyway) which is actually below the stall point for most petrol engines. There is no torque whatsoever at this level - in fact on my car there is no torque below about 1000rpm. You know that thing where Tom said about 10% variation in torque ? He was talking about the middle bit of the curve, the bit which you try to keep your engine in all the time. The bits outside that collapse to zero pretty quickly. Rob |
From: Graeme H. <alg...@ha...> - 2006-04-27 13:31:25
|
My point was that it takes no more FORCE to accelerate from 4-5 kph in 1second as it does to accelerate from 140-141 kph in 1 second. a =3D F/m has no dependence on speed in it! The key thing is that, because these two speed ranges will be done in very different gears (with very different gear ratios), the TORQUE required is very different!! Rob and Willem have said this already I guess :-) G |
From: Madoc E. <tm...@ti...> - 2006-04-27 13:46:14
|
Okay, this was my initial thought but what Tom said concerned because it seems to me that in my simulation high gears generally behave too well at low velocities and something else must be missing. My engine stalls < 800 rpm and goes up to 7000, I did try som non-linear RPM- torque relations but they didn't seem right. I guess at this point I'll try pluggin something like a real torque curve in and see what happens. Perhaps by tweaking some stuff I'll get good results. Discussing this has also cleared up my ideas about a number of issues. I'll let you know how it goes. Thanks for all the help, Madoc ---- Messaggio originale---- Da: bli...@go... Data: 27-apr-2006 3.17 PM A: <gda...@li...> Ogg: RE: [Algorithms] Car engine behaviour > Now, if it > is just as easy to accellerare from 4 to 5 kph as 40 to 41, then why > can high gears do the latter and not the former? Even if it's not from > a stand-still, accellerating in 5th gear from 20mph is not very > effective, to the point that I don't think I've ever even attempted it, > I expect that commonly the RPM would drop to the point of stalling. Take a look at a torque curve and you will see why. Put a car in 1st gear at 10 mph, and it may well require 2000rpm, which is certainly well into the part of the torque curve where you actually get some power, and probably quite a decent amount of it on most cars. Now put it in 5th gear and it would require 400rpm (it would on my car anyway) which is actually below the stall point for most petrol engines. There is no torque whatsoever at this level - in fact on my car there is no torque below about 1000rpm. You know that thing where Tom said about 10% variation in torque ? He was talking about the middle bit of the curve, the bit which you try to keep your engine in all the time. The bits outside that collapse to zero pretty quickly. Rob ------------------------------------------------------- Using Tomcat but need to do more? Need to support web services, security? Get stuff done quickly with pre-integrated technology to make your job easier Download IBM WebSphere Application Server v.1.0.1 based on Apache Geronimo http://sel.as-us.falkag.net/sel? cmd=lnk&kid=120709&bid=263057&dat=121642 _______________________________________________ GDAlgorithms-list mailing list GDA...@li... https://lists. sourceforge.net/lists/listinfo/gdalgorithms-list Archives: http: //sourceforge.net/mailarchive/forum.php?forum_id=6188 |
From: Willem de B. <wd...@mi...> - 2006-04-27 14:02:20
|
In the absence of any friction you may well find that it's possible to drive off from stand still in 4th gear.. -----Original Message----- From: gda...@li... [mailto:gda...@li...] On Behalf Of Madoc Evans Sent: 27 April 2006 14:46 To: gda...@li... Subject: RE: [Algorithms] Car engine behaviour Okay, this was my initial thought but what Tom said concerned because=20 it seems to me that in my simulation high gears generally behave too=20 well at low velocities and something else must be missing. My engine=20 stalls < 800 rpm and goes up to 7000, I did try som non-linear RPM- torque relations but they didn't seem right. I guess at this point=20 I'll try pluggin something like a real torque curve in and see what=20 happens. Perhaps by tweaking some stuff I'll get good results.=20 Discussing this has also cleared up my ideas about a number of issues.=20 I'll let you know how it goes. Thanks for all the help, Madoc ---- Messaggio originale---- Da: bli...@go... Data: 27-apr-2006=20 3.17 PM A: <gda...@li...> Ogg: RE:=20 [Algorithms] Car engine behaviour > Now, if it > is just as easy to=20 accellerare from 4 to 5 kph as 40 to 41, then why > can high gears do=20 the latter and not the former? Even if it's not from > a stand-still,=20 accellerating in 5th gear from 20mph is not very > effective, to the=20 point that I don't think I've ever even attempted it, > I expect that=20 commonly the RPM would drop to the point of stalling. Take a look at a=20 torque curve and you will see why. Put a car in 1st gear at 10 mph, and=20 it may well require 2000rpm, which is certainly well into the part of=20 the torque curve where you actually get some power, and probably quite=20 a decent amount of it on most cars. Now put it in 5th gear and it would=20 require 400rpm (it would on my car anyway) which is actually below the=20 stall point for most petrol engines. There is no torque whatsoever at=20 this level - in fact on my car there is no torque below about 1000rpm. You know that thing where Tom said about 10% variation in torque ? He=20 was talking about the middle bit of the curve, the bit which you try to keep your engine in all the time. The bits outside that collapse to=20 zero pretty quickly. Rob =20 ------------------------------------------------------- Using Tomcat=20 but need to do more? Need to support web services, security? Get stuff=20 done quickly with pre-integrated technology to make your job easier Download IBM WebSphere Application Server v.1.0.1 based on Apache=20 Geronimo http://sel.as-us.falkag.net/sel? cmd=3Dlnk&kid=3D120709&bid=3D263057&dat=3D121642 _______________________________________________ GDAlgorithms-list=20 mailing list GDA...@li... https://lists. sourceforge.net/lists/listinfo/gdalgorithms-list Archives: http: //sourceforge.net/mailarchive/forum.php?forum_id=3D6188 ------------------------------------------------------- Using Tomcat but need to do more? Need to support web services, security? Get stuff done quickly with pre-integrated technology to make your job easier Download IBM WebSphere Application Server v.1.0.1 based on Apache Geronimo http://sel.as-us.falkag.net/sel?cmd=3Dlnk&kid=3D120709&bid=3D263057&dat=3D= 121642 _______________________________________________ GDAlgorithms-list mailing list GDA...@li... https://lists.sourceforge.net/lists/listinfo/gdalgorithms-list Archives: http://sourceforge.net/mailarchive/forum.php?forum_id=3D6188 |
From: Graeme H. <alg...@ha...> - 2006-04-27 14:27:10
|
> In the absence of any friction you may well find that it's possible > to drive off from stand still in 4th gear.. Or a hill ;-) G |
From: Danny K. <dr...@we...> - 2006-04-27 14:47:27
|
>In the absence of any friction you may well find that it's possible to drive off from stand still in 4th gear.. I'd have thought in the absence of any friction you'd have a hard job starting in any gear (although I suppose your exhaust fumes might give you a little bit of jet propulsion). Danny |
From: Robert D. <bli...@go...> - 2006-04-27 14:17:18
|
You are dividing your torque down by the gear ratio aren't you ? > -----Original Message----- > From: gda...@li... [mailto:gdalgorithms- > lis...@li...] On Behalf Of Madoc Evans > Sent: 27 April 2006 14:46 > To: gda...@li... > Subject: RE: [Algorithms] Car engine behaviour > > > Okay, this was my initial thought but what Tom said concerned because > it seems to me that in my simulation high gears generally behave too > well at low velocities and something else must be missing. My engine > stalls < 800 rpm and goes up to 7000, I did try som non-linear RPM- > torque relations but they didn't seem right. > > I guess at this point > I'll try pluggin something like a real torque curve in and see what > happens. Perhaps by tweaking some stuff I'll get good results. > Discussing this has also cleared up my ideas about a number of issues. > I'll let you know how it goes. > > Thanks for all the help, > > Madoc > > > ---- > Messaggio originale---- > Da: bli...@go... > Data: 27-apr-2006 > 3.17 PM > A: <gda...@li...> > Ogg: RE: > [Algorithms] Car engine behaviour > > > Now, if it > > is just as easy to > accellerare from 4 to 5 kph as 40 to 41, then why > > can high gears do > the latter and not the former? Even if it's not from > > a stand-still, > accellerating in 5th gear from 20mph is not very > > effective, to the > point that I don't think I've ever even attempted it, > > I expect that > commonly the RPM would drop to the point of stalling. > > Take a look at a > torque curve and you will see why. > Put a car in 1st gear at 10 mph, and > it may well require 2000rpm, which is > certainly well into the part of > the torque curve where you actually get some > power, and probably quite > a decent amount of it on most cars. > Now put it in 5th gear and it would > require 400rpm (it would on my car > anyway) which is actually below the > stall point for most petrol engines. > There is no torque whatsoever at > this level - in fact on my car there is no > torque below about 1000rpm. > You know that thing where Tom said about 10% variation in torque ? > He > was talking about the middle bit of the curve, the bit which you try to > keep your engine in all the time. The bits outside that collapse to > zero > pretty quickly. > > Rob > > > > > ------------------------------------------------------- > Using Tomcat > but need to do more? Need to support web services, security? > Get stuff > done quickly with pre-integrated technology to make your job easier > Download IBM WebSphere Application Server v.1.0.1 based on Apache > Geronimo > http://sel.as-us.falkag.net/sel? > cmd=lnk&kid=120709&bid=263057&dat=121642 > _______________________________________________ > GDAlgorithms-list > mailing list > GDA...@li... > https://lists. > sourceforge.net/lists/listinfo/gdalgorithms-list > Archives: > http: > //sourceforge.net/mailarchive/forum.php?forum_id=6188 > > > > > > ------------------------------------------------------- > Using Tomcat but need to do more? Need to support web services, security? > Get stuff done quickly with pre-integrated technology to make your job > easier > Download IBM WebSphere Application Server v.1.0.1 based on Apache Geronimo > http://sel.as-us.falkag.net/sel?cmd=lnk&kid=120709&bid=263057&dat=121642 > _______________________________________________ > GDAlgorithms-list mailing list > GDA...@li... > https://lists.sourceforge.net/lists/listinfo/gdalgorithms-list > Archives: > http://sourceforge.net/mailarchive/forum.php?forum_id=6188 |
From: <c.s...@ph...> - 2006-04-27 14:24:30
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It's more like in the absence of any automatic transmission; if you're = careful with the cluth you can do it. -----Original Message----- From: gda...@li... = [mailto:gda...@li...] On Behalf Of = Willem de Boer Sent: Thursday, April 27, 2006 4:02 PM To: gda...@li... Subject: RE: [Algorithms] Car engine behaviour In the absence of any friction you may well find that it's possible to drive off from stand still in 4th gear.. -----Original Message----- From: gda...@li... [mailto:gda...@li...] On Behalf Of Madoc Evans Sent: 27 April 2006 14:46 To: gda...@li... Subject: RE: [Algorithms] Car engine behaviour Okay, this was my initial thought but what Tom said concerned because=20 it seems to me that in my simulation high gears generally behave too=20 well at low velocities and something else must be missing. My engine=20 stalls < 800 rpm and goes up to 7000, I did try som non-linear RPM- torque relations but they didn't seem right. I guess at this point=20 I'll try pluggin something like a real torque curve in and see what=20 happens. Perhaps by tweaking some stuff I'll get good results.=20 Discussing this has also cleared up my ideas about a number of issues.=20 I'll let you know how it goes. Thanks for all the help, Madoc ---- Messaggio originale---- Da: bli...@go... Data: 27-apr-2006=20 3.17 PM A: <gda...@li...> Ogg: RE:=20 [Algorithms] Car engine behaviour > Now, if it > is just as easy to=20 accellerare from 4 to 5 kph as 40 to 41, then why > can high gears do=20 the latter and not the former? Even if it's not from > a stand-still,=20 accellerating in 5th gear from 20mph is not very > effective, to the=20 point that I don't think I've ever even attempted it, > I expect that=20 commonly the RPM would drop to the point of stalling. Take a look at a=20 torque curve and you will see why. Put a car in 1st gear at 10 mph, and=20 it may well require 2000rpm, which is certainly well into the part of=20 the torque curve where you actually get some power, and probably quite=20 a decent amount of it on most cars. Now put it in 5th gear and it would=20 require 400rpm (it would on my car anyway) which is actually below the=20 stall point for most petrol engines. There is no torque whatsoever at=20 this level - in fact on my car there is no torque below about 1000rpm. You know that thing where Tom said about 10% variation in torque ? He=20 was talking about the middle bit of the curve, the bit which you try to keep your engine in all the time. The bits outside that collapse to=20 zero pretty quickly. Rob =20 ------------------------------------------------------- Using Tomcat=20 but need to do more? Need to support web services, security? Get stuff=20 done quickly with pre-integrated technology to make your job easier Download IBM WebSphere Application Server v.1.0.1 based on Apache=20 Geronimo http://sel.as-us.falkag.net/sel? cmd=3Dlnk&kid=3D120709&bid=3D263057&dat=3D121642 _______________________________________________ GDAlgorithms-list=20 mailing list GDA...@li... https://lists. sourceforge.net/lists/listinfo/gdalgorithms-list Archives: http: //sourceforge.net/mailarchive/forum.php?forum_id=3D6188 ------------------------------------------------------- Using Tomcat but need to do more? Need to support web services, security? Get stuff done quickly with pre-integrated technology to make your job easier Download IBM WebSphere Application Server v.1.0.1 based on Apache Geronimo http://sel.as-us.falkag.net/sel?cmd=3Dlnk&kid=3D120709&bid=3D263057&dat=3D= 121642 _______________________________________________ GDAlgorithms-list mailing list GDA...@li... https://lists.sourceforge.net/lists/listinfo/gdalgorithms-list Archives: http://sourceforge.net/mailarchive/forum.php?forum_id=3D6188 ------------------------------------------------------- Using Tomcat but need to do more? Need to support web services, = security? Get stuff done quickly with pre-integrated technology to make your job = easier Download IBM WebSphere Application Server v.1.0.1 based on Apache = Geronimo http://sel.as-us.falkag.net/sel?cmd=3Dk&kid=120709&bid&3057&dat=121642 _______________________________________________ GDAlgorithms-list mailing list GDA...@li... https://lists.sourceforge.net/lists/listinfo/gdalgorithms-list Archives: http://sourceforge.net/mailarchive/forum.php?forum_ida88 |
From: Madoc E. <tm...@ti...> - 2006-04-27 14:25:26
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Can anyone come up with a simple formula for an approximate torque curve given some basic input parmeters? I found this link: http: //lancet.mit.edu/motors/motors3.html which seems to suggest a linear relation between "stall torque" and "no load speed" but I'm not sure this is the kind of thing I need in my case. I'm not sure the terms are pertinent, even. Any magic approximations like the way we use exponentiation and Gaussians for so many things? Thanks, Madoc |
From: Tom F. <tom...@ee...> - 2006-04-28 08:35:30
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> I found this link: http: > //lancet.mit.edu/motors/motors3.html That's a DC electric motor. Totally different characteristics to a = piston engine! This one's quite good. By an _astonishing_ coincidence, their chosen modelling target is an R34 RB26DETT :-) http://www.welltall.com/ymc/discovery/car/shiftpt.html You know how I was saying most engines have fairly flat torque curves? = Well, this is what happens when you add a turbo - Mount Vesuvius appears on = your dyno chart. I did notice his approximation is pretty ropey in one fairly important respect - torque does not go in a straight line from zero at standstill = to peak. The official torque line there goes from 200NM@1500rpm to 400NM@4500rpm. That line doesn't go through the origin! Doing an image search for "torque curve" gives you a really good = selection of torque curve shapes. You can see that within the useful range, normally-aspirated cars are basically a rounded hump. I think I was on = the small side with 10% - maybe 30% or so. On the other hand, cars with = turbos do the Everest thing. TomF. > -----Original Message----- > From: gda...@li...=20 > [mailto:gda...@li...] On=20 > Behalf Of Madoc Evans > Sent: 27 April 2006 07:25 > To: gda...@li... > Subject: RE: [Algorithms] Car engine behaviour >=20 >=20 >=20 > Can anyone come up with a simple formula for an approximate torque=20 > curve given some basic input parmeters? I found this link: http: > //lancet.mit.edu/motors/motors3.html which seems to suggest a linear=20 > relation between "stall torque" and "no load speed" but I'm not sure=20 > this is the kind of thing I need in my case. I'm not sure the=20 > terms are=20 > pertinent, even. Any magic approximations like the way we use=20 > exponentiation and Gaussians for so many things? >=20 > Thanks, >=20 > Madoc >=20 >=20 > ------------------------------------------------------- > Using Tomcat but need to do more? Need to support web=20 > services, security? > Get stuff done quickly with pre-integrated technology to make=20 > your job easier > Download IBM WebSphere Application Server v.1.0.1 based on=20 > Apache Geronimo > http://sel.as-us.falkag.net/sel?cmd=3Dlnk&kid=3D120709&bid=3D263057& dat=3D121642 _______________________________________________ GDAlgorithms-list mailing list GDA...@li... https://lists.sourceforge.net/lists/listinfo/gdalgorithms-list Archives: http://sourceforge.net/mailarchive/forum.php?forum_id=3D6188 |
From: <epa...@ko...> - 2006-04-29 08:17:57
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Tom Forsyth wrote: > > Doing an image search for "torque curve" gives you a really good selection > of torque curve shapes. You can see that within the useful range, > normally-aspirated cars are basically a rounded hump. I think I was on the > small side with 10% - maybe 30% or so. On the other hand, cars with turbos > do the Everest thing. > An additional data point... For normal passenger cars or commercial vehicles (bus, truck etc) the vehicles with turbo might actually have very flat "torque curve" This is because the curve is not caused by the mechanics of the engine, but instead it is controlled by the electronics of the engine control unit (ECU). Manufactures also have available families of engines with different power output. Looking from the torque and power curves it very much looks like that the engines have just been limited to a specific maximum torque. It is of course a different thing with sports vehicles, although also there boost pressure limiters etc have been used. Eero |
From: Madoc E. <tm...@ti...> - 2006-04-28 13:09:01
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>That's a DC electric motor. Totally different characteristics to a piston >engine! Yeah, doh, I did notice that, eventually. No wonder it didn' really seem pertinent... That link does seem useful. Thanks. I did doo a google image search for torque cruves. The variety was a bit disorienting at first but I got an idea of the basic common shape. I made a vague approximation and it does add some realism but it didn't exactly solve my problems. Now I'm tearing everything up and building it again using what I've learned. I found this pdf which seems like a good overview of what's involved: www.etse.urv. es/EngInf/assig/si2/cardynamics.pdf Cheers, Madoc |