Method

Experimental Method

    The goal of our experiment was to capture the indentation of a golf ball when being struck by a golf ball and also find the velocity of the ball off the clubface. To do this we needed to use a photogate that was triggered by a laser when the clubface passed through the laser beam just before it struck the ball. To find the velocity of the ball coming off the clubface we needed to use a double exposure using two flashes taped on top of one another. The first flash would be an immediate flash or with a very short delay and the second would be delayed slightly longer than the first flash. This would allow the ball to be captured twice: once while in contact with the club and another with it slightly off the club face. To capture these images, Drew would get the ball in focus using a flashlight. Then he would turn the flashlight away so Tate could still see the ball somewhat.  He would then press the laser pointer and open the shutter, Tate would swing, and the club would trigger the flashes capturing the image. The laser and photogate were mounted on a device that we used to stabilize the laser and receptor and allow Tate to swing through without danger of damaging any equipment. The balls were hit into a net, so that we could safely capture the images and avoid injuries.

            We also used the MotionScope 8000s High speed video camera to capture footage of the ball being struck. Using a bright light source and filming at 8000 frames per second, we were able to capture 2-4 frames of the ball actually being hit and shortly afterwards. Using the diameter of the ball and two fixed frames, we were able to measure the velocity of the ball just after leaving the clubface.

 Equipment:

• Nikon D1 with 55mm fixed focus
• 2 Vivitar 283 flashes
• Small Vivitar tripod
• Breadboard photogate with RCA cords
• 9 volt battery
• Laser pointer
• Stabilizing device “Golfers ‘Laser Beam’”
• Tee mat
• Soft golf balls (Titelist pro-v1, and Pinnacle Exception recommended)
• Wooden Tee (rubber also works)
• Nike Ignite Driver 10°
• Net
• MotionScope 8000s High Video Camera set up
• Dark Sheets to block light
• Stroboscope
 

Setup Diagrams

Overhead Picture

Equipment Setup

         In order to have a consistent set up each day, we built a device to hold the laser, photo gate, breadboard, and ball and tee in the same place; we called it the "Golf Ball 'Laser Beam'". We used a piece of plywood one meter in length to support the blocks that held the laser on one side and the photo gate on the other. The laser was set three inches high so that it would hit the ball close to the center and give us the best trigger. We used an artificial turf teeing pad on which to hit the ball. This pad was about one inch thick so the height of the laser was able to clear the pad easily. The green pad also added to the asthetic beauty of the shot because it appears to be on a real course, not just in a lab. We set the camera directly behind the laser, right in line with the ball. We used a table-top tripod (Vivitar) to hold the camera. We set the camera and tripod on a small box about six inches high so Drew’s finger would not be in the shot because he had to hold down the button on the laser. Directly to the right of the camera (when looking through the lens at the ball) is where we put the flashes. This was so that we would get a shadow coming backwards which would give depth to the shot. Also, the flashes were raised off the ground to a distance of one foot. Because the camera was pointed almost level at the ball, Tate’s shoes were getting into the preliminary shots so we used a green piece of cloth to cover his white shoes.  Half way through we thought to color the wood green so everything would be uniform. Finally, we used a net in the balcony of the PEC to catch the balls and a giant cheerleading pad to catch the balls when we were in the wrestling room.

Imaging Methods

         We decided from the beginning that a sound trigger would be too slow to catch the club in impact with the ball. The sound trigger would be to slow because Tate is swinging the club at over 100 mph. Thus, the sound trigger would catch an image after the club made contact with the ball. Instead, we used a laser and photo gate trigger. The laser we used was an ordinary red LED laser pointer much like ones used in presentations. The only unfortunate obstacle with using this type of laser was that there was no “on” setting or switch; Drew had to hold down the button for it to shine.

        In order to get a good photo, we went through the same timing process each time. Tate would turn out the lights while Drew had a flashlight on for light before the shot. Using the flashlight light, Tate lined up the club, ready to swing. Then, Drew pointed the flashlight away so as not to get any light into the camera. While holding down the button on the laser pointer, Drew said, “Swing,” to Tate. During Tate’s backswing, Drew released shutter on the camera. When Tate hit the ball, the flashes flashed in sequence (or just one flashed depending on the shot) and caught the ball off the club and in the air shortly after the hit. Drew had to line up the laser just right each time or else the beam would have been broken if it missed the sensor. So, even after the ball was hit, Drew had to make sure to hold the laser still until the shutter closed so that another flash would not go off and affect the image.