Context
This was the B.Tech final-year interactive robot project. The IRJET DOCX manuscript is the control-system and subsystem-integration part of the project, covering the central control architecture, cloud and voice control, remote operation, surveillance, SOC indication, environmental sensing and steering/locomotion control integration. The frame and locomotion publication provides the mechanical design evidence that supports the same final-year system.
The goal was a wheeled robot capable of operating in hazardous environments as a remote-actuated substitute for human presence. The full project combined a rolling base, robotic arm, sensing/control system and remote supervision into one integrated platform.
Control-system integration
The control manuscript describes the robot as an interdisciplinary mechanical-control project rather than a pure CAD exercise. The control system was divided into subsystems so that each function could be activated, tested and integrated separately.
- Central control: Raspberry Pi-based system coordination with cloud connectivity and remote-control logic.
- Voice and cloud control: Google Assistant / cloud control pathway for high-level robot commands.
- Surveillance: camera and Pi-camera support for remote observation, object detection and locomotion assistance.
- Locomotion control: BLDC motor controller driven by acceleration and braking commands from the control system.
- SOC and charging indication: battery state-of-charge sensing and display logic integrated into the control architecture.
- Environmental sensing: humidity, pressure, temperature and luminosity sensing for operating-environment awareness.
- Steering control: servo steering controlled through PWM and a 2-H bridge servo-control module, constrained by the Ackermann lock points from the mechanical design.
Wheelbase stability analysis
The minimum wheelbase was derived from rollover stability at 30° inclination, modelling the total mass distribution as triangular with the resultant weight acting at one-third of the frame height.
The governing condition (taking moments about the outer wheel contact point):
- 4/3 × h × sinθ ≤ b
- At h = 386 mm, θ = 30°: minimum b > 255.33 mm
- Final wheelbase selected: 280 mm (margin above the rollover threshold, accommodating wheel size and ground clearance)
Weight estimation
Weight was built up from material density and geometry at each sub-assembly, then iterated after motor and battery selection:
- Main frame (AISI 4130 cylindrical shell): OD 224 mm, ID 222 mm, height 386 mm → volume 2.704×10³ mm³ → 2.14 kg
- Head assembly (square tube + shaft + sheet metal): 1.6 kg
- Base and skeleton (from CAD model): 20 kg
- Arm assembly: 14 kg
- Motor and battery (initial estimate): 10 kg
- Initial total: 47.74 kg → rounded to 50 kg for force analysis
- Revised total after motor selection: 75 kg (motor and battery actual weight higher than estimated)
Drivetrain torque sizing
Force analysis was performed at the revised 75 kg system weight, 30° gradient and 0.5 m/s² acceleration target:
- Gradient resistance: FR = 750 × sin 30° = 375 N
- Normal force: FN = 750 × cos 30° = 649.5 N
- Friction resistance (μ = 0.4): μFN = 259.8 N
- Total tractive force at equilibrium: F = 375 + 259.8 = 634.8 N
- Torque at rear axle (wheel radius 0.1 m): 63.48 Nm
- Acceleration torque (F = 75 × 0.5 = 37.5 N): 3.75 Nm
- Total required torque at rear axle: 68 Nm
Wheel speed requirement (target 20 km/h → 5.56 m/s, wheel diameter 200 mm): 532 rpm at the rear axle.
Compound gear system
A four-gear compound system with a coaxial pair at gears 2–3 transmits motor torque to the rear axle in two reduction stages:
- Stage 1 (Gear 3 → 4): reduction ratio 3:1 — D3 = 30 mm, D4 = 90 mm; T3 = 22.6 Nm, T4 = 68 Nm; N4 = 532 rpm, N3 = 1,596 rpm
- Stage 2 (Gear 1 → 2): reduction ratio 1.89:1 — D1 = 25 mm, D2 = 47.25 mm; T1 = 12 Nm (motor output), T2 = 22.68 Nm; N1 = 3,016 rpm
Motor selection criteria: 12 Nm minimum torque, ≥3,016 rpm. A BLDC motor meeting these specifications was selected; the battery was sized accordingly.
Ackermann steering
Servo-actuated Ackermann geometry was chosen over a rack-and-pinion mechanism for compactness and direct digital control. The Ackermann condition ensures the inner and outer wheels follow concentric arcs without side-slip during turns.
- Turning radius: R = 510 mm
- Wheelbase: b = 280 mm; track width: a = 400 mm; rack+tie-rod span: c = 300 mm
- Inner wheel lock angle: Φ = 35.26°
- Outer wheel lock angle: θ = 71.06° (from cotΦ − cotθ = c/b)
The servo torque requirement was derived by modelling an equivalent rack-and-pinion: rack force 60.2 N, pinion radius 7.5 mm → torque = 450 Nmm (4.5 kgf-cm). A servo with 4.2 kgf-cm rated torque, 4.8–7.2 V operating range, 180° rotation and 55 g mass was specified.
Structural deformation screening (ANSYS)
Two structural checks were performed in ANSYS with 190 N applied at each wheel contact point:
- Base plate: 190 N applied at corners A–D, fixed supports at E–H → maximum total deformation 4.946 × 10³ m (sub-millimetre, structurally acceptable)
- Rear axle: 190 N applied at A and B, fixed at C and D → maximum total deformation 6.41 × 10² m
Both values confirm that the AISI 4130 tube selection provides adequate stiffness for the loading condition. The analysis was limited to total deformation; stress and factor-of-safety checks were not included in the published scope.
Component selection summary
- Frame material: AISI 4130 chromoly steel (OD 21.3 mm / ID 16.7 mm tube; square tube for head assembly)
- Drive motor: BLDC, 12 Nm, ≥3,016 rpm
- Battery: Lithium-ion (capacity sized to drive motor and full system load)
- Steering actuator: Servo motor, 4.2 kgf-cm, 4.8–7.2 V, 180° rotation
- Wheels: 200 mm diameter