An Engineer's Perspective

Comment

Comment by feihuxin on April 9, 2009 at 11:29pm

cool, thanx for the tip! look forward to getting my new racket :D

Comment by Marty on March 28, 2009 at 11:35am

Just a footnote about vibration...if muscles rebound in resonance with the combination of the string tension, racket flex and associated geometries, the effect on the body can be multiplied many times. Resonance depends on damping and stiffness. Damping depends on material composition and geometry. Poor damping negatively affects the player and shot accuracy.

Comment by Marty on March 28, 2009 at 11:27am

Muscles produce force to move the racket. Changing the speed and direction of the racket head requires acceleration. As long as your racket head moves considerably slower than the speed of sound or light (which badminton at times seems to approach) they combine inversely proportional to the mass of whatever’s moving (m=F/A.)

Minimize the mass (“weight” if you remain on Terra Firma) and the distance between the moving object and the muscle acting. Lighten the racket, use one head light, shorter if permitted, more wrist, less shoulder, etc. Shorter strokes also minimize wear and tear on joints, tendons and muscles as long as movement remains smooth (not jerky.)

Regarding flex and string tension, vibration during a stroke produces small bursts of stress repeatedly just after impact. Less string tension in a well-damped frame should minimize vibration. Thump the frame and listen. A well-damped frame will sound like a tuning fork vibrating in mush. A lower pitch indicates more flex that will produce a smoother impact transition as well. The same acoustics apply for strings.

Comment by feihuxin on March 27, 2009 at 10:25pm

Hi:
I'm actually a badminton player who is doing some research on what kind of badminton racket to get as my old one broke. I've seen some conflicting information on the web, and is confused about what to get, so was trying to reason my way through science, unfortunately, I suck at physics. Thought you might be able to help me as tennis and badminton are pretty similar.

Anyways, I have a shoulder injury from doing gymnastics when I was young, and my shoulder still bugs me at times when I play too hard (ie, doing too many smashes & clears). The deceleration part of the overhead swings is what aggravates the muscle the most. I would like to get a badminton racket that would help me maximize power & speed for smashes & clears, but at the same time, decrease the stress to my shoulder muscles. I'm a beginner/intermediate player. What should I be looking for? stiff or flexible frame? high or low string tension? heavy/light racket? head-heavy or even balance or head light?

Look forward to your reply. Thanks.

Comment by Marty on March 26, 2009 at 12:37pm

Playability of different rackets depends on literally hundreds of factors. The above comment addressed only the question posed related to tradeoffs between stiffness and string tension. Other factors such as weight, balance, vibration, anthropomorphism, playing style and personal preference also weight in.

Tournament players can discern subtle differences between identical model rackets from the same production run. No manufacturing process produces precisely identical results.

With modern composite rackets, individual fibers move in the containing matrix and eventually change playing dynamics. The wear can dramatically effect playability and even lead to catastrophic failure. The type of fiber, volumetric ratio of fiber to resin, mechanical differences between fiber and resin, tiny voids in the matrix and geometric distribution of fibers combine to produce racket qualities.

Rackets respond to ball impact with non-linear dynamics. Players must anticipate and compensate for these dynamics with split-second timing to direct shots.

Comment by Marty on March 19, 2009 at 1:45pm

A detailed analysis would require inclusion of about 400 parameters boiling down to how long the ball stays on the strings at impact. A flexible racket with low string tension maximizes contact time allowing transfer of racket energy to the ball. Conversely, a stiff racket having tight strings causes the ball to rebound quickly requiring more racket speed to achieve comparable energy transfer.

A moving tennis ball presents kinetic energy measured in Joules calculated as half the product of the ball’s mass times its velocity squared. Power requires including a time element, i.e., one watt equals one Joule/sec. Reversing the balls direction calls on Newton’s F=ma law. In summary, while the ball and racket are in contact, the ball’s mass remains fixed, the reversing force is nearly constant and the acceleration, i.e., the ratio of the change in velocity to the contact time we can approximate as constant. Contact time becomes the value that determines the returning velocity.

The energy returned with the ball depends on three variables: Its arriving energy, the reversing force applied and how long the force acts. If the contact time remains identical for various combinations of racket stiffness and string tension, the power effect should be similar.

Comment by Marty on March 19, 2009 at 11:20am

Hmmm...might be an interesting analysis. I'll get right on it.

Comment by Mark / The Mayor on March 19, 2009 at 10:48am

Great start. How about the analysis of the way a head-heavy racquet affects your stroke and power vs. a balanced or handle-heavy racquet.
We all know that looser strings means more power, but what happens if you put tight strings in a powerful frame vs. loose strings in a player's frame (non-powerful) - at some point the total aggregate power could be equal, but how would the two assemblies play differently?

Comment by Marty on March 18, 2009 at 2:48pm

A good starting point would be to develop contacts in research and engineering departments at manufacturers. They have a vested interest in delivering accurate information about products.

The materials technologies involved in rackets alone could fill volumes. Long term, I would like to establish an independent testing lab for sports equipment to provide services similar to those offered by Underwriter's Labs (UL). Pure science could be used to generate comparitive studies for consumers and professionals. I want to provide technical information that helps non-technical tennis players choose equipment. Certifications might also be developed that would help level the "fluff" field.

Technology can address questions like "Why do two "identical" rackets seem to play differently?" and "How does the weather affect my game?" More?

Comment by Mark / The Mayor on March 17, 2009 at 4:38pm

Marty,
This sounds like a fascinating endeavor. To strip away the advertising fluff from the actual mechanics of a frame (or frame system) is a challenge worth pursuing. I can't wait to see the fruits of your labor and hear all about what you learn.

Do you have any ideas on where to start?
M