4. MOTOR BASED SYSTEMS

4.1 Types of electric motor

Most electrically powered mechanical equipment contains some sort of electric motor. By damaging the electric motor, you disable the whole machine. In practice this can be easy to do since electric motors (with the exception of those designed to be used in extreme conditions) are delicate objects which must be kept cool, dry, lubricated, and free from dust.

There are a wide range of electric motors, in different shapes, sizes and constructions. You should also be aware that most generator systems use devices almost identical to electric motors 'in reverse' - by turning the motor manually you create electricity. Therefore this section could be equally applied to generator systems.

4.2 DC, AC and 3-phase motors

Motors come in different physical sizes, but they also run on different electrical supplies. Some run on single phase alternating current (AC) supplies like you have in your home. Others have 'three phase' supplies, equivalent to three domestic supplies with the alternating currents out of phase, to give the motor more power (these are generally used in industrial plants). Finally, some motors use direct current supplies - this is mainly when the motor draws its power from batteries, solar cells, or generators which power 'through' a bank of batteries (most vehicles use this system).

All motors work on electromagnetism, that is, the action of the electricity creates a magnetic force within the motor which turns the shaft. AC and DC systems operate this system rather differently, but the principle is essentially the same.

The diagrams on the previous page show the essential parts of electric motors. Note also that although the workings are similar, they come in different constructions - some are flange mounted (a good example of flange mounted motors are pumps, such as hydraulic pumps), and some are foot mounted (most mechanical systems use foot mounted motors).

The design of electric motors (figures 6-8)

4.3 Generators

As noted above, a similar device to a motor used in reverse can create electricity. The energy expended by turning the shaft creates electrical energy which flows out of the device.

When sabotaging generators the considerations are essentially the same, but you must always consider the practicality of your actions (as noted earlier in this volume). By sabotaging a generator you deny equipment electrical power - but a generator is easily replaced. On a work/cost/benefit analysis it may be a better option to actually sabotage the equipment that the generator powers rather then just doing the generator itself. However, in certain situations (such as building sites) taking out a generator can be much faster than doing every piece of machinery.

4.4 Basic sabotage of electric motors

There are various options for disabling electric motors. Essentially it is a matter of cutting the supply of energy to the system, damaging the moving parts of the system, damaging the electrical circuits or attacking the bearings/workings using abrasives or glue.

Electrical supply:

Cutting the supply to an electric motor can be done in a few seconds - taking all the normal precautions when cutting high voltage cables. The only problem here is that the cables can be very quickly reconnected by even amateur electricians. In practice when disconnecting the supply you have to do a little more.

Many electrical motors do not simply have the power cable entering the motor - often it is necessary to have additional electrical components to modify the electrical current, or proven the emission of electrical noise into the power system. On larger electrical motors the electrical components needed to do this are large, and are often mounted within a metal enclosure on the side of the motor housing. Smaller motors may actually have the components just wired onto the outside.

Motor power control (figure 9)

The diagram above shows a typical layout for the enclosure. The cover plate is held in place by screws or bolts - these can either be removed, or if they are fixed (or riveted) drilled out. Beneath the plate you will find a few electrical components (normally cylindrical or disc like, perhaps some fuses, and a number of terminal where the wires from the mains cable and the motor are connected.

You now have three options...

• Forget removing the cover, just smash the entire enclosure off the side of the motor - effective but noisy;
• Cut the wires inside the box, and if possible remove the electrical components and dispose of elsewhere;
• More infuriating to your target, carefully remove the cover plate, remove the components/cut wires, then replace the cover plate and fix with superglue and/or threadlock on the screws.

Taking this approach creates more difficulty. It is highly likely that the operator will have to employ professional motor servicing people to fix the damage - which might take a day or two.

Moving parts:

The power from an electric motor is used for something - the simplest option if easy access to the coupling between the shaft and the drive mechanism is exposed it to damage or disconnect it. Drive shafts are hard things to break, so this will normally entail unscrewing things or taking bolts out.

Alternatively, you could weld or solder up the shaft where it leaves the motor. If there is no surge protection or fuses in the system (possible on old equipment) this will burn out the motor when it is turned on.

Another option is to damage the air cooling fan. Electrical motors produce large quantities of heat as they run. On large motors this heat cannot be dissipated quickly enough through the metal body of the motor, and so air is blow through the motor housing by a fan connected to the shaft.

There are two simple options to make the motor overheat:

• Remove the fan - but replace the motor housing so no one notices. Eventually the motor may overheat and burn out, but this is dependent upon the load put on it;
• The best option for a motor that is actually running is to pour fine dry sand, or some sort of powder, into the fan, or the air inlet (depending on where the air enters the housing). This will be sucked through the motor and will either gunge up, melt or abrade the internal workings of the motor until it either burns out, falls apart, or catches fire.

Electrical circuits:

The flaw in any motor is the integrity of the hundreds of feet of copper cable that are wound in coils within the motor. If you can break or cut some of these cables the whole motor will have to be replaced - which could take some time.

There are four main ways of doing this:

• If the cables are exposed enough, cut them with side cutters or a small hacksaw blade (copper is soft and cuts easily using a hacksaw blade on its own - not actually set in its frame holder);
• If it is difficult to get at the cables, or they are some distance in, use a screwdriver or chisel to part the coils;
• Pour acid over the coils or inside the motor housing - do not do this when the motor is running or you'll splash acid everywhere!;
• Tip some form of home-made incendiary compound into the motor housing and set it off (this makes the biggest mess of all).

There is another option for breaking the electrical circuits. On some motors power must be transferred to the coils of wire which rotate on the shaft. To do this there are a set of electrical contacts (called brushes) and a metal contact surface called the commutator. You should be able to remove the brushes fairly easily (often they just screw in on the end of springs) and get rid of them. Better still, if you can see the commutator (perhaps after removing the brushes) pour acid over it. The corrosion this causes can only be fixed by taking the motor apart.

Bearings:

Small motors do not have bearings - big ones have various types depending upon the amount of energy they put out. The easiest way to damage bearings is to pour abrasives such as sand or grinding powder into them. Sometime the abrasive has to be suspended in grease to get it into the bearing.

Glue:

There are two options for gluing up the workings of a motor:

• On small motors, you can put epoxy on/around the shaft to stop it turning;
• Most effectively on large motors, pour epoxy potting compound into the motor housing and let it set.

Glue tends to be an expensive option for damaging motors, but it can be used to best effect where you want to damage something very specifically - the motor mechanism controlling part of a larger machine for example.