Other tools

Screwdrivers are obviously essential but only small sizes with regular blades up to 4 mm wide. Metric bolts usually need a small-size Posidrive screwdriver. A set of jeweller's screwdrivers is useful on occasions.

An assortment of small files of various shapes is handy for smoothing cut edges and shaping parts of mechanisms. A set of needle files is also worth having.

An engineer's steel rule 300 mm long, graduated in millimetres, completes the tool kit.

Things to think about before starting on the building.

Things to think about before starting on the building.

Chassis:

0 Ready-made chassis such as a plastic food storage box. Easy and quickly built. See Project 6.1, the Scooter, p. 165.

0 An existing toy. Generally easy and quick, but there could be snags. See Project 6.3, p. 246.

0 Chassis made from sheet plastic or foam board. Easy but takes longer. Gives scope for invention. See Project 6.2, the Android, p. 209 and Project 6.4, p. 258.

0 Chassis made from sheet aluminium. You need tools and experience to make it.

Wheels:

0 How many? Three is a popular number.

0 Drive (traction) wheels at front or rear.

0 Steering by tank method (two independent drive wheels, two motors).

0 Steering by automobile method, one motor, with differential gear (complicated).

Copyright © 2007, Thomas Murray

The terrain it is to run on:

0 Hard, level, smooth surface such as wooden or tiled floor, or concrete or brick paving. Wheels may need composition treaded tyres for good grip.

0 Carpeted floor. Mount wheels low down on the chassis to give clearance between the chassis and the carpet. Rugs are often difficult to negotiate, especially rugs with fringes. Wheels of larger diameter ride on to rugs more easily. Steps and stairs are really difficult — instead of wheels use tracks or abandon wheels and go for legs.

0 Lawn. Large diameter wheels, with good clearance.

0 Sloping terrain. Make the robot broad and squat, so that it does not overbalance.

Size:

0 Small size (under 200 mm in all directions) is good for robots run at home. They can find their way between the furniture more easily.

0 Small size may not provide enough space for battery, motors, all the sensors and actuators that are intended.

0 Small size may lead to cramped conditions, making it hard to access circuits for testing, and difficult to insert and remove the PIC microcontroller.

0 Large size leads to greater weight, need for stonger chassis, need for more power to drive it, more powerful (larger and heavier) motors, more powerful (larger and heavier) battery — the situation can get out of hand! Small is beautiful!

Shape:

0 A robot that is about as long as it is wide turns much more easily in a confined space (such as the average family room).

0 A robot that is much taller than it is wide is more likely to fall over on uneven surfaces, if it hits an obstacle, or when it accelerates or decelerates quickly.

0 If the robot is to have jaws for picking up a load, it needs to have a broad base for stability.

There are more detailed design points in the next two sections.

1

1

Wheels

i

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