Pushcarts - Frame

How has it been done before?

Questions and decisions

How can you design your frame to make it strong and light? Where will you need to create triangles? Remember, the lighter it is, the easier it is to start and stop.

Where should your centre of gravity be? Where will you put your seat?

How can you make your frame comfortable and safe for the driver? What sort of seat? Where will they rest their feet?

How can you make your frame comfortable and safe for the pusher? How high does the pushbar need to be?

How can you keep the pusher and driver safe in a crash?

How wide and how long should the pushcart be?

What specifications must you remember?

Suggestions and Choices

You will need to think about

• materials
• structures
• joining methods

First think about your frame in side view, front view and top view.

The important things about to consider about shape design include:

• a pivot point for the front axle
• a push bar at the right height for the pusher
• no sharp corners or edges
• triangular bracing to make it strong
• symmetry
• length of wheel base

You might want to investigate some frame shapes used by makers of go-karts, trailers towed by cars, cars themselves or successful pushcarts from other events for ideas. They use shapes like these below:

Remember that triangles will make your structure stronger. Where would you need to add triangles to the shapes above to make them stronger.

Try This

Whatever shape you choose for the frame, you may need to test answers to these questions...

• What is the lightest, yet strongest material to make the frame out of? (should I use balsa wood, PVC pipes, flat solid wooden planks, steel or aluminium ( I, H, box or U shaped cross-section), plywood sheet or laminated wooden beams…any others you can think of?) You may want to have a look at options in your local hardware store and work out the different names of things so that you can talk about them in your group.
• If I make it out of or planks, how do I join all the bits together (bolts, screws, nails, taped together…any others you can think of?
• How do I make sure the joining method I use will keep things together for the whole time I need them to?
• When testing the frame, from what directions will the largest forces come that are likely to break the frame?
• How can I safely test the frame itself?

Does the wheel base (distance between your wheels - on each axle, between axles) make a difference? You should investigate the effects of different wheel base lengths before you make final choices about your frame design.

For each type of frame option you have available you should list the choices you have. Write down the 'strengths and weaknesses' for each choice to help you make your final decision.

Test your frame options for

• ease of use and comfort for driver and pusher
• strength
• durability
• safety for working with it
• safety for broken pieces

For Teachers

Link to the 'Making a frame for the cart' document.

Support Materials developed by engineeringLinks at UTS

Build your own 60's timber billy cart (scroll down to find the instructions)

Bob Rich's billy cart (Part 2 is about making billycarts)