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An introduction to electronics
An introduction to electronics

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1.2 The sensing–logic–actuation cycle in practice

Watch the video below, which is a promotional video for Oxboard showing a child riding one of their two-wheeled devices. It is remarkable how the board responds to the way the rider moves his feet and body, and how controllable it is.

Download this video clip.Video player: A child riding an Oxboard
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Transcript: A child riding an Oxboard

[BACKGROUND NOISES]

[MUSIC PLAYING IN BACKGROUND]

[BACKGROUND NOISES]

[GIGGLING]

[CHILD SPEAKING]

[MUSIC PLAYING IN BACKGROUND]

[BACKGROUND NOISES]

[BELL RINGING]

[MUSIC PLAYING IN BACKGROUND]

[BACKGROUND NOISES]

End transcript: A child riding an Oxboard
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A child riding an Oxboard
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This video shows a child riding an Oxboard. He stands on the board with his hands behind his back. The board moves smoothly around people and obstacles in response to the rider’s smallest movements.

A child riding an Oxboard
Interactive feature not available in single page view (see it in standard view).

Figure 6 gives some of the details of the Oxboard’s construction and use.

Described image
Figure 6  The Oxboard product description
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On the left of this image is a description of the Oxboard, as follows:

The Oxboard is a personal transporter. It is a board with two wheels, one each side. Oxboard has two built-in motors fed by a battery pack. You can go forwards or backwards with the Oxboard but also take left or right-hand bends. The compact design also ensures that you can use the Oxboard both inside and outside.

The Oxboard is a clever device that reacts to how your weight is distributed. The trick is in particular to relax when standing on the Oxboard; the Oxboard will then ensure the best balance. The Oxboard wil react directly if you distribute your weight ‘unevenly’; lean forward and you will move forwards, lean to the left and the Oxboard veers to the left. etc.

On the right is a photograph of the Oxboard with the following components labelled: crash bumpers; rubber mat with sensors below that sense how you are leaning on the Oxboard; battery indicators; motor, wheels and tyres; LED lights; on button; connector for charger.

Figure 6  The Oxboard product description

Think about the sensing–logic–actuation cycle for the Oxboard transporter system. The board has sensors to detect the way the rider moves his feet and body. It uses logic to compute all the complicated forces associated with the motion; based on that information, it controls the two actuators (motor-driven wheels) to transport the rider in his desired direction.

SAQ 1

Draw a sensing–logic–actuation cycle for the Oxboard transporter using Figure 1 as a template.

Answer

A possible answer is shown in Figure 7.

Described image
Figure 7  The sensing–logic–actuation control cycle for the Oxboard transporter
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This is a sensing–logic–actuation cycle for the Oxboard. The sensing box contains the words ‘Sensors – detect position of rider, various forces, speed, etc.’ The logic box contains the words ‘Logic – calculation of forces, reasoning, planning and control used to decide what power to apply to the motors’. The actuation box contains the words ‘Actuation – the motors turn the wheels to create forces keeping the rider upright and moving in the desired direction’. The environment shape at the bottom contains the words ‘Environment – flat ground’ and ‘Rider in charge’, meaning that the rider is in the environment of the machine, and that the machine responds through its sensors to how the rider leans his body.

Figure 7  The sensing–logic–actuation control cycle for the Oxboard transporter