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Using a force sensor to identify the type of surface on a model of

By Todd Murphy,2014-11-26 13:50
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Using a force sensor to identify the type of surface on a model of

The Cassini-Huygens Mission to Saturn and its Moons

    Identifying the type of surface on a model of Titan - Technicians’ Guide

    Figure 1 Assembly of testing jig

Equipment required

computer and associated monitor, mouse etc.

    datalogger*and any associated power supply

    force sensor** with collision bumper

    testing jig (see construction details)

*See list of suppliers

    ** See list of suppliers and construction details for DIY version

Construction details for testing jig

4 gully raising pieces - Marley UG52X (B&Q)

    1 pkt Lok joints (B&Q or garden centre)

    4 15cm Sankey Soft TC Colormatt saucers (B&Q or garden centre) 4 24cm saucers Sankey (B&Q or garden centre)

    threaded rod (studding) to fit sensor mounting thread (B&Q) plastic clothes peg

    plastic tubing to just allow threaded rod to slide freely inside it (model shop

     or W Hobby***)

    2 nuts and bolts

    clay (Art/Pottery Department) or Play-Doh if sensor range is small (Toy shop) fine grit for use in bird cage (pet shop)

    fine gravel for use in an aquarium (pet shop)

    silver sand (B&Q)

    access to sieves 2.36mm and 5.00mm or near (Geology/Geography

     Department)

    4 paper labels c. 6cm x 3.5cm

    1 pkt fluorescent circular labels c.1cm diameter

V1.2 Chris A Butlin Generic version February 2006

    First saw 22cm long x 1cm wide vertical cut-outs from the top of each of the gully raising pieces. These are to allow free movement of the sensor cable. 10cm up from the base on the inside of these gully pieces stick eight or so of the fluorescent labels. Their baseline will mark the fill levels of the sand, clay, grit and gravel.

    Saw off a 10cm length of the plastic tubing. Drill a hole in the centre of the 15cm saucer to take this piece of plastic tubing. Drill out the central holes of two of the Lok joints (pieces without protrusions) to fit the plastic tubing. Position one of the Lok joints so that its central hole is over the hole in the saucer and mark the positions of its other two holes on the saucer. Drill holes through the saucer at these positions large enough to take small nuts and bolts that can be fitted through one Lok joint on one side of the saucer and another on the opposite side. Screw the Lok joints to the saucer and fit the plastic tube through the central hole and the Lok joints with about 3.5cm protruding on each side.

    Screw the collision bumper into the force sensor. For some sensors you will have to make a solid collision bumper from a piece of plastic tubing and a bolt to fit the bumper hole’s screw thread. Saw off a 35cm length of threaded rod (studding) and fit it into the mounting hole of the force sensor. Alternative methods will need to be found for the few designs of sensor that do not have a mounting hole. Place the rod holding the force sensor into the plastic tube fitted to the 15cm saucer so that the sensor is up against the lower Lok joint. Secure it in position by clamping the rod above the opposite side of the saucer with a clothes peg. Set the force sensor on its highest range if there is a choice; ;50N

    is ideal. Where necessary, connect a long sensor cable to the force sensor.

    Sieve the gravel so that it has a particle size between about 2.36mm and 5mm. The grit should be OK as it is, likewise the sand and clay. If your force sensor has a rather small maximum range (10N) then you will almost certainly need to substitute Play-Doh for the clay.

    Place the gully raising pipes on the 24cm saucers and fill with silver sand, clay, fine grit and fine gravel respectively to the 10cm level indicated by the fluorescent labels. Stick labels on the outside of each pipe indicating ‘Titan surface A’, ‘Titan surface B’, Titan surface C’ and ‘Titan surface D’.

Production of specimen Force-time graphs

Using each ‘Titan surface’ in turn to obtain Force-time graphs (or Voltage-time

    graphs if using the DIY sensor and recalibration is not possible) and print off copies of each. Label them with what they consisted of sand, clay, fine grit

    and fine gravel.

    Also, for use in discussion sessions, make copies of the annotated and unannotated impact signature (Force-time graph) shown in Figure 2 that was produced as the Huygens probe landed on Titan.

    V1.2 Chris A Butlin Generic version February 2006

Huygens impact signatures (Force-time graphs)