Steampunk assault walker

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Steampunk assault walker

Unread post by John73 » Sat May 02, 2020 6:12 am

So I thought I'd share what I've been doing while stuck indoors.

It's a steam-powered assault walker called the Armadillo.

2:44 full simulation

2 heavy cannons on the turret.
4 Gatling guns with overlapping areas of fire.
Water and fuel (oil) are stored in the middle section, this ensures that as they're used the weight distribution doesn't change.
Monotube flash boiler feeding a 4 cylinder double-acting compound steam engine.

In the forward section, 1 commander and 1 driver/navigator.
In the main turret, 1 target spotter, responsible for aiming and firing, and 1 to reload the cannons.
4 gunners for the Gatlings.
1 engineer in the rear section, who controls the engine speed and boiler.
A small squad (6 or 8) of infantry who can deploy from the forward ramp.

Details, for those interested:
The boiler:

Steam is generated in a monotube flash boiler. This consists of a single tube (hence the name) which is coiled around and around. Water is pumped into one end, and superheated steam comes out the other. The outer shell and inner flue are formed by welding each coil to the one before it to form a solid wall. Incoming water is flows through the shell first to preheat it before it enters the internal coils where boiling and superheating take place.

A blower forces air and a spray of oil into the toroidal combustion chamber at the top. They enter on a tangent, which causes turbulent swirling within the chamber. This promotes air/fuel mixing for more efficient combustion.

The engine:

This is a 4-cylinder, double acting engine. High-pressure steam from the boiler enters cylinders 2 and 3 and expands part way. The steam then flows into cylinders 1 and 4, which have a larger diameter so they can produce the same torque from the lower pressure steam. The steam is expanded the rest of the way in the larger cylinders before being exhausted. This is called compounding, and was used on some larger steam locomotives and most ships. Many large ships had 3 or even 4 stages of expansion. The engine needs to be a little larger for the same power output, but it significantly reduces the amount of steam needed (meaning a smaller boiler and less fuel consumed).

There is a 3:1 gear reduction between the engine and the main shaft and a further 4:1 reduction between the shaft and each leg crank, for an overall 12:1 reduction and corresponding torque multiplication.

It's not fast, but it isn't meant to be. It's supposed to move along with and be supported by infantry units, so high speeds aren't as important.

Low-pressure exhaust steam leaving the engine goes into a small turbine (copper-colored part at the center). This is similar to the turbocharger on a car. The exhaust steam spins the turbine, which drives the blower that forces air into the combustion chamber. As the engine demands more steam, the blower delivers more air. An airflow sensor (basically a metal flap that moves according to how fast the air is going past) adjusts the amount of oil going to the burner accordingly. This automatic setup works pretty well, but the engineer still makes small adjustments to maximize power and efficiency.

After leaving the turbine, the steam is now at atmospheric pressure. It goes into the two large rectangular heat exchangers. Air comes in through a vent in the roof and absorbs the residual heat in the exhaust steam. This isn't a full condenser like you'd find on a ship -- it can't dissipate nearly enough heat, so the majority of the steam ends up escaping up the stack. However some of the steam does condense, and the water drains back into the feedwater system. The preheated air is pulled from the exchangers into the blower.

Mobility and Steering:

Of the 6 legs, there will always be 3 on the ground: the front and back legs on one side and the middle leg on the opposite side. Think of it like 2 alternating tripods, for a very stable footing.

The main chassis has 2 articulation points for steering. The legs also help with steering:

The lower black part is the leg crank, which is driven by the engine. This can be seen in action in the engine video above. The upper black part is the pivot slider. This moves up and down on hydraulic pistons and determines the leg's pivot point, which controls the length of the stride. If the slider moves down toward the crank, it increases the angular swing of the leg (since the effective lever arm is shorter) and makes it take a longer step. If the slider moves up, the leg takes a shorter step. The bottom section of the leg (slightly less transparent, with the black foot attached to it) also telescopes in and out. This can be seen in the first video by looking closely when the Armadillo turns. The telescoping leg section allows even more flexibility in the step length. It also allows the whole vehicle to "kneel" (like some buses) when opening the forward ramp.

The drive shafts and axles have no differentials like in a car; the legs have to stay synchronized at all times. So to steer, we instead use the pivot slider and the telescopic action in tandem. Legs on the outside of a turn telescope out and their sliders move downward to take longer steps. Meanwhile those on the inside contract and take a shorter step. So even though all legs are taking the same number of steps per minute, one side is effectively walking slower than the other. In combination with the articulation, this allows very tight turns while minimizing the amount that the feet would need to drag across the ground.

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