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Many new or old motors are not running at optimum performance. This is not a design flaw, but may be attributed to poor quality control in manufacturing, wear, poor break-in, dirty commutator, worn brushes, poor brush contact, lack of proper lubrication etc. Do not assume that a new motor is exempt from some or all of these. Although most are fairly rugged, to assure long life and good performance, they should be treated as delicate devices, without abuse. This may be mechanical or electrical. NOTE: Can or other enclosed motors may not be very amenable to many of the methods suggested, since they must be disassembled. If removing the end bell, WITNESS MARKS must be scribed to ensure proper alignment after reassembly. This is particularly critical with round versions, where twisting bell effects brush orientation. Before use, to avoid disappointment and problems, all motors should be checked for any possible quirks, using your BUILT-INS . The shaft should be rotated by fingers after removing couplings, if practical. Feel for high friction points or hang-ups. Look for contaminants , loose connections, worn brushes charred insulation. After correcting any problems, an electrical test should follow. Since they frequently cause poor performance,check the motor, pickup and leads. Intermittent connections often appear to be motor problems or transmission snags. Correct brush pressure is necessary for optimum output. Too often relatively stiff wires are soldered to arms close to brushes, where they interfere with brush movement and pressure. Very flexible leads should be soldered to the arms close to the fulcrum on the end opposite the brushes. The object is to obtain maximum RPM and minimum current, indicating the least friction. Some basic test equipment is necessary. If you have a good ear for pitch, it can be a very sensitive instrument for detecting slight changes in RPM to obtain the maximum. A good sensitive ammeter can be used to obtain the lowest current. A tachometer can indicate the maximum RPM. The RPM of a motor is difficult to judge without a tachometer, unless you are blessed with absolute pitch and have calibrated it to RPM. Current is a far better judge of motor conditions. If the amperage seems high for the given motor, there may be a serious problem like a weak magnet or dry bearings. Before a motor is subjected to any use or thorough testing, it must be properly lubricated. This may be inadequate or totally lacking, resulting from a bad day for assembler or tester. Especially in older motors, lubricant may have evaporated, caked or collected dirt. Remove any contaminants with a solvent. A small drop of very light oil (Labelle 101) should be placed on shaft at bearings. Open frame motors usually have exposed thrust bearings, which need an small drop of oil. Within a few seconds, in most cases, there will be a noticeable rise in RPM accompanied by a drop in current. However some extreme cases may require hours. A very small drop of a conductive oil (101) may be placed on commutator to reduce brush friction. This is an art that requires some knowledge and experience. Both can be acquired quickly and easily through some trial examinations of motors that run satisfactorily and the hints given here. Excessive end play can cause brushes to rub against or ride on raised rings on commutator or to be partially off one edge. Adding thrust washers to center will correct. These may be c-snap or those with a small VEE cut to pass over shaft and deburred. If possible place them between other existing washers, but a least away from any snags. If play is too tight friction will increase. One of the major contributors to excessive play is PRESSING OBJECTS ON or PULLING THEM OFF the shaft. At no time should pressure be applied to the motor housing or bearings. This may squeeze the windings, increasing play or worse. Serving as switches for motor windings, commutators often require attention. Dirty or rough segments cause excessive arcing and brush wear. Often they will reduce RPM and power through higher contact resistance, even to the point of stalling motor at slow speeds. This is sometimes mistaken for a faulty winding. The corner of a lintless cloth or paper towel can be twisted into a tight cord and saturated with a solvent. This is pushed between commutator and frame until the pointed end can be held by fingers. While running light pressure will remove the contaminants. Q-tips tend to fray too freely. Heavier pressure may be used by finger turning the shaft. In more stubborn cases a sharpened stenographer's pencil (not ink) eraser may be applied lightly. For pitted plates, a strip of crocus cloth may be used to burnish the surface. Avoid using abrasives, which may scratch surfaces and collect dirt or increase sparking. Emery cloth may deposit conductive particles in grooves, shorting them. Grooves may collect shorting debris from soft brushes or other types, which may rise above plate level enough to bounce brushes causing pitting. A wooden or plastic tooth pick may be run through them without burring edges. In some rare cases edges are burred or sharp causing rapid brush wear. These may be carefully CHAMFERED very slightly to improve. Check for the correct brush spring positions. These may be upset by handling. Springs must be free to move in order to apply correct pressure. Under some conditions brushes may pop out of alignment. Brush contact is very important. Excessive pressure increases brush friction, which slows motor and increases current. Insufficient pressure increases contact resistance, reducing current, torque and RPM plus it may cause arcing. Observing the changes, from very slight finger pressure on the brush area to increase or beyond the fulcrum to decrease, will point to the right direction of any needed change in pressure. Adjusting spring force should be done slowly in small increments. Hair spring types can be bent outward to increase pressure and vice versa. These are common in can and older open frame motors. Coils springs are used in either compression or extension modes. Some motors have screw caps over the brush holders into which brushes are inserted with compression springs behind them. In some cases, small disks serve as spacers to help align brushes and increase compression. Thinning these reduces pressure and vice versa. The cap may be loosened to test. Common on open frame are compression springs with plungers. These can be stretched to increase pressure or coils may be cut of to decrease. Some Japanese open frame motors have tension springs hooked at brush ends of arms. Springs are stretched to reduce pressure and coils are removed to increase. In most can motors, the springs are enclosed, requiring bell removal for access. New brushes usually have flat faces with small contact area, which eventually wear to conform to commutator curvature presenting a larger area. As brushes wear pressure decreases, usually compensating for the changes. However well worn brushes will present lower pressures, which may need correction. Bearings may be misaligned, by jolts or loosened screws, causing increased friction. These may be adjusted, by careful twisting with slightly loosened screws, using the same tests. Watch closely while tightening screws. In extreme cases armature may rub pole pieces. Wrapping several turns of a paper strip around armature, as a spacer, will help center it. SEE OTHER IMPROVMENTS BACK TO METHODS INDEX BACK TO MOTOR EVALUATION INDEX BACK TO REGEARING BACK TO REMOTORING BACK TO REPOWER |
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