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| Analysis of the Warthog *long with images* | |
| Posted By: Speedy | Date: 3/6/05 2:48 a.m. |
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A Thorough Examination of the Mechanical Aspects of the M12 Warthog LRV
First, I'd like to apologize for the MS Paint images, it's the best I could do without my copy of photoshop or time to download GIMP on dial-up. As an engineering student, I was immediately fascinated by the Warthog when I first got to drive it in March of 2002 (Has it been three years already?). Many people have made Lego models of the Hog, or compared it to the Peugeot Hoggar concept SUV. However, most people don't realize how inherently different the construction of the Warthog is from any vehicle of today. It's actually a very unique vehicle, centering mainly on the suspension and transmission. As a result of this, I've decided to write up my observations of the vehicle's structure, and present a few of my ideas about how it would all work. I based this little examination on various screenshots I've taken using the debug camera in Halo CE. Due to this, I've gone to Halo 2 to check up on the differences, and have determined they are all purely cosmetic, and do not effect the fundamental construction of the vehicle. The Chassis, Transmission, and Steering The suspension and chassis of the Warthog are where it differs from any modern vehicle. In short, it doesn't really have a chassis. Each wheel has its own separate suspension, and each of the 4 suspensions are identical. There is a large strut that extends out of the body of the Warthog, on the end of which is the wheel.
Given the fact that each wheel has its own separate axle, suspension, and complete housing, it would be extremely impractical to have a normal mechanical transmission.There would be a tremendous amount of power loss, as well as an uneven distribution of power as each of the four required transmissions (would be 2, but this is a four wheel drive vehicle.) ages and wears down differently. My theory for the solution to this transmission problem is electricity. Simply put, the Warthog's engine would act as an electrical generator, sending power to an electric motor mounted in the "pod" attached to the end of the strut. this would mean that to transmit power to the wheels, you would only need 2 wires: a positive and negative. Using this system, you also don't need to worry about having several gears for acceleration, which could explain why the Warthog never shifts. In order to have a reverse, all you've got to do is reverse the rotation of the magnets, which could be done by throwing a gear in between the engine and the electricity generator. That would literally be the entire mechanical extent of the transmission, which is very, very simple compared to most modern transmissions. Also mounted in the pod would be the brakes. The calipers would be secured against the wheel housing, allowing them to clamp down on the discs when needed.
The biggest difficulty with this pod-wheel system is the steering. I think the best method would be something similar to the electric motors powering the wheels.... a small motor that drains a bit of power from the engine to turn the wheels back and forth by rotating the "ball" of the ball and socket joint that the wheel is mounted with. However, it would also be possible to have a hydraulic steering system as well. The Suspension The suspension is where the Warthog's design really shines. Using the simple physical properties of leverage, the Warthog's entire suspension can be reduced to a mount for the strut (which would serve as the fulcrum) and a relatively low-strength spring. Since each strut/pod system is identical, I will only describe one. Note: you could use a lever where the spring and wheel are on the same side of the fulcrum, but this would mean you would have to cut out a hole in the body large enough to account for the up and down motion of the strut. With the fulcrum-centered lever used for this system, the hole only has to allow for several inches of travel. So, we'll make the Warthog's suspension a lever system. This will transfer the up and down forces of the wheels to a spring connected to the body of the Warthog. To maximize the efficiency of the spring, you would have to put the fulcrum (in this case, the point the suspension actually mounts to the body) as close to the wheel as possible, with the spring connecting to the strut as far from the mount as possible. With the system as such, the spring would have to exert less force to counter the up and down motion of the wheels. This is because the force transmitted in a lever is relative to the distance from the fulcrum, such that: F1*D1 = F2*D2 To put it in simpler terms for those who don't know physics, basically it works like this: You have a 100 pound girl and a 10,000 pound elephant standing on a very strong see-saw. If the Elephant is standing 1 foot from the fulcrum of the see-saw, and the girl is standing 100 feet from the fulcrum (Like I said, it's a strong see-saw.), their weights will actually balance out. This is roughly similar to how those scales at the doctor's office work. Thus, if you mount the spring the same distance from the fulcrum as the wheel, it will have to exert exactly the same amount of force in the opposite direction to balance the vehicle. If it's mounted twice as far, It only has to exert half the force, and so on. However, due to the appearance of the Warthog, I've decided the spring can only be positioned roughly the same distance away. Actually, the front struts enter the body directly in front of the two seats, and the rear struts directly behind. With the angle at which they go up, extending them just as far into the body would make a Marine's ride a bit uncomfortable. This can be fixed very simply by offsetting the spring's side of the strut a bit on the mount.
Also, since the mounts require no up or down travel, both front wheels and both rear wheels can actually share the same mount to swivel around, decreasing cost, and allowing you to make the body stronger by using the mounting rod to brace it. With the struts now offset to avoid spearing the driver, the Warthog's springs can now be mounted under the center console, which I would suspect would be very strong to prevent the cockpit from crushing closed in case of a head-on collision. Engine With the suspension settled, all we need to figure out now is were to fit the engine. There simply isn't room at the front of the vehicle, and the center console now houses the suspension. So where does all the power come from?
Right from under the turret, that's where. You may notice the bulge downard below the gunner's seat on the underbody. You may also notice the four holes that look like exhaust pipes. The biggest problem here is that even this space is kind of small, so I decided to do some analysis. Now think about it. The Bungie guys have mentioned before that the vehicle can only reach about 50 miles an hour in perfect conditions. It doesn't really need to go much faster considering the work it's used for anyway. To reach 50 miles an hour, even when accounting for power loss in generating electricity and converting it back to mechanical energy, you do not need very much energy. But instead of just saying it doesn't need much, I'm going to do some physics: First: the guess. I'm going to be realistic and say if the Warthog were real, it'd take about 10 seconds to reach a maximum speed of 50 miles per hour. This is also going to be a "perfect" system, meaning there's no loss of power between the engine and the wheels, and allows us to assume things like constant acceleration. Now, our givens: Our velocity is 50 mph (22 meters/second), it takes us 10 seconds to get there. The Warthog weights 3.25 tons (2954 kilos) according to the Halo 2 manual Alright, so we begin with Power = Work/time. Work is defined as Force*displacement, so we can redefine power as Power = Force * displacement/time Displacement/time = Velocity, so Power = Force * Velocity Since we gave the Hog a 0-50 time of 8 seconds, we can use Force = mass * acceleration to get: Force = 2954 kg * 22 m/s / 8s = 8123.5 Newtons (kgm/s/s) Thus, Power = 8123.5 Netwons * 22 m/s = 178717 Watts Now, 1 Horsepower is roughly 750 Watts, so converting that, we get 238.3 Horsepower needed at the wheels to reach 50 mph in 10 seconds We'll give it some leeway, and estimate that we lose about 30% of the horsepower between the engine and the wheels (modern mechanical transmissions lose about 15%, so this is a very conservative estimate). This gives us 310 horsepower required at the engine. Now the question is, can you fit a 310 horsepower engine in that space? It would be a bit of a feat today, but it's been done. Giving us 500 years of a benefit of a doubt, it's very easy to see a normal internal combustion engine as the power source for the Hog. And that's about it, hope you enjoyed it. | |
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