(40+) Poly Ball Use in Robo-Pong

White Paper On Using 40+ Poly (Plastic) Balls In Newgy Robo-Pong Table Tennis Robots September 15, 2014.

 

Since the beginnings of the sport in the early 1900’s, table tennis has used a ball made of celluloid. Non-celluloid balls have been made in the past, but were never as popular as celluloid balls. In 2012, the International Table Tennis Federation (ITTF) mandated that in their sanctioned competitions, a new, as yet undeveloped, non-celluloid ball would be used as the tournament ball starting July 1, 2014. I will refer to these non-celluloid balls as poly balls henceforth.

 

Poly-Ball Background

There are only 5 actual ball manufacturers at the time of this writing and all poly balls, regardless of the brand, come from these 5 companies. Poly balls can be categorized as either seamed or seamless. Seamed poly balls use a similar manufacturing technique as has been used for decades to manufacture celluloid balls, all of which are also seamed. Seamless balls use a more recent manufacturing process called rotational molding, which has not been used previously to manufacture TT balls.

 

The majority of poly balls available for sale today are of the seamed variety. Most major TT brands—Butterfly, Stiga, Nittaku, TSP, Double Happiness, Double Fish, Joola, Donic, and Tibhar— and several minor TT brands—Andro, Adidas, Cornilleau, Giant Dragon, Sunflex— have seamed poly balls approved by the ITTF. So far, there are 3 brands of seamless poly balls—XuShaofa, Palio, and Hanno.

 

Poly balls tend to produce less speed and spin as compared to celluloid balls. However, the spin tends not to dissipate as quickly so by the time the ball is struck again, the amount of spin is similar to celluloid and possibly even a little more, especially for longer traveling shots like chops and lobs. Speed seems to dissipate faster. Poly balls tend to bounce lower than celluloid and with a flatter trajectory.

 

Slow underspin can hang up or stop as compared to celluloid’s more forward bouncing behavior. Topspin shots also seem to not drive as far outward from the table. I believe many of these differences are explainable by the slightly larger size of poly balls. Also poly balls tend to be manufactured at marginally heavier weights compared to celluloid (see chart below).

 

Until January 2016, ITTF allows poly balls to be approved up to 2.82 grams. After that date, they must meet the standard for celluloid balls—2.77 grams. Another factor is the actual material the balls are being made of. Current seamless balls are being made from cellulose acetate or cellulose diacetate, close relatives of celluloid, which is cellulose nitrate mixed with camphor. I am uncertain what plastic is used for seamless poly balls. But each different material will produce different results due strictly to the individual characteristics inherent in that material.

 

Please keep in mind that we are in the beginning stages of manufacturing these new balls. As such, I believe many of these weight and size variations will improve as the manufacturers refine their processes to produce a more consistent product. The end product will probably be a poly ball that is even closer to celluloid performance than today’s iterations are. In the meantime, the occurrence of balls that don’t meet ITTF specifications is significantly higher than with celluloid balls. With celluloid balls, it’s unusual to find an out of spec ball. With poly balls, it’s quite common. 

 

Ball Size Shift

As part of the ITTF mandate, they also instituted a different acceptable range for the poly ball’s diameter. For celluloid balls, the acceptable range is from 39.5mm to 40.5mm. For poly balls, the new range is from 40.0mm to 40.6mm. This white paper will discuss the compatibility of poly balls with the Robo-Pong line of table tennis (TT) robots manufactured by Newgy Industries.

 

To date, I have been able to test 6 brands of seamed poly balls and 2 brands of seamless poly balls. All have similar measurements, except the XuShaofa Sports seamless balls being slightly bigger in diameter on average.

 

Here’s the breakdown:

Brand/Model Stars Avg Dia SD Dia Hi Dia Lo Dia Avg Wgt SD Wgt Hi Wgt Lo Wgt Smpl Size

Double Fish 3 40.19 0.034 40.32 40.12 2.73 0.009 2.75 2.70 49

Double Fish 1 40.15 0.035 40.28 40.00 2.73 0.017 2.76 2.67 50

Nittaku SHA 3 40.16 0.052 40.35 40.03 2.79 0.019 2.82 2.75 36

Joola Super P 3 40.16 0.048 40.24 40.02 2.79 0.011 2.80 2.76 24

Andro Speedball 3 40.14 0.050 40.27 40.03 2.76 0.023 2.80 2.73 24

Donic 40+ 3 40.18 0.065 40.33 39.88 2.79 0.020 2.84 2.75 24

Cornilleau P-Ball 3 40.13 0.056 40.26 40.00 2.79 0.037 2.89 2.74 24

XuShaofa Sports 3 40.29 0.028 40.35 40.24 2.80 0.051 2.95 2.74 24

Palio 3 40.21 0.027 40.30 40.16 2.78 0.022 2.85 2.75 24

Nittaku Premium Celluloid 3 39.70 0.040 39.81 39.54 2.75 0.012 2.77 2.74 24

 

Avg Dia = Average Diameter, SD Dia = Standard Deviation of Diameter, Hi Dia = Highest Diameter recorded, Lo Dia = Lowest Diameter recorded, Avg Wgt = Average Weight, SD Wgt = Standard Deviation of Weight, Hi Wgt = Highest Weight recorded, Lo Wgt = Lowest Weight recorded, Smpl Size = Number of balls tested in this sample.

 

As can be observed from this chart, the average diameter ranges from 40.13 to 40.19mm for seamed and 40.21 to 40.29mm for seamless. It’s significant to note that this average for seamed poly balls is comparable to the averages observed with celluloid 40mm balls (seamed) and, prior to 2001, celluloid 38mm balls (seamed). For 40mm celluloid balls, the average was 39.65~39.70mm. For 38mm balls, the average was 37.65~37.70mm. So we can see that in all cases so far the average diameter for each ball size was @ 0.15~0.20 above the minimum acceptable range when comparing similar manufacturing processes.

 

Since both the 40 and 38mm celluloid ball markets were mature, it can be postulated that manufacturers learned that players preferred, and bought, balls toward the lower end of the acceptable range. Therefore they manufactured them at that size. And it appears as if they are following that same strategy with these seamed poly balls as all brands measured are in or very close to that relatively narrow ideal range of 0.15~0.20mm above the minimum size allowed. The largest diameter of any ball measured was 40.35mm. Just as we occasionally see a celluloid ball significantly larger than the norm, this will also occur with the poly balls. but probably on a more frequent basis until the manufacturing processes used with poly balls mature.

 

 

Do Changes In Ball Size Affect Robo-Pong Play?

Many players have wondered if the larger size of the poly ball will affect how the Robo-Pong robots perform when using these new balls. Poly Ball Types & Behavior Poly balls have begun appearing in the marketplace and most TT brands have released, or are scheduled to soon release, versions of the poly ball. It is the conclusion of our research that poly balls can be used in all current production Robo-Pong robots with little to no problem.

 

 

Making Poly Balls Work in Older Robo-Pong Robots

Older robots, depending upon manufacture date and degree of wear, may have minor issues that can be addressed by following the recommendations given in Recommended Procedures For Use Of Poly Balls. Read the remainder of this white paper to learn more about this issue. We will soon post videos on the Newgy YouTube channel showing our robots being used with a variety of different poly balls. But for now, the first step is to understand how a ball interacts with a Newgy Robo-Pong.

 

Newgy Robot Ball Channel & Poly Ball Use

The ball channel inside a Newgy robot starts at the bottom where the ball is picked up and pushed into the channel at the lower end of the Back Panel. Upon leaving the Back Panel, it enters the Upper Guide where it changes direction from vertical to horizontal. It then briefly passes through the Pivot Guide that determines the side–to-side location of a thrown ball. Immediately, it enters the Discharge Tube that carries the ball to the robot head and determines the trajectory (up/down) angle of a thrown ball. Lastly, the ball is pushed into the robot head where it is captured between the spinning Discharge Wheel and the opposing Friction Block before being thrown out of the robot through the discharge hole at the front of the robot head.

 

I tested a total of 11 Newgy robots, representing all the different models (540, 1040, 2040, 1050, 2050), various ages (from 2001 to 2014), and degree of use (from brand new to well worn). Measurements were taken at various points throughout the ball channel. The sample robots exhibited a range of widths at each measured point, some below the average diameter of a poly ball (40.13~40.29).

 

So it would be natural to conclude that Newgy Robots would have a problem if any of these measurements were less than the diameter of the ball passing by that point. But this is not what I found in my research. There are two factors other than width of the ball channel that determines whether or not a particular robot can use poly balls without issue; these are discussed below.

 

Type Of Newgy Control Box

The type of Newgy Control Box (CB) is a significant factor in determining if a robot will run normally when poly balls are used. There are 3 types of Newgy Control Boxes in use at present—the digital CB, used with the 1050 and 2050 models; the 3-knob analog CB, used with the 1040 and 2040 models, and the 2-knob analog CB used with the 540.

 

The digital CB is by far the most robust in design. Our digital design allows for maximum torque to push the balls through the ball channel regardless of the ball frequency. This CB also contains a Ball Jam Alarm that senses the amount of resistance in the ball channel and then shuts down the motor if too much resistance is sensed. Typically crushed balls or foreign objects entering the ball path cause the added resistance. But this resistance can also be increased by having to push a ball that is larger than the width of the channel, as can be the case with poly balls in some Newgy robots.

 

There is less torque available with the 3-knob and 2-knob analog CB’s when using lower frequencies. With the analog control boxes, the normal result of the Ball Feed Motor straining due to increased resistance is heating up of the motor and lowered ball frequencies. Indeed, comparing balls per minute at a certain frequency setting is a way for an analog robot owner to determine if use of poly balls is causing extra resistance in the ball channel as compared to celluloid balls.

 

The 2-knob analog CB operates at even lower frequencies than the 3-knob analog CB (because it was designed primarily for beginners and lesser skilled players). This means at the low end there is less torque available to push the balls through the ball channel. Also there is no Ball Jam Alarm incorporated into this CB. If the resistance of the balls exceeds the torque of the motor, the balls will simply stop being pushed up the channel and no alarm will sound.

 

Another difference between our digital and analog control boxes is that balls are pushed in pulses with the digital design. So the balls are pushed, then there is a rest cycle until the next push. With analog CB’s, the motor is constantly trying to push the balls through the robot with no rest cycles, even when extra resistance is encountered. This cycling of pushing/resting enables our digital CB to better deal with variances in the resistance of pushing balls through the ball channel.

 

Wear Of The Ball Channel

The remaining factor in determining if use of poly balls will affect a particular robot’s performance is the amount of wear inside the ball channel. It is considered normal wear and tear for the balls to wear a groove in the sidewalls of the channel. This happens with celluloid balls and it will happen with poly balls. As balls are pushed through the channel, the balls are pushed in a slightly staggered manner so that each ball is almost always in contact with one sidewall or the other.

 

This constant rubbing of the balls against the sidewalls wears a groove in them. And the longer this wear takes place, the deeper the grooves becomes. This creates extra space for the ball and this extra space varies widely with each individual robot. What typically happens inside the ball channel is that the most wear occurs in areas that are the narrowest. So these narrow openings will enlarge over time and resistance is lessened.

 

Recommended Procedures For Use Of Poly Balls

What was learned from the above examination of the various factors that may affect how well individual Newgy robots handle the poly balls, is that no one factor by itself is normally a cause for concern. Rather it is an accumulation of resistance that determines whether or not a robot will properly handle a poly ball. Correct one or two factors and a robot that was not initially operating properly with poly balls may well start operating the way it should.

 

When fully loaded, the ball channel of Newgy Robots contains 11 balls. It is the overall resistance in the Ball Feed Motor of pushing these 11 balls through the channel that is the primary determinant. Pinch points in the channel, ball roughness (from dirt and/or the powder that is on new balls), balls that are exceptionally large in diameter, and ball channel parts that are not worn all contribute to increasing the overall resistance of pushing balls through that channel.

 

When this resistance surpasses a certain maximum, the Ball Jam Alarm activates and ball delivery stops (or in the case of the 540, the balls just stop). Additionally, with analog robots, slow ball frequencies provide less torque to the motor for pushing balls through restrictions and can cause Ball Jam Alarm activation where higher frequencies would not. So the overall goal should be to reduce this resistance as much as possible.

 

Some recommendations will apply to all models and some to only specific models. For All Models The most important action that robot owners should take when they first start using poly balls in their Newgy robot is to thoroughly wash the balls in soapy water, rinse and then dry them before using them in the robot. Newgy has always recommended this, even for celluloid balls. This helps remove dirt and the gritty manufacturing powder that is left on the balls during manufacture and once removed, the resistance of pushing those balls through the ball channel is reduced.

 

After washing the poly balls, it is further recommended to rubdown the balls by running them through the machine at high frequency. Just like a break-in period for a new car, there is a break-in period for new table tennis balls and your Newgy robot.This is especially important for analog robots and even more important for the 540 model.

 

The easiest way to accomplish this is to hang a box or similar object on the head of the robot and then turn ball speed to low and Ball Frequency (or Wait Time) to the fastest rate. The balls will be ejected out of the robot, hit the bottom of the box, then roll out of the box and back into the Ball Bucket or Ball Trays.

 

Let the robot continue feeding itself like this for about 15-20 minutes. This rubdown procedure also helps to begin breaking–in the ball channel parts on new robots. Another way to break-in new balls, either celluloid or poly, is to only put in 12–18 new balls at a time along with at least the same number of well-worn balls. In such case, you can usually get away with not washing the balls or doing the rubdown procedure.

 

The next thing is for robot owners to weed out balls that are significantly bigger than the average diameter. The easiest way to do this is to simply roll each ball up and down the ball channel of the Back Panel. Balls that stick more at particular points in the channel as compared to the majority of the other balls should be weeded out and not used in the robot.

 

As a side note, 2040 & 2050 owners also have a ball gauge that is integrated into the two Ball Dams that come with their robots. However, this gauge may not work at all with poly balls, or will work differently. For older 2040/2050 robots, the ball gauge hole was almost exactly 40.0mm in diameter, so no poly balls should fit through that hole unless they happen to be at the very minimum allowable diameter. For newer 2040/2050 robots, the hole was increased to 40.6mm so all poly balls will fit through that hole, but it is less useful for identifying balls that are significantly larger than the norm.

 

The next thing that all Newgy robot owners can do is to manually adjust the top of the Back Panel by loosening and then tightening the two interior screws that attach the Upper Guide to the Back Panel: After loosening these screws, retighten them while you pull or press outward on the sidewall with one of your hands as you’re tightening the screw with your other hand. Doing this often gains 0.5mm or more to the channel width at that location. It also helps, if your (older) robot has screws with a head larger than 5.28mm in diameter (the size used on current robots), to replace the screws with smaller head ones. Order 2000-328A screws from Newgy or you may find similar screws at a local hardware store.

 

Some robots, particularly older ones, can be improved for poly ball use by adjusting the space between the Friction Block and the Discharge Wheel in the head. Not only will this adjustment reduce resistance to the Ball Feed Motor, but it may also correct or improve the ball trajectory. For a few robots I tested, this was an essential adjustment, as the ball trajectory was quite erratic when using poly balls—balls would be ejected up, down, off to the side, but rarely straight ahead.

 

After making this adjustment, ball trajectory went back to normal. Newgy is in the process of making new parts for this and when ready, these parts will be 2040-192B for the Friction Block and 2050-193A for the Friction Block Bushing. If you have a Friction Block Spring instead of a Friction Block Bushing, it is unnecessary to replace the spring—just keep using the same one. You can order those parts from your Newgy Service Center.

 

For Ball Bucket Robots (540, 1040, 1050) To increase the space between the hub of the Pickup Wheel and the inside surface of the Ball Bucket, there is a very simple fix. First, loosen the two wing nuts that hold the robot onto the Ball Bucket. Then place a small spacer about 0.5mm thick between the bottom of the locating tongue on the rear of the Back Panel and the top edge of the Ball Bucket: The locating tongue is the part of the robot that has the serial number label on it.

 

The white spacer underneath it is a small piece of cardboard from the box that the poly balls came in (@0.4mm thick). After making this adjustment, I noticed an immediate reduction in the straining noises coming from the Ball Feed Motor and from the balls being pushed through the robot. This is a simple adjustment that is highly recommended for all Newgy robots with a Ball Bucket when poly balls are used.

 

For Robo-Pong 2040 models Older Robo-Pong 2040 models have a Clear Front Cover on them that has angular corners. 2040’s that have this type of Clear Front Cover may experience problems with balls damming up in the ball trays to the right of the robot: This ball damming problem can be greatly reduced, if not eliminated entirely, by changing the Clear Front Cover to the current design that has a rounded shape.

 

You can order the improved version of this part by contacting your Newgy Service Center and requesting part #2040-162A. Conclusions Our tests revealed that our current production models work well with the poly balls. No significant issues were observed when using the latest models as several improvements were made in preparation for the poly ball’s introduction.

 

Things can always be improved further and Newgy will continue to work on, and incorporate, these improvements into our robots. Older Newgy robots may exhibit various issues with handling the poly ball. The biggest factor is how worn the ball channel is. We expect that most older Newgy robots will already have significant wear in the ball channel and will handle the poly ball OK. Older robots that don’t have significant wear may need some of the adjustments as described in the Recommended Procedures For Use of Poly Balls section.

 

All Newgy robot owners should be diligent at performing the washing and rubbing down procedures when using any new balls, poly or celluloid. Furthermore, owners need to keep the playing area clean and occasionally re-wash the balls to prevent dirt and grime from accumulating on the balls.

 

The above conclusions are based on what we’ve been able to test so far. We’ve gone to great lengths to test a variety of Newgy robots old and new and examine how well they perform with as many different types of poly balls as we’ve been able to get our hands on. As more brands of poly balls become available, we will continue to update this white paper should the test results change our conclusions and recommendations.