Chassis Design

Step-by-Step chassis design

This detailed guide describes the all the steps required to create your own SMARS in a CAD package, so that you can go on to design and build more SMARS parts and customisations.



Profiles

The chassis is made of several sketch profiles:


The Chassis Base

The Chassis Base is made of up 2 dimensions:

Chassis Base Cad Drawing

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Extrude the Base

2 The base is then extruded up:

Chassis Extruded Base Cad Drawing

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Shell the Extruded Base

Next a shell is applied to the extruded base cube, making it more into the familar shape, if not a little blocky.

Chassis Shelled Base Cad Drawing

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Fillet the Shell

The Chassis is now given a fillet around the bottom edges and each of the corners, to make it pleasing to the eye.

Chassis Fillet the Shell Cad Drawing

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Thin the Front and Back sides

The Front and Back sides are currently the case thickness from the shell we applied earlier. This needs to be trimmed down so that they are only 2mm thick.

Chassis Front and Back sides Cad Drawing

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Front Cutout Profile

The Front and Back sides need to have a section cut out of them, first we need to create a profile for the cutout.

There are 2 main dimensions.

Chassis Back Cutout Cad Drawing

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Front Back Cut

The profile created previously is now used to extrude a cut all the way through the body.

Chassis Front to back cut Cad Drawing

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Side Profile

The profile for the side cutout is created next. This is a inverted trapesium shape, with three main dimensions:

Chassis Side Profile Cad Drawing

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Side Cutout

The side profile is now extruded to cut all the way through the main body.

Chassis Side extrude and Cut Cad Drawing

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Fillet applied to side cutouts

A small fillet of 1.5mm is applied to round the inner edges of the cutout that has just been applied.

Chassis Fillet applied Cad Drawing

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Back cutout profile

A profile is created for the back cutout section. This has 2 dimensions:

Chassis Back profile Cad Drawing

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Back profile cut

The profile created above is used to extrude a cut through the back side of the body. This is where the arduino will slide in. The slots will come shortly.

Chassis Back profile cut Cad Drawing

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Chassis Wheel hole profile

The profile for the wheel holes is created next. This has 2 dimensions:

Chassis Wheel hole profile Cad Drawing

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Wheel hole extrude cut

The wheel hole profile is used to extrude a cut all the way through the body.

Chassis Wheel hole profile cut Cad Drawing

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Arduino slot profile

The slots for the arduino are sketched next. They go all the way from the back edge to the inner front edge. The dimensions of the Arduino slots are:

Chassis Arduinio slot Cad Drawing

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Arduino slot cut

The Arduino slot profile created above is used to extrude a cut into the body, to a depth of 0.5mm.

This feature is mirrored across to the other side of the chassis.

Chassis Arduinio slot cut Cad Drawing

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Motor holder profile

The profile for the motor holders within the body is created next. There are a couple of dimensions on this sketch:

The top half of the sketch can be created and then a circular pattern used to rotate this around the centre to create an asymetric mirror for the bottom half of the sketch.

Chassis Motor holder profile Cad Drawing

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Motor holder profile extruded

The Motor holder profile is used to extrude up the motor holders. The dimesions are:

Chassis Motor holder extrude Cad Drawing

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Motor nub profile

A small nub needs to be sketched - this is to prevent the motor from sliding backwards into the chassis body.

The dimensions are:

They are aligned to the top of the motor holder sides and centered with in that area.

Chassis Motor nub profile Cad Drawing

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Motor nub extrude

Using the Motor nub profile created earlier, we extrude the Motor nub up by:

Chassis Motor nub profile Cad Drawing

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Motor holder and nub chamfer

A small chamfer is applied to the tops of the extruded motor holder profiles and motor nubs.

The dimension of the chamfer is:

Chassis Motor holder and nub chamfer Cad Drawing

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Front profile

A profile sketch is needed to make a final cut to the front side.

The dimensions of the cut are:

Chassis Front profile Cad Drawing

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Front cut

The Front profile created above is used to extrude a cut into the front side of the chassis.

Chassis Front cut Cad Drawing

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Slave wheel stub profile

The slave wheel stub profile is sketched next.

This has several dimensions:

Chassis slave wheel stub profile Cad Drawing

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Stub extrude profile

A small extrusion is needed to join the stub wheel to the fillet at the bottom of the chassis.

Dimension:

The center of the circle is located at the centre of the previously extruded motor hole.

Chassis stub extrude profile Cad Drawing

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Stub extrude

The Stub extrude profile is extruded into the chassis body. The dimensions are:

This feature is replicated to the other side of the case using a circular pattern.

Chassis stub extrude Cad Drawing

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Stub wheel profile

The stub wheel is actually created using a profile that is then revolved around an axis to form a rounded part.

This is a complex part to describe so please refer to the diagram below for dimensions.

Chassis stub wheel profile Cad Drawing

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Stub wheel revolve

The Stub wheel profile created above is revolved around the center of the wheel hole to create a solid body. The revolve operation also joins this to the chassis.

Chassis stub wheel revolve Cad Drawing

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Stub wheel cutout profile

The stub wheel needs a cut out section to allow the two halfs of the stub wheel to squeeze together when pushing on a slave wheel.

The dimensions are:

Chassis stub wheel cutout profile Cad Drawing

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Stub wheel cutout

The Stub wheel cutout profile is used to extrude-cut the section into the stub wheel to create two halfs.

The cut operation goes through the stub wheel to the surface of the side of the chassis body.

Chassis stub wheel cutout Cad Drawing

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Motor holder slots profile

Two slot profiles need to be sketched above each of the areas where the motors live. This will enable a motor holder part to be snaped into place later once the motors are installed. The parts are pressure fit, so this part will only need to be a few mm deep.

Dimensions:

Chassis motor holder slots Cad Drawing

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Motor holder slot extrude-cut

The Motor holder slots profile is used to extMotrude-cut the slots into the chassis.

The dimensions for the cut are:

This feature is then mirrored across to the other side of the chassis.

Chassis motor holder slots cut Cad Drawing

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Final view

You should now have a finished Chassis design, ready for saving out to an STL file and printing.

(Note this design has a few extra florishes)

Chassis final Cad Drawing