Destructive Haptics
A kinesthetic haptic feedback device simulating cutting and tearing in VR.
My Role
Research, System Design, CAD, Circuits, Programming
Team
Yu Zhang, Leon Zhao, Sizhang Xu, Xijie Wu
Timeline
May – September, 2024
Tools
ESP32, Brushless DC Motor, Force Sensor, Unity
⌗ Context
Vibration feedback is used pervasively in VR. However, there is a lack of sensory feedback of the forces, especially for destructive actions. The goal of this research is to provide kinesthetic haptic feedback using a wire attached to controllers. By controlling the force on the wire, we can simulate the resistive force applied to the hand.
⌗ Methods
First, we need to guide the direction of the wire to simulate the target direction of the force.
Then, we need to regulate the force on the wire to match the desired force during interaction.
To simplify the idea, we limited the structure directing the force to 1 DoF. By only adjusting the relative position of the wire on a line, the device demonstrates 4 different scenarios.
Use Scenarios
Tearing / Opposite Movement
Cutting / Vertical Movement
Compressive Stress / Moving Towards
Tensile Stress / Moving Away
⌗ Directing the Force
The wire guiding component includes a double ratchet structure and a gear rack with an opening on one end for the wire to pass through. The user can wear it on the forearm with hook-and-loop straps. The position of the gear rack can be adjusted by cranking the handle on the other side of the ratchet. The double ratchet ensures the gear rack can only be moved from the handle side, thereby locking the wire to a target angle relative to the hand. A force-sensing module can be attached to the beam to verify the current force on the wire or used as feedback for the system.
▲ Wire Guiding Mechanism
CAD Model
⌗ Simulating the Force
When destructive action is not detected, the wire is loose, enabling the user to move their hand freely. When the action starts, the wire becomes tight, as the controller pulls the wire. The motor module controls the rotation of the spool and how much load to apply. It includes a dual-motor structure, brake pad, sliding platform, and spring. One motor is responsible for winding and unwinding the wire to synchronize with the actual interactions in VR and adapt to the distance between the user and the motor. The other motor applies pressure to the bobbin to impede its rotation via a sliding platform.
⌗ Force Calculation
Through experiments, we mapped motor's angle of rotation to the force on the wire. We also established a relationship between displacement and resistance for various destructive interactions. This allows the system to translate the displacement caused by the player in Unity into the corresponding resistance, which is then converted into the motor angle, providing real-time force feedback.
For instance, when the user grabs the virtual knife, the spool motor starts working. As the user moves their hand, the spool motor releases the wire slightly longer than the user's movement to keep it loose. When the user starts cutting, the spool motor quickly retracts to tighten the wire, and the brake motor starts to apply force. The target force in real time can be determined by experimental data or estimated by formula.
▲ Cutting Experiment & Data Collection
Cutting Force Measurement
System Design
Force Sensing Module Circuit Diagram
BLDC Motor Control Circuit Diagram
⌗ Reflection
Through user testing, we found that hardware latency and side effects (e.g. the weight of our device imposed on the arm) are two main limiting factors that affect our system’s fidelity. To improve our device, we can focus on reducing latency in brake motor and making the wearable component more ergonomic. Additionally, increasing the degrees of freedom can further expand its use cases.
