BUYING A MACHINE FAQs
1) Can I trade in my old Silent Partner Machine?
We'd be happy to help dispose of your old machine but we do not offer trade ins. However, returning customers are eligible for a discount on new machines.
2) I just bought a new machine and really regret not getting the model with more features. What can I do?
Just box up your Silent Partner Machine and we'll have UPS pick it up. You'll be required to pay the difference for your new machine, the return shipping and the shipping of the new machine to you.
3) I've had a machine for years and am looking for a new model. Do you offer any discounts for returning customers?
We love that you were so happy with your first Silent Partner that you are looking to get a new one! We offer a 15% discount on a new machine for repeat buyers. Conditions apply. Call our office for details.
4) Ball machines are a bit out of my budget, is there anywhere I can find discount machines?
Demos and used machines are a great way to buy quality machines at a discounted price. If you are interested in a demo or a used machine, please check our auctions on eBay. We sell demos and blemished machines on eBay under the name "silentpartnerbyauction". All Silent Partner ball machines that we sell on eBay have been checked by us at the factory, and are sold with a 1-year warranty (the satisfaction warranty is not provided for machines sold by auction).
5) I live outside of North America, can I still order a Silent Partner Tennis Ball Machine?
Silent Partner currently ships to addresses in North America. If you wish to place an order internationally please call or email us for more information.
6) How can I track my order?
If you send us an email at sptennis.on.aibn.com with your name we can send you a tracking number so you can follow your Silent Partner's movements right up until it arrives at your doorstep.
7) I want my Silent Partner to last as long as possible. How can I do this?
Check out our Caring For Your Silent Partner page for full instructions from arrival to years later.
8) How long should I expect the battery to last?
The batteries last from 2-5 years depending on use and care over the years.
9) Is my Silent Partner machine only compatible with batteries sold on your site?
Our machines are compatible with any brand of battery, and you can often get them cheaper locally than paying the shipping from our site. Just make sure you get a battery with F2 terminals.
10) Do you offer a discount for multiple machine purchases?
Yes - if you would like to purchase more than one machine please contact our office.
11) I bought a Silent Partner machine and told all my pals about it. Now they are buying one too! Do you offer any incentives for referrals?
It would be great to send you a free machine cover to thank you for sharing your love of Silent Partner machines! We just need your friend to include your name in the order or send it to us by e-mail after they've placed their order. That way we can look up which machine you have and an address to send it to!
BALL MACHINE FAQs
1) How are balls thrown by ball machines?
All quality tennis ball machines presently available on the market use wheels to throw the ball. Normally there are two wheels that turn in opposite direction (thus the label "counter rotating wheels") with a small space between them. The ball rolls down a chute and is squeezed by the counter rotating wheels which then eject it. The situation is similar to gravel being thrown from under a spinning tire, though in the case of the tire only one wheel is responsible for the "throwing".
2) Do machines with a tube that makes them look like a canon work the same way as machines that use counter rotating wheels for ejecting balls?
No, machines that look like a canon work by air pressure. Pressure is usually supplied to a drum by a vacuum cleaner motor. A ball is lodged at the throat of the tube and is retained by a collar that is slightly smaller in diameter than the ball. When pressure builds sufficiently to push the ball through the collar, the ball is ejected. Because these machines work on air pressure, they are called "pneumatic".
3) Is there any other way for a tennis ball machine to throw balls?
Yes, some machine use a "hammer" to strike the ball, and various spring loaded designs have also been developed. The performance of such machines is so limited that they are not discussed further here.
4) What's better: Counter rotating wheels or pneumatic pressure?
Today no machine costing more than about $700 works on the pneumatic principle. All better machines use counter rotating wheels. There are a number of reasons for this. Pneumatic machines are noisy and do not provide the high level of performance achieved by the better wheel driven machines. Pneumatic machines also require a lot of electrical current and cannot, therefore, be adapted to battery power. The only advantage of pneumatic machines used to be their low cost. Today they are a dying breed.
5) How does a machine put spin on the ball?
Wheel driven machines put spin on the ball by varying the relative speed of the upper and lower wheel. When the upper wheel turns faster than the lower wheel, the ball is ejected with topspin. When the lower wheel spins faster than the upper wheel, the ball is ejected with backspin. Of course, when both wheels turn at the same speed, the machine throws a flat ball. Pneumatic machines use friction in the canon tube or just outside the tube to impart spin. When the bottom of an ejected ball is rubbed as it exists the machine, the ball acquires topspin, and vice versa.
6) Can all machines put spin on the ball?
No, some wheel driven machines do not have spin capabilities. This is usually because the wheels are arranged in a horizontal plane rather than a vertical plane. By changing the relative speed of the wheels in a horizontal wheel machine, one could achieve side spin but no topspin or backspin. Because side spin is not an important element of tennis, manufacturers of horizontal wheel machines do not usually provide a spin adjustment.
7) What is an oscillator?
An oscillator is a mechanism that allows the machine to throw balls in different locations on the court. The most common type of oscillator, known as a random oscillator, causes the machine to sweep the court from side to side repeatedly much like an air fan sweeps a room. Balls are thrown in different and somewhat unexpected locations to simulate play with an opponent.
8) What is an adaptive all-court oscillator?
Some more advanced tennis ball machines provide for vertical oscillation as well as for horizontal oscillation. Vertical oscillation is achieved by varying the angle of elevation - the higher the ball is thrown, the deeper in the court it lands. Some brands of machines achieve vertical oscillation with a mechanical cam that varies the angle of elevation within a fixed range. The ball must be thrown within a narrow range of speed and spin or it will hit the net or fall beyond the baseline. The adaptive all-court oscillation of the Silent Partner Quest and Smart computes an appropriate vertical range to suit the speed and spin selected by the user. The benefits of this adaptive approach are particularly dramatic at high speed and topspin, where the all-court feature provides a pro-level challenge.
9) What is Select-A-Drill?
Select-A-Drill is the name given by Silent Partner to the ability of an advanced machine such as the Smart, to memorize and replay sequences of shot locations. The user can enter a sequence of shots, and then practice the drill over and over. Because the user also selects the speed, spin and feed interval for the drill, a near infinite number of programs can be created to challenge all levels of players.
10) What are Match Play presets?
Play simulation involves programs that simulate play with an oponnent. The computer of the Smart will provide preset speed, spin and ball interval and will simulate actual match rallies with breaks between points. The user can override the preset speed, spin and ball interval rates to suit their own level of ability.
11) How important is top speed in selecting a ball machine?
Although an intermediate player usually practices ground strokes at speeds of about 40 to 60 miles per hour, a higher top speed is a crucial consideration in a ball machine. There are a number of reasons for this: 1) As the trainee improves, higher and higher speeds are required to keep practice challenging; 2) reflex volleys require much higher speeds than ground strokes; 3) to put spin on the ball, the machine needs to slow one of the propulsion wheels down in relation to the other one, and this reduces top speed accordingly; 4) competitive players require very high speeds to simulate their opponents hard shots. All in all, a ball machine with a poor capacity for speed is quickly outgrown by its user.
12) What kind of batteries are used in battery powered ball machines?
The batteries used in portable ball machines are sealed and do not leak even when used upside down. The batteries are not motorcycle or car batteries, nor are they "gel cells". The batteries are known as "sealed lead-acid" batteries. Batteries are rated by the number of Amp/hour reserve charge they carry. All Silent Partner ball machines except the LITE use a 21 Amp/hour battery. The LITE has a 9 Amp/hour battery. Unlike certain types of batteries that have a "memory" and that need to be discharged completely before being recharged, lead acid batteries do not have a memory and can be recharged from any state of discharge.
13) How are batteries recharged?
Battery powered ball machines are usually supplied with a battery charger that plugs into a household outlet and that connects to the control panel of the machine. Because the batteries in ball machines are sealed, they must not be charged very quickly. This is why charging time for a dead battery is usually about 10 hours. Faster charging can reduce the life of the battery, although occasional fast charging on an emergency basis will not damage a battery.
14) What is an AC-powered machine?
An AC-powered machine is a machine that can only run on household current (120 volts in North America, 220 volts in most other countries). Such machines do not contain batteries and can only be used when an electrical outlet is available. Owners of private courts and clubs often prefer AC-powered machines because they can be used indefinitely without worrying about batteries running out. Silent Partner machines that are built to run on AC current cost a little more than their battery-powered counterparts and offer similar performance. The AC converter is housed inside the machine, and the machine remains completely portable and can be carried in the trunk of a car.
15) What is an AC-DC machine?
An AC-DC machine contains batteries but is built to also receive an adapter for use with household current. In the case of Silent Partner machines the adapter consists of a convenient hand-carried unit that is separate from the machine. The machine can run on its internal batteries or on the AC adapter. The AC adapter plugs into a normal AC outlet at one end and into the machine at the other. The AC-DC option is desirable in cases where the availability of an AC outlet is not certain, but can be anticipated in some situations or in the future. Silent Partner machines that are equipped with the AC-DC option are just as portable as battery-powered models.
1) What is synthetic gut?
The string commonly known as synthetic gut is made of nylon and is constructed in the way shown in the picture on the right. That is, the string is composed of a solid nylon core surrounded by a single wrap of thinner filaments. A coating of silicone is applied to reduce friction. As the name implies, this type of string was developed to simulate the playing characteristics of natural gut.
2) What are the main attributes that distinguish different types of strings?
The material used in a string (for example "nylon" in the case of synthetic gut), the construction of the string (a solid core surrounded by a single wrap of thinner filaments in the case of synthetic gut), and the gauge, or thickness, of the string define the essential characteristics of a string.
3) Do different brands of strings play differently?
Strings of same material, construction and gauge have very similar playing characteristics regardless of the brand name they are sold under. Although string companies go to great length to create a distinctive image for their strings, the results of scientific tests published by the USRSA (United States Racquet Stringers Association, June and July, 2000 issues of Racquet Tech ) demonstrate that the material, construction and gauge are a lot more important than string brand in determining the playing characteristics of a string. Among these three variables, the material that a string is made of is by far the most important in determining the playing characteristics of the string.
4) Since the material a string is made of is so important, what materials are there to choose from?
The most common materials for tennis strings are natural gut, nylon, polyester and kevlar. USRSA tests revealed that the dynamic stiffness of a string (think of this as the elasticity of the string after it has been tensioned) "determines almost everything" in the playing characteristics of the string. The less stiff a string is, the better it plays. Natural gut is the least stiff string material, followed by nylon, polyester and kevlar. While natural gut is the least stiff string material, nylon is not far behind, and polyester is a bit stiffer still. Kevlar, however, is way stiffer than any of the other materials, so one takes a bigger jump into stiffness when going from polyester to kevlar than when going from natural gut to nylon or from nylon to polyester.
5) If natural gut is best, why doesn't everyone use it?
Natural gut is undeniably the best string a tennis player can use, and the majority of top professional players do use it. Unfortunately, natural gut is very expensive, the price for a coil for stringing one racquet ranging from $25 to $35 (by mail order). The reason natural gut is so expensive is that it is made from cow or sheep intestine and requires a lot of labor to turn into string. Long strips of intestine are cleaned to expose the collagen sheath known as the serosa, they are then cut into strips, dried in salt for several weeks, twisted together to form a string which is put in a drier for about a day and is then covered with a protective polyurethane coating and finally packaged. The elasticity of natural gut apparently derives from the need for the intestine to expand dramatically when accommodating a big meal, and then to contract after digestion. The best known brand of natural gut is Babolat VS (you have noticed the logo consisting of two lines near the throat of professional tennis player's racquets). Pete Sampras used it and was reputed to have had his racquets restrung before a match whether the strings have been used or not! Natural gut has gradually lost a lot of its popularity with top players and Silent Partner does not sell it.
6) Given that natural gut is too expensive for most players, how does one choose a less expensive string?
Earlier we saw that string commonly known as synthetic gut is made of nylon and has a construction consisting of a solid core surrounded by a single filament wrap. The reason synthetic gut is the most commonly used string in tennis is because nylon is only a little stiffer than natural gut, and the solid core/single wrap construction is inexpensive to produce. In a nutshell, synthetic gut achieves an excellent balance between quality and price. One can increase the elasticity of a nylon string by using a different construction. Instead of having a solid core surrounded by thin filaments, the string is constructed entirely of thin nylon filaments. These are known as multifilament strings and USRSA tests show them to come closer in elasticity to natural gut than solid core/single wrap synthetic gut. The picture on the right shows the multicore/single wrap construction of Silent Partner Filament Frenzy. The single wrap of slightly larger filaments is used to enhance durability because multifilament strings are not usually as durable as synthetic gut. The USRSA tests mentioned above have shown that strings with this multicore/single wrap construction are as elastic as strings that are composed entirely of thinner filaments. Multifilament strings (with or without an outer wrap) cost more than solid core strings, but they offer improved playability.
7) If natural gut and nylon offer excellent elasticity, why are some strings made of polyester or Kevlar?
Elasticity (or low dynamic stiffness) is a property that contributes to the playability of a string. The other important characteristic of a string is its durability. Natural gut and nylon strings offer acceptable durability for most players, but hard hitting players usually break them in a few hours of play. Polyester and Kevlar offer much better durability at the expense of increased stiffness. Polyester resists notching where strings cross, and therefore lasts longer than nylon (at least three times longer, in our experience). Polyester is usually extruded as a single thick filament (outer wraps do not adhere to polyester) and polyester is the only true "monofilament" string available for tennis. Kevlar is the registered trademark for Dupont's famous material that bullet proof vests are made of. Generically, strings like Kevlar are known as aramids (Technora is another aramid string). Aramids provide outstanding durability (perhaps five or more times the durability of nylon), but they are extremely stiff.
8) I am a "string breaker". What's my best choice of string?
Silent Partner recommends polyester over Kevlar. This is because polyester's dynamic stiffness is nearly as low as that of nylon, and its durability is nearly as high as that of Kevlar. Polyester, therefore, offers an excellent compromise between playability and durability. Also, whereas Kevlar is a particularly expensive synthetic string material, polyester is among the cheapest. Silent Partner sells polyester as well as Kevlar strings.
9) I need the durability of polyester or Kevlar, but I do not want my racquet to feel stiff like a board. What can I do?
Stringbed stiffness (the stiffness of the entire stringbed rather than of individual strings) can be reduced in a number of ways, even when very stiff strings like Kevlar are used. The main contributor to stringbed stiffness is the tension at which the racquet is strung. One way to reduce stringbed stiffness is to reduce tension. It is often recommended that a player adopting Kevlar for the first time reduce tension by 10% compared to prior stringings with nylon. Polyester does not require nearly as much of an adjustment. The main other way that stringbed stiffness can be reduced is by using a "hybrid".
10) What is a "hybrid" string job and how is it achieved?
A hybrid consists of a stringbed with a different string for the "mains" (strings that run lengthwise in the racquet head) and the "crosses" (the shorter strings that run at a right angle to the mains). Hybrids are often used to maximize durability while keeping stiffness as low as possible. Because mains usually break before crosses, a durability oriented string such as polyester or Kevlar is used for the mains while a more elastic string is used for the crosses. Silent Partner recommends that a 17 gauge synthetic gut be used for the crosses when polyester is used for the mains and that an 16 gauge synthetic gut be used for the crosses when Kevlar is used for the mains. Interestingly, for most of his career Andre Agassi used Kevlar for the mains and natural gut for the crosses. This is an unusual combination that worked for Agassi because a hard hitter like him wants the durability of Kevlar and is not concerned about the cost of natural gut in the crosses.
11) Are hybrids ever used for reasons other than maximizing durability and minimizing stiffness?
Hybrids can be used to maximize playability while keeping cost low. Because the mains are the longest strings in a racquet, and because string length is an important determinant of the playability of a stringbed, it makes sense to install the most playable string in the mains. For example, a player who wants the playability of natural gut will get most of the benefits of natural gut by stringing the mains with it while stringing the crosses with an inexpensive 17 gauge synthetic gut. This cuts the cost of a string job with natural gut in half while providing playing characteristics that are practically indistinguishable from an all-gut string job. Andre Agassi's Kevlar/gut hybrid is unusual because most players would not notice the qualities of natural gut when it is used for the crosses. Andre Agassi's sensitivity to the properties of a stringbed are, of course, not those of the common player.
12) What is the gauge of a string and how should it be chosen?
The gauge of a string is its thickness. Tennis strings range from 15 gauge (about 1.4mm) to 18 gauge (about 1.1mm). "L" in a string gauge such as 15L refers to a slightly thinner variation of that gauge (so 15L is between 15 and 16). The most common string gauge for synthetic gut in North America is 16, but players looking for durability can choose a thicker string such as 15 or 15L, while players looking for more elasticity can choose a 17 or 18 gauge string. The gauge of string has a major influence on its elasticity and playability. The USRSA reports that a 17 gauge string is about twice as elastic as a 15 gauge string of the same material and construction.
13) What is the most elastic and playable synthetic string?
The most elastic synthetic string has a thin gauge (such as 18 gauge) and is made of an elastic material (such as nylon), using a construction that promotes elasticity (such as a multifilament construction). Few players use 18 gauge strings, especially for the mains, because they would break too quickly. Even 17 gauge string is not very durable when used in the mains. But a 16 gauge multifilament nylon string is a very good choice when the emphasis is on elasticity with acceptable durability. Silent Partner's Filament Frenzy falls in this category.
14) What string characteristic contributes to power?
The conventional answer to this question is that the more elastic the string, and the lower its tension, the more power it generates because of a trampoline effect. This notion is correct, though it oversimplifies the issue a little. This is because when a ball hits the stringbed, the strings deform like a trampoline, but the ball also deforms. This dual deformation reflects the storage of energy (from the hit) in the stringbed as well as in the ball. The stiffer the stringbed, the less it deforms, but the more the ball deforms. The looser the stringbed, the more it deforms and the less the ball deforms. The important question is, how much of the energy stored in the stringbed and in the ball is reimparted to the ball as it leaves the stringbed? Because strings regain their shape faster than balls, more of the energy stored in the stringbed is reimparted to the ball than energy stored in the ball (the ball leaves the racquet before totally regaining its shape, and this results in a loss of energy). So it should be true that low string tension results in more power than high string tension. If this is not complicated enough, consider that recent tests and calculations published in the USRSA magazine (in particular an article by Professor Rod Cross in Racquet Tech, September, 2000) suggest that string tension and elasticity have negligible effects on power (that is, Kevlar strung at 65 LB generates the same power as natural gut strung at 55 LB). This is a rather controversial claim that flies in the face of years of player experience, and Silent Partner endorses this claim only after clarifying what "negligible" means. Silent Partner has conducted tests comparing natural gut to Kevlar strung at 60 LB. Balls were shot by a ball machine at a stationary racquet head. Test conditions were carefully controlled, the identical racquet and string tension was used in the two tests. Balls shot at the natural gut stringbed rebounded 7% farther on average than balls shot at the Kevlar stringbed. The difference was statistically significant an represented what would amount to a difference of several feet in where a blocked serve would land on the server's side. So, one physicit's "neglibible" difference may be a player's "OUT" call. In a game where differences of mere inches determine whether a ball is in or out, the differences observed in Silent Partner's tests were substantial. The position taken by Silent Partner is that empirical tests with criteria that are related to call outcomes need to guide the choice of labels used to describe the differences caused by variations in string tension.
15) What string characteristics contributes to control?
Control is the flip side of power. Advanced players who hit with full swings and high racquet head speed do not have trouble generating pace. For them, keeping the ball from flying farther than they wish is of greater concern. The problem with the trampoline effect discussed in Question 14 is that it is not under tight player control, and it creates more variation in where the ball goes than pace generated by the swing itself. For this reason, advanced players prefer tight stringbeds that do not introduce variability due to the trampoline effect. Perhaps a good analogy is with a sports car that keeps the driver in more direct contact with the road, much like a tight stringbed keeps the player in more direct contact with the ball. So how can one promote control? Primarily by stringing at a higher tension (did you know that Bjorn Borg was sometimes woken at night in his hotel room by the sound of strings snapping spontaneously? His racquets were strung at more than 80 lbs!). Another approach is to use a stiffer string like Kevlar, though subjectively such stiff strings are not as "playable" as more elastic strings, and this is probably the reason that they are seldom used by professional players.
16) What string characteristics contribute to playability?
Playability is a highly subjective impression about strings that is generally related to the elasticity of the string. So strings that generate power (like natural gut or multifilament strings) tend to also be playable. Little is known about the exact characteristics that contribute to the subjective impression of playability, but along with elasticity, the gauge of the string as well as the finish applied to it during manufacturing seem to be factors.
17) What string characteristics contributes to spin?
The texture of a string contributes to its ability to generate spin. A thicker filament is spun around the core of spin oriented strings like Silent Partner's Headspin in order to create a texture that bites into the ball. The gauge of a string also contributes to spin, thinner strings having a better ability to bite into the ball. Perhaps the most important equipment factor that contributes to spin has nothing to do with the string itself. It consists of the "string pattern" or the density of the checkerboard pattern formed by the strings. Open string patterns, consisting usually of 16 mains and 18 crosses configured so that the strings sit far from each other, allow the ball to imbed itself more in the string bed and this causes the main strings to brush more effectively against the ball.
18) Why do strings break?
The primary reason strings break is that "main" strings rub against "cross" strings when the ball is hit with spin. Gradually, this rubbing cuts a notch in the main string. When the notch gets deep enough the string cannot withstand the stretch caused by a strong shot, and it breaks. The thicker the string, the deeper the notch it will tolerate before breaking. That's why thicker strings last longer than thinner strings. The more abrasion resistant a string is, the longer it will take for a notch to grow. This is why polyester strings last longer than nylon strings. The higher the tensile strength of a string (the tension it can withstand without breaking) the deeper a notch it will tolerate before breaking. This is why Kevlar is very durable. Another factor that contributes to string wear is the abrasiveness of court material that is picked up by the ball and deposited on the strings. That's why strings break more quickly on clay courts than on hard surfaces. Rallies also tend to last longer on clay courts, and the corresponding increase in hits during a match contributes to string wear. Notching is not the only reason for string breakage. A ball hit near the frame can cause a shear break, even on a new string. Strings that are damaged during stringing can also break prematurely. So can strings that are installed in cracked or damaged grommets.
19) Can anything be done to make strings last longer?
The only effective method for extending the life a strings during play is the insertion of little plastic pads at the cross points between main and cross strings, especially in the area of the sweet spot. These inserts work by reducing the notching effect that the crosses have on the mains. You have seen professional tennis players insert these during matches. The most popular inserts are made by Babolat and are called ElastoCross. Although these inserts do extend the life of strings, many players who have used them do not find that they are worth the cost (about $6 for the applicator and inserts) and the trouble (it takes time to install the large number of pads necessary to protect the vulnerable strings in a stringbed, while waiting and protecting only the strings that fray reduces the effectiveness of the approach). The pads can also be a nuisance because they can fall on the court during play, and they need to be contained in a plastic bag when old strings are removed from a racquet.
20) How often should strings be replaced if they are not broken?
The rule of thumb is that strings should be replaced as many times a year as one plays in a week. Why should one replace strings before they break? Because two things happen to tensioned strings over time. The first is tension loss. For example, a freshly installed synthetic gut will typically lose close to 10% of its tension within 24 hours. The rate of tension loss drops substantially after this, but it is still a factor and its impact can be felt, especially months after strings have been installed and hit with. Some players think that their racquet becomes more powerful because of the enhanced trampoline effect created by the loss of tension. This is probably a misconception because of something else that happens to strings over time. The second thing that happens to strings over time is that they lose their resilience (think of it as zing, or the string's ability to reimpart energy to a ball quickly after being deformed by a hit). This loss of resilience comes across as string fatigue, or the feeling that the strings are dead and mushy. For these two reasons, therefore, strings sometimes need to be replaced before they break. You may wonder if some strings lose their tension faster than others. The answer is yes. Multifilaments lose their tension faster than synthetic gut (monofilament with one wrap). Polyester is also reknowned for losing its tension relatively fast (Silent Partner only sells polyester in 17 gauge because it is very durable and will need to be replaced for reasons of tension loss if not for breakage. There is no point, in other words, going for the extra durability of 16 gauge or 15 gauge polyester).
21) What is the shelf life of strings?
Strings made of synthetic material can last several years in their original packaging without noticeable change in their playing characteristics. This assumes that extremes of temperature and direct sunlight are avoided during storage.
22) I have tennis elbow, what string should I use?
Players who suffer from tennis elbow, or any other form of arm or shoulder tendinitis, should do everything they can to reduce the stiffness of their racquet's stringbed. This means selecting the most elastic string possible, such as natural gut or a nylon multifilament, using a thin gauge of that string, and reducing the tension at which the racquet is strung. One should not count on these measures alone to cure tendinitis. The advice of a doctor should be sought.