Whack-A-Mole!

Project team member(s): Magaly Aviles, Ayaan Chand, Ethan Le, Odommoly Tranin

Give a one-paragraph description/summary of the project, which includes information like the motivation for the project, the goals of the project, and the resulting implementation and success of the project.

Introduction

Explain the motivation for your project in terms of the educational objectives and why your haptic device is an appropriate approach.

Background

Explain the relevant prior work in the field of haptics and provide references. These will likely be different from the references in your project proposal. Make sure to do a thorough literature search on relevant haptic devices/application.

Methods

Provide a detailed description of your project, such that another student from the class could generally re-create your project/experiment from the report if necessary. (You don't need to document every screw, but the design should be clear.) Add images and videos as needed to support the description. You can refer to downloadable drawings and code in the "Files" section (later). You should divide this section into subsections, which can vary depending on your particular project. Here is an example set of subsections:

Hardware Design and Implementation

System Analysis and Control

Demonstration / Application

Results

Describe the results, which may include qualitative responses from users at the open house.

Future Work

Describe how your system could be tested (e.g., through experiments if you have not already done so), how it can be improved, and how it might be applied.

Acknowledgments

Here you can list any individuals or groups who helped you with your project. (e.g., another student in the class, a course assistant, or an especially helpful PRL TA). Optional, so delete this section if you aren't using it.

Files

Code and drawings should be linked here. You should be able to upload these using the Attach command. If you aren't willing to share these data on a public site, please discuss with the instructor. Also, in this section include a link to a file with a list of major components and their approximate costs.

References

List the referenced literature, websites, etc. here.

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Appendix: Project Checkpoints

Checkpoint 1

To highlight the progress we have made to finish our tasks we will outline the progress for each section separately below:

CAD Progress:

The CAD of the pantograph system is primarily done, with the exception of hardware, which we plan on purchasing from AMPS. The pantograph design is inspired by the previous years’ work and utilizes components from the HapKit, with the addition of two magnetic encoder sensors (AS5600) for each motor.

Rendering Virtual Environment Progress:

We built an interactive screen-side prototype of our game as a single standalone HTML file. The prototype renders the arena with a configurable hole grid (3×2, 3×3, or 4×3), a cursor representing the pantograph end-effector, and moles that pop from random unoccupied holes.

Inside the sticky terrain zone, lag is produced to mimic high damping. Inside the magnetic region, a constant inward force is added to the velocity command, equivalent to a one-sided spring rendered by the motors.

We chose the 3×3 hole layout as our default because it provides adequate target density without crowding the hammer footprint, and it keeps the workspace edges, where the Jacobian condition number is worst, clear of game elements. The magnetic region is positioned to overlap one hole in the top-right so that it functions as an aim-assist target rather than a hazard in dead space, though we are still deciding whether to keep this overlap in the final design. The sticky band along the lower edge of the arena gives us a controlled location for testing the stiffness-classification effects.

Acquiring Materials and Hardware Progress:

As stated previously in our CAD progress section, our hardware will be purchased from AMPS. In addition, we will be using the motors provided with our Hapkit, paired with magnetic encoder sensors we will purchase from Amazon. For any 3D printed parts, we will also be printing them at AMPS. The virtual game will be displayed on a laptop and no additional hardware will be required.

Motor Calculation Progress:

Originally, we had planned to perhaps purchase motors with integrated encoders to use for our device, like the following Pololu motors (https://www.pololu.com/product/4881 .) However, after further discussion we as a team decided against it due to the relatively high cost. Instead, we will be using the motors provided with our Hapkit, and have purchased magnetic encoder sensors to be paired with these motors in a similar setup to how the Hapkit is assembled. As a result, since no new motors are being purchased, there is no need for motor calculations.

Electronics Schematic:

Since we plan to use two AS5600 magnetic encoder sensors, we ran into a communication issue because both sensors use I2C and share the same fixed I2C address. Although the Hapkit board only provides one I2C communication bus, two devices with the same address cannot be connected directly to that bus because the controller would not be able to distinguish between them. To solve this, we will use a TCA9548A I2C multiplexer, which allows each AS5600 sensor to be connected on a separate I2C channel. The Hapkit board can then select which channel to communicate with, allowing it to read both encoders independently. The finalized electronics schematic can be seen below:

Pantograph Force Feedback:

Since our system uses a pantograph driven by two motors, we needed a way to determine the motor torques required to produce a desired x direction and y direction force at the end-effector. To do this, we referenced The Pantograph Mk-II: A Haptic Instrument by G. Campion, Qi Wang, and V. Hayward, which provides the kinematic relationships used to map end-effector forces to motor torques.

Using the following diagram, forces were rendered by applying the transpose of the Jacobian matrix as shown in the figure below. This maps desired forces into corresponding joint torques.

Finally, the partial derivatives used to build the Jacobian were calculated from the expressions shown below. These equations describe how the pantograph’s geometry changes as the joint angles vary, making them necessary for the computation of the motor torques in real time.

Next steps will focus on global position tracking of the pantograph end-effector, as in order to render forces accurately, we need to continuously track the horizontal and vertical position of the handle. This would include us mapping the traced path of the pantograph to better understand its full range of motion, and define the usable workspace of the device.

Overall, we are very pleased with the progress we have made and we feel very confident to meet our future checkpoint. We are excited to begin printing and assembling our final device.

Checkpoint 2

Here you will write a few paragraphs about what you accomplished in the project so far. Include the checkpoint goals and describe which goals were met (and how), which were not (what were the challenges?), and any change of plans for the project based on what you learned. Include images and/or drawings where appropriate.

Example Video: https://www.youtube.com/watch?v=i_aLBql4Ufo