Modular Vehicles

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Since the Power Cube is interchangable, it makes sense that the rest of the vehicle should be interchangable too.

Kit In Progress

Unsuspended Rotor. This design is largely based on the industry standard for connecting wheels to skid-loaders. As illustrated by Flaviano Crespi. The tube would have a bearing at each end supporting the rotor. The main unit could be mounted in any orientation using the two orthogonal and identical mounting plates. The adapter plate would go on the opposite side of whatever surface the main unit is mounted on and four bolts would create a strong connection to the vehicle frame. The adapter plate itself would be identical to the mounting plates on the main unit, except that it would have studs welded to it in the correct arrangement to mount the rotational power source (hydraulic motor, electric motor, universal joint, etc).

Suspended Rotor. This design is structurally similar to the unsuspended rotor, but with differences that allow it to move at the end of some sort of suspension system. Again, the two mounting plates are identical and the tube contains two bearings and a rotor shaft. This rotor design would probably be modified for higher rpms since a suspension most likely means greater speed. The adapter plate would again be sized for the particular motor being fitted, but in this case the studs would mount it to the rotor.

I'm referring to this ideas as the CabCube. Basically, it would be a crash cage shrunk down to just big enough for a single person to fit inside. By adding "walls" it would be impervious to the weather. Thus, this modular unit would be responsible for keeping one person "safe, dry and warm." The most significant benefit of this approach is that we only have to verify the safety of one frame. By reusing this frame on every vehicle we know that the person is safe without having to build a cab into each vehicle and then test it individually. Additionally, the CabCube is being designed to be physically interchangeable between different vehicles. So, you might drive to work in your OSE car, then use the tractor to lift the CabCube off the car, put it on the tractor, sit inside it to drive the tractor all day, then put it back on the car and drive home. Something along those lines.

Modularity Concept

The decision to make something modular is simple enough. What's hard is figuring out how small to make the individual subsystems.

For example, two straight forward ways of breaking up a series of vehicles into standardized parts are presented below. One system takes the vehicle down to individual wheel units while the other simplifies the vehicle into axle (two wheels side by side) units.

Modular vehicle wheel units concept.jpg
Modular vehicle axle units concept.jpg

Modularity absolutely requires pre-defined, rigidly enforced standards. Modularity doesn't mean choice of any feature. Instead, it means carefully selecting combinations of pre-defined features. Each pre-defined feature does one thing really well. It also must be designed such that it has an interface that overlaps with one or more other units. Combining features via their overlapping interfaces allows the bridging from one small mission to another small mission. The amalgamation of all the small missions results in the accomplishment of the overall mission.

For example, a suspension/drive (drision?) unit only applies force to the ground. A frame unit only supports the vehicle components. A cab only houses the vehicle driver. Different versions of each category, with common interfaces, allows "new" vehicles to be created out of a set of components. A dual-wishbone suspension/drive unit, combined with an medium-duty frame, combined with a passenger cab would create a sedan. The same thing, but with a box cab, would create a van.

It is important not to combine the frame and cab into one "modular" unit. The missions are sufficiently different that making one unit do both jobs results in a unit that can only do one thing. In the same way, don't combine the suspension/drive unit and the frame. Being able to change out only the cab is too limiting.

A good compromise for designing 3-dimensional modular systems is to start with a 1-dimensional or 2-dimensional unit and then go up or out, rather than start with a 3-dimensional shape. This is the abstract version of the "don't combine the frame and cab" rule above. Mostly, this rule is the result of two facts, 1) gravity dictates that pretty much everything can be simplified into "the ground plane" and "up/down," 2) stock materials tend to be 1-dimensional more often then they are 2-dimensional and much more often then they are 3-dimensional. Any vehicle is going to have to support at least its own weight against gravity, using stock materials, which naturally leads to a flat, 2-dimensional frame being the "backbone" of the vehicle. Things that move also tend to move forward/backwards, which naturally leads to a rectangular shape to optimize force transfer and obstacle avoidance.

Modularity Application

Combining frames, transmission, suspension (transion?), power production and actuators into a final system could produce any number of vehicles for a diverse array of missions, limited primarily by the "weight class" or the amount of force the vehicle is supposed to deal with.

The open source car and truck, the tractor, the micro-tractor, and anything else that moves under its own power could all be considered vehicles. Transion units that have a lot of travel could be used for the car and truck, while transion units with little-to-no travel could be used by the construction vehicles. They could both use pretty much the same set of frames depending on vehicle size. They already use the same power unit. The cab, which goes on top of the frame, would simply carry some sort of tool (like a backhoe or loader) to do work.

Passenger Vehicles

Motorcycles, ATVs, side-by-sides, sedans, etc. These are vehicles primarily intended to move one or more people around, although they can be adapted to other purposes. Weight should be minimized as much as possible. Safety is not really a concern in the smaller vehicles because the person is supposed to be aware of the inherent danger of operating a vehicle so small. In the upper range, which includes cars, safety becomes of paramount concern.

The lowest end isn't really relevant to OSE's mission. The vehicles there can't do much work, or the work they do is highly specialized, or the work they do could be replaced by big bicycles or small utility vehicles. The upper end is relevant to the sustainment of OSE's mission, but woudn't be much use during the execution (building a village).

It looks like Team Wikispeed, a competitor in the Progressive X-Prize, has already implemented a lot of these modular vehicle ideas.

Utility Vehicles

Trucks, big trucks, etc. These are vehicles primarily intended to move cargo around. Some are intended to work in controlled environments, others can be taken into harsh, unpredictable environments. Weight is only an issue at the lower end of the scale where the operator values the potential to do some work more than the capability to do actual work. Operator comfort can be sacrificed for increased capability and easier maintenance.

This class of vehicle will be quite useful.

Construction Vehicles

Tractors, excavators, cranes, etc. These are vehicles primarily intended to get their tool to a job site, then perform some sort of specific activity. The vehicle sometimes moves cargo but primarily moves the tool around. Far from weight not being much of an issue, more weight is often advantageous due to the need to maintain 70/30 weight distribution while manipulating heavy loads. Additionally, the inherent weight of heftier components decreases the effects of vibration and stress.

This class will be indispensable to the construction of the village. However, the question of whether or not it's practical to build a giant bulldozer is still up for debate. The bottom end of this range of vehicles is definitely something that could be fabricated. They are generally called "compact" or "mini" versions of the standard vehicle. For example: mini-excavator, compact tractor, etc.

It looks like the sides of construction vehicles are around about the same height as the frames of heavy trucks. We can probably use the big pieces of c-channel truck frame as the frames of at least small construction vehicles.

Skid-steer side view.jpg


Intended primarily to carry a single person. Examples are...

  • ATVs
  • Motorcycles
  • Scooters

4-wheeled P-style vehicles are characterized as...

  • $4-10K
  • 430-695lbs
  • 70 mph max
  • 45-51" wheelbase
  • 71-84" long
  • 41-47" wide
  • 30-36" seat height


Intended primarily to carry one person and their cargo. The cargo can be replaced by one or more people. Examples are...

  • Utility Vehicles
  • ROVs
  • UTVs
  • Side by sides

4-wheeled, P+-style vehicles are characterized as...

  • $8-11K
  • 111-141" long
  • 56-59" wide
  • 73-75" wheelbase
  • 1200-1500lbs
  • 1-1.5K pounds payload
  • 2-5 seats


Intended primarily to carry several people and their cargo. Examples are...

  • Automobile
  • Car
  • Sedan
  • Coupe

4-wheeled PC-style vehicles are characterized as...

  • $18-30K
  • 174-197" long
  • 73-77" wide
  • 103-110" wheelbase
  • 58-60" height
  • 5 seats
  • 17 cubic feet cargo
  • 26-19mpg


Intended primarily to carry cargo. Examples are...

  • Truck
  • Pickup truck
  • Lorry

4-wheeled C-style vehicles are characterized as...

  • $18-30K
  • 194-240" long
  • 74-90" wide
  • 115-152" wheelbase
  • 67-78" height
  • 3.5-6K pounds wet
  • 44-61 cubic feet cargo
  • 20-13mpg
  • 4-12K tow capacity
  • 3K pounds payload


Intended primarily to carry a lot of cargo. The cargo can be replaced by a job-specific tool (like a crane). Examples are...

  • Commercial truck
  • Box truck
  • Dump truck
  • Cherry picker
  • Flatbed

Cab forward, 2-axle C+-style vehicles are characterized as...

  • 208-225" long
  • 81-90" wide
  • 96-108" height
  • 10-13K pounds wet
  • 7.5-11.6K pounds GAWR front
  • 13.5-20K pounds GAWR rear
  • 162-252hp


When driving on public roads, the vehicles should be 3-wheelers with two front wheels.

  • 3-wheeled vehicles, in nearly all cases, are not considered "cars" and are not as strictly regulated.
  • They are lighter and easier to manufacture
  • Less rolling resistance and more aerodynamic

The single front wheel layout naturally oversteers and the single rear wheel layout naturally understeers. Because some degree of understeer is preferred in consumer vehicles, the single rear wheel layout has the advantage in this department. Another consideration is the effect of braking and accelerating turns. A braking turn tends to destabilize a single front wheel vehicle, whereas an accelerating turn tends to destabilize a single rear wheel vehicle. Because braking forces can reach greater magnitudes than acceleration forces (maximum braking force is determined by the adhesion limit of all three wheels, rather than two or one wheel in the case of acceleration), the single rear wheel design has the advantage on this count as well. Consequently, the single rear wheel layout is usually considered the superior platform for a high-performance consumer automobile. But much depends on the details of the design. Three Wheel Cars

Licensing the driver of a 3-wheel vehicle is not as straightforward, varying greatly from state to state. In California, for instance, all that’s needed to pilot a 3-Wheeler is a car license. Most everywhere else a motorcycle license is required, and to further complicate matters, some states require that the driving test be taken on a 2-wheeler in order to get a license to drive a 3-wheel vehicle. NYT

However, there is a real question of whether or not a 3-wheeler can be practical as a working vehicle. OSE is primarily a farm, and making everything you need at home is kind of the point, so commuting isn't expected to be a core competency. 4 wheels make more sense for carrying heavy/awkward loads over rough/soft terrain.

Truck manufacturers, particularly commercial trucks, provide "body builders" manuals that detail the dimensions of their parts.

C-Channel vs Fully Boxed

Commercial trucks seem to use straight c-channel frames 34" apart (outer dimension). Passenger trucks have frames with a lot of curves in them. They vary from 34" to 44" outside. 90cm is about 35.5".

There are several advantages to using C-channel over a fully boxed (tube) frame. One simple one is that corrosive stuff doesn't get caught inside a C-channel frame. Related to that point is that there is no "inside" to c-channel, so it's a lot easier to work on since you can access all areas, at least compared to a boxed frame where you can't get at the inside. However, the most important reason is that c-channel is much easier to manufacture than tube. Not only does it require fewer bends, it doesn't require a weld down the middle. Finally, boxed is stronger when welding but c-channel is stronger when using bolts, and bolts are mandatory in modular construction.

Running Gear

The goal is to create a system of suspension/driveline components that can allow pretty much any object to become a "vehicle." By combining the spring, shock, steering and propulsion units into a single package it could be "bolted" on to nearly any frame and, with some hydraulic connections, and maybe some electrical connections, it would do what a suspension and driveline do.

"Commercial" examples:

The various options can probably be broken down into three classes"

Since OSE vehicles would be for utility first, and comfort/commuting second, it is logical to start with solid axles. However, the modular vehicle system should be designed in such a way that a solid axle can be replaced with struts or double wishbones if the user wishes to carry people rather than cargo. The progression, from utility to comfort, should probably happen in that order (solid to strut to DW). Also, each category should be designed such that the more utilitarian option is cheaper than the more comfortable option in the same weight class.

On that topic, what payload classes should we use? It doesn't seem to make a lot of sense to classify P, P+ and PC vehicles by payload since their volume will limit how much weight people can force them to deal with. However, OSE builds farm equipment, so all of them will be expected to do work at some point. Perhaps the P*-style vehicles can be classified based on how much weight in people they're expected to carry. That leaves the C*-style vehicles. Regular trucks (C) seem to be rated for about 3,000 pounds of payload (on average), but that seems to vary from 1,000 to 7,000 pounds. The big commercial trucks (C+) seem to be rated per each axle (front and rear) with front axles handling 8-12K pounds and rear axles handling 13-20K pounds. If you wanted to use the same axle you could get away with one rated to around 12,000 pounds.

  • Light: rated based on the number of people it's expected to carry, plus some standard cargo weight per person. The average weight of a person, according to the Coast Guard, is 185lbs. The old definition of excessive luggage the airlines used was 70lbs.
  • Medium: rated primarily based on the weight of the cargo it's expected to carry.
  • Heavy: rated based on the weight each axle is expected to carry. Additional axles can divide up excessive cargo weights.

(You can save a copy of this spreadsheet from the original Google spreadsheet)

The P-style vehicle (basically an ATV) would be mostly a power cube with the suspendrive units bolted on to the sides. Assuming the power cube is 24" wide that leaves about 10" on each side for the tires and suspendrive units to fit into a standard ATV width. That might not be enough given that it should have around 8" of suspension travel. Also, apparently ATV tires start at about 8" wide. That means the suspension units are going to have to be moved in front of (or behind) a standard 24" power cube.

It is possible the P+-style vehicle could have suspendrive units attached to the side of a power cube. They have about 15" on each side.

PC-style could definitely fit suspendrive units on either side of a power cube; they have about 25" on either side.

C and C+-style vehicles have about 30" on either side of a 24" power cube.

Beam Axle Suspension

"The beam axle is a familiar design but it is no longer considered appropriate for automobile application. It is strong and inexpensive, and as a result, it is ideally suited to heavy trucks and smaller utility vehicles. The advantages of the design include its simplicity, low cost, and rugged layout, as well as a naturally high roll center which reduces body roll in turns. The disadvantages have to do with its performance. A bump at one wheel is transferred across to the other wheel. In addition, the gyroscopic forces of both wheels work together to induce shimmy, and the design results in greater unsprung weight and a rough ride." R Q Riley

Double Wishbone Suspension

"The upper and lower A-arm suspension has been the predominate system of U.S. cars for nearly half a century...When the concept of unequal length A-arms was developed, designers were given a new design tool that provided almost infinite control over the movements of the wheels. Today, handling characteristics are limited only by the limits of tire performance and the basic weight and balance of the vehicle, not by the mechanical limitations of the suspension system. The unequal length, non-parallel A-arm system allows the designer to place the reaction point of the wheel at virtually any point in space...Anti-dive is another feature that is easily designed into the double A-arm suspension. Vehicles with a soft ride tend to dive when braking. This is due to the weight transfer toward the front of the vehicle. The tendency to dive on braking can be partially alleviated by tilting the upper A-arm" R Q Riley

Mac Pherson Strut Suspension

"The MacPherson strut front suspension system was invented in the 1940's by Earl S. MacPherson of the Ford Motor Company. It was introduced on the 1950 English Ford and has since become one of the predominate suspensions systems of the world. This simple system utilizes the piston rod of the built-in telescopic shock absorber to also serve as the kingpin axis. Normally, a coil spring is mounted over the strut assembly, in which case, a thrust bearing at the top of the spring prevents spring wind-up during turns. The lower link may be in the form of an ordinary A-arm. More commonly, a narrow transverse link (sometimes called a track rod) locates the lower end of the strut in the transverse direction and a separate member called a radius rod locates the assembly in the longitudinal direction. However, the anti-roll bar can serve as the longitudinal link and thereby eliminate the separate radius rod. The advantages of the MacPherson strut include its simple design of fewer components, widely spaced anchor points that reduce loads, and efficient packaging. From a designer's viewpoint, its disadvantages include a relatively high overall height which tends encourage a higher hood and fender line, and its relatively limited camber change during jounce." R Q Riley

Dead Axle

"Every layout of the powered rear suspension system becomes a dead axle layout when power is not transferred to the wheels...The most popular dead rear axles include the beam axle and the trailing arm and semi-trailing arm suspensions." R Q Riley

One Piece Live Axle

"The live rear axle is similar to the beam front axle or the dead rear axle, except that it is subjected to the torsional loads involved in transmitting power to the road. The design is rugged, simple, and relatively inexpensive, but its high unsprung weight results in a poor ride...unsprung weight is very high and as a result the design produces a rougher ride and is very susceptible to wheel hop and tramp...The traditional live axle of older American cars is the Hotchkiss drive. The Hotchkiss drive is distinguished by its semi-elliptical leaf springs that also serve as the suspension links. Difficulties with the Hotchkiss drive have to do with its limited ability to transfer torque, its high interleaf friction and high unsprung weight, and the imprecise location of the rear axle assembly. Consequently, it is difficult to achieve a good ride and to appropriately manage the torsional loads of braking and power transfer. Braking and acceleration transfer high torsional loads to the axle, which can rotate off plane due to the flexibility of the springs. Designers have attempted to overcome the limitations of the live axle by replacing the leaf springs with coil springs and locating the axle with linkages of various configurations. Such systems do improve cornering performance, as well as smooth out the ride. When linkages are introduced, control is also gained over the dive and squat characteristics associated with acceleration and braking." R Q Riley

Swing Axle

"Ride and handling are greatly improved when the wheels can respond independently to disturbances...With swing axles a disturbance on one side is not transferred to the opposite wheel as it is with a solid axle. Ride and handling are therefore improved.

The first swing-axle design to gain wide popularity in the U.S. was the immortal VW Beetle...Swing-axles produce large changes in camber and tread during bounce, and the design can become unstable in turns due to the "jacking" effect. Setting the wheels at a negative camber can reduce the tendency to jack. However, too much negative camber can also produce a vehicle with a vague, mushy feel of directional instability. Slings under the axles or zee brackets can be designed to limit downward travel and thereby avoid wheel tuck-under. A correctly designed swing axle suspension works reasonably well, but its undesirable characteristics can never be fully overcome." R Q Riley

(Semi) Trailing Arm

"With trailing arm and semi-trailing arm suspensions the wheels are free to bounce independently. Each wheel moves up and down around the axis of a trailing or semi-trailing arm. The difference between the two designs is that the axis of the trailing arm is at right angles to the vehicle centerline whereas the semi-trailing arm axis angle inboard and toward the rear. Both configurations are popular for either powered or non-powered rear suspension systems...Body roll produces camber and toe changes in the semi-trailing arm design. Consequently, camber thrust and modest slip-angle forces can combine to produce steering inputs as the body rolls to the outside of the turn. Roll-steer effects are at a minimum when the arm axis is parallel to the ground and increase when the inboard end is raised or the outboard end is lowered. The degree of camber change depend primarily on the distance to the instantaneous center. The instantaneous center is normally located no closer than the centerline of the opposite wheel. A closer location will produce wheel movements that emulate the swing-axle, along with the negative attributes of tuck-under and unfavorably large camber change." R Q Riley

Strut & A-arm

"The rear suspension system can emulate the design of the MacPherson strut or the upper and lower A-arm front suspension system. At the rear, a MacPherson style suspension is referred to as a "Chapman strut", or simply a "strut" suspension. The geometry, mechanical layout, and wheel travel characteristics are essentially the same, except the strut rear suspension does not steer (at least in the traditional sense). Upper and lower A-arm systems come in a variety of unique configurations. Designs sometimes utilize the drive axles as suspension links, such as with the Jaguar and Corvette rear suspension systems." R Q Riley

See Also