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Discussion Starter · #1 ·
Thinkin' about doin something different this year
...doing a lot of research

Here is some info on chassis design/construction

http://autozine.org/technical_school...ch_chassis.htm

Ladder Chassis
This is the earliest kind of chassis. From the earliest cars until the early 60s, nearly all cars in the world used it as standard. Even in today, most SUVs still employ it. Its construction, indicated by its name, looks like a ladder - two longitudinal rails interconnected by several lateral and cross braces. The longitude members are the main stress member. They deal with the load and also the longitudinal forces caused by acceleration and braking. The lateral and cross members provide resistance to lateral forces and further increase torsional rigidity.

Tubular Space Frame
As ladder chassis is not strong enough, motor racing engineers developed a 3 dimensional design - Tubular space frame. One of the earliest examples was the post-war Maserati Tipo 61 "Birdcage" racing car. Tubular space frame chassis employs dozens of circular-section tubes (some may use square-section tubes for easier connection to the body panels, though circular section provides the maximum strength), position in different directions to provide mechanical strength against forces from anywhere. These tubes are welded together and forms a very complex structure, as you can see in the above pictures. For higher strength required by high performance sports cars, tubular space frame chassis usually incorporate a strong structure under both doors (see the picture of Lamborghini Countach), hence result in unusually high door sill and difficult access to the cabin. In the early 50s, Mercedes-Benz created a racing car 300SLR using tubular space frame. This also brought the world the first tubular space frame road car, 300SL Gullwing. Since the sill dramatically reduced the accessibility of carbin, Mercedes had to extend the doors to the roof so that created the "Gullwings".
Since the mid 60s, many high-end sports cars also adopted tubular space frame to enhance the rigidity / weight ratio. However, many of them actually used space frames for the front and rear structure and made the cabin out of monocoque to cut cost.

Monocoque
Today, 99% cars produced in this planet are made of steel monocoque chassis, thanks to its low production cost and suitability to robotised production.
Monocoque is a one-piece structure which defines the overall shape of the car. While ladder, tubular space frame and backbone chassis provides only the stress members and need to build the body around them, monocoque chassis is already incoporated with the body in a single piece, as you can see in the above picture showing a Volvo V70.

In fact, the "one-piece" chassis is actually made by welding several pieces together. The floorpan, which is the largest piece, and other pieces are press-made by big stamping machines. They are spot welded together by robot arms (some even use laser welding) in a stream production line. The whole process just takes minutes. After that, some accessories like doors, bonnet, boot lid, side panels and roof are added.

Monocoque chassis also benefit crash protection. Because it uses a lot of metal, crumple zone can be built into the structure.

Another advantage is space efficiency. The whole structure is actually an outer shell, unlike other kinds of chassis, therefore there is no large transmission tunnel, high door sills, large roll over bar etc. Obviously, this is very attractive to mass production cars.

There are many disadvantages as well. It's very heavy, thanks to the amount of metal used. As the shell is shaped to benefit space efficiency rather than strength, and the pressed sheet metal is not as strong as metal tubes or extruded metal, the rigidity-to-weight ratio is also the lowest among all kinds of chassis bar the ancient ladder chassis. Moreover, as the whole monocoque is made of steel, unlike some other chassis which combine steel chassis and a body made of aluminium or glass-fiber, monocoque is hopelessly heavier than others.

Although monocoque is suitable for mass production by robots, it is nearly impossible for small-scale production. The setup cost for the tooling is too expensive - big stamping machines and expensive mouldings. I believe Porsche is the only sports car specialist has the production volume to afford that.

ULSAB Monocoque
Enter the 90s, as tougher safety regulations ask for more rigid chassis, traditional steel monocoque becomes heavier than ever. As a result, car makers turned to alternative materials to replace steel, most notable is aluminium. Although there is still no mass production car other than Audi A8 and A2 to completely eliminate steel in chassis construction, more and more cars use aluminium in body panels like bonnet and boot lid, suspension arms and mounting sub-frames. Unquestionably, this is not what the steel industry willing to see.
Therefore, American's steel manufacturers hired Porsche Engineering Services to develop a new kind of steel monocoque technology calls Ultra Light Steel Auto Body (ULSAB). As shown in the picture, basically it has the same structure as a conventional monocoque. What it differs from its donor is in minor details - the use of "Hydroform" parts, sandwich steel and laser beam welding.

Hydroform is a new technique for shaping metal to desired shape, alternative to pressing. Conventional pressing use a heavy-weight machine to press a sheet metal into a die, this inevitably creates inhomogenous thickness - the edges and corners are always thinner than surfaces. To maintain a minimum thickness there for the benefit of stiffness, car designers have to choose thicker sheet metal than originally needed. Hydroform technique is very different. Instead of using sheet metal, it forms thin steel tubes. The steel tube is placed in a die which defines the desired shape, then fluid of very high pressure will be pumped into the tube and then expands the latter to the inner surface of the die. Since the pressure of fluid is uniformal, thickness of the steel made is also uniformal. As a result, designers can use the minimum thickness steel to reduce weight.

Sandwich steel is made from a thermoplastic (polypropylene) core in between two very thin steel skins. This combination is up to 50 percent lighter compared with a piece of homogenous steel without a penalty in performance. Because it shows excellent rigidity, it is applied in areas that call for high bending stiffness. However, it cannot be used in everywhere because it needs adhesive bonding or riveting instead of welding.

Compare with conventional monocoque, Porsche Engineering claimed it is 36% lighter yet over 50% stiffer. Although ULSAB was just annouced in early 1998, the new Opel Astra and BMW 3-Series have already used it in some parts. I believe it will eventually replace conventional monocoque.

Backbone Chassis
Colin Chapman, the founder of Lotus, invented backbone chassis in his original Elan roadster. After failed in his experiment of glass-fibre monocoque, Chapman discovered a strong yet cheap chassis which had been existing for millions of years - backbone.

Backbone chassis is very simple: a strong tubular backbone (usually in rectangular section) connects the front and rear axle and provides nearly all the mechnical strength. Inside which there is space for the drive shaft in case of front-engine, rear-wheel drive layout like the Elan. The whole drivetrain, engine and suspensions are connected to both ends of the backbone. The body is built on the backbone, usually made of glass-fibre.

It's strong enough for smaller sports cars but not up to the job for high-end ones. In fact, the original De Tomaso Mangusta employed chassis supplied by Lotus and experienced chassis flex.

TVR's chassis is adapted from this design - instead of a rigid backbone, it uses a lattice backbone made of tubular space frames. That's lighter and stronger (mainly because the transmission tunnel is wider and higher).

http://articles.sae.org/9522/

Well, this gets the wheels a turnin'
...this Backbone Chassis design is kinda interesting
...let me see what I can come up with.

Ima gonna call 'er the Torsk, just cause it sounds kool
...seen a documentary on the U.S.S. Torsk a couple of weeks ago (a bad azz piece of machinery)
 

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Discussion Starter · #2 ·
Here is some more interesting info I found, it's for designing racecars but, most info should still pertain :cool:

Chassis explained

As you design a racing car, it is important that you know the requirements of your engineering work. The nature of the race car's normal operation and fatigue life depend on the structure and material composition of the car. Therefore, topics such as metallurgy and structural design are important for the designer to grasp. The whole concept of engineering considerations is that you keep in mind four aspects, where they are appropriate:

Any good chassis must do several things:
•Be structurally sound in every way over the expected life of the car and beyond. This means that nothing will ever break under normal conditions.
•Maintain the suspension mounting locations so that handling is safe and consistent under high cornering and bump loads. This means that there is no flexing of the body, or at least to reduce flexing on lowest possible value.
•Support the body panels and other components so that evevrything feels solid and has a reliable life span.
•Protect the driver from external intrusion.

Structural stiffness is the basis of what you feel at the seat of your back bottom. It defines how a car handles, body integrity, and the overall feel of the car. Chassis stiffness is what separates a great car to drive from what is merely OK.
Contrary to some explanations, there is no such thing as a chassis that doesn't flex, but some are much stiffer than others. Even highly sophisticated Formula 1 chassis (actually, Formula 1 has monocoque structure) flex, and sometime some limited and controlled flexing is built in the car.
The range of chassis stiffness has varied greatly over the years. Basic chassis designs each have their own strengths and weaknesses. Every chassis is a compromise between weight, component size, complexity, vehicle intent, and ultimately, the cost. And even within a basic design method, strength and stiffness can vary significantly, depending on the details.
There is no such thing as the ultimate method of construction for every car, because each car presents a different set of problems.
Some think an aluminium chassis is the path to the lightest design, but this is not necessarily true. Aluminium is more flexible than steel. In fact, the ratio of stiffness to weight is almost identical to steel, so an aluminium chassis must weigh the same as a steel one to achieve the same stiffness. Aluminium has an advantage only where there are very thin sections where buckling is possible - but that's not generally the case with tubing - only very thin sheet. And even then, aircraft use honeycombed aluminium to prevent buckling. In addition, an aircraft's limitation is not stiffness, but resistance to failure. Aluminium problems are overcomed something with Audi Aluminium Spaceframe (ASF), very expensive and for now made in limited models.

Ladder Chassis (Body on frame technology)

This is the earliest kind of chassis. From the earliest cars until the early 60s, nearly all cars in the world used it as standard. Even in today, most SUVs still employ it. Its construction, indicated by its name, looks like a ladder - two longitudinal rails interconnected by several lateral and cross braces. The longitude members are the main stress member. They deal with the load and also the longitudinal forces caused by acceleration and braking. The lateral and cross members provide resistance to lateral forces and further increase torsional rigidity. Since it is a (little bit more than) 2 dimensional structure, torsional rigidity is very much lower than other chassis, especially when dealing with vertical load or bumps.
This technology you can find today in some basic auto racing categories. Most known is kart. On picture below you can see chassis of an Superkart car without bodywork.

Backbone chassis

Backbone chassis is a type of a car construction chassis that is similar to the ladder design. Instead of a two-dimensional ladder type structure, it consists of a strong tubular backbone (usually but not always rectangular in cross section) that connects the front and rear suspension attachment areas. The tunnel or backbone becomes a primary load bearing member.

Backbone chassis is very simple: a strong tubular backbone connects the front and rear axle and provides nearly all the mechanical strength.

Inside backbone is space for the drive shaft in case of front-engine, rear-wheel drive layout like in the case of Lotus Elan. The whole drivetrain, engine and suspensions are connected to both ends of the backbone. A body is then placed on this structure.
It is almost a trademark design feature of Czechoslovak Tatra heavy trucks (cross-country, military etc.), but this type of chassis is also often found on small sports cars. It also does not provide protection against side collisions, and has to be combined with a body that would compensate for this shortcoming.

http://www.formula1-dictionary.net/chassis.html

On an electric car/kart the battery pack is, usually, the heaviest (single)component after the driver.

I am thinkin' about a backbone chassis design that incorporates the battery box as a structural member rather than something to be supported.

This way most of weight of the batteries could be centrally located & spread out along the length of the frame.
The driveline (the battery cables, speed controller & most of the wiring connections) could be mounted & ran thru the inside of the tunnel/tube & would be protected in the true spirit of a backbone chassis :D
__________________
 

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Discussion Starter · #4 ·
In current terms, a pickup truck would be a much better example of a ladder frame than an SUV, since most current SUVs are unibody.

The information about aluminum in the second post is quite outdated and has some blatant errors. I suggest checking other sources for a more balanced view.


It was, but not in recent decades. I can't think of a single one still in production, offhand; although of course I may have missed one or two, they're not common.


I understand the logic, but it's hard to find enough space in a backbone box of reasonable dimensions to fit the entre battery; for instance, the Volt (which has only 16 kWh of capacity) fits only about half of the battery in the tunnel. To be workable, the backbone/box would need to be as long as possible, from nearly the drive axle to the other axle or even beyond.

The Bollinger 4WD, which is still really a concept at the stage, has a box beam backbone for most of the structure... but hangs the battery boxes off each side as seating area floor sections, with just motors and electronics within the backbone.

Thanks for the feedback :D

I am just adventuring & exploring with different chassis/frame ideas & concepts
...& sharing some of the interesting info that I came across :cool:

Most of the vehicles with backbone chassis that I have seen, usually incorporate a differential & half shafts into the rear axle

But, I'm thinking of using a live axle on a light & balanced backbone chassis style kart

Still researchin' & bouncing ideas around ;)
 

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Discussion Starter · #5 ·
Here is more frame/chassis info :cool:


Spaceframe

The two most important goals in the design of a race car chassis are that it be lightweight and rigid. Lightweight is important to achieve the greatest acceleration for a given engine power. Rigidity is important to maintain precise control over the suspension geometry, that is, to keep the wheels firmly in contact with the race course surface. Unfortunately these two goals are often in direct conflict. Finding the best compromise between weight and rigidity is part of the art and science of race car engineering.

As ladder chassis was not strong enough, and provide small rigidity values, motor racing engineers developed a 3 dimensional design - Tubular space frame.

The spaceframe chassis is about as old as the motorsport scene. Its construction consists of steel or aluminum tubes placed in a triangulated format, to support the loads from suspension, engine, driver and aerodynamics. A true space frame has small tubes that are only in tension or compression - and has no bending or twisting loads in those tubes. That means that each load-bearing point must be supported in three dimensions.

Tubular space frame chassis employs dozens of circular-section tubes (some may use square-section tubes for easier connection to the body panels, though circular section provides the maximum strength), position in different directions to provide mechanical strength against forces from anywhere. These tubes are welded together and form a very complex structure, as you can see in the left picture.

For higher strength required by high performance sports cars, tubular space frame chassis usually incorporate a strong structure under both doors, hence result in unusually high door sill and difficult access to the cabin.

In the early 50s, Mercedes-Benz created a racing car 300SLR using tubular space frame. This also brought the world the first tubular space frame road car, famous 300SL Gullwing. Since the door sill dramatically reduced the accessibility of cabin, Mercedes had to extend the doors to the roof so that created the "Gullwings".

Since the mid 60s, many high-end sports cars also adopted tubular space frame to enhance the rigidity / weight ratio. However, many of them actually used space frames for the front and rear structure and made the cabin out of monocoque to cut cost.

There are also some inherent advantages to using spaceframes at the amateur level of motorsport as well. Spaceframes, unlike the monocoque chassis used in modern Formula 1 or CART, are easily repaired and inspected for damage.

Triangulation

How does triangulation work? The diagram below shows a box, with a top, bottom and two sides, but the box is missing the front and back. The box when pushed collapses easily because there is no support in the front or back.

Of course, race cars (or any other car for that matter) need to be supported in order to operate properly, and so we triangulate the box by bracing it diagonally. This effectively adds the front and back which were missing, only instead of using panels, we use tubes to form the brace. See below:

The triangulated box above imparts strength by stressing the green diagonal in Tension. Tension is the force trying to pull at both ends of the diagonal. Another force is called Compression. Compression tries to push at both ends of the diagonal (Shown above in the horizontal yellow tube). In a given size and diameter tube or diagonal, compression will always cause the tube to buckle long before the same force would cause the tube to pull apart in tension. As an experiment, try pulling on the ends of a pop can, one end in each hand. Then, try crushing the can by pushing on both ends. The crushing is much easier, or at least humanly possible, compared to pulling the can apart.

Spaceframes are really all about tubes held together in compression and tension using 3D pyramid-style structures, and diagonally braced tube boxes. A true spaceframe is capable of holding its shape, even if the joints between the tubes were hinges. In practice, a true spaceframe is not practical, and so many designers "cheat" by using stronger materials to support the open portions of the structure, such as the cockpit opening.

Torsional rigidity applies to spaceframes too, but because a spaceframe isn't made from continuous sheet metal or composite panels as in monocoque design, the structure is used to approximate the same result as the difficulty to twist "cigar car".

Another reason torsional rigidity is mentioned here is that it greatly affects the suspension performance. The suspension itself is designed to allow the wheels/tires to follow the road's bumps and dips. If the chassis twists when a tire hits a bump, it acts like part of the suspension, meaning that tuning the suspension is difficult or impossible. Ideally, the chassis should be ultra-rigid, and the suspension compliant.

It is important to ensure that the entire chassis supports the loads expected, and does so with very little flex.

Advantage of spaceframe is that is very strong in any direction compared with ladder chassis and metal monocoque chassis of the same weight. Disadvantage is that is very complex, costly and time consuming to be built. Impossible for robotized production. Besides, it engages a lot of space, raise the door sill and result in difficult access to the cabin.

Monocoque

In contrast to Spaceframes, the monocoque chassis uses panels, just like the sides of the box pictured below. Instead of small tubes forming the shape of a box, an entire panel provides the strength for a given side.

A common shape for 1960s racing cars of monocoque construction was the "cigar". The cylindrical shape helped impart something called Torsional rigidity. Torsional rigidity is the amount of twist in the chassis accompanying suspension movement.

Monocoque, from Greek for single (mono) and French for shell (coque) (monoshell), is a construction technique that supports structural load by using an object's external skin as opposed to using an internal frame that is then covered with a non-load-bearing skin. Monocoque construction was first widely used in aircraft in the 1930s. Structural skin or stressed skin is other terms for the same concept. A welded unit body is the predominant automobile construction technology today.

Modern car monocoque chassisToday, 99% cars produced in this planet are made of steel monocoque chassis, thanks to its low production cost and suitability to robotized production.

Monocoque is a one-piece structure which defines the overall shape of the car. In fact, the "one-piece" chassis is actually made by welding several pieces together. The floorpan, which is the largest piece, and other pieces are press-made by big stamping machines. They are spot welded together by robot arms (some even use laser welding) in a stream production line. The whole process just takes minutes. After that, some accessories like doors, bonnet, boot lid, side panels and roof are added.

Monocoque chassis also benefit crash protection. Because it uses a lot of metal, crumple zone can be built into the structure. Another advantage is space efficiency. The whole structure is actually an outer shell, unlike other kinds of chassis, therefore there is no large transmission tunnel, high door sills, and large roll over bar etc. Obviously, this is very attractive to mass production cars.

There are many disadvantages as well. It's very heavy, thanks to the amount of metal used. As the shell is shaped to benefit space efficiency rather than strength, and the pressed sheet metal is not as strong as metal tubes in spaceframe construction or extruded metal, the rigidity-to-weight ratio is also the lowest among all kinds of chassis bar the ancient ladder or backbone chassis.

Although monocoque is suitable for mass production by robots, it is nearly impossible for small-scale production. The setup cost for the tooling is too expensive - big stamping machines and expensive moldings.
 

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Discussion Starter · #7 ·
Wow, Well put! :cool:
Thanks again for the feedback, that is some great info!

The researching & planning that I am doing is to build an electric go kart/fun kart
...for some "hands on" learning
...on a smaller scale
...that doesn't cost thousands of $

But, not just "another" go kart
...something kool & different
...maybe even "Bad Azz" (we'll have to see how it comes out)

It seems like an interesting challenge ;)
 

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Discussion Starter · #8 ·
Now, lets look into the "load" that the chassis/frame will have to support.
There are a couple of different kind "loads" to keep in mind.
The static load is the weight that the frame has to support when the kart is standing still.
The dynamic load is the weight of the kart plus the force of moving that weight & stopping that weight.

* This helps explain it a bit more :cool:

Static Load vs. Dynamic Load
The main difference between a static and dynamic load lies in the forces produced by the weight of an object. When static, the load remains constant and doesn't change over time. With a dynamic load, some outside factor causes the forces of the weight of the load to change. Some of the factors that can affect a load and make it dynamic include:

Movement: If the holder of a load is in motion, chances are that the force created by the weight distribution could change. This means that such changes in force must be taken into account when moving a load from one place to another.
Increased tension: Tension is created when two loads struggle against one another. This increase can make the forces of the weight shift from one load to another. The result is that the bigger load has a greater impact on the smaller load, maybe even causing it to become unbalanced.
An outside force: Air, water and ground movement can cause a load to shift. This shifting usually causes changes to the force of the weight as well. This means whatever is holding the weight needs to adjust to compensate for the changing force.


Examples of a Static and Dynamic Load
A good example of a static load is a truck with cargo inside sitting still in one spot. The force of the weight of the load has little chance of changing as long as the truck remains still. Once the truck begins to move, the load becomes dynamic, as the force of the movement can cause the load to shift, changing the effect of the force of the weight of the cargo. If the truck goes too fast, it could even cause the forces of the load to shift greatly, causing it to fall or to at least make it harder to drive the truck on the road's surface. Also, when stopping, the force of the weight of the load can shift forward, making it harder to stop the vehicle as quickly.

A bridge represents another example of static and dynamic forces in play. The weight of the bridge is a static load, as it doesn't change over time, as long as nothing moves across it or outside forces, such as the wind, don't move against it. A truck moving across the bridge places a dynamic load on the bridge by increasing the weight of the bridge as it crosses. A wind blowing against the bridge can also change the forces of the weight of the bridge, as it moves it from side to side, creating a dynamic load on the bridge. That is why it is important that engineers take all of the forces that might apply to a particular bridge in order to design a stable and safe structure. Another important force to keep in mind is torsion, with any twisting of the bridge in the wind causing additional tension on the structure, which in turn can affect how much of a load the bridge can handle.
 

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Discussion Starter · #14 ·
Competition go-karts usually are limited by rules to the materials used in their frames and to not an active suspension or drive axle differential. This is to keep the costs down to encourage the greatest number of participants. But, they're not practical at all on any kind of rough driving surface. Here's an in depth analysis of this type of vehicle frame: https://www.witpress.com/Secure/elibrary/papers/OP07/OP07018FU1.pdf

If your intent is to have an active suspension and maybe a drive axle with a differential, the design is much more complex. It might be more practical to adapt an existing 4 wheeler(quad, ATV) where most of the design heavy lifting has already been done. If you're into it, the Bad Ass golf cart stuff looks like a great way to waste a lot of time and money!
Thanks, that is some very interesting info :cool:

Not into competition or golf carts
...I do functional art :D
 

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Discussion Starter · #15 ·
Functional
You appear to be missing the point of a Kart

Karts don't have suspension - or more accurately the suspension is the chassis twisting - the stiffness of a Kart chassis is one of the performance variables and is tuned by altering various parts for different track layouts and driver weights

A super stiff Kart will drive terribly!
And a Kart with suspension will weigh far too much and will not pass scrutineering
IMO The "point of a kart" is to have fun :cool:

Nope, not planning for suspension on this one
...all of that info was for learning, more about what does what & why
 

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Discussion Starter · #16 ·
If the kart seats two, it follows all of the usual structural and packaging considerations of a two-seat car.

If it seats only one (just the driver), then the situation changes. If you want the driver centred on the vehicle centreline, then a backbone chassis doesn't make much sense (since the driver would need to straddle the backbone). It is possible to build a single-seater with the driver on one side of the backbone and something (typically an engine, but in this case likely the battery) on the other side - the backbone can be offset somewhat (typically to give the driver a greater share of the body width).

galderdi's latest autocross special has some modules of the battery beside the driver's legs, but in spaceframe, not a backbone chassis.
You are full of useful info, thanks again :cool:

I am workin' on a chassis all ready :D
 

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Discussion Starter · #18 ·
Then, as others explained, planned chassis flex is important. Tires form part of the virtual suspension too, but unless they are mushy off-road tires they won't provide enough compliance to work well.

A backbone of well-planned torsional stiffness (that is, not very stiff) can certainly work, but you need to be careful about where loads are attached to it.
Yup, right again :cool:

"Another important force to keep in mind is torsion"

IMO I think, "torsional rigidity" is what is needed to be considered when designing & choosing materials for a chassis or frame. (especially on a backbone chassis)

...& as you say "where the loads are attached"

More info:
"Rigidity is the maximum resistance an object can offer before it deforms, in other words, it is the minimum force required to deform an object.

Torsional Rigidity : The minimum force required to deform an object by twisting through a unit dimension..(in this case, for twisting the dimension is in angle of twist)

Lateral Rigidity : Again, the same logic.. The minimum force required to deform an object by bending along the lateral axis through a unit dimension..in this case, the dimension of bending is normally in mm or other length measure scale.. (if the bending load is applied on the longitudinal axis, then the object will not bend, instead the load will act like a compression load)"


So, for a backbone chassis the design & the materials used for the backbone have to be rigid enough to
...support the weight of the kart (everything between the wheels-frame, motor, batteries, driver etc.)
...support that weight while moving, turning & stopping
but, also flexible enough to take some bumps, while supporting that weight @ ~20mph

* Think about the dynamic load that is applied to a kart frame when doing a "Power Slide"
...or while doing donuts
...that's a lot of load :eek:
 

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Discussion Starter · #19 ·
Also, can't forget about balance & symmetry

So, lets examine the weight on a kart & how it is spread out

Rear wheels ~30 lbs, (~15 lbs. ea.)
Motor ~20 lbs.
Batteries ~35 lbs. (~8 lbs. ea.)
Operator ~150 lbs.
Front wheels ~15 lbs. (~7 lbs. ea.)

The design in the (top) pic is pretty well balanced :cool:
~50 lbs. in the rear (motor & rear wheels), ~150 lbs. in the middle (operator) & ~50 lbs. in the front (batteries & front wheels)

The (middle) pic shows how unevenly the weight is distributed on the !ARRIBA! kart. :eek:
~100 lbs. in the rear, ~150 in the middle & only ~20 lbs. in the front

The (bottom) pic shows (top view) how nicely everything could be balanced.
...& symmetrical (left half is a mirror image of the right half)
 

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Discussion Starter · #20 ·
Starting to "zero in" on where were going with this :cool:

I need to design a frame that is
...strong & light weight
...rigid but, slightly flexible
...& also evenly balanced

Choosing materials:
What shape would work best to make this thing out of?
round, square, custom?


I first contemplated using 4' round tube but, it seems like it would be easier to attach to flat surfaces

Then, I was leaning toward 4" x 4" x 1/8" square tube (~6.5 lbs. per ft.)
But, the 12V 12AH batteries, being 4" wide, would not fit inside a 4" square tube (~3 3/4" ID.)

So, now I'm thinkin' 2" x 6" x 1/8" rectangular tube
...it's also ~6.5 lbs. per ft. (same as 4" x 4" square tube)
...but, I can cut out 4" (for the batteries) of the 6" wide tube & still have ~1" of steel wrap around to help maintain the "rigidity" of the backbone

Front Axle, could be made of 1" x 3" x 1/8" steel, ~18" wide
...proportionally reduced from the backbone dimensions (2" x 6" to 1" x 3")
I am thinkin' of leaving the axle as (1) piece, cutting 1" x 3" slots on each side of the backbone & running it right thru
...the left side axle stub would be 6", the backbone is 6" wide & the right side axle stub is 6" also (kinda of a 1:1:1 ratio)

Rear Axle Housing, could be made of 2" x 1/8" round tube ~14" wide
...it could cap off the rear end of the backbone

I am thinkin' of running the 1" axle thru it (like a true backbone chassis) & just having the bearings mounted right on the ends
...the left side axle housing would be 4", the backbone is (of course) 6" wide & the right side axle housing would be 4" (kinda of a 0.8:1:0.8 ratio)
...the sprocket could be mounted between the bearing & the wheel, on one side
...& the brake rotor/drum, between the bearing & the wheel on the other side
 

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Discussion Starter · #24 ·
Next, I did some grinding
...because the trailing arms are 2 1/2" & the backbone is only 2" & the trailing arms are centered on the backbone so, they stick up ~1/4" above & below.
(which is no big deal except where the motor mounting plate sits)

The motor mounting plate needs to set level with the backbone
(across from the backbone to the trailing arm)
...which (in turn) should also ensure it's squareness with the rear axle

I made sure that
...the backbone chassis was sitting level on the workbench
...then ground the edge of the trailing arm down
...checking progress several times
....until the motor mounting plate was sitting nice-n-level

Before assembling & aligning everything, I drilled (2) 1/8" holes near the inner edge of the motor mount plate so, once the motor mount plate is where it needs to be
...I can mark the (2) spots & drill them out (to use as alignment points)
...& also to install small screws (so, I can "tack it down" in "that exact spot" for testing & then welding)

Reassembled everything again, each time adding a piece to the puzzle
...bolted the bearings in place
...slid the axle thru 'em
...installed the sprocket on the right side
...bolted the motor to the motor mount plate (at lowest adjustment)
...added a piece of #35 chain
...& adjusted/aligned everything (with the square, straight edge & the level)

After triple checking ALL of the alignment points
I drilled out & added the (2) small screws to "lock 'er in place"

Gave 'er a spin by hand (gripping the axle)
Yup, spins pretty good

I also, hooked up (1) 12V battery, just to quadruple check the alignment of the propulsion unit (motor) with the drive unit (axle) before welding the motor mount in place.

https://www.youtube.com/watch?v=qwh9nPT2hvM
 

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Discussion Starter · #26 ·
Moving right along (or forward)

Now that the backbone is pretty much established
...& the rear axle housing
...& the motor mount

Next, would be the "Cockpit" or the operator compartment

I figure
...my signature rollbar/seatback ~40" tall
...the floor should be ~16" from the bottom of the seat to the bottom of the steering support
...& the steering support should be ~16" tall

So, I got the bender out
...& a 10' piece of water pipe

I started off by measuring & marking the piece of pipe right in the middle, 60" from each end
(this will be the top of the rollbar)
...& also @ 40", each way, from the center mark
(these will be where the seat back will curve into the floor)

So, it's marked at 20", then at 60" then at 100"

Then, put 'er in the bender, lined up @ the center mark & bent 'er to the max
(to help bring the bottom, seat back area, as close together as possible)

When the pressure is released it springs back pretty good
...but, we can work with that

Once we had the rollbar/seatback next, was the (2) side bends
...one @ the 20" mark
...& the other @ the 100" mark

Before each bend, I angled one side up a bit & the other side down a bit

The idea was to get them to angle inwards, toward the backbone because, the bottom of the seat back (rear part of the cockpit) should be ~16" wide

Where as the steering support (front part of the cockpit) should (nearly hug the backbone) only be ~8" - 10" wide (quite a bit narrower)

They didn't angle in as much as I had in mind but, should be able to work with 'em
 

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Discussion Starter · #27 ·
Steering support (front part of the cockpit) is next

I had a ~48" piece of water pipe

Measured & marked it in the center (~24") then, marked it @ ~14" each way from the center mark
...which should leave ~10" going back, on each side, from the lower bends

Put it in the bender, lined up @ the center mark & bent 'er to the max
...then, bent each side (~35 pumps) @ the 14" from the center marks
...but, only this time, with each side angled outward away from the backbone
(to be able to (hopefully) meet up with the (2) ends of the rollbar/seatback bar)


The floor of the cockpit needs to be ~16"

Set the backbone on the workbench
...positioned the cockpit over it
...& aligned the floor bars @ 16" apart (just on one side for now)

First thought about splitting the difference & just cutting them both @ 8" (8" from the front & 8" from the rear)

The front section is about where it needs to be, it's the rear section that needs to be worked a bit

I figured that I should leave a few inches more, on the rear section
(longer arms should give additional leverage, for workin' it)

So, I wacked the rear sections arms off @ 10" & @ 6" for the fronts


There is gonna be some pressure on these "floorboard" connection joints
...not really structural but, more from my bends being a little off
...& having to do some "tweakin" to bring 'em together

So, I'm not gonna just butt weld 'em together
...I'm gonna pin 'em
...then, butt weld 'em

5/8" rod (like for steering shafts) fits nicely inside this water pipe & will make good strong "splints"

I wacked off a couple of 3" pieces (should give us ~1 1/2" inside each end)

Drilled an 1/8" hole ~1" from the end of each pipe end (on the inside edge as to not be so visible)
...then inserted a "pin" ~1 1/2" into the ends of both of the front sections pipe ends
...then, drilled an 1/8" hole about 1/4" into the 5/8" rod & inserted a small screw to "pin" the pin in place


Slid the left end of the front section onto the alignment pin of the rear sections left side
...still a bit off

Wrapped a ratchet strap around the lower part of the rollbar/seatback
...to help draw the sides together (in a precise & controlled manner)

It took a little tweakin' but, I got 'er together

Inserted the front pin/screws to lock 'er in place
...& double checked everything

Looks pretty good
...all of the bends came out deicent
...all of the rails (seatback, floorboards & steering support) are mostly even
...& it even sits nice-n-level

Placed the cockpit on the bench, over the backbone & double checked everything again

Everything still seems to line up pretty good

So, cleaned up the connections & welded a nice bead around both of 'em

Removed the "pin" screws & drilled thru the outer layer of pipe to a 1/4"

That way I could put a good "inner" spot weld, to help "lock 'em in from the inside"
...& fill up the holes too

Then, cleaned 'er up a bit so, it's ready to be installed onto the backbone chassis
 

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Discussion Starter · #28 ·
Next gotta figure out where, exactly, is the cockpit gonna be positioned
...& how is it gonna be attached?

We know for sure (kinda) that it needs to be
...centered over the backbone chassis
...& as far back as possible but, still leaving adequate room for motor adjustment

As for attachment

I could just weld some short sections of pipe in between the backbone & the cockpit
(in all (4) corners)
...but, that's only a 2D (2 dimensional) connection & wouldn't be very structurally sound

There won't ever be very much weight pulling down on the cockpit
...but, without a 3D (3 dimensional) connection (some type of triangulation or structural back up) in a roll over situation & it would probably just snap off

Then, I thought about using a couple of pieces of 1/4" x 1" flat steel
...just welded to the bottom of the backbone
...extending out on each side & have the cockpit sit in top & welded to them

Again, not too structural, still only 2D

Then I thought, how about putting the cross bars on angles

In the rear across the backbone & the bottom of the seatback
...angled toward the rear
& in the front across the backbone & the bottom of the steering support
...angled toward the front

I like this set up, 'cause it will
...look better & be stronger
...give many good welding (junctions) on the backbone & the cockpit
...should allow the backbone chassis & the cockpit to twist/flex together
...& ain't gonna snap off on a roll over

So, I drilled & used small screws to "pin" the cross bars in place for welding

Then, I centered the cockpit, on the backbone chassis
...double checked the motor (rear) & battery (front) clearances (for the last time)

A couple of decent welds in the rear
...then a nice long bead in the front (I was on a roll)

Here's another video of progress :D

https://www.youtube.com/watch?v=Q9VBw-dMtZk
 

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Discussion Starter · #29 ·
Been working on the kart here & there, from time to time :D

Once I got the steering assembly finished up
...then, the chassis is pretty much done

Cleaned everything up "super good"
...& gave it a good coat of "self etching" primer
...to seal up all of that "bare" metal

I made a custom seat for it too :cool:

Here is another video of progress so far

https://www.youtube.com/watch?v=1eY7ctOPQTE
 
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