We present Mod2Hap, a two-level modular haptic system that enables both body-scale and hand-scale interactions using magnetorheological (MR) fluid. The system comprises (1) configurable frame modules for constructing spatial interaction structures, which can be flexibly assembled to suit various body postures and environments, and (2) haptic modules—rotary (e.g., for dials or pedals) and linear (e.g., for sliders or handles)—that provide customizable handscale feedback interfaces. Each haptic module utilizes MR fluid, whose viscosity varies with applied magnetic fields, to generate tunable resistive feedback. Our design achieves a wide feedback range (0.12–0.52 N·m torque, 41–212 N force) by optimizing the solenoid coil for power efficiency and validating magnetic field distribution via simulation. We demonstrate Mod2Hap through three interactive scenarios—cycling, kayaking, and fishing—and evaluate its performance in a user study with 12 participants. Results show high perceived realism and engagement, supporting the system’s versatility, scalability, and effectiveness as an immersive haptic interaction platform.

Grain-based compliance illusion mimics the mechanical vibrations that occur when a compliant object deforms with grain-like, short (∼15 ms) impulse-response vibrations. Previous work has demonstrated its robust effect on various types of devices. However, the impact of the device’s inherent compliance (i.e., base compliance) on perceived compliance remains unclear. This paper investigates the influence of base compliance on the perception of illusory compliance through three psychophysical experiments. The results show that (1) the compliance illusion remained effective with base compliance, (2) the description of compliance was affected by both illusory and base compliance, and (3) it is possible to render the compliance with the same magnitude but multiple different feelings.