Lab 0 - Ping Pong Shooter

1. Problem Definition

Before beginning any design process we clarified the task and any job the machine would have to fulfill. In a short sentence the task can be described as to build a machine which moves at least 10 ping pong balls in 40 seconds into one of a several buckets, which are located at a distance ranging between two and five meters. The material for the construction is taken out of a toy containing a DC motor and additionally purchased on campus shops. The time for the construction is limited to one week.

2. Divide the Task into Subfunctions

In the next step the main function of moving the ball over a certain distance was divided into subfunctions in order to find appropriate solutions for each task in the ensuing brainstorming. The subfunctions can be defined as:
-Carrying/preserving of the balls
-Triggered grabbing of each ball
-Mechaniscm of moving the balls (e.g. by shooting)
-Specifying direction/trajectory of the balls
-Switch to start machine
-Automatisation of each consecutive process

3. Brainstorming

During a brainstorming among our four teammembers we found several solutions for each of the previously defined tasks.
Due to the fact that the ball must hit a bucket the only considered way of transportation is shooting it, there where no other possibilities coming up during brainstorming. Therefore several approaches were found:
i. Shooting the ball by expanding a previously loaded spring. The spring would be loaded by a DC motor.
-Loading of the spring by a rotating plate which contains catches that load and unload the spring continually
-Loading of the spring by coiling up a fishing line with the motor. The force application point of the translationally guided hammer will be switched from one hook to another while shooting the balls consecutively.
ii. Shooting the ball by hitting it with a continously rotating puncher propelled by a DC motor.
iii. Shooting the ball by pinching it between two rotating wheels with a soft/adhesive surface.
iv. Shooting the ball by hitting it with an translatory oscilating hammer which is powered by a DC motor with an excentrically fixed plate.
v. Shooting the ball with swinging hammer

For the way of grabbing and providing the balls the following options have been elaborated:
i. Dropping the balls downwards (by gravitation)
-controlled by electromechanical sensor
-controlled by photoelectric sensor
-releasing the balls from their container by a rotating plate wich is provided with several holes.
ii. Moving the balls with a conveyor belt

Loading of the spring in (i) by a clutch which engages and disengages the spring from the motor alternately.Second way of loading and unloading the spring in (i). Fixing point of fishing wire at puncher jumps from nail at the right to the left, triggered through stationary ramp.

Approach described in (ii) - a hammer is driven by a rotating wheel connected to the motorConnection between punching mechanism and hopper with triggered dropping of balls


Pursued Solution

The first solution we aimed at was the loading of a spring with the motor and several gears which slow down its angular speed and increase its momentum.
It became clear that the thereby achieved momentum didn't suffice to load a spring adequately. This fact was very surprising considering that the gear transmission ratio was very high and the spring easily loadable by hand. Another problem was the great friction between hammer and guide which lead to too small impact on the ball.
Due to the nonexistance of other motors/gears another solution was chosen: The ball should be shot by a continously rotating puncher. This solution seemed to be easier to realize and first trials showed promising results.
After we had many mechanically interesting ideas this one seemed to be very conventional but it lead better to the aimed goal.

Pros and Cons of our final design

Cons

• Final design overestimated the distance and size of buckets
• Overshot buckets, no time to adjust input voltage
• Exact aiming is still a problem.
  
• The continuously dropping balls get stuck from time to time and need to be moved by hand.

Pros

• Great distance out of very small motors, very efficient design
• Good repeatability
• Adequate load for toy motor
• Adjustable launch pad
• Hopper connected to launch pad, hence feeding of the balls is no problem when adjusting shooting angle
  

Designing Process

First of all a platform with an adjustable angle was prepared. This platform should bear any kind of shooting mechanism we would design later on. In a next step the motor was placed and the attached wing fixed to its axle. We found out that the balls rolling down in opposite direction of their destination is most efficient. Optimizing the shape of the hammer and with it the angle of impact improved the results. The wing was changed from foam to wood due to stability and was provided with several weights (bolts, washers) in order to store more energy in the rotation and thus increasing the impetus.
The balls should be carried by a container and dropped to its track to the puncher. The triggering is realized through a rotating plate with a clearance below the container. The flight distance can be adjusted by varying the voltage of the DC motor. Therefore a voltage divide was assembled due to the minimum value of 6V provided by the power supply.
Finally the whole construction was stabilized by different gussets in order to reduce vibrations. Nevertheless some kind of vibration is useful to keep the dropping of the balls running.

Generally it can be said that we had many creative ideas during brainstorming but eventually had to simplify them as much as possible due to limited ressources with respect to facilities, tools, materials and time.







Conclusion

After finishing this first lab we realized that our procedure was not sufficient enough during the first days. Instead of experimenting with different approaches directly we spent much time drawing sketches and composing drafts. Eventually it can be said that a second brainstorming after a possible solution is roughly figured out makes a lot of sense. Hence no time is wasted by elaborating digressive manners.