Online Experiment Journal
Tim Reibold and Brandon Winterling - 5/02

Photo Journal

4-10-02
Today we set up the speed measurement part of our project. We made a Plexiglas box to shoot the balls into and still allow us to take pictures without getting everything messy. We also set up the Apple II computer to use as our time and interval delay for our flashes. No pictures were taken today because we have no air for our gun, but we did get a free windmill cookie from Dr. Winters. 

4-15-02
We finally got our air and set everything up but we were not able to take any pictures because of timing problems. Hopefully tomorrow we will be able to capture the ball on film - we could not catch the ball on the film today.

4-16-02
We finally captured the paintball on film using a 7 ms delay and a 15 ms interval between flashes.  Something interesting of note was a distortion in our picture. The marked off pole was slightly curved downward on the right side of the picture. Both the ball and pole are clear but they bend. We will further investigate this so we can figure out what is going on. Tonight and tomorrow we will work on the speed measurement for the paint ball.

4-17-02
We have started taking pictures in the box and they look great. The shots from the back are just paint splats but the shots from the side are great. They are clear, focused, and show what we want to capture. It would be nice if we could get a whole sequence of the ball crushing in our next shoot. The problem presented in getting the ball just before it is crushing. With our current setup, we can't get the ball just as it hits. We will also bring a sponge and water to the next shoot for a quicker cleanup. 

4-21-02
We have gone back to using the photo gate for our triggering device. By measuring the distance from the photo gate to the box we should be able to use the speed to find out how long the ball will take to reach the box. This yielded a delay of 44 ms for the ball to hit the Plexiglas. In our new setup we will stack 4 flashes together and put different color filters on them. These flashes will sit inside the box facing the surface the ball will hit. The camera is setup for a side view. 
Then we decided not to do this, but instead use a rotating mirror, described in next journal entry.

4-30-02
We have decided to try the rotating mirror method to take a picture of the paintball smashing into the Plexiglas. A description of how the mirror works can be found in Stroboscopic Study of High Speed Projectiles in Water by Matthew Hinshaw, 1991. 

To shoot the paintball gun we built a stand for the solenoid to sit on so we did not have to mount it directly to the gun. The solenoid stand and rifle rest are c-clamped to the lab table. The gun is taped down the rifle rest.

5-1-02
Today we tested the solenoid fired by the yellow annunciator box. By looking at the LED on the box you can tell what state the switch is in. The command A=PEEK(49240) turns the switch on and A=PEEK(49241) turns it off. The solenoid is hooked to annunciator 1 (0 on the yellow box). To fire - turn on the annunciator, then push in the optoisolator and PB1 at the same time.

5-2-02
We finished setting up the mirror and gun today. We mounted the laser over the mirror with 3 ring stands and tested to see if it worked with padletester. All we have left is to find/rewrite the correct program that will put it all together for us.  
Calculations needed to make:

             a) How long it takes for the ball to get to the Plexiglas from photogate 1.
             b) The time it takes for the mirror to reach its effective angle range once it has
                  crossed the laser photogate.
             c) The interval for the flashes to fire to reflect the image off the rotating mirror to 
                  film.

5-8-02
We will assume it takes the mirror 0.218 seconds to rotate into position after the laser is broken. This is based on the fact that it takes 0.214 s to rotate once and 0.004 s to reach its effective angle. The reason we made  the mirror fully rotate once before coming into position is so there is enough time once the laser is broken by the mirror for the computer to fire the gun and for the ball to reach the Plexiglas. 

From the mirror delay we were able to find that we needed a delay of 0.073 s from the time the laser is broken to when the solenoid should be activated by the computer.

Timeline:

Laser is broken                 Solenoid is                     Mirror rotates to                   Complete;
on mirror box              activated, gun fires              position; first flash                  fourth flash
|-----------------------------------------------|---------------------------------------|---------------------------------------|

0                                          0.073 s                            0.218 s                              0.220 s  

We found a program that worked!!!! called Ball and Mirror on the Multiplexer + Demo + cal. prog. Disk.  We at first thought that there was a problem with the program and that we were going to have to let the mirror rotate twice (to increase mirror delay) in order to get it to work.  Then we realized that the problem was that the mirror delay had to be bigger than flight time. In reality, we could have reworked our number so that mirror only rotated once but letting the mirror go around twice should work as was easier, and  there was more room for error.

5-9-02
Looking back on what we wrote yesterday we realize that what we thought was not completely true. When we were putting our mirror delay for the mirror with one rotation we put in 0.073 s (The delay until the solenoid need to be pulled after the laser was broken). However, that is not the correct definition of mirror delay. The correct definition is how long it takes for the mirror to rotate into position to take a picture after the laser is broken. We should have been inputting 0.218 s for mirror delay instead of 0.073 s. 

Our values could be (with only one mirror rotation):

           Mirror Delay - 218
           Flight Time -   140
           Interval -           1.5
           Frequency -    667.55
           Synch Time -  78

Because our Plexiglas box is too big to be used for this type of picture we are going to sue a single sheet of Plexiglas spray painted black instead. The box would overlap in our images because it is not black and takes up most of the picture anyways. Today, we spray painted.

Note: Make sure the receiver for the laser is pushed up in the hole on the mirror box really far. We learned this when we went to test yesterday's setup between spray paint sessions. If you run the Ball and Mirror program and the mirror is all over the place when the flashes go off or the flashes don't go off no matter if the mirror is spinning or not, your problem is most likely that the laser receiver is not pushed up far enough.

5-12-02
We were finally able to take pictures today. Throughout taking pictures we experimented with different intervals and flight times. Sadly, all of our pictures came out very dark and the paintball splash was pretty small in our field of view. To fix this we will open our aperture and move the rotating mirror closer to the paintball splash.

5-20-02
Today we got some really good pictures and experimented a little with shooting the ball at different objects. These objects included a ring stand, a knife, and even ourselves. WARNING: Shooting yourself with a paintball really hurts from 1 m away. This was our last picture session. We are very happy with the shots that we got today.

All photos on this site are copyrighted by Brandon Winterling and Timothy Reibold, 2002. 
To inquire about picture use please contact Loren Winters at winters@ncssm.edu