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I have been trying to design an offroad/all-terrain/rough terrain type vehicle for a story but i am split on what type of propulsion it uses.

The vehicle i envision is supposed to be able to race and (quite literally) jump across sand dunes (like one would encounter in the Desert) and still be able to climb rocky terrain while having armor comparable to a light/medium tank and being able to carry a gun on the back having a caliber anywhere between an LMG and a light AA Gun (20mm)

Wich would be best for such a vehicle? (and what would be the advantages one type has over the other?)

P.S. If it matters, the military using this vehicle heavily favors speed in combat (think blitzkrieg on steroids, even the heavy tanks reach speeds above 100km/h)

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  • $\begingroup$ "Best type of vehicle propulsion for rough terrain". Are you asking for an engine? $\endgroup$ – RonJohn Aug 15 at 21:18
  • $\begingroup$ Why not aircraft? $\endgroup$ – tuskiomi Aug 16 at 15:20
  • $\begingroup$ Do we ONLY need to account for sand and rocky terrain, or does this thing need to be able to handle swamp and woodland and all that other sort of stuff too? $\endgroup$ – Morris The Cat Aug 16 at 15:26
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It all depends on terrain type. My advice: pick your terrain type and find an human vehicle that operates in that terrain type.

Low Pressure Tires

Low pressure tires are fairly standard things. They're used on nearly all agricultural equipment and some unusual offroad vehicles such as the sherp. In my mind this is probably what you want.

Low pressure tires work really well on soft terrains. Similar to tank tracks, they help distribute the weight of the vehicle, helping it to "float" on mud, snow, sand. In general, the bigger the wheel, the better.

--edit--
Since the question now involves the military, you probably want tracks instead.
--end edit--
In fact, I've picked a vehicle for you: the Sherp. The sherp is a vehicle that can go just about anywhere and drive over just about anything. It's fuel efficient, spacious, and for all that - it's only 44HP. How can a vehicle with 44HP be so good: big tires.

However, the large rubber tires need to be in the operational range of rubber. So you're limited to temperatures between -40C and +80C or therabouts. Fine for earth. If you're on another planet, maybe not. If you're on earth and are looking to do an expedition across the middle of nowhere, well, that's what the Sherp was designed for.

Mars rover style

Mars rovers have what's known as rocker-bogie suspension and typically have thin metal wheels with spikes on them. There are many reasons for this. Rocker-bogie evenly distributes weight across all the tires. This means that it's less likely to get stuck on bumps. Metal tires have adequate grip on rocky/sandy surfaces, don't get punctures and a few other odds and ends.

However, a mars rover sucks at high speed. They suffer from picking up the front wheel in sharp corners, the suspension doesn't absorb any shock (it conforms to the surface, but in a static way rather than a dynamic way).

Mars rovers have motors in the hubs of the wheels. This means that the total energy output per wheel is quite small (If you had one motor six times bigger routed to all 6 wheels, a stuck wheel would get six times more power). This is unfeasible on a rocker-bogie suspension system. It's worth noting that having six small motors is better for redundancy.

Bear in mind that some of the decisions about mars rovers are to do with the spaceflight there: lightweight, surviving a vacuum etc.

I can't find any videos of mars-rover-like man carrying vehicles, so here's another fully articulated vehicle: https://www.youtube.com/watch?v=OXQZMmCvTEg

It isn't winning any contests unfortunately

Tank Tracks

Tank tracks are heavy, complex and have many moving parts. The places they excell are where the ground is soft. A tank track spreads the weight over the vehicle over square meters of terrain. This offers big advantages in mud, snow and similar surfaces. Tracks can be made from metal or have spikes/cleats to dig into hard materials. This is what makes them good for sno-cats which drive on ice.

However, tank tracks have issues with manouverability and energy loss. Moving a tank track takes a lot more energy than moving a wheel because it all has to flex and bend, and when you turn, that huge big contact area with the ground is now fighting your efforts to turn.

If your vehicle is light enough for low pressure tires, take those instead. Lower pressure tires are simpler, lower maintenance, and just about as good in terms of getting over things. If your vehicle needs 50 tonnes of Armour and maintain off-road capability, go with tracks. Just be aware that it'll impact your vehicles fuel efficiency a lot.

High Pressure Tires

Similar to low pressure tires. High pressure tires can carry heavier loads than low pressure tires, but they start to suffer from sinking in to to surface. However, they require less maintenance than tank tracks, and that's why they're used for high-payload mining trucks.

Legs

Legs are, strange. On humans they allow us to do everything from swim to crawl to walk. It seems like they'd be ideal on vehicles. Unfortunately making walking vehicles is hard. They tend to be slow, weak and not that great off road. They concentrate all their weight on really small points, so sink into most terrain. If you're only operating on rock, legs may be an option. They do have the cool factor!

Boats

Boats work well on the ocean. Like, really well. They suck on land though: https://www.youtube.com/watch?v=6Tp90AnMaos

Hovercraft

Unfortunately hovercraft generally suck(tm). They can't go up hills, they get stuck on small obstacles, they are noisy and consume a lot of power.

Others

Have a browse of http://www.unusuallocomotion.com/ to see just how strange the vehicles we can build are

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    $\begingroup$ LMAO -> "Boats work well on the ocean. Like, really well. They suck on land though." $\endgroup$ – Nosajimiki - Reinstate Monica Aug 15 at 18:57
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    $\begingroup$ @Nosajimiki Video proof added!!!!!! $\endgroup$ – sdfgeoff Aug 15 at 19:06
  • $\begingroup$ Re: Legs. This is BigDog from 2008. youtube.com/watch?v=W1czBcnX1Ww Boston Dynamics has been busy. It's certainly better than the six-leg design you posted. They now have one that can gallop much faster than a human. Load isn't going to be as big as a tracked vehicle. But, when they were firing a round they could likely brace against terrain. Humans do. $\endgroup$ – puppetsock reinstate Monica Aug 15 at 19:26
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Given your clarifications, I'll just simplify this and say go with tracks. Wheels don't do fast in sand very well because they they don't have much surface area. Instead of pushing against the terrain, they mostly just send the terrain flying backwards wasting lots of fuel and energy. Tracks however can distribute the force of the wheels much better maintaining traction.

Also, and they don't carry the weight of armor and heavy firepower as well. All that weight would push your wheels so deep into the sand that you'll just get stuck.

Since this is a military vehicle, the resilience of tracks when being shot at should also be a determining factor.

All this said, many tanks are beginning to go towards bullet proof wheels for better highway speeds and fuel efficiency than tracks, but this is mostly just because more and more fighting is being done in urban environments where roads are smooth, hard, and reliable. Tanks designed to fight in deserts, swamps, etc. still do better with tracks.

====

But there is a problem... the fastest production tank ever built maxed out at 82kph on good terrain; so, it probably still won't be hitting your 100kph desires on sand; so, you'll need to some up with something that does not really exist yet to get to 100+ kph.

If you don't mind delving into more exotic methods of transportation look at hydrofoil jet boats. Most hydrofoil warships can reach speeds of ~80-90kph with some newer ones like the W-18 Interceptor which tops out at 110kph. While boats "theoretically" suck on land, sand is a bit of a special medium. When bombarded with sonic waves, it acts a lot like water; so, a sand-boat could possibly be designed that shoots the sand ahead of it's hydrofoil with a sonic device liquifying the sand, then uses jet engines to let you ski over the sand-dunes like they are water at unnervingly fast speeds.

So your sand tank/boat/jet/somethings would basically look like this, but on sand:

enter image description here

I won't do rocky very well at all though; so, it will come down to the question of whether you are going for top speed or maximum versatility.

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  • $\begingroup$ I always loved those pictures. $\endgroup$ – Morris The Cat Aug 16 at 15:19
  • $\begingroup$ @sdfgeoff I believe the answer may actually be a boat... who knew... $\endgroup$ – Nosajimiki - Reinstate Monica Aug 16 at 15:27
  • $\begingroup$ Woah, sand hydrofoils. The future's going to be awesome. $\endgroup$ – sdfgeoff Aug 18 at 14:16
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This is Boston Dynamics BigDog. It's a 4-leg robot that can walk, run, climb stairs, gallop on a treadmill, and recover from being kicked in the side. One model is powered by a small engine about the size of a motorcycle engine.

This thing could be scaled up. It could have assist legs that got it standing when it was carrying a specially heavy load. It could have the ability to brace against terrain when firing a heavy gun. Top speed could be pretty fast over good surface. Maybe not as fast as a car, but faster than a tank-tread type vehicle. It could have a good range on a tank of fuel.

It could fairly easily be customized for different purposes. One with less armor, longer and wider-set legs, and room for passengers could be a personnel carrier. Heavy short legs might be a heavy equipment carrier. Stripped down to basics and long springy legs like those things that amputees use to compete in athletics, it could be a scout. Expandable feet might make it able to walk on quite soft ground. Conceivably it could be made amphibious. Maybe add water proofing and a snorkel. Give it some specialized probes and it's a mine sweeper or bomb sniffer. Give it some grippers and such, and it might climb quite steep cliffs.

Probably you would want to combine with a variety of other vehicles to cover the things that it has trouble with. For those exceptionally heavy loads you still want tank treads. When you get some good roads you probably want wheels. And when it absolutely positively has to get there as fast as possible you need something that can fly.

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  • $\begingroup$ I'm a fan of legs as an all-terrain option, but do you really think that they could go 100km/h and more in sand? $\endgroup$ – Ruther Rendommeleigh Aug 16 at 15:59
  • $\begingroup$ I don't think any surface vehicle can satisfy all the requirements on all possible surfaces. That's why I put in the paragraph about combining with other types of vehicles. $\endgroup$ – puppetsock reinstate Monica Aug 16 at 16:08
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Motorcycle with armored fairing.

You want desert and you want fast. You want to catch air. You want a motorcycle.

But you want armor. OK; give it an armored fairing.

Sportmax 1955

https://en.wikipedia.org/wiki/Motorcycle_fairing

Here is the sweet Sportmax from 1955. A fairing can be extended up over the driver to protect from dust and rocks. It is not going to protect from mines or shells like the armor on a tank but it will give a modicum of protection against bullets. The idea can be that your armored bike is so light and has such a small footprint it will not set off mines. Your driver can ask about shells and be advised to stay away from those.

A problem: will the driver be too busy driving to lay down fire? One could have a rider and a second rider as gunner but that gets crowded and ruins the aesthetic. I like the idea of a semiautonomous droid gunner on the cycle - sort of like R2D2 with a gun. It could be called Gun, or Gunny. Gunny can swivel its barrel thru a hemisphere of positions and - surprise - rotate down and shoot across under the cycle when events warrant. Exchanges between rider and Gunny would be fun to write!

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Low altitude aircraft or hybrid design

Driving a (real life) tank across rough terrain at full speed already takes a certain degree of skill. At the speeds you propose, keeping a land vehicle stable enough for the gunner to hit anything (and not crashing in the process) while going over rocks and steep hills seems like a tall order. No matter how low your center of gravity is, bumping into a rock at 100 km/h is going to ruin your day.

Also, the kind of suspension required for jumping is quite different from what you'd use on a vehicle that's designed to go fast. Oh, and neither your suspension nor your crew will react particularly well to the stress of 50 tons hitting the ground after a fall of several meters.

I'm not saying that it can't be done, but it sounds more like something a renowned stunt driver would attempt on television than an effective military tactic.

Legs might mitigate a lot of the issues, if your tech base is really mature, but they're not going to be efficient enough to handle your vehicle's mass and speed at the same time.

If speed is key, and terrain is an issue, you fly.

While current doctrine doesn't favor heavily armored aircraft, a 20mm gun and medium armor are well within the limits of what such a vehicle could carry. It would not be the most efficient in terms of maintenance cost and fuel consumption, but could extend its operational range by driving where terrain permits it, and lifting off only to engage or to cross difficult terrain. It would easily outmaneuver any land vehicle, though.

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If the terrain is soft but fairly smooth (like plowed fields, or forest floor), a tread -- possibly more like a tractor than a tank -- will get better traction and flotation.

If it's primarily an issue of bumps and unevenness, rolligons (see the Landmaster that's the best thing in Damnation Alley the 1970s movie) will do better; they'll also handle extreme soft (as in more liquid than solid) better than treads, and can act as paddle wheels if things are so soft your vehicle is floating. They can run faster than treads, can be steered like wheels (steering the entire rolligon assembly as if a single wheel), and tires can be changed much like conventional tire/wheel units (plus, if provision is made to lock the rolligon from rotating, they can run with a flat as if nothing was wrong).

If you can combine a rolligon with very wide, very soft tires (or driver-controlled variable pressure tires), you can probably get the best of both.

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