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


    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)

     Figure 2 Impact signatures (Courtesy Rutherford Appleton Laboratory Space Electronics

    Group and the Planetary and Space Sciences Research Institute at the Open University)

    V1.2 Chris A Butlin Generic version February 2006

Construction details for DIY force sensor

    Figure 3 DIY force sensor

piezoresistive force sensor FSG15N1A (Farnell 721-6671)

    force sensor mounting bracket (Farnell 721-6683 pk5)

    socket housing 4-way (JPR 710-604)

    crimp terminals (JPR 710-660 pk100)

    ABS box MB1 black (JPR 880-020B)

    PP3 battery snap (JPR 440-006)

    PP3 battery alkaline

    sub-miniature toggle switch SPST (JPR 800-205)

    Velcro Stick On tape

    two-core cable 0.75m

    plastic rod 6mm diameter (Hobbys MR25 or local model shop)

    nut, bolt and washer

    sticky label

    glue Araldite Super-Metal (B&Q)

    2 nuts to fit threaded rod/studding

    plug or plugs to terminate cable to fit datalogger as appropriate

    First drill holes in the ABS box to take the threaded rod, switch, two core cable, sensor mounting bracket, wires to socket housing and at back of vent hole in force sensor. Fit the switch so that when in the down position it is ON. After passing through respective holes in the box, solder the battery snap leads and sensor cable to the crimp terminals. Fit the crimp terminals into the socket housing according to the wiring diagram of the force sensor shown in Figure 4.

    V1.2 Chris A Butlin Generic version February 2006

    Figure 4 Connections to force sensor/socket housing

    Cut the red lead of the battery snap half way between the socket housing and the battery connector and solder the free ends to the switch terminations. Push the force sensor into the socket housing, fit its mounting bracket over it and bolt this to the box. Adjust the force sensor’s position so that its silver sensing button is centrally placed over a hole keeping its vent hole clear. Bolt the threaded rod to the box using a nut each side of its mounting hole. Connect an alkaline PP3 battery to the battery snaps. Use a piece of Velcro Sticky Tape

    to secure the battery to the inside of the ABS box. Solder appropriate plug(s) to the two-core cable so that it can be connected to the datalogger, either directly, or via a voltage sensor.

    Put a label on the lid of the sensor box showing that it is a force sensor, indicating its maximum load of 15N and its output in mV/N (it is likely to be around 20mV/N), and secure the lid to the box. Finally saw off 2.5cm of plastic rod and round off one end. Glue the flat end of the plastic rod to the silver sensor button using Araldite Super-Metal.

    With some dataloggers it is possible to recalibrate a force sensor such as this which provides a voltage output so that, instead of displaying a Voltage-time graph, they display a Force-time graph.

Components suppliers***


    Canal Road

    Leeds LS12 2TU

    Tel: 0870 1200 200



JPR Electronics Ltd

    Unit 4 Circle Business Centre

    Blackburn Road

    Houghton Regis


    Bedfordshire LU5 5DD

    Tel: 01582 470000



    V1.2 Chris A Butlin Generic version February 2006

W Hobby Limited

    Knight’s Hill Square

    London SE27 0HH

    Tel: 020 8761 4244

    Web: E-mail:

    Suppliers of dataloggers and associated force sensors


    Force sensor B3-1100.00

djb microtech Limited

    Delfie House

    1 Delfie Drive


    Scotland PA16 9EN

    Tel: 01475 786540



    Casio EA-100 and EA-200 Data Analysers Dual range force sensor DFS-BTA

    Oxford Educational Supplies Limited Weston Business Park

    Weston on the Green

    Oxford OX6 8SY

    Tel: 01869 344500

    Web: E-mail:

DrDAQ, ADC40, ADC42 and most of their other dataloggers

    Force sensor see DIY version

Pico Technology Limited

    The Mill House

    Cambridge Street

    St Neots

    Cambridgeshire PE19 1QB

    Tel: 01480 396395

    Web: E-mail:

V1.2 Chris A Butlin Generic version February 2006

Easy Sense Advanced, Easy Sense Q Advanced, Fast, Link and Flash


    Force sensor Prod No 3143

Data Harvest Group Limited

    1 Eden Court

    Leighton Buzzard

    Bedfordshire LU7 4FY

    Tel: 01525 373666

    Web: E-mail:

ELogII and eLogIIS

    Force sensor S28L11409 (A special means of attachment will need to be

    devised and range is only ;20N)

Philip Harris Education

    Findel House

    Excelsior Road

    Ashby Park

    Ashby de la Zouch

    Leicestershire LE65 1NG

    Tel: 0845 120 4520

    Web: E-mail:

    Flowlog Lite and Standard Flowlog Dual range force sensor HSDFS

Matrix Multimedia Limited

    The Factory

    Emscote Street South

    Halifax HX1 3AN

    Tel: 0870 700 1831

    Web: E-mail:

    Fourier MultiLog Pro, TriLink and TriLog Force sensor DT272

    Economatics (Education) Limited Darnall Road

    Sheffield S9 5AA

    Tel: 0114 281 3311

    Web: E-mail:

V1.2 Chris A Butlin Generic version February 2006

    Go!Link, Vernier LabPro and Texas Instruments CBL2 Dual range force sensor DFS-BTA

Instruments Direct (Services) Limited

    Unit 10 The Courtyard

    Stenson Road


    Leicestershire LE67 4JP

    Tel: 01530 832 500



Logbook WL, UL, ML, SE and XD

    Force sensor S1642

    (Means of attachment will need to be specially devised or use made instead of

    the DIY sensor with Voltage sensor S1032)


    Abington House

    146 London Road West

    Bath BA1 7DD

    Tel: 0870 225 6175



LogIT Datavision BX and CX

    (LogIT, LogIT eXperiment, Data Meter 1000 and LogIT Live have a maximum

    sampling rate of 500 samples/second which is of borderline use) Force sensor CRD-130-695D + extension lead CRD-130-500V (Means of attachment will need to be specially devised or use made instead of

    the DIY sensor with the 1V sensor adaptor CRD-130-545W)

Griffin and George Limited

    Bishop Meadow Road


    Leicestershire LE11 5RG

    Tel: 01509 233344



Commotion Group

    Commotion House

    Morley Road


    Kent TN9 1RA

    Tel: 01732 773399



V1.2 Chris A Butlin Generic version February 2006

Pasco Xplorer GLX, Xplorer, Power Link, and USB Link

    Force sensor PS-2104

Feedback Instruments Limited

    Park Road


    East Sussex TN6 2QR

    Tel: 01892 653322



Pasco 500 and 750 Interface

    Force sensor CI-6746

Feedback Instruments Limited

    Park Road


    East Sussex TN6 2QR

    Tel: 01892 653322



Sensor CASSY, Pocket CASSY and Mobile CASSY

    Force sensor S 524-042

Didactic Systems Limited

    The Pump House

    Rowdens Road


    Somerset BA5 1TU

    Tel: 01749 677111



Final note

    Whilst I have listed quite an array of dataloggers in current use, you may have one that is not listed here. It may still be of use if it can sample at rates in excess of 1kHz, record data for times between around 100ms and 250ms, and has a ‘trigger’ setting that allows data to be collected on impact.


    To Professor John Zarnecki and Mr Mark Leese of the Planetary and Space Sciences Research Institute at the Open University, Milton Keynes, UK, and Dr Ralph Lorenz of the Department of Planetary Sciences Lunar and Planetary Laboratory at the University of Arizona, Tucson, USA, for their help in developing this activity.

    V1.2 Chris A Butlin Generic version February 2006

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