Cue Testing Unit

The cue testing unit is a device which makes it possible to strike a reference cue ball at a specified point by the cue under research with preset force and at a predetermined angle to the surface of the table. The unit provides good repeatable accuracy in a series of identical measurements. The design of the unit has a light but sufficiently sturdy base in the form of a rectangular thin-walled aluminum tube. All the basic elements of design are also made of aluminum and are attached to the base either with aluminum rivets or with aluminum insert nuts. The design of the unit has eight key elements, including the front jig of the shaft, back carriage with a carriage rail, triggering mechanism, driving system and controls of strike force, system of pre-adjustment and control of the unit position, front and back unit support, speed counter of the cue, and cue ball marker for adjusting the position of the cue ball to the axis of the cue. The general view of the unit is shown below.

 

Front Jig of the Shaft

A special solution of the front jig is the use of three bearings which secure the exact movement of the cue along the sight line.

The use of bearings in the design of the jig provided good holding capacity for the shaft without significant increase in friction. The upper bearing of the jig is mounted on a movable spring-controlled bracket which secures free movement of the cue in spite of its taper.

http://www.youtube.com/watch?v=AoOB096QQaY

http://www.youtube.com/watch?v=AoOB096QQaY

http://www.youtube.com/watch?v=57i4wmiIKp8

These features of jig design make it possible to simulate the strikes using the so-called closed bridge, when the player’s fingers form a tight grip around the shaft. However, if necessary, this design also allows for simulation of the strikes with open bridge. For this purpose, the bracket and the upper bearing can be removed. In addition to regular bearings, rollers with elastic outer casings can be installed on the jig for imitating soft hand tissues.

http://www.youtube.com/watch?v=9xo9XEk2AmU

 

The use of sealed bearings in the design of the shaft made it possible to create a maintenance-free construction, protected from possible soiling.

 

Back Carriage with a Carriage Rail

A movable carriage was designed for securing straightline motion of the back part of the cue (the butt). The carriage moves along a rigid rail with the help of two rollers.

 

 

For reducing the weight of the carriage its base as well as the carriage rail were made of aluminum. When carriage rollers roll along the rail, they rest upon its planes inclined at an angle of 90 degrees. This solution made it possible to securely fix the carriage from both horizontal and vertical biases. The gap between the carriage rollers and the working surfaces of the carriage rail is regulated by the convergence of the rollers’ axes on account of the elasticity of the carriage base. As with the front jig of the shaft, sealed bearings were used for the rollers of the back carriage.

A special profiled cutter was made for creating the working surfaces of the carriage rail.

 

Technological recesses / daps were made on non-working surfaces of the rail for reducing its weight.

The cue butt is fastened with an aluminum clamp which braces the cue on three sides and presses it to the base of the carriage through rubber gaskets.

 

The joint work of the front jig and the back carriage rail is shown in this video: http://www.youtube.com/watch?v=nbzbwP4SXKI

We also made an attempt to create a “mobile” fastening of the cue butt, more realistically simulating a hand grip. However, due to the use of too “tender” elastic elements, the construction of the movable grip turned out to be unworkable.

http://www.youtube.com/watch?v=aXXP6GJkepk

 

Triggering Mechanism and Carriage Limiter

The triggering mechanism of the unit is designed as a release trigger connected to the lock of the back carriage by an inextensible cord. When the trigger is turned, the cord starts to wind up on its axis, which results in lowering the stopper into a special recess in the rail of the back carriage. The stopper of the back carriage is made of steel elastic plate which provides for the return of the trigger to its original position after release.

http://www.youtube.com/watch?v=hMe2AJwi-Hc

Special limiters were designed for stopping the motion of the back carriage. The front carriage limiter has a rubber damping element in its design which ensures smooth damping of cue speed after striking the cue ball.

 

Driving System and Strike Force Controls

Initially, we were planning to use the drive system on the basis of the air-operated cylinder, similar to the solution used in this work:

http://www.youtube.com/watch?v=IQciG4jr3vo.

Special power brackets were made for mounting the air cylinder on the unit.

 

Designing the driving system, we also worked on the idea of “arming” the air cylinder to its initial position as with the bolts of Henry-Winchester rifles.

However, the need to deal with the additional and virtually uncontrollable friction in the air cylinder, as well as the need to use a high pressure compressor in the design suggested a more simple and reliable cue driving system based on an elastic rubber band.

The adjustment of striking force is provided by changing the preload pressure of the elastic band. The change in tension is carried out by moving the slider along the cylindrical guide set in the place of the air cylinder:

http://www.youtube.com/watch?v=cbo3hoiNf8g

 

Pre-Adjustment System and Unit Position Control

For controlling the position of the unit on the playing surface of the pool table, the unit has a built-in laser “knife” with the working part taken from a laser aiming device for hunting rifles. A cylindrical lens was used for expanding green beam into a plane. Despite the fact that a part of the beam on the shaft is covered by the bearing of the front jig, the green line from the beam can be clearly seen on the ball, on the cloth and even on the cushions. The aiming device is mounted on a makeshift Weaver rail, similar to the one used on guns for mounting optics. The design has the option of adjusting the position of the beam plane by turning, tilting, or moving the aiming device.

 

A liquid-vial indicator was set on the body of the unit for ensuring the horizontality of the strike.

Front and Back Unit Support System

The unit design has two options of front support.

The first option does not have rigid fastening to the surface of the table. It allows for setting the unit on any part of the table. The base of the front support base is pivotally connected to the unit frame. The turning pair gives the unit two degrees of freedom and makes it possible to incline the unit and to turn it around in a horizontal plane. The presence of a semi-circular cut-out in the front support base makes it possible to strike the cue ball even in the upright cue position, that is, to carry out masse shots.

 

However, the present design of the front support does not allow for horizontal strikes in the central and lower parts of the cue ball. The smallest available distance from the axis of the horizontal cue to the table is 58.7 mm.

The second support option is a steel clamp which provides a rigid attachment of the unit to the surface of the table.

This design involves the installation of the unit though a pocket or removal of one of the cushions. In addition, with this option the unit is capable of changing the “height” of the strike, while retaining the ability of striking with inclined cue at slightly smaller angles:

As a back support the unit uses a massive photographic tripod with smooth regulation of supporting point height.

 

Cue Speed Counter and Its Calibration. Synchronization system.

Cue speed is determined using a velocity meter based on the Hall sensor.

 

Speed is defined by measuring the time needed for a magnetically conductive curtain with the width of 10.04 mm to pass through the sensor. This is the typical signal from the sensor on the screen of the digital oscilloscope:

Since the sensory element is not zero-sized,  the detection of cue speed occurs at a slightly larger distance than the width of the moving curtain of the sensor. The sensitive area of the sensor was measured using a dial test indicator mounted on the unit frame. In the process, the cue was moved by a microscrew that pushed the cue from the tip.

The sensitive area of the sensor was found to be 13.5 mm; it is at this distance that the average speed of the cue is determined. Sensor calibration was performed by comparing the measured cue velocities for different tensions of the elastic strap with similar values found in high-speed photography:

http://www.youtube.com/watch?v=3QxmKQWcbwA

In order to synchronize the triggering mechanism and high-speed camera in the unit design, there is an outboard button “Enter” based on a standard keyboard with USB port.

Ball Marker

The ball marker is designed for the precise setting of the needed offset of the cue ball relative to the axis of the cue. Its design includes a massive base, electronic displacement meter, and a movable stop.

 

The base of the ball marker is a polished eight kilogram steel plate which provides immobility to the entire construction. The offset meter is made using an electronic caliper with modified body allowing it to be attached to the ball marker base and to the movable stop. The working part of the stop is made of plexiglass. It touches the cue ball at the center, which makes it possible to visually monitor how close the ball is in relation to the stop. To prevent the bending of a ruler, the moving part of the ball marker rests on a table with rollers.

Using the Unit for Testing Cues

The joint use of the unit and high-speed video recording makes it easy to define the main characteristics of the tested cues.

Determining the dependence between the cue ball squirt and the offset value:

 

determining the “endmass” parameter:

determining cue energy conversion efficiency:

determining the dependence between the contact time and the striking force: