Ever since keyed locks were invented thousands of years ago, man has attempted to circumvent the need for keys by picking them. And it was only a matter of time before special tools and machines would be developed in an effort to make this tedious job faster and easier. In the early 1930's, locksmiths began developing "guns" that used mechanical or electrical energy to speed up the picking process. Here's an article for those who thoroughly understand the practice of manual lock picking and would like to know more about the details of lock pick guns and how they work. It will explain the principles involved in both mechanical and electrical lock pick guns, but will make no attempt to teach the techniques of using one or comment on which type is most effective.
2. BASIC TYPES OF LOCK PICK GUNS. Most lock pick guns try to speed up the picking process by working all or most of the tumblers at the same time. Generally, these devices have a straight, thin blade (often called a needle) on the business end that is inserted into the keyway. In most cases the blade has no features such as bumps or wiggles. It does its work by simultaneously bouncing all the pins in an attempt to briefly separate the bottom pins from the drivers at the shear line so that the cylinder can be rotated.
Note that this is not quite the same as "raking" or "scrubbing" the pins. That's more of a "shotgun" approach to manual picking, where the pins are actuated in rapid sequence rather than at the same time. There has been speculation about converting electric bread knives, tooth brushes, and other reciprocating devices into motorized raking tools, but to my knowledge there are no commercial pick guns built like that. There is a patent (U.S. Patent No. 5,956,984 dated September 28, 1999) for a motorized pick gun that uses a mechanism almost identical to that of a bread knife, with two reciprocating blades side by side. However, the main objective of this invention is to pick locks having pins that must be rotated as well as positioned axially, and the reciprocating motion is necessary to turn the pins.
The pick guns this article will describe may be classified as either mechanical or electrical according to the means for actuating the blade. Mechanical guns have a hammer and/or spring that drives the blade against the pins suddenly when released. Each blow requires a separate action by the operator. Electrical guns use a motor or electromagnet to cause continuous motion of the blade.
3. THE MECHANICS OF PIN TUMBLER MOTION. Billiard balls are often used as an analogy to explain what happens when the pick of a mechanical gun impacts the lower pin tumblers in a lock cylinder, as shown in Figure 1. When the cue ball in Figure 1(a) strikes a pair of balls B and C that are touching, the cue ball stops, ball B remains stationary, and ball C moves away, as in Figure 1(b). Thanks to the law of conservation of energy, the kinetic energy is transferred first from A to B, and then immediately from B to C. Figures 1(c) and 1(d) show how this principle is applied to the action of a lock pick gun, where the lower pin represents ball B, its follower represents ball C, and the pick blade represents the cue ball A.
(a) (b) (c) (d)
Figure 1. Analogy Between Billiard Balls and Pin Tumbler Impact
The situation in an actual lock cylinder is a little more complex because there are perhaps four or five sets of pins with unequal weights, and the resistance of the springs and friction against the walls of the holes prevents the followers from moving as freely as the billiard balls. But the general principle is still applicable. Instead of sliding pins slowly with a pick, they are hammered, like hitting a baseball with a bat. The fact that bottom pins are usually longer (and thus heavier) than their followers is not critical. You can demonstrate that by replacing ball B in Figure 1(a) with two or three balls lined up tightly in the direction of motion. When the cue ball strikes the first ball in line, all the intermediate balls remain stationary while only the farthest ball moves away.
Ideally, the pick gun blade is positioned so that all the bottom pins are hammered at about the same time. Otherwise, some of the followers may rebound off their springs before the others have been thrown above the shear line. The amount of torque applied to the cylinder is also critical. It must be light enough to avoid binding of the followers when they are hammered, yet sufficient to respond in the brief instant when all the followers are separated from their bottom pins. Many amateurs buy snap guns expecting that they will make lock picking almost automatic, only to learn what experienced locksmiths already know: Pick guns still require plenty of practice and patience to be used effectively.
All the foregoing applies primarily to mechanical guns, where each actuation of the blade results in a single, sudden, sharp impact with the bottom pins, causing the followers to make one trip up and back. Even if you tried to squeeze the trigger repeatedly as fast as you could, all pin motion stops between successive snaps. There's just no way that mechanism can be operated as fast as the pins can bounce off their springs. With some electric guns the situation is different because the blade is oscillating or vibrating rapidly and continuously. That brings an additional factor into play, namely the resonant frequency of the pins and their springs.
Any combination of weight and spring force has a self-resonant, or natural frequency. Hang a weight from a spring, stretch the spring slightly, and release it. The weight will bob up and down for a while at the natural frequency of the spring-weight combination. Increase the stiffness of the spring by a factor of two and the frequency of oscillation will double. Increase the weight by a factor of two and the frequency will be reduced by half. With tumbler locks the situation is similar. The pins and springs in each hole have a resonant frequency, although not necessarily the same from hole to hole because of the variation in length (weight) of the pins.
If you drive your car very slowly over a "washboard" road the car's suspension system allows the wheels to ride up and down gently as they roll over the corrugations in the road surface. But if you increase speed you'll reach a point where all hell breaks loose. That happens when the ripples in the road's surface are occurring at precisely the resonant frequency of the car's suspension system. Even though each bump is shallow, and applies only a small force to the suspension, it occurs at just the right moment to reinforce the motion already present. The effect is regenerative, and the motion of the suspension increases until it is being driven all the way to the limit of compression of the springs. Things are even worse if your shock absorbers are worn out.
Nearly all mechanical things have a resonant frequency. Think of resonant frequency as something a thing wants to do at the drop of a hat. It loves that frequency more than anything, and can be coaxed to vibrate at that rate with a minimum amount of stimulation, such as by the blade of a pick gun. So electric guns that vibrate rapidly do their work not so much by brute force, as impact guns do, but rather by trying to apply a subtle force repetitively at just the right frequency to cause the pins to "dance".
Just like the car's suspension system, lock pins can be induced to bounce wildly if they are agitated by a pick at just the right frequency. At the resonant frequency the amount of power in each stroke of the blade, as well as the distance the blade moves, can be quite small and still be effective. Some electric guns allow you to vary the frequency of oscillation so you can search for the most effective frequency for a particular lock.
4. MECHANICAL GUNS. The earliest evidence I could find for a mechanical lock pick gun is U.S. Patent No. 1,944,006 granted January 16, 1934 to Louis Hanflig. Figure 2 shows the inner workings of this gun with the side cover removed. The pick needle is fastened securely to a hook-shaped holder riveted to a long curved spring. Normally the pick holder is pressed against the top of the gun as shown in (a). When the trigger is squeezed the hook on the pawl catches the corresponding hook on the needle and pulls it down, as shown in (b). At some point the pawl hook slips off the end of the needle hook, allowing the needle to snap back up. The pawl is pivoted at the front end of the trigger so it can rotate and re-engage the hook as the trigger is returned to its normal position. The distance the pick travels before it snaps back can be adjusted with the screw in the trigger, which sets the amount of initial engagement of the hooks. Although not illustrated in Figure 2, the actual patent also shows an adjustable spiral shaped tension wrench fastened to a block on the top surface of the gun.
(a) (b)
Figure 2. Early Mechanical Lock Pick Gun from Patent No. 1,944,006 dated January 16, 1934
(a) (b)
Figure 3. Homemade Pick Guns
Similar in principle to the gun in Figure 2 are the "coat hanger" or "clicker" snap guns shown in Figure 3, that are commonly homemade from a piece of spring wire. Not very elegant, but very cheap and easy to make. To use the unit shown in (a) you hold one arm of the "safety pin" while deflecting the other with a finger tip, then allow it to snap back. The illustration shows the pick deflected, but it probably works better to deflect the hooked arm and let it swing back and impact the pick, which is being held stationary in the keyway. Whatever works. By comparison, the design of (b) is a little more sophisticated. In this version the trigger is deflected and allowed to snap back and impact the pick. It may help to add some weight to the hooked arm so it really "smacks" the pick, but now we're talking about complicating the design.
The mechanical pick gun familiar to nearly everyone was designed in 1932 and patented in 1934 by a gentleman named Solomon Wakstein. Amazingly, the details of units sold today by Brochage, Unlock Tech, LockAid, DINO, Pistolpick, and others are almost identical to the original concept. If you look at the patent drawings you will see the same parts that are found in current units, including all the stamped sheet metal components, the thumbwheel, and even the "L" shaped rocker lever that holds the pick.
Figure 4. Pick Gun from Patent No. 1,977,362 dated October 16, 1934
Gun enthusiasts may recognize a certain similarity between the mechanism shown in Figure 4 and that of a double-action revolver. Squeezing the trigger causes the upper tip of the "V"-shaped actuator lever to engage the lower leg of the "U"-shaped hammer and pull it back against a compression spring. The inclined surface of the lower arm of the actuator lever causes it to rotate downward as it moves back, eventually releasing the hammer, which snaps forward and strikes the rear end of the "L"-shaped rocker lever, driving the pick blade upward.
The impact force can be adjusted by rotating a knurled thumbwheel captured in the housing, which moves a screw fore and aft to change the preset compression of the hammer spring. The head of the screw is square so it will not rotate within the hammer. The return spring for the trigger and actuator is combined as a single extension spring, and a flat "U"-shaped leaf spring keeps the rocker lever pressed against the hammer. The original patent even shows an alternate blade configuration that extends upward (or downward) at an angle of about 30 degrees, just like the ones supplied with guns purchased today. Things haven't changed much.
Another pistol type pick gun, patented in 1943 by Sam Segal, is illustrated in Figure 5. Judging from the excessive complexity and method of construction, I would guess Mr. Segal was a gunsmith as well as a locksmith. It uses a rotary hammer instead of a linear one. The motion of the pick blade is strictly vertical, rather than in a slight arc as with the earlier design. Other than that it doesn't seem to add a lot to the technology of pick guns.
Figure 5. Pick Gun from Patent No. 2,309,677 dated February 2, 1943
The pick holder has slots on each side to guide it vertically on ribs projecting from the sides of the gun, with upper and lower stops to limit the travel. The rotary hammer normally holds it in the upper position. A rocker lever on the hammer engages a hook on the end of the trigger. Pulling the trigger rotates the hammer and lowers the pick holder. Because the trigger and hammer have different pivot points, the hook eventually slides off the end of the rocker lever, allowing the hammer to snap back and drive the pick holder upward. The spring-loaded rocker lever allows the trigger to return. The thumbscrew on top adjusts the force of the hammer spring.
5. ELECTRICAL GUNS. Electrically powered pick guns can be sub-classified into two basic categories, motor actuated and vibrator actuated. Vibrator actuated guns use an electromagnet to excite a resonant mechanical structure of some sort that holds the pick blade. One of the earliest patents for an electrical lock pick gun is U.S. Patent No. 2,565,254 dated August 21, 1951, awarded to William Miskill. Figure 6 shows this contraption, which is basically just a hand-held door buzzer with a lock pick attached.
The design includes a pair of electromagnet solenoid coils, a set of normally-closed contacts like those of an electromechanical relay, and a pushbutton switch. A flat leaf spring is anchored at each end to the "U"-shaped frame. A block of steel that serves as the armature is fastened by a screw at the center of the spring. The upper end of the screw is slotted, and a wing nut clamps a pick blade in the slot.
Pressing the pushbutton applies power to the coils through the normally-closed contacts, pulling the armature down (and the pick with it) by flexing the leaf spring. As the armature approaches the coils it bumps the contacts open, interrupting the current. The spring then pulls the armature back up, restoring the circuit. So the armature and pick holder jiggle up and down, just like the clapper of a buzzer, until the trigger is released.
The design has obvious shortcomings, and was probably never commercialized. There are no adjustments for stroke or frequency, and nothing is mentioned about that in the patent. The use of battery power ensures there is no lethal voltage present, but you would not want to come into contact with any part of the exposed circuit while this thing is running. Each time the contacts interrupt DC current through the solenoid coils there's a voltage spike.
Figure 6. Electric Buzzer Type Pick Gun from Patent No. 2,565,254 dated August 21, 1951
caused by the inductance of the coil. That's what causes all the sparking at the contacts, and it can give you quite a jolt. This unit might hold the record as one of the mechanically noisiest pick guns ever built, and it would wreak havoc with radio and TV reception as well, at least until it burned out its contacts after a few hours of use. The pick shown in Figure 6 looks more like a rake than a pick gun blade, but that's the way it is illustrated in the patent.
Some later pick guns tried to adapt the principles of electric shavers and electric engravers of the type that must be powered by alternating current. AC powered vibrators generally use a spring mounted armature whose vibration is mechanically "tuned" to approximately 120 cycles per second. Each cycle of 60 cycle AC power applied to the electromagnet actuator consists of a positive swing in voltage followed by a negative swing. That causes current to flow through the electromagnet first in one direction, then in reverse. The electromagnet doesn't care which way current flows, so the result is two pulses of magnetism for each cycle of line voltage, or 120 pulses per second. Remember the discussion about natural frequency? By giving the vibrator mechanism a natural frequency close to that of the magnetic pulses a minimum amount of electrical energy is required to keep things moving. That translates to less power, less heat, lighter weight, etc.
This type of vibratory mechanism pretty much dominated the design of personal electric shavers until the advent of miniature DC motors and rechargeable batteries. It is still widely used in commercial barber shop products because of its simplicity, low maintenance requirements (no gears or motor brushes), and relatively low noise. The requirement for AC power is no problem for a pick gun used in the shop, but can be a problem on location if there is no nearby wall outlet.
I found only one reference to an electric pick gun powered strictly by alternating current, U.S. Patent No. 3,264,908 dated August 9, 1966, awarded to Lloyd Moore. Note its simplicity in Figure 7, only two moving parts and no contacts or brushes. The solenoid coil is wired in series with a pushbutton switch and a small lamp that lights whenever the unit is running, to illuminate your work. The long, pivoted armature lever is spring-loaded against an adjustment thumbscrew in the top of the enclosure, and carries the pick blade at the outer end. The nominal stiffness of the spring and the weight of the armature lever are selected for mechanical resonance at approximately twice the line frequency, or 100 to 120 cycles per second. The patent suggests using an electric circuit (known technically as an inverter) to convert DC battery power to AC. That's certainly possible, although it's an inefficient and costly way to make the unit portable.
Figure 7. Vibratory Lock Pick of Patent No. 3,264,908
The characteristics of blade motion and the velocity with which it strikes the pins has a great influence on the performance of a pick gun. Tuned vibrator mechanisms like that used in Figure 7 oscillate in what is known as sinusoidal, or simple harmonic motion. That's sort of like the motion of a clock's pendulum, which slows down at each end of its swing. The vibrating lever slows down as it nears the top and bottom of its stroke, changing direction smoothly. One of the limitations of such a device is that the maximum velocity of the pick occurs at a point midway through its stroke, and the velocity at the end of the stroke is zero. So to achieve a significant impact against the pins the pick may need more room for travel than is available in the keyway.
Motor-driven pick guns, on the other hand, can be designed with mechanisms that convert rotary motion of a shaft to oscillating motion of a pick blade in ways that deliver high impact velocity with minimum stroke. Furthermore, the motor's high speed rotor acts as a small flywheel whose momentum helps meet peak torque requirements.
Figure 8. Motorized Lock Pick of Patent No. 4,156,375
Figure 8 shows a motorized design that produces rapid impacts rather than sinusoidal motion. The idea was granted U.S. Patent No. 4,156,375 to Serge Crasnianski on May 29, 1979, who assigned it to a French company. It is basically a trip hammer mechanism, similar to those used for forging, except that the hammer depends on a spring for its driving force instead of just its weight. The pick needle is held by a collet chuck that's part of a pivoted rocker arm located beneath the hammer. A motor at the rear of the unit drives a gearbox in the center of the unit. The output shaft rotates a cam that engages a "D"-shaped lug on the hammer, raising it until it falls off the edge and slams back down against the rocker arm. The force of impact is adjustable by a thumbscrew that varies the compression of the hammer spring. A pin in a blind hole at the rear end of the rocker arm limits its travel. No information is given in the patent regarding the output shaft speed, but it does specifically describe varying the frequency of impacts by changing motor speed using a variable resistor between the battery and the motor.
Since a gearbox is used, my guess is that the impact frequency is probably in the range of five to ten snaps per second. At speeds higher than that the hammer may begin to "float" because it doesn't have time to complete its impact. This gun can be thought of as a sort of "motorized Brochage" that repeats its snap rapidly without giving you cramps from continually squeezing the trigger, not to mention being easier to hold in correct position within the keyway because your hand is steady.
A search of U.S. patents failed to uncover any motorized pick guns similar to the units currently made by Southord, HPC, Electropick, Multipick, and others. This may be due to the fact that these devices are generally based on old technology and therefore don't qualify for patents.
Figure 9. SouthOrd Model E100C Electric Pick
Figure 9 shows a partial cross-section of the popular SouthOrd E100C gun. The rear half of the unit screws into the front half and holds two C-cell batteries, with the negative terminal grounded. The positive terminal of the forward battery presses against one terminal of a small 1" diameter x 1" long motor in the center section. The other motor terminal is an insulated leaf spring that makes contact with the motor housing (ground) when a pushbutton is pressed, completing the circuit.
An eccentric cylindrical cam is fastened to the motor shaft with a setscrew. The replaceable pick blade is attached with a screw to a "Y"-shaped oscillating lever that is pivoted on a cross shaft. The lower rear arm of the lever carries a roller that is bumped downward by the eccentric cam during the bottom portion of its revolution. The upper arm of the lever acts as a backstop and is pressed against the end of a setscrew by a rat-trap spring. The setscrew allows the stroke distance to be adjusted. So the upward motion at the tip of the pick is positive (driven by the cam), and the downward motion is passive (driven by the spring if not obstructed).
(a) (b) (c)
Figure 10. Motion of SouthOrd Pick
If the roller remained in continuous contact with the eccentric cam the pick would make a sinusoidal up and down motion, as shown in Figure 10(a). But if the setscrew is adjusted so that the pick moves only about 1/16 inch, the cam loses contact with the roller below the dotted line in (b), and the resulting pick motion is just that portion of the sine wave above the dotted line, as shown in (c). The pins are bumped at each of the little blips, and if the bump rate is close to their resonant frequency they will "dance". The normal method of obtaining some speed variation with the SouthOrd is to pulse the motor, the same as with most other motorized guns.
The setscrew adjustment of the SouthOrd's stroke seems intended to be more or less a permanent setting. Other manufacturers of guns with motor-driven oscillating arms, such as HPC, MS Electric, and Wendt, to name a few, have provided a more prominent thumbscrew adjustment, with locking knob.
Most of the popular electrical guns use some variation of the SouthOrd mechanism, with the pick driven positively in one direction, and passively by a return spring in the other. An exception is the European product, Multipick, which is unique among motorized pick guns. It uses a mechanism that drives the pick sinusoidally in both directions, with a stroke of only about 1mm at the tip of the pick blade. The gun is powered by an external 24 volt battery, and with no batteries in the handle there's room for a large engine. The manufacturer boasts that it is the most powerful pick gun made, and claims that its motor delivers 60 watts peak power. The gun has a reputation for its ability to punish locks brutally, no doubt due to concentrating the torque of its powerful motor over a very short stroke.
An optional control unit includes a large, rechargeable battery pack with a smart microcomputer-based controller that provides many ways to vary the speed of the motor, and consequently the vibration frequency of the pick. This includes patterns that cycle through different speeds, slew up and down like a siren, and even memorize a speed you found to be successful on a particular lock, for later recall. The motor speed can be varied from almost nothing up to about 700 pick strokes per second, more than fast enough to resonate the pins of any lock.
Figure 11. Lock Pick Apparatus of U.S. Patent No. 4,606,204
An unusual motorized pick gun patented by Robert Cooke, Jr. on August 19, 1986, is shown in Figure 11. One part of the invention includes a reciprocating rod driven by a gear motor using a scotch yoke mechanism. Another part is a special adapter that fits tightly in the bottom of a keyway, where a torsion wrench would normally be placed. A flat spring connects the adapter to the reciprocating rod mechanism, which is being held off to one side, above, or below the lock, as convenient. When the motor is switched on, the reciprocating rod wiggles the end of the spring so that it transmits an oscillating torque to the plug, changing from clockwise to counterclockwise about 3500 times per minute. The inventor claims the gentle rotary vibration of the plug makes it easier to pick the lock by raking or individual picking, using any standard lock pick. He also describes a method where all the pins are lifted at the same time, then allowed to fall below the shear line one by one as pressure on the oscillating spring is relaxed.
6. HOMEMADE ELECTRICAL GUNS. Considering the cost of electrical pick guns, it's no wonder there's so much interest in experimenting with homemade designs, not to mention the fun involved. The following comments are not intended to criticize nor suggest specific ideas, only to summarize some of the ones that have been discussed in the forum.
The first step is usually to look around for something that oscillates or vibrates, and here there is no limit to the imaginative ideas that have been proposed. Motors with off-center weights are found in massagers, vibrators, and even tiny ones in pagers and cell phones. One forum member put batteries and a motor of this type in a piece of plastic pipe, then attached a pick needle directly to one end of the pipe. That's not a very efficient approach, because the motor must shake the mass of the entire pick gun instead of just a pick holder. Also, the hand tends to absorb or dampen the vibrations. It might work better if the pick were attached to just the motor, and the motor were enclosed in foam rubber within the pipe.
Another forum member just attached a needle to the shaft of a small motor so that it jiggled around as the shaft was spinning. The sideways motion of the needle is wasted, and may cause premature failure. But this design certainly wins the award for the simplest motor driven pick gun, with only one moving part.
Although many electric toothbrushes these days are of the rotary type, you can still find some that provide a vertical brush stroke, and these often seem like an ideal candidate for a pick gun. They are small and inexpensive, have built-in batteries, and all that's needed is to replace the brush with a pick. The results are usually disappointing, not only because of the limitations of speed and power, but because these products are manufactured so cheaply and with such poor quality that they don't last very long. A very common design of low-cost toothbrushes, as well as electric scissors, electric groomers (nose clippers) and similar products, is a very small motor whose shaft has been bent in an offset and engages a slot in a plastic arm so that as the shaft spins it moves the arm back and forth. Usually the arm pivot is just a molded plastic pin. The plastic parts wear quickly, particularly the slot for the eccentric shaft. It really is a disposable product.
Another toothbrush idea that surfaces periodically is to use a Sonicare, although it amazes me that anyone would think of converting such an expensive product into a pick gun. Figure 12 shows a cross section of this toothbrush, which is a vibrator type unit with a fixed speed and very short stroke. Replacement brushes are fairly expensive because you must replace the whole vibrator arm assembly, which includes all of the moving parts.
Figure 12. Sonicare Toothbrush
Completely sealed inside the handle, so that the unit can be submerged without harm, are the batteries, microcomputer control, charger coil, and a strong electromagnet positioned close to the forward bulkhead. To eliminate external battery charger contacts the charging energy is AC-coupled, like a transformer, from a coil within the charger base to a coil in the end of the handle. This is definitely the Rolls Royce of toothbrushes.
A steel frame with cross shaft and swing arm is pressed into the plastic head. The steel parts are all brazed together, and the arm doesn't rotate on the shaft as it moves up and down, but rather twists it like a torsion spring. A plastic toothbrush is pressed onto a tang at one end of the arm, and two small rare-earth magnets are cemented to the other end, one with its north pole facing the electromagnet, and the other its south pole. The electromagnet is driven with an AC signal at about 261 cycles per second, which is almost precisely the frequency of middle "C" on a piano. The swing arm's weight distribution and the stiffness of the torsion shaft give it a matching resonant frequency, so it vibrates like a tuning fork and provides the product with its characteristic hum.
If you have a head that has been discarded because of a worn out brush you can experiment without endangering the rest of the unit. Pulling the old brush off the swing arm is nearly impossible because, not shown in Figure 12, the tang of the arm has barbs on both edges. Your best chance is to saw off the plastic neck carefully around the arm, struggle with the silicone rubber boot seal, and ultimately destroy the brush by cutting it away from the tang. If you attach only a very light weight pick to the arm you probably won't disturb its natural frequency. If you want to be absolutely sure, cut off as much material from the end of the tang as you estimate to be the weight of the pick you are adding. With care, you may be able to drill a 1/32 inch diameter hole lengthwise in the end of the tang and press in a stiff wire, such as a sewing needle.
Another type of product frequently considered for "conversion" to a pick gun is an electric screwdriver, no doubt encouraged by the fact that the popular HPC Electropick was made by replacing the gearbox of a Black & Decker screwdriver with an oscillating arm mechanism. You probably recognize the B&D Model VP730 in Figure 13, a U.S. version with NiCad battery cartridge that snaps into the rear.
The section forward of the plastic body consists of a 2-stage planetary gearbox with 80-to-1 speed reduction and an adjustable torque limiter on the front end. The gearbox is fastened to the handle with a couple of 3/32" diameter x 1-1/4" spring pins, which are easily driven out with a drift punch. The motor itself is nothing special, about 1-1/8" in diameter x 1-1/2" long, with non-replaceable brushes and a .090" diameter flatted shaft that extends 3/16" beyond the front face of the plastic housing. The first stage drive gear has a "D"-shaped hole and just floats on the motor shaft, but you could probably attach something else having a 3/32 inch diameter bore and setscrew.
Figure 13. Black & Decker VP730 Electric Screwdriver
The motor has a DC resistance of a couple of ohms. With a NiCad battery of 3.6 volts it draws about 1/4 amp at no load, and maybe twice that at full load. Stall current can be as high as a couple of amps.
7. Controlling Motor Speed. If you use a SouthOrd, or Electropick, or even a homemade motorized gun, you were probably taught to pulse the unit on and off so it will vary its speed, thereby maximizing the chances of finding the best frequency for opening a particular lock. The biggest problem with this technique is that the motor might coast through the optimum speed briefly, just long enough for you to "almost" catch it with the tension wrench. That's why Multipick added speed control to their gun, to allow you to concentrate your efforts at feeling the instant of pin separation instead of worrying about cycling the motor. They have an obvious advantage, since power for the motor comes from a source external to the unit where there's plenty of room to add the electronic components necessary.
It is sometimes suggested that simply putting a variable resistor in series with a DC motor is an effective speed control, but that's simply not true. To begin with, the variable resistor must be able to handle the worst case motor current (with the motor stalled), which might be a few amps. The maximum resistance would typically be a dozen ohms or less. Low ohm variable resistors rated for high current (often called rheostats) are not easy to find. If you connected one to a small motor you would probably be able to vary the speed just fine -- under no load. But load the motor down a bit and you may find that it won't start until you crank the voltage up to a certain point, then it starts suddenly and runs faster than you want. Then as you try to turn the speed back down, the motor stalls because it has very little torque at slow speed. Another fallacy is that you can make a good speed control with an electronic component called a variable output voltage regulator. It's slightly better than a series resistor, but still performs poorly at slow speed. The reason for this exasperating behavior is related to the fundamental way a DC motor works, and probably not worth a technical explanation.
Most model railroad hobbyists know that good speed controls are pulse width modulated (PWM) instead of just varying the DC voltage. Figure 14 shows waveforms of voltage delivered to a motor from a PWM speed control.
(a) (b) (c)
Figure 14. PWM Voltage Waveforms
For this example we'll assume we're working with a 5 volt DC motor. At full speed the motor receives a constant 5 volts, and of course at zero speed it receives 0 volts. At any speed in between, the voltage cycles rapidly between 0 and 5 volts at a duty cycle (the percentage of time the voltage is turned on) that is proportional to speed. In (a) the voltage is turned on for 8 milliseconds, then turned off for 2 milliseconds, then back on, and so forth. To calculate the average value of a waveform such as this you divide the total on-time for any number of cycles by the total on and off time combined for that same number of cycles, and multiply that fraction by the peak voltage, which is 5 volts in this case. The dotted line in (a) shows the average voltage being supplied to the motor is 4 volts, so the motor is running at about 4/5 of full speed. In (b) the duty cycle is 50 percent, and the motor is running at about half speed, and in (c) the duty cycle is only 20 percent and the motor is running at about 1/5 speed.
In this example, the motor receives one pulse of voltage every 10 milliseconds, or 100 pulses per second. The exact frequency is relatively unimportant so long as it is high enough that the motor cannot respond to individual pulses, and uses its inertia to average them out. A voltage waveform of 200 pulses per second, with each pulse having 4 milliseconds on and 1 millisecond off, still has an 80 percent duty cycle, and would still give an average voltage of 4 volts and drive the motor at about 4/5 of full speed.
Do not confuse the PWM frequency with the RPM of the motor, which is the pick vibration frequency. The two are completely unrelated. The PWM frequency remains fixed, and it is only the shape of the waveform that affects motor speed. Wide pulses are high speed. Skinny pulses are slow speed.
If you want to try and add speed control to your gun you'll find lots of circuits on the internet, some with construction details. Also check out HO gage model railroad magazines and hobby stores. This is not a project for the technically disadvantaged. It probably means adding a cable to the gun and using an external battery. One problem you'll have is that most of these controls are designed for motors that run on 6 to 24 volts DC, whereas the motors in SouthOrd and HPC guns may be running on 3 to 4 volts DC. One solution is to use a 6 volt external battery and arrange the circuit to supply a maximum duty cycle of 50 or 60 percent when cranked all the way up.
Article Written by Tommy Tyler
* Thank you Tommy for this amazing article
I was in a frantic rush to copy and save all those pictures onto my computer before this thread got removed or edited when it was first posted. 
