For this project we were asked to design and prototype an object for the kitchen area so naturally we came up with the idea of a 'virtual' fruit slicer that we like to refer to as ninji chop. My partner and I had done some experimenting with an accelerometer after lab one day and we thought it was pretty cool so we decided that we wanted to implement this into our project in some shape or form. All of our first ideas incorporated the accelerometer in such a way as to cause some type of pouring action for perhaps a pitcher or a measuring cup. This idea flopped after we realized that liquids handled in the kitched are generally too heavy for the type of devices we have access to in the lab and it just didn't seem very innovative. After wrestling around with several other ideas that were simply preposterous we came up with the accelerometer controlled knife.
Here is a video of our first test to see if a servo could exert enough force to cut a banana.
Check.
After some brain storming we realized that our design process would circulate around the knife being controlled by our acceleromter, so clearly the next step was to get the thing chopping! After mapping the values of the y-axis inputed from our accelerometer to the values outputed by the servo connected to the knife we came up with the following.
Notice the "glove of power".
The idea of a 'virtual' fruit chopper in which every physical action exerted by the device could be controlled from a glove raised one design question after another when we realized that there were more factors at play here other than a simple chopping motion. We of course wanted to make it as interactive as possible. As you can see in this next video we mounted our knife/servo to our main platform in order to keep it stable, as to apply the maximum amount of force on the food item being sliced, but we needed a way to pull the food along to create uniform cuts.
You would not believe the number of systems we thought of to pull our little cutting board along. From linear actuators to complex systems of gears we knew there had to be a perfect design out there that could fulfill our needs. We finally realized the elegance of simplicity when we setteled on a dual spindle/pulley system that would give the operator ultimate control over the cutting board, anywhere from thinly sliced to chunky. In order to mount the servos that would control the spindels we had to raise the main platform that the cutting board would slide on. This was done using blocks of wood. The peice of wood you can see mounted to the knife servo was placed there for added support.
We then mounted two buttons to our "glove of power" in order to control what directions the the spindels would pull. We had to run through trial and error in order to figure out what values would cause the servos to spin in certain directions at certain speeds. We then fixed a block of wood with a hole drilled through the middle to each end of the cutting board. Next we hot glued some string from each spindle to it's corresponding block. Here is a video of the first demonstration of one of our spindels in action.
We then had to coordinate each spindel such that they would spin in the same direction when a button was pressed (depending on which button was pressed) such that one would pull the cutting board along while the other would release it's line. We ran into a minor problem in our code while sorting this out when we could only get it to pull one way. We actually created an if statement for each button when instead we simply needed to apply both buttons to one if statement. In doing so our program no longer skipped checking to see if the second button was pressed. Our cutting board also ended up in several "truck pulls" before we got the rotations figured out as well.
Another element we needed to think of was a way to keep the slices of fruit from falling off of the cutting board. This problem was solved by fixing two "walls" on both sides of the path that the cutting board would take, helping to contain the fruit and to funnel the cutting board at the same time.
Next we needed a way to stop our spindels if they were to reach the end of the platform. This was done by placing a switch at both ends of the platform. When one switch is pressed our program skips the part of the if statement that checks to see if the button that would pull the cutting board toward the currently pressed switch and simply checks to see if the other button is pressed, and this will of course loop until the other button is pressed.
After we got both servos that control the spindels functioning we experienced a problem with our servo controlling our knife, that being it became nonresponsive. After some research we discovered that the arduino power source is simply not enough when it comes to powering multiple servos. We then found an external power source as you can see below.
We did however experience the persisting problem of our knife randomly locking up, usually happening whenever you hold the glove (with the accelerometer attatched of course) still for a few moments. The knife would become responsive again from a simple tap but it is simply annoying. If you have any comments on the matter feel free to indulge us on what it is that you think the problem may be.
Last but not least here is a video of our final project. Our final design implemented a blade gaurd as to stop any slices of fruit from getting stuck to the blade. We think it turned out pretty well.
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