Micromodel (model making)
Micromodels are very small, usually less than 50 cm long and very light models , which are functional (often remote-controlled) despite their small size.
definition
A precise definition of the term is not possible.
Due to their small footprint, micro-models are often used in living spaces when they are operated, which is why the following distinction is useful:
- Airplanes that can fly in small halls, sometimes even in a living room.
- Car models that fit in one hand, which means that it is already possible to drive on a table.
- Ship models floating in a hand basin. A bathtub or a small biotope are already suitable as fairways.
history
Model aircraft
Micro-flight models with rubber engines have existed since Alphonse Pénaud's invention (1871). When the first model makers appeared around 1930, such planes were already in the program.
Ultralight hall pilots also appeared around 1990, with good results being achieved with gas engines driven by propellant cartridges for whipped cream. However, these models had to do without remote control for a long time, as it would have been too heavy.
The correspondingly light electronics followed around 1995 with receivers under 10 grams (but mostly with a limited range) and servos under 10 grams.
The interplay of increasingly lighter remote control components, new, automatically processable materials ( polystyrene , Depron) and new battery technologies (NiCd, NiMH, LiIon, LiPoly) made small and light flight models (e.g. Shockflyer ) attractive to more and more buyers, who also bought them paid correspondingly higher prices. The industry honored the growing interest with ever lighter products.
Now the buyers could finally have both advantages: low noise pollution and easy handling of the electric drives and attractive flight performance, which were previously reserved for large models with combustion engines. In addition, the small models are more manageable and, due to the lower accelerated mass, less dangerous and less fragile. But even the rotating propeller of a small model can still cause deep cuts.
Automobile models
In the beginning, the twisted bobbin cars were driven with twisted rubber bands
In 1990 there were radio-controlled trucks on a scale of 1:87 (gauge H0). These were driven by servomotors and in some cases were even offered ready-built. The batteries were rechargeable button cells. Even at that time, larger models offered everything that was necessary for a mass market: compact size, attractive driving performance, easy handling.
Especially the particularly handy 1:28 scale (in the car model range 1:32, corresponding to model railroad size 1 gauge) has been growing rapidly since 2000 with a large number of ready-made models (Siku).
Ship models
The first small models were certainly among the ship models, in the beginning these were still equipped with spring drives and mechanical sequence control (rudder). It already existed around 1930. With remote control, small models started around 1970 with moderate performance (displacement ride), finished models were soon available in every toy store. Small models with high performance (gliding) did not come into existence until the miniaturization of the components in 1995, but rarely as finished models and when then more power boats without a specific model. The number of finished models in the toy and model making trade has been increasing since around 2000 and there are also scale planing boats such as yachts or off-shore racing boats. Due to the particularly small and light remote control and drive technologies developed mainly for model aircraft construction, a lot can be expected in the future in the field of micro boat model construction.
Technical and physical requirements
With flight and ship models, the weight is most important, with car models it is more the size of the components, but smaller components are also lighter.
Battery technologies
- Lead batteries : 30–50 Wh / kg
- NiCad : 40-60 Wh / kg
- NiMH : 60-80 Wh / kg
- LiPoly : 150 Wh / kg
The currently most powerful and most expensive battery technology in relation to their weight are lithium polymer batteries. In contrast to nickel batteries, these are charged with constant voltage and current limitation, similar to lead batteries. The end-of-charge voltage is more critical with lithium batteries.
Engine technologies
- Motors with brushes and collector:
- Micro motors wire / sheet metal brushes
- Motors with sprung carbon
- Bell armature motors
- Brushless (brushless) motors
- External rotor (copper-wound stator fixed, bell rotates around stator)
- Internal rotor (multi-pole magnetized rotor turns inside)
- Stepper motors
The miniature motors with sheet metal brushes are by far the cheapest (e.g. 17 g, 3 V for 2.50 euros) but are very limited in terms of load (max. Approx. 2 A). But are often used in Ultralight finished models. Another disadvantage is the limited service life even with moderate loads. They last a few hours under heavy loads. They are available in weights of up to 0.5 grams!
Motors with sprung carbon brushes are more powerful and have a longer service life. d. Usually much more expensive and not available in any small size.
Brushless motors ("Brushless", "BL") are extremely resilient and have a long service life. These require a special, electronic controller that generates the rotating field. The smallest series engines currently weigh around 3 grams. It is possible to convert the motor of an optical drive into a cheap, small brushless motor (examples: Schnurzz, Chipsledde, ...), also stators from other drives such as streamers (e.g. Ditto), floppy disk drives and hard drives (more rarely usable) are also often suitable for conversion.
Remote control technologies
There are receivers well under 1 gram in weight, proportional servos under 2 grams and actuators (electromagnetic control devices) under 0.5 grams, speed controllers from 0.5 grams.
Understandably, there are strong limitations in resilience. Due to the naturally low forces, masses, performances and lever arms, this is not a problem in most cases. (A 0.5 gram “heavy” motor, for example, never needs the 0.5 A that a 0.5 gram motor glider can deliver - the microscopic metal brushes would be overloaded.)
Physical boundary problems
The media air and water in which models are moved do not change their physical properties with the scale of the model. Therefore, the water does not foam in the same way as in the original and propellers lose their efficiency rapidly with increasing size, and wings generate less and less lift in relation to their size. That is why slow flyers often have huge propellers compared to the original and must have a very low wing loading. A wing loading that was scaled exactly and transferred to the model would lead to the flight unfit.
The area / weight ratio shifts when the scale is reduced, which in the case of ship models means that the rudder area usually has to be increased and the volume (weight) of the model becomes smaller faster than the hull area to be created. In model aircraft, the wing area is linked to the scale to the power of two. 1/2 size means 1/4 area.