MUTR.co.uk

Ask John

John has been a professor at Middlesex University for some 18 years, and has wide ranging interests in technology and science (and their history) and likes to make things. He particularly enjoys weird materials, bizarre anecdotes and unusual facts - hence the title of this section.

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Q. I will be teaching the EM in September ,... if you cannot get sunburnt through the glass i.e. window or wind screen of a car why then does furniture fade? - Sandra

A. If I understand your question correctly, I think the answer is that it depends on the UV blocking agents used in windows or windscreens.

Q. Regarding your Faraday Film - Transparent Conductive Film (234-313A), what is the electrical resistivity of the film? Also, is this product in stock? - Ken, aatdesign.com

A. Thank you for your enquiry. The coating is on one side of the film and there is some variation over the surface but if you take a strip – say – 1 cm x 100 cms over a 100 cm length, a typical resistance measurement would be 20 Ohms or less which is sufficient to energise an LED over a larger length. The product is in stock.

Q. I have just been given the task of introducing an element of Control into KS3 DT. I am wondering if you sell any projects that would cover this. I saw the "message in a box" advertised but could not find any details of what this is about. I also the jitterbug project but again could not find out how much this costs. It looks rather complicated for someone who hasn't taught Control. Can you suggest anything, please? - Karen, Wilmington

A. Thank you for your enquiry. If you look at our complete product range online – (www.mutr.co.uk) or phone our warehouse for a catalogue (01992 716052) you will spot potential projects available as physical resources and publications. The Message in a Box is not as suitable as some. I would recommend the Bug – as a starting point. One or two of our products use the IQ3 board and this is extremely simple to program. It might be useful to get one of these and have a go. Once you feel confident in using it, you will have more opportunities to apply the board.
If you are still not sure, please come back to us.

Q. I am interested in a conductible material that can laminate to another material like a sandwich. It needs to conduct things as we have a request for a taser dart that can be tested against a material to make sure it conducts. We need it as a minimum of 150cm wide. I have a sample of shiny silver aluminium conductible foil that we have which does the job we need it to do. It has a sticky back and this can be laminated but it only comes in strips 7.3cm wide which is no good to us and is about 1 - 2mm thick. Do you have anything like this? We don't mind that it isn't raised but we need it to have aluminium in to conduct the taser. - Lynne

A. Thank you for your enquiry. We have a number of conductive fabrics whose fibres are metal coated with nickel, copper or silver. All can be successfully laminated to others depending on the glue/adhesive available. We sell them by length with a minimum width of one metre. I think any one of seven materials would satisfy your requirements as we think these conductive materials are just as effective as pure aluminium foil. See HERE for more.

Q. I am looking at building a solar powered cars as part of a sustainabity day at school for year 7. I am planning on charging one of your 10F super capacitors using one of your (3V 90mA) Solar panels, is this possible ? how long willit take?. Will this then run a motor e.g MM10 or MM28? for how long? - Mark, Halifax

A. Thank you for your enquiry. The answer is slightly grey as it all depends on the amount of light falling on the solar panel. Roughly, in very bright sunlight the capacitor will charge up sufficiently to run either of the two motors in about 30 secs. In less ideal conditions it will still work but will take longer, eg, up to two mins to get moderate light.
We are working on and hope to have available in September a kick-start circuit which can be filled between the solar panel, capacitor and motor so that when the capacitor is charged it switches the capacitor to the motor automatically.

Q. hi could you please advise me on what LED'S and resistors to purchase. i am fitting 5mm led's into a battery box and using a 900mAh 3.6v -4.2 battery - Michael

A. Thank you for your enquiry. We have a large range of LEDs any one of which you might want to choose. Please see what we have HERE. To make life simple, I suggest you fit any of them with a 1k resistor for protection. It is ‘over the top’ to use a 1k resistor if you apply the ‘official’ formula but it will keep the LEDs safe!

Q. I am looking for any material, chemical, or gadgets that can be used in Engraving and plating processes.
This could be machanical, photographic or electrolysis... in fact anything I can experiment with. - Peter, essexhistory

A. Thank you for your enquiry. We have some items that might suit you: Engraving laminate, Anodised aluminium, Ferric Chloride, Titanium micro- anodising kit.
I'm sure at least one of these meets your needs adequately.

Q. I am looking to make some bionic arms with our KS3 classes. Please could you advise me on what smart wire and connectors I will need. - Nicholas, Penarth

A. Thank you for your enquiry about bionic arms. The wire that you require would be what we describe as ‘smart wire’, which contracts about 5% on heating using a low voltage power supply or battery. Either of the two diameters will do but the larger one requires more current. It can be soldered so you need a mechanical connection. We supply tubular crimps, which are crushed with wires around the smart wire and conductor.

Q. I am hoping to make up an electro conductive fabric sensor pad for the start/stop button so would be very interested in obtaining some samples of your various electro conductive fabrics. Obviously to separate the positive and negative elements of the sensor pad when no pressure is being applied, I will need a semi insulative fabric to sit between the layers, are you able to supply this as well?
I aim to carry the signal from the sensor pad down the thumb and to the wrist of the glove via silver conductive thread so it would be very useful if a meter or two could be included in the sample pack as well if at all possible. - Ed, Rochester

A. Thank you for your e-mail. We have made up a sample pack of the conductive materials etc. and you can view this on the website (it has just become available).
I guess this is what you will need for any experiments. I can confirm that almost all of these can be used to make ‘soft’ switches on a similar principle to the three layer membrane panels used in thin calculators, vending machines etc. The circuitry is a different matter, and I’m afraid that we have nothing really relevant. However, we have done some work for Maplin, and I think that you will have some luck there either by calling into a store or going onto their website. www.maplin.co.uk

Q. Please can you describe the effects of the 'Chameleon Nano Flakes'. I have read that a black background will achieve emerald green to copper red. Can you give an indication of the effects if one is using different colour bases, ie red, green, blue, yellow etc. - Tone, plusoneproducts.

A. Thank you for your enquiry about nanoflakes. They produce a complex light scattering effect and colour is achieved by reflection and interference. If you use a base colour other than black you will get a colour bias due to both reflection and absorption. However, the only way to see the effect is to do experiments – and I should add it also depends on the thickness of the film condition of the nanoflakes.

Q. I am trying to create a sound reactive textile collection using conductive thread. The conductive thread will be embroidered onto a silk or cotton fabric. I am aware that I need to create a circuit but really don’t know where to start! My aim is that when the embroidery is touched by hand a sound which varies in tone is created. I have purchased the conductive thread but would really appreciate any advice as to what electrical components I need in order to make this work.
I have seen two examples of the technique I am trying to create (http://www.vimeo.com/1904793)
(http://www.fashioningtech.com/profiles/blogs/conductive-threads-weave-a-new) but as I have little electrical knowledge I don’t know where to begin.
Any advice or tips you could give me would be greatly received. ? - Sarah, Doncaster

A. Thank you for your question about a sound reactive textile. It is a very big question! The creation of a circuit to do what you want is extremely complex. It will take a short book to explain all the options.

However, I suspect the solution would be to look at some introductory electronics books – eg, those in Maplin Electronics – and to get some ideas from projects already done. Also, if you look in WH Smith along the electronics hobbyists’ shelf, you may see some magazines with projects that are suitable for adapting for your needs.

Q. I have to investigate the properties of oils for my GCSE exam this year.As I am an independent student i have to arrange for my experiment.What is a cheap and reliable way of using something instead of a cup viscometer.
Maybe a graduated funnel ? - Shubnum, Ilford.

A. Thank you for your question about oil. MUTR supplies a low cost viscometer.
This will be ideal for your experiments. You might be able to use other containers, eg, yoghurt pots but I don’t know how successful these will be.

Q. Is Polymorph thermosetting plastic or thermoplastic? - Thomas, Ruislip

A. Polymorph is a thermoplastic..

Q. I am a 66year old retired butcher at this late stadge has taken up building various crystal radio sets with some delightful results,i also have a very old 2 valve radio set with a horn type speaker could you recommend a mini amplifer that would enhance the performance where it could be bought,thanking you in advance. - William C., Coleraine.

A. We share your interest, and produce a reproduction postcard crystal radio for several museums as well as other novelty radios such as this matchbox crystal radio
We also stock a low-cost stereo amplifier which I think might work as you intend – using just one of the two channels. It only costs about £1.50 and so is worth a go.
Alternatively, we designed a range of electronic kits for Maplin, and so if you have a local store, take a look. They are also on their website HERE.
The two-valve radio you have sounds fascinating – a rare survival.

Q. My year 11 students have to research smart materials for their final textiles examination this summer. They have been asked to design a product suitable for a child’s bedroom that incorporates the use of smart materials. Have you any thought or ideas, as much of the research I have done is suitable for an older market or not really appropriate for a bedroom.
I have briefly discussed the following technical textile categories:
• Build-tech • Geo-tech • Pro-tech
• Pro-tech • Agro-tech • Cloth-tech
• Mobil-tech • Home-tech • Indu-tech
• Medi-tech • Pack-tech • Biomimetics
• Thermo chromic and phosphorescent pigments.? - Hannah C., Surrey

A. I think that your survey is pretty comprehensive and I guess that y11 students should be able to think seriously about the applications of most of the materials we stock – including, possibly our new conductive threads and woven fabrics (soft switching/lighting). See our link

In practice, I agree that the phosphorescent and thermochromic sheet(s) and pigments

will be of interest since these are easily used; producing glow in the dark effects is always popular and can even be useful as lighting. It is also worth noting that that our range of hydrogels are used commercially for babies’ nappies etc. so this might lead to a new context.

Good luck with the project.

Q. I am in interested to know about the types of Thermochromic plastics available. I have done a bit of research but there doesn’t seem to be much information about the specific characteristics I am looking for.
I need to know how far the colour can spread in Thermochromic plastics - by this I mean can a spoon I am holding at one end completely change colour?
I am designing something where I would like the handle to be Thermochromic plastic and the heat source someones hand, ideally the whole handle would change colour in response to someone holding it.
Do you think this is possible to be achieved? How about if the handle is some highly sensitive heat conductor coated with themrochromic plastic. - Martin P., London.

A. The requirement makes perfect sense but I am afraid you might be slightly disappointed. In principle the colour will spread from the heat source given time but because plastics are such a poor conductor we think the heat loss from the end of the handle would more than equal the amount of heat you are putting into the handle at one end. This will mean you will just get colour change near the handle.
Perhaps you could have a metallic conductor inside the handle with a layer of thermochromic material, eg, a painted surface. However, even this I think would be tricky because you will have the same heat loss problem.
It may just work if you had a thermochromic pigment with a much lower temperature threshold but I think it will be a difficult balancing act.

Q. What is the best product to mix Phase Change powder with to use the phase change properties? - Simon Johnson, Sheffield

A. It all depends on your application, but the easiest material to mix the phase change powder with is plaster which then provides the kind of ‘smart’ building block used in the building trade to reduce the cost of air conditioning within buildings. I hope this helps.

Q. What are shadows made of? Shadows have always fascinated me. I thought about this question myself, and it can get quite deep. What are your thoughts on this? - Doug, Haverhill/Suffolk.

A. This is an intruiging one and it can be tackled from various angles. Perhaps a more philosophical approach is needed. Instead of asking what they are; maybe we should ask what they are NOT. They lack energy (light) due to whatever is casting the shadow, blocking the light and is therefore made up of the matter which is present minus the energy of light.

Q. Is there a ‘How to use’ information sheet on High Impact Polystyrene Sheet please, if you do not have a vacuum former? - Jeremy King, London

A. There is no single comprehensive sheet on working with ‘HIPS’ but generally the material can be formed by laying a section over a shape to be formed then heating using a heat-gun. HIPS can also be cut by simply scoring and snapping. It can be drilled like or machined easily due to its inherent softness.

Q. I‘m planning to use LEDs for my art, but not sure what type of resistor to use with the LEDs? - Justina Lok, Bourne.

A. The value of resistor(s) to use is dependant upon two factors; firstly the voltage you will be using (the higher the voltage, the greater the value of the resistor required), and secondly whether the LEDs are to be used in series or in parallel.

Q. How strong is Kevlar 49 and what is the thickness ratio to strength? - David Clews, Sines, Portugal.

A. Kevlar 49 combines high tensile strength (43,000 PSI) and high modulus (19 million PSI) with light weight and toughness superior to other reinforcing fibers for plastics. The ratio of thickness to strength: 200lb per inch for a piece of 0.004 inches.

Q. Why do water droplets in winter,stay liquid on a car windscreen,but when it is smeared by wipers,it freezes? - Colin J Gray, Somerset.

A. This is primarily due to the relative volume of droplets of water compared to a thin smearing. Temperatures need to drop further in order for the freezing conditions to fully ‘penetrate’ a droplet.

Q. I sometimes get an electric shock off a tiny 3 volt electric buzzer. Why?

A. You must be touching two bare wires leading to the buzzer while it is working. Most buzzers contain an electromagnet that switches on and off at high speed. When this switches off, its magnetic field collapses and produces a high voltage ‘spike’ for a very short period. This spike provides a much higher voltage than the battery, but is normally fairly safe - if a little painful.

Q. What is an air muscle? - Peter, Barnet.

A. This is a device that contracts with a pulling force when supplied with compressed air. It consits of a rubber balloon inside a woven expanding braid material. When the balloon is expanded with compressed air it forces the braid outwards causing it to contract end to end. It is believed that air muscles were first used for puppet movements in the Spitting Image TV series, but they are now used widely in industry and for robotics development.

Q. We are a war-gaming group and want special effects like lighting and movements on a battlefield model. We don‘t have much money. Any ideas?

A. There are lots of programmable control systems many of which hook up to computers. These can control anything electrical like LEDs turning on and off. If you want something low-cost then our own IQ2 controller might do. This lets you program up to four outputs on and off simply by operating on-board switches (i.e., no computer needed). The 1Q2 can control LEDs (lights), buzzers (sound) and electric motors (movement). For the latter, you might consider using a motor and an off-centre mass like wheel loaded on one side with Blue Tack. This will cause a significant vibration -perhaps simulating an explosion.

Q. I‘ve just seen a car that seems to change colour. How does that work? - Adam, Brighton.

A. Its probably because the car is sprayed with a special light-scattering paint. This stuff is sometimes referred to as a chameleon colour - after the animal that can change its colour at will to fit in with its background. The paint contains tiny micron-size particles that give a light scattering effect leading to the appearance of different colours when you view from different angles. The car is fist sprayed black and then given a coat of clear lacquer containing the chameleon particles. (N.b.There are many other colour switching examples in the natural world. The cuttle fish can change colour more or less instantly to blend in with its background.)

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