Cardboard Racer

This project will describe the process of making a functional cardboard racing car that is powered by an elastic band and with it how STEM (STEAM), [not forgetting the Arts]; can be applied.

Science will explore Newtons 3 laws of motions.

Technology - Practical application of the Science using the car to perform experiments.

Engineering - Design and building the car.

Arts - Creative expression to customise and individualise the car by modifying it visually whilst maintaining functionality.

Maths - Calculation used to generate numerical data for analysis.

Corrugated Card Board (370 x 230 x 4 mm) * 3

Scissors

Cutting Blade

Clear Adhesive Tape

Glue

Ruler

Pencil or Pen

Elastic Bands * 5

Cloths Pegs as required.

Bamboo Skewers * 2 (160 mm min)

M4/10mm screw * 2

M4/20mm threaded standoff

M4/20mm screw

M4 washers * 6

4 mm drill bit

Bradawl

What are Newtons 3 law of Motion.

1: An object at rest or in motion will continue to do so unless acted upon by an external force.

The car continues in motion once the initial force is applied but will eventually come to a stop as a result of frictional forces. Frictional forces can be significantly reduced by the use of bearings and rolling on a hard surface.

2: When a force acts on an object, it will cause the object to accelerate. The larger the mass of the object, the greater the force needed to cause it to accelerate. Therefore, force = mass x acceleration.

The mass is constant but we can change the force to cause greater acceleration.

3: For every action, there is an equal and opposite reaction.

The more you pull the elastic the more force it generates. The applied force is stored as potential energy and is released as kinetic energy with an equal and opposing force.

Newtons 2nd law states that Force = mass x acceleration

The mass of the car of 0.115kg

If it accelerates at 1m/s then the force required is 0.115 * 1 = 0.115 N (assuming no losses in the system)

m/s * 2.237 = mph.

Greatest acceleration will occur upon release and thereafter reduce due to external forces.

If you time the car over a fixed distance you will get an estimation of speed.

For acceleration (1m/s), mass (0.115kg), and the measured displacement of the elastic (18cm).

Elastic Potential Energy (Joules) = 1/2 * Force (N/m) * Elastic displacement^2 (m)

The Force is the spring constant = F/dX = 0.639N/0.18 = 3.55N/m

EPE (Joules) = 1/2 * (3.55N/m * (0.18m^2)) = 0.0575J

Velocity = sqrt((2*EPE)/kg) =sqrt((2*0.0575)/0.115) = 1 m/s

More force is required to overcome frictional losses & elastic efficiency in the system 0.639N versus 0.115N.

Further experiments looking at the effects on distance and speed can be conducted.

1: With stronger and weaker elastics. (greater or weaker force).

2: For variation in mass..

3: On hard floors (wood/cushion floor) compared to carpet.

4: The ratio of elastic stretch.

Review the data using Excel with charts to visualise the results pictorially and numerically.

This is the body and chassis of the car all in one..

Its designed for rigidity in the 3d form with minimal pieces.

Orientate the piece of card (370 x 230 mm), with the long edge horizontally.

With the pencil and ruler, proceed to mark the card as per the diagram.

Once the card has been marked, proceed to cut the card with a sharp blade using the ruler as a guide

Folds are marked with dotted lines

Holes are marked with a cross.

Once the pattern for the car has been cut out folds are required to give it shape and strength.

Align the centre line on the card with the edge of a table or box and carefully apply pressure close to the line on the card overhanging the edge of the table/box, pushing the card down to form an angle of ~60 degrees.

Proceed to bend the two short tabs inwards to an angle of ~90 degrees.

The long tabs require three bends, one down at 90 degrees, one up at 180 degrees and one down at 90 degrees

Apply glue to three surfaces on both tab sections and stick together using clothes pegs or other suitable clamps to hold the surfaces together until they have dried.

Re-enforcement struts are required to add rigidity to the tabs through which the axles for the wheels will enter.

The struts are easily identifiable with regard to which tabs they attach too.

Cut out the rectangular strut 16 x 6 mm and mark 3mm in from the edge at both ends to fold it in to a wide "U" shape. Invert it and align it with the similarly shaped tabs and glue in place using clamps or clothes pegs to hold the parts in place.

Cut out the shape with the two trapezium ends and bend along the fold lines in to a wide "U" shape. Invert it and align it with the similarly shaped tabs and glue in place using clamps or clothes pegs to hold the parts in place.

The wheels are also made of cardboard consisting of 5 parts each . Rim, Hubcaps * 2, Hub and Hub support.

First make the Rim using cardboard strips.

Cut 4 strips 17cm long by 26mm wide.

Next mark out with a compass or draw around a circular object of the appropriate size and cut out 8 circles for the hub caps with diameter of 53mm and with a skew to be used as an axle make a hole all the way through the centre.

If you change the diameter of the wheels you can calculate the length of the rim from the following:

Circumference = 2 * PI * (Diameter/2)

Additionally, the length of the internal support coil will also vary and can calculated from the following

Length = Pi * N * (Ro + Ri) where PI =3.142, N = number of coils, Ro = outer radius & Ri = inner radius.

If you have used a circular object such as a tin can to draw around to create the circles this can be used to wrap the strips around and taped or glued to create a circle cutting off any excessive overlap.

If not wrap one of the strips around one of the hubs and tape or glue to form a circle.

Check that the 2 hubs on either side of the rim have a snug fit and glue one of the hubs into the rim on the far outer edge making sure its flush to the rim edge. Placing it on a flat surface allows levelling of the rim to the hub.

Then cut 4 more strips 38cm long by 18mm wide these will form the inner support of the wheels.

Wrap these into a loose coil with a tighter centre or form the tighter centre from another strip.

Form the tighter centre around one of the skews that will form the axles and apply tape to the tight coil to maintain its form when pressure is released. Attach this to the loose coil.

Apply glue to the loose coil and tight centre ensuring not to get glue on the skewer or close to the centre hole of the tight centre.

Push this assembly into the container made by the rim and hub and insert a skewer to maintain alignment.

Apply glue to the exposed surface of the coil and tight centre and apply the other hub, ensure the skewer is able to pass all the way through without obstruction or contamination with glue. If glue is seen on the skewer do not leave it in the wheel else it becomes permanently attached.

This should result in 4 wheels.

For surface grip wrap one or more elastic band around the rim to create a tyre.

Make 4 holes into the axles tabs of 4mm diameter and push the axles through and push the wheels onto the ends of the skewers and cut to length ~160mm allowing ~5mm of skewer to be visible beyond the outer rim

The wheels are held on by a friction fit but can also be held in place with rubber grommets or small elastic bands slid on either side of the wheel to prevent sliding and slipping.

Although glue offers a permanent attachment if desired.

The car dimensions when assembled are:

Width = ~16 cm

Length = ~19.5 cm

Height = ~6 cm

Weight = ~115 g

The car is powered by an elastic band configured to perform as the projectile in a catapult but with the elastic band permanently attached.

The elastic band is attached to the car via a post attached at the front.

In the centre of the horizontal part of the axle strut 1cm from the edge drill two 4mm holes, one at the bottom and one directly in line at the top.

Between the gap ~2.6cm and the holes attach a threaded stand-off or stack multiple stand-offs if one does not fill the gap.

Place an elastic band around the post and secure the post in place with two M4 bolts and washers.

The elastic band could be placed over the post or looped around the post.

Its easier to remove if looped but this also shortens the band and tends to pull the car to one side.

As an alternative to stand-off and bolts a skewer could be pushed through the struts in this case the holes would need to be smaller ~2.5cm to maintain a friction fit and using elastic bands or grommets either side the outer top and bottom to hold the skewer in place. A bolt could also be used but ensure the portion around which the elastic band it attached in not threaded or fit a smooth sleeve over this section to prevent the elastic band from being damaged pulling against the thread.

We now need something with which to hold the elastic band in place to create the required tension to propel the car forward.

This is achieved with a plate and pin.

The plate consists of a cardboard sheet, in this case 250mm by 230mm and the pin is a M4/10mm bolt/screw which is fitted in the midline ~1cm from the front. The plate however, could be made from a sheet of hardboard, MDF, Perspex, laminate floorboard or Aluminium sheet.

This specific size enables the majority of the plate to fit under a mat (a rubber mat works well being both flat, firm and heavy whilst woven mats are less effective), with a small portion protruding at the front, held down by the weight of the mat.

Much smaller and it will be pulled out when tension is applied against the mat.

A longer plate (made of a robust material as listed previously), could be used allowing the user to stand or kneel on its length and thereby eliminating a mat.

This is the critical part of the process, if the post in the car is not secure or robust it could fail the same applies to the pin on the plate and also the elastic band.

No not use a thin wooden skewer, bamboo is more robust but metal is much better to prevent failure under tension. Setting the post/pin further back reduces the likelihood of it pulling out as does using washers to increase the surface area of contact to reduce stress on the cardboard.

Make sure that the Elastic band does not require excessive pull force to create a stretch as this will over stress the post and/or pin.

The plate is placed under the mat with the pin visible.

The pin is positioned in front of the car in the direction of travel.

The elastic band is looped over the pin and below the washer securing it in place.

Holding the car at the back it is then pulled back extending the elastic band to the desired length and then the car is released.

The car is then propelled forward by the tension on the band pulling it forward toward the pin.

As the band is not secured to the pin but only looped around it the car is able to move past the pin and continue forward under its own momentum.

Hope you found it interesting enough to build your our version and conduct some of the experiments.