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Electric Motors Electric motors are very popular with builders as they are easy to get hold of and come in various sizes and degrees of power. They can be controlled easily via an electronic RC speed controller and require a minimal amount of maintenance. Most of these will be DC (Direct Current) motors as they are powered straight from a battery. An AC (Alternating Current) motor can be used, but has the added hassle of generating the AC in the first place - this can be done in one of two ways: a) Using an inverter from a battery (though the power generated is not that great), or b) Generating AC from an alternator driven from another source ((e.g. a car alternator). If However powering a DC motor from a battery to drive an alternator to generate AC current to drive an AC motor is not the quickest and most effective method to use. Driving the alternator from a small IC engine is viable, but this system is really for the dedicated and its overall advantages have yet to be proved! NOTE: There is an upper voltage limit of 30 volts DC (should you go the AC route, it is 50 volts AC). However practicalities dictate that you will probably use 6, 12 or 24 volts. It is possible to 'over-run' a motor - running a 6 volt motor on 12 volts for example, which will give extra power, but will shorten the life of the motor. Alternatively, batteries can be arranged so that, for example, a 12 volt motor normally runs on 12 volts, but for that extra boost of power the circuits are switched (via RC) to give 24 volts for a short period. A simple example is to have two 12 volts/6 amp batteries normally wired in parallel, which will give 12 volts at 12 amps. By switching to a series connection, this provides 24 volts at 6 amps. La Machine is famous for its 'turbo boost' using a similar method. Batteries These are likely to be the biggest single outlay in cost. Really there are only two practical type of batteries that are fairly easy to get hold of, but both types are expensive. Ni-Cads (Nickel-Cadmium) - these are rechargeable batteries and can be used as replacements for non-rechargeable AA, C, D type batteries. Each Ni-Cad 'cell' is 1.2 volts, but can be connected together to form a series and thus create higher voltages. It is possible to buy them ready packed in specific voltages. The advantage of Ni-Cads is that they can be fast charged, however, they are not really suitable for powering large motors. Sealed Lead Acid 'Gel' - these are similar to car batteries, but the electrolyte is a gel rather than a liquid. They are also totally sealed and can be used upside-down if necessary. The advantage of these batteries are that they remain charged on 'stand by' for a long period of time and they can also stand a large current drain. However they cannot be fast charged and the largest ones can take over a day (24 hrs) to charge up from flat, therefore spares are essential during recording. Please take note of the following: a) Standard car-type liquid electrolyte batteries are not allowed - even the supposed 'sealed for life' batteries are not fully sealed and if damaged will leak liquid sulphuric acid! b) Both of the above batteries have a low voltage, so there is no danger of electrocution. However, they can contain a considerable amount of power and if short circuited they can heat up rapidly and either explode or start a fire. So all circuits must be adequately protected by thermal circuit beakers and all wires, whether from battery to equipment or between cells of a battery, should be properly insulated. c) Whichever battery you decided upon, you will probably need a minimum of three sets. | |||||||||||||||||
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