What it shows
A rocker-bogie suspension lets a six-wheeled rover climb over rocks about as big as its wheels without tipping. The body stays almost level because the arms pivot.
The science
The rocker arm on each side carries the front wheel and is joined by a pivot to a smaller bogie arm that carries two wheels. When one wheel climbs an obstacle, its rocker tilts, and a cross rod makes the body take the average of the two sides, so it tilts only by half as much. All six wheels stay in touch with the ground, so the rover keeps its grip and traction on rough ground.
Materials
Cost: under Rs 50. Many items come from home or from waste; spare parts such as LEDs, motors and wire are in the store.
- Corrugated cardboard and ice-cream sticks
- Six bottle caps as wheels
- Wooden skewers for axles and pivots
- Straws as bearings
- Glue, tape and a hole punch
- A small tray with pebbles for a test track
Safety
For this project: An adult should cut cardboard and trim skewer points.
Never use mains electricity: power models with cells, batteries or a low-voltage adapter. Sharp and hot tools, flames and lab chemicals need an adult or your teacher beside you. Keep magnets, button cells and small parts away from young children, and wash your hands after making.
Step by step
8 steps. Do them in order, and test each part before you go on to the next. Write what you notice in a notebook as you go.
Cut two long rocker arms and two short bogie arms from cardboard, one rocker and one bogie for each side.
Fix one wheel at the front end of each rocker arm and a pair of wheels on each bogie arm, using skewer axles through straw bearings.
Join the rear end of each rocker to its bogie arm with a skewer pivot, so the front wheel is on the rocker and the middle and rear wheels are on the bogie.
Check that the second side matches the first and that the arms swing freely.
Connect the two rockers to a body box using a skewer pivot through each rocker near the point where the bogie joins.
Add a cross rod so the left and right rockers tilt in opposite directions.
Push the rover over a stone about the size of a wheel and watch the body.
Compare with a rigid chassis rover that has four fixed wheels and note the difference.
What you should see
A rover that climbs a pebble with the body tilting about half as much as a wheel lifts, and with all wheels touching, while a rigid version tips or stalls.
Viva questions
A teacher or a judge will ask how it works. Try to answer each question before you open it, then compare.
01Which space rovers use rocker-bogie?
NASA’s Curiosity and Perseverance, and India’s Pragyan rover in a similar design.
02Why six wheels?
They share the load and keep traction on rough ground.
03Why does the body tilt only half?
The pivot links average the movement of both sides.
04Why is slow speed good for a rover?
It lets it move safely over rocks and saves power.
Take it further
Add a small motor and battery so the model can climb a ramp by itself.
Change one thing, measure what happens, and add a table or chart of your readings: that is what turns a model into your own investigation.
Free ebooks for this project
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