The picture shows some of the fans we have found and used, or tried to use. Inevitably, the older types are the best (and the hardest to find). The three fans on the left of the picture are all basically the same type. The black fan-blades are hard, sharp-edged plastic and seem to work best. The white blades are now more common - they are a more flexible plastic and work fairly well. The white fan is a promotional item, presumably given away by the business whose name is on the side - we found it for fifty pence in one of those stores that specialise in cheap/remaindered items.
The next fan has a sort of five-blade rigid impeller inside a safety cage. We thought this would give lots of push, but it is not as good as the two-blade type. Nevertheless, we have used these successfully - particularly on small boats. The safety cage is not really necessary, and you get more push with it removed.
The next two fans have soft floppy blades. These "safety" blades are not much use for pushing models, although we have found that the smaller one, with the angled head, is quite good for its intended purpose as a cooling fan. The orange one with the big blue and yellow fan is not much use as it stands, but it could be fitted with a gear or a pulley and has conveniently flat sides for mounting.
On the right of the picture is a small desk fan with a comparatively large blade - we thought we could just stick this on a wheeled platform and watch it zoom away. In the event, it was not very impressive and it is too noisy to use as a desk fan! Of course, we might fit the blade onto a bigger motor...
The motors in the fans tend to have 2mm shafts. This is handy, not only because the fans are interchangeable, but also because 2mm is one of the standard sizes for which you can easily buy cheap plastic gears and pulleys.
We regard the fans as re-usable, so we try to avoid anything permanent. Rubber bands are favourite, and most of the models on the projects page use this technique. Providing pegs for the rubber bands is straight forward in Lego Technic or K'Nex. On fabricated chassis, a piece of foam packaging material with kebab sticks pushed through works well.
If the fans have to be stuck on then adhesive foam pads are quite secure and not too hard to peel off.
Pretty much anything small and light that can roll along the ground or float on water could have a fan put on it. Discarded bottles and bits of old toys can be pressed into service - we have included the bottle buggy and the boats in our projects page to show how simple (and cheap) it can be.
Construction toys, such as Lego and K'Nex, are great, and several of our models use these.
There is satisfaction, however, and lots of learning value in designing and building your own. To do this, youngsters need materials that they can cut and fix without using anything too dangerous - such as cardboard and corriflute plastic sheet. (See picture.)
For those unfamiliar with corriflute, it is a sort of plastic equivalent of corrugated cardboard. It is quite tough, reasonably rigid especially in the direction of the channels, and comes in bright, primary colours. Axles can be put through the holes. The neatest way to cut corriflute is probably with a craft knife and a steel rule, but youngsters can cut it quite satisfactorily with shears or even scissors. Holes can be made with a gimlet or a small punch. Pieces of corriflute can be joined using split paper clips, nuts and bolts, various types of plastic clips and adhesives.
Our corriflute buggies have the corrugations running fore and aft for strength. Strips running left to right are then glued on to carry the axles.
We buy corriflute from Tech-Supplies (sources), but it is worth noting that lots of temporary signs are made from a similar material, including estate agents' signs and those "Vote for Bloggs" signs that appear everywhere in the run up to elections. This sort is bit softer than the real thing, but it is free!
Cardboard must be one of the most common materials for budding designers. As well as the usual shoe boxes, etc, we use an interesting product called TechCard, which we get from Hands On (sources). TechCard consists of pre-punched and scored bases, girders and beams which can be cut and glued to form all sorts of structures. There are card or wooden wheels and wooden axles to go with it. It is made from recycled materials and looks vaguely like a sort of cardboard Meccanno. It can be cut with scissors, glued with ordinary white PVA adhesive and held together with paper clips while the glue sets. All very safe and suitable for youngsters - and it makes surprisingly rigid structures.
You are spoiled for choice. Bottle-top wheels on kebab stick axles, running in plastic drinking straws, are quite effective, colourful and almost free. Models made from bottle tops, kebab sticks, toothpicks, drinking straws, CDs, cotton reels, rubber bands and the like were a regular feature of a brilliant, but now sadly defunct, British TV show for kids called The Big Bang. There was also a website with detailed instructions for building the models shown in the programme. If you want posh, model shops have very pretty model aircraft wheels and quite butch RC racing car slicks; you can get inexpensive plastic wheels from Tech-Supplies and plastic or wooden ones from Hands On (sources) and no doubt many other places besides. Metal and wooden axles to fit the wheels are available from the same sources.
TechCard has ready-punched holes for axles. Corriflute has channels, and when they run fore and aft we glue on transverse pieces to carry the axles. Plastic drinking straws make quite good bearings for axles and can be hot-glued to most things. Of course, if you are using a construction system such as K'Nex or Lego Technic then compatible wheels and axles, not to mention gears, pulleys, etc, are all part of the system.
Part of the point of using fans is to make simple, working models that don't need pulleys or gears. But if you get bored with fan-drive, then using pulleys or gears to couple the drive to the wheels can be quite instructional. You will need some sort of gearing - the shaft speed is too high to drive a wheel directly. A belt drive and a worm drive are included among the buggies on our projects page.
We bought small pulleys that are a push fit on the 2mm fan motor shaft from Craftpacks (sources). Tech-Supplies do a quite interesting and colourful range of wheels, gears and cams which fit their 3mm axles, along with a 2mm bore worm gear which fits directly onto the motor shaft.
And of course, if you are using a construction system such as K'Nex or Lego Technic then compatible pulleys and gears, as well as wheels and axles, are all part of the system.
Adults will probably use steel rules, craft knives and so on, but these are not very suitable for children. Scissors can be used but are limited. We have an excellent pair of shears, bought from Craftpacks (sources) which are very safe and can handle cardboard and corriflute with ease.
For making small, neat holes, safely, in a range of sizes it is hard to beat an adjustable leather punch. I think we got ours at a car boot sale.
Adhesives are a problem. Super glue is not safe for youngsters. We do use hot glue, under careful supervision, and we should probably investigate "warm" glue. Youngsters can do a lot with adhesive tapes and sticky pads quite safely and white PVA glue is great for paper, cardboard, wood, cloth and most things porous.