MECH5720 Sensors And Signals

ASSIGNMENT:    Bat Catcher

TOTAL VALUE:        10%

DUE DATES:            Design Report: Friday 6 October (5pm)



  • Most of the information required to complete this assignment is not available from your notes. You may use any reference works including the internet so long as these are acknowledged
  • Include diagrams and notes of all of your thinking on the problem, but be brief and clear. Pages of information on the topic downloaded from the net does not constitute a thought process and will be marked accordingly
  • Innovation and “lateral thinking” will be rewarded
  • Submit a single report for your Lab Group (maximum 3 people)
  • If too many similarities are detected between reports, the students concerned will be severely penalised
  • Reports returned after the due date will be allocated a mark that is reduced by 20% per day (or part thereof) unless accompanied by valid doctor’s certificates.
  • The combined literature survey and design report must be typed, but can include clear hand drawn diagrams
  • Soft copies submitted using Turnitin
  • The title page of the reports should include the following information:
  • Sensors: Design Assignment
  • Names
  • Student Numbers
  • E-mail addresses 



MECH5720 Sensors And SignalsProf. Fledermaus is the world-renowned expert on cave dwelling bats. In 2015 he observed, albeit briefly, a hitherto unknown Ghost bat (Macroderma ?) feeding on cave crickets above the water of an underground lake.

Observations were difficult because the bat never left this underground habitat and illuminating the cave resulted in the bats becoming agitated and removing themselves to an inaccessible chamber deeper underground.

In an attempt to capture a number of these creatures, Prof. Fledermaus contracted the Sensors & Signals class of 2016 to build an autonomous boat equipped with a thermal infrared camera and a butterfly net as shown in the sketch.

To the dismay of all concerned, when the boat was tested, it was discovered that the insulating properties of the bats fur covering was so effective that no IR signature could be detected.

It was also noted that, even though the tests were conducted while a number of bats were feeding over the water, not a single one flew into the net. It was presumed that the bats were able to detect the fixed net and avoid it.

MECH5720 Sensors And Signals

Prof. Fledermaus has heard that the Sensors & Signals class of 2017 are good, so he is prepared to sponsor one last attempt to catch the illusive Ghost Bat.

The Solution

  1. To minimise additional expenses, the same autonomous boat will be used.
  2. The net will be fitted with a linear actuator that will allow it limited, but fast vertical movement so that it can be popped up into the path of a bat.
  3. Design an active sensor system that can determine the bats trajectory and control both the direction of travel of the boat (it always travels at full speed), and the instant that the net should be popped up into the bats path.
  4. Because the boat runs from batteries, power consumption is important, so make sure the sensor performance matches the requirements of the task.
  5. Though this is a sensor design, any peripheral items that will be required for the system, should be specified and briefly analysed.

Design Information

The Ghost bat

  1. Flies at a maximum speed of 6 m/s
  2. Turning circle with a diameter of 0.5m (15g acceleration)
  3. Hunts between 50mm and 1.5m above the surface of the lake
  4. Uses FM-CF-FM, but the calls are irregular
  5. Wingspan of between 100 and 150mm and beat rate between 5 and 8 per second.
  6. Mass between 50 and 80g

Figure: Typical Irregular Call of Ghost Bat

The Boat

  1. Length 2.5m, breadth 0.6m
  2. Free board 100mm
  3. Sensor Payload 15kg at the stern of the boat
  4. Continuous speed of 10 knots
  5. Turning circle with a diameter of 4m
  6. Net hatch at bow
  7. Net diameter 300mm
  8. Net travel from boat deck up to 1.2m

The Environment

  1. Totally dark underground lake
  2. Constant temperature 20°C
  3. Relative humidity 85 to 100%
  4. Continuous dripping of water from some areas of the cave ceiling (equivalent to 5mm/h rainfall rate)
  5. The air is mostly still, but from time to time wind gusts of up to 2m/s disturb the surface of the lake and blow the falling water about.
  6. Cave crickets fly erratically at anything up to 3m/s, they are 15mm long on average and their wing beat is a fast 30 per second.
  7. Note that this assignment is deliberately open ended to allow students the scope to be innovative and to develop interesting solutions to the problem