RE: [Algorithms] Car engine behaviour

 RE: [Algorithms] Car engine behaviour From: Tom Forsyth - 2006-04-27 08:20:25 ```Oh, you mean accellerate _from stationary_. Yeah, that makes more sense. Even a little deuce coupe is only burning rubber in fourth _while = moving_. TomF. -----Original Message----- From: gdalgorithms-list-admin@... [mailto:gdalgorithms-list-admin@...] On Behalf Of = david pangerl Sent: 27 April 2006 00:34 To: gdalgorithms-list@... Subject: Re: [Algorithms] Car engine behaviour Hi, In real life with a "normal car" you need to shift into 1st gear and = release the clutch very carefully to start moving without stalling. But with a = 1337 car (@Tom) or in a game you can do just about anything :D Cheers, DAVID Tom Forsyth wrote:=20 If you do your gear ratio and power distribution from engine to the wheels right you should not be able to accelerate in gears higher than 3rd (with a normal car). =20 Er... what? I think you need to have a talk to Brian Wilson: And comin' off the line when the light turns green Well she blows 'em outta the water like you never seen I get pushed out of shape and it's hard to steer When I get rubber in all four gears TomF. -----Original Message----- From: gdalgorithms-list-admin@... [mailto:gdalgorithms-list-admin@...] On Behalf Of = david pangerl Sent: 26 April 2006 23:21 To: gdalgorithms-list@... Subject: Re: [Algorithms] Car engine behaviour Hi, On more add :) Be carefully when shifting gears; you need to adjust the engine RPM to = the wheel(s) RPM with the new gear ration before applying the torque from = the new gear otherwise your car will jump on gear shift. I managed this with a simulated clutch. I release the engine connection = to the wheels, shift the gear and in interpolate the current engine RPM into wheel RPM * new gear ratio and connect the engine again = (aka release the clutch). Here is also a perfect place to put in a "shift = gear" sound :) If you do your gear ratio and power distribution from engine to the = wheels right you should not be able to accelerate in gears higher than 3rd = (with a normal car). Cheers, DAVID Tom Forsyth wrote:=20 To add to this - the torque of a normally-aspirated engine (without = turbo- or super-charger) is moderately constant (pus or minus about 10%) = throughout the usable rev range, which is typically around 2000rpm to 7000rpm (revoloutions per minute) for most normal petrol road cars. If it's a diesel, more like 1500 to 5000. Well-made lightweight sport engines can = rev higher up to numbers like 9000rpm, and the F1 cars rev to something nuts like 19000rpm. But still fairly flat torque all the way through. Turbos add some wacky stuff to engine dynamics, and what they do depends massively on what size turbo relative to engine size, what the setup is = and suchlike. On most well-set-up road cars with turbos, they start helping around 3500-4000rpm (below that they actually steal a bit of power!), = and it's basically a linear amount of torque boost up to redline. But it's = so dependent on your setup that it's hard to generalise too much. I believe superchargers are far more predictable, but whether it's a = fixed amount of torque or rev-dependent, I'm not sure. Never owned a = supercharged car. The final aspect is gearing. Typically, each gear is a constant = multiplier over the previous one. So if second is 1.5x of first, then third with be 1.5x over second, and fourth will be 1.5x over third, etc. This means = that when you change up at maximum save revs ("redline"), you will always = land at the same lower rev speed, which ideally is the start of the power band = for your engine. For example, whatever gear you are in, if you change up at 7000rpm, you will be at 4000rpm - or whatever the numbers are. Racing drivers vary their gear ratios so that certain corners are taken right in the power range for certain gears. But road cars generally = don't do this - they stick with a fairly even ratio between successive gears. The usual exception is top gear, which is often much "taller" than the rest = to give good motorway fuel consumption figures. Also on 4x4s, first gear is often much shorter to give better traction on rough terrain, and in = things like old Landrovers you pretty much ignore first when on the road and = pull away in second. Obviously this is all a gross generalisation, but if you're simulating a = car in any finer detail than this, then you need to go and find some real = car mechanics and they'll tell you the truth, rather than this load of old cobbler's. Obviously real car nuts will kill me for these gross simplifications, but I've got a Seven and they don't, so stuff 'em :-) TomF. =20 -----Original Message----- From: gdalgorithms-list-admin@...=20 [mailto:gdalgorithms-list-admin@...] On=20 Behalf Of Jon Watte Sent: 26 April 2006 17:37 To: gdalgorithms-list@... Subject: Re: [Algorithms] Car engine behaviour I'd like to add that when simulating, you can break this down=20 into a few=20 simple steps: 1) Decide what velocity the user controls mean that the wheel should=20 spin at. (This is a cheat, as the throttle really just lets=20 more gas/air=20 mix into the engine...) 2) Measure the spin of the wheels, and divide by the differential and=20 gearbox ratios to get the engine RPM. Look up the maximum=20 engine torque=20 based on this RPM and your engine model. 3) Apply torque or counter-torque to get them spinning at=20 that speed, up=20 to the maximum torque for whatever the current RPM of the=20 engine is. If=20 you want to slow down, you may use a lower torque max, because the=20 engine isn't actively working against the rotation, just=20 rotating slower=20 through friction. Note that this will work right even when the drive wheel(s) is/are=20 spinning, i e, you're doing a burnout. The wheels will spin=20 faster, the=20 RPM will go up. The actual movement of the car comes from the friction model=20 between the=20 tire collision and the road, and is not directly a result of=20 the engine=20 spinning the wheel. Cheers, / h+ Dan Glastonbury wrote: =20 On 4/27/06, *Madoc Evans* > wrote: =20 I'm implementing=20 =20 some vehicle physics and I'm not =20 sure how to simulate the behaviour of an engine. I'm completely ignorant in that I don't really understand the=20 =20 difference between =20 horsepower and torque and how RPM affect engine power etc.=20 To paraphrase from http://www.overboost.com ;: =20 ------------------------------------------------------- Using Tomcat but need to do more? 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