Land Vehicles: General Overview & Discussion

27 Apr 2015 18:33 - 27 Apr 2015 18:56 #23126 by Algernon
So, what is the best way to do land vehicles?

I figure this is a good subject to kick off the new subforum as, off the top of my head, there are a number of ways of doing it, some of which I am familiar with, others I suspect could be highly effective but are outside of my experience. Here's what I know:

The most complete land vehicle in my collection is the Knight Industries 2000. There are some pics here (am going to move that thread over here) and it's in the cloud now too, if you want to play with it.

It runs on a YASim FDM with four gear for wheels, fitted with brakes and a parking brake, and, erm, a jet engine (because supposedly the KI2000 was turbine-powered). Because it's a fantasy vehicle, I concentrated on finding a realistic and workable real-world configuration based on its fictional specifications, and doesn't make it a good testbed for a real car powered by an internal combustion engine. Also, it doesn't cope with its 300mph top speed very well at all on aircraft suspension, but I don't know much about that and rarely have any success doing gear in YASim, so the chances are it could be improved by someone who knows what they're doing.

So, a YASim FDM not designed to take off can work quite well. I suspect JSB might do this quite well too, possibly better. Without an off-the-shelf dynamics model, we could experiment with the AI system, as this takes care of a few things for us, like collision awareness and the possibility for the vehicles to act autonomously as part of an AI scenario, unless an MP player takes control (this is how ships pretty much have to operate, and there are some advantages to doing it this way, but I suspect it would be a cumbersome way to do things in the first person). And then there is writing a brand new solution, which might not be an awful job...

My personal favourite of the methods I know about is the YASim alternative. I'd be tempted to try creating an FDM with a prop engine, if it can be made to rev freely enough to emulate a car engine (starting with what I presume is a monstrous diesel in a mobile military AA unit is probably a good thing here, in terms of power, RPM and rev-up/down times). I would then design a custom script which handles the transmission, and output power information to a pair of YASim thrusters positioned at the action point of each wheel, carrying out a rough approximation of power transmission in both forward and reverse (hence two thrusters each, one facing aft for reverse).

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27 Apr 2015 19:04 #23127 by Tomaskom
Replied by Tomaskom on topic Land Vehicles: General Overview & Discussion

(hence two thrusters each, one facing aft for reverse).

No need for this, one of the things I discovered when building the Nasal and YASim thruster-based parachute was that a thruster can operate with a negative thrust too ;)
I feel the YASim way is quite well explored, so I will stick to that for the start.

"There are no problems in the air. The only problem is hitting the ground."

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27 Apr 2015 19:24 #23128 by Algernon
Replied by Algernon on topic Land Vehicles: General Overview & Discussion

No need for this, one of the things I discovered when building the Nasal and YASim thruster-based parachute was that a thruster can operate with a negative thrust too ;)


Ah, good news! I was wondering whether it would work :) Ta.

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28 Apr 2015 16:00 #23148 by Tomaskom
Replied by Tomaskom on topic Land Vehicles: General Overview & Discussion
I had a brief look at the KI2000 FDM, and also the YASim Type-45, as both are not intended for flying. I was surprised to see the YASim solver exited after 0 iterations, computing just the CG and inertia tensor, giving some default values for everything else. This is probably on purpose, but I failed to notice anything unusual that would make it behave that way...
So far I guessed you simply make a semi-aircraft FDM with tiny wings, which could fly at extreme speeds never reached by the vehicle on the ground (like ~5000kts, which you would give to the solver for approach and cruise). The jet/prop engine would then be disabled and everything would be done by thrusters.

My question is, what does it mean for the FDM when the solver behaves this way (benefits over my original guess) and how do you achieve it?

"There are no problems in the air. The only problem is hitting the ground."

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28 Apr 2015 16:14 #23149 by Algernon
Replied by Algernon on topic Land Vehicles: General Overview & Discussion
Well, firstly, don't assume that anything is intentional in those two vehicles - they were both blind stabs in the dark based upon work by Detlef on floating and land-living vehicles, and mostly the result of trial and error experiments not properly worked through. They work more by luck than judgement, and especially with the YASim T45, slight changes send it spinning off into orbit.

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