Ninji Chop!


Our task was to design and prototype a novel kitchen object. This could have been an improvement on an existing kitchen artifact or an entirely new one.


My lab partner and I created Ninji Chop. Ninji Chop is an interactive system that uses a person’s hand motion to cut fruit. The user wears a glove with an accelerometer attached to it. The user then moves his or her hands up and down to control a servo attached to a knife. The knife moves up and down in unison with the user’s hand. The knife cuts a fruit on a moving platform controlled by two buttons on the user’s glove. The buttons control the direction the platform moves (forward or backward), allowing the user to cut fruit with great control and precision.


Our idea for this project stemmed from our practice with an accelerometer during a lab assignment. We were so intrigued that we could control the movement of a servo by simply moving our accelerometer. We knew that this type of interactive, “hands-free” control could be useful for a kitchen object marketed toward the physically limited. Ninji Chop is perfect for those with no hands (or missing fingers), children, and those with severe arthritis. Ninji Chop allows the user to cut fruit from a safe distance away using only the movement of a body part (the glove can be attached to a hand, arm, elbow, head, or even a foot). Of course, to allow for control of the sliding cutting board, a simple code change would be needed to allow for movement of the accelerometer in the “x-direction”. Another motivating factor for us is entertainment value. We thought it would be entertaining to be able to cut fruit by simply chopping at the air. It turns out it is!



My lab partner Garret and I began this assignment by observing the daily routine of a kitchen. I monitored the life of my apartment’s kitchen. I noted that my roommates used the knife very frequently. Garrett and I both came to the consensus that it would be hard for people with physical limitations such as no hands or arthritis to prepare food with a knife like my roommates could. We ruled out many ideas and decided to design and prototype a knife cutting system controlled by the motion of an accelerometer.


Our circuit required many wires. This meant a lot of soldering!

Garrett bought us a cheap, sharp knife from Walmart. We attached the knife to a servo by screwing it in to the plastic. We then programmed our Arduino to move the servo up and down repeatedly. Our goal was to see if the knife could cut through a banana.

It cut through!

Our next step was to control the motion of the knife by using an accelerometer. We programmed the accelerometer to map the values of the movement in the y-direction (up and down) to the corresponding values of the servo. It took some fine tuning of the values to ensure the knife never went “too high” (about 70 degrees), or too low so as to cut through the cutting board!

Behold the glove of power!

We needed a way to move the fruit along so that the user could keep chopping. We wanted to also keep the system as interactive as possible. We cut a platform for the fruit to sit on, along with 2 other blocks of wood(glued to the main piece of wood) to guide the fruit platform. We knew at this point that we would eventually need something to move the platform forward and backward, but we weren’t sure how to do that just yet.

After brainstorming many different ways (from linear actuators to complex systems of gears) to move the platform forward and backward, we settled on the simplicity of a dual spindle/pulley system that would give the user total control over the cutting board. We had to raise the main platform that the cutting board was sitting on in order to mount the servos. We also attached the servo holding the knife to the main platform.

As you can see in this picture, we also exchanged our old white glove for a more aesthetic black glove. We attached two buttons to the breadboard on the “glove of power”. When pressed, these buttons control the movement of the sliding cutting board. We also added walls to contain the banana slices and a cutting groove in the walls for the knife to slice through.

We made sure to program the spindles so that they would spin in the same direction when a button was pressed so that one spindle would wind up the cutting board while the other would release it’s line.

Modifications/Fine Tuning/Adding Features

After the foundation of Ninji Chop was laid, we made a few changes. The first was to add a switch at both ends of the cutting board. We programmed the switches to turn off the servos if a switch is pressed.

After this modification was made, we realized that with the addition of the new switches and the two servos that control the sliding cutting board, our knife began to randomly lock up when in use. The knife would become responsive again from a simple tap to “restart” the servo. We researched the problem and concluded that the Arduino was not a sufficient power source for all the electronics we had on it.

We added a separate power source in attempt to alleviate this problem. This problem of “locking up” still remained after adding the power source, although to a lesser degree.

Ninji Chop

After many hours spent in the lab designing and prototyping a novel kitchen object, Garrett and I are happy with the outcome of Ninji Chop.

Our final design implemented a blade gaurd to stop any slices of fruit from getting stuck to the blade

The outcome: a well sliced banana!

Ninji Chop 2.0 and Beyond

There are many more modifications and additions I would like to add to Ninji Chop. I think that it would be great if the motion of the cutting board is simply controlled by the accelerometer’s motion in the “x-direction”. This would allow for easier and more fluid control of the cutting board with just a flick of the hand. Like mentioned earlier, this would also allow for access to those with physical limitations.

Another feature that could be added in Ninji Chop 2.0 is a “safe dome” placed around the cutting area. Ninji Chop sits on the counter top or is stored in a cabinet so it could be dangerous to have an exposed blade near children.

I could see in the very distant future a robot in the kitchen controlled by a user lying in bed. The user can put on a wireless glove and use some video display to view the position of the robot. The user can then control the movements and kitchen preparation actions of the robot through the use of the “glove of power”. Perhaps a second “glove of power” would be needed by this point.

The brainstorming, designing, and prototyping of Ninji Chop raised many new project ideas in my head about Ninji Chop and other projects. I can not wait to begin working on them!

Speical thanks to Kung Fu Hillbilly for the Ninji Chop name!

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