Flat Belt Tire Tester · Senior Design
Senior design capstone for testing GEM vehicle tires under controlled belt speed and load.
Overview
The Flat Belt Tire Tester is my Kettering University MECH 493/495 senior design project. The machine drives a treadmill-style belt beneath a loaded GEM tire to reproduce tire-road interaction under controlled laboratory conditions.
The project is divided between a six-person mechanical team and a separate instrumentation and controls team. The mechanical scope covers the frame, belt propulsion, belt support and tensioning, tire-loading mechanism, GEM wheel hub, braking interface, and mounting provisions for the controls hardware.
The Spring 2026 phase covered requirements, concept selection, calculations, final CAD, structural verification, budgeting, and purchasing preparation. Manufacturing, assembly, controls integration, and physical validation are planned for Fall 2026.
My Role
Designer. As the main designer, I completed the engineering calculations and all mechanical CAD for the test stand.
My contributions included:
- Developed the test stand and subsystem architecture
- Modeled the full mechanical assembly in Onshape
- Calculated motor power, belt speed, drivetrain ratios, roller loading, shaft loading, and structural requirements
- Designed the crowned drive roller, dead axle, chain drive, belt deck, tensioning system, four-bar loading mechanism, actuator mounts, and frame
- Built the Bill of Materials and purchase-order sheet
- Wrote Section 4.2, Concept Generation / Test Concept Planning, of the final report
- Contributed to the final report and project presentations
- Exported the CAD for Siemens NX structural analysis
A different mechanical team member performed the FEA.
Outcome
I completed the mechanical design phase of the Flat Belt Tire Tester. The deliverables included the final Onshape assembly, subsystem CAD, engineering calculations, BOM, purchase list, final report content, presentation material, and CAD prepared for structural analysis.
The finalized design fits within the Mott Lab space claim and has a purchase total of $1,490.37 against the $1,500 mechanical budget. Calculations support a 25 mph belt speed and 350-550 lbf tire-load range, while FEA results show low displacement and stresses below the modeled steel yield strength.
Manufacturing, assembly, controls integration, and physical validation remain scheduled for Fall 2026. Repeatability and measured operating performance have not yet been physically verified.
Key Specs
| System | Final Design |
|---|---|
| Test tire | GEM e2 4-lug wheel with 21.1" tire |
| Final packaging | Approximately 50" wide x 53" deep x 48" tall |
| Belt speed | 25 mph target with 26.4 mph calculated capability |
| Tire load | 350-550 lbf operating range |
| Mechanical budget | $1,500 |
| Current purchase total | $1,490.37 |
| Drive motor | 5 HP, 1,800 RPM, 3-phase NEMA 184T |
| Motor service factor | 1.25 |
| Drive transmission | 45T to 32T #35 chain step-up |
| Drive ratio | 1.41:1 |
| Roller speed | 2,531 RPM before VFD limiting |
| Drive roller | 3.5" OD x 0.1875" wall x 18" long 6061-T6 tube |
| Roller crown | 0.030" diametric crown |
| Roller covering | 85A rubber |
| Belt width | 16" |
| Belt support | 1/2" UHMW-PE over six butted 2" x 2" x 1/4" steel tubes |
| Loading mechanism | 38" parallel 4-bar first-class lever |
| Lever ratio | 1:1 |
| Linear actuator | 900 lbf with 6" stroke |
| Load cell | 1,100 lbf S-beam |
| Wheel travel | Approximately 3" |
| Main frame | Welded 2" x 2" x 1/4" steel box tubing |
Problem & Goal
The customer's previous testing method placed a complete vehicle on a dynamometer roller. This made it difficult to isolate tire behavior from suspension and vehicle-system effects, and the curved roller did not reproduce a flat road contact patch.
The goal was to design a safe and cost-conscious machine that could independently test a GEM e2 tire at representative speed and load. The machine needed to support steady-state rotation and longitudinal slip testing while remaining within the available Mott Lab space and the $1,500 mechanical budget.
Design Requirements
- Interface with a 4-lug GEM e2 wheel and 21.1" tire
- Drive the belt at speeds from 0 to 25 mph
- Apply a controlled vertical tire load from 350 to 550 lbf
- Measure tire load within 20-30 N
- Measure rotational speed within 5%
- Support steady-state rotation and longitudinal slip testing
- Maintain a dynamic factor of safety of at least 1.5
- Remain within the 143" x 96" Mott Lab space claim
- Remain within the $1,500 mechanical budget
- Guard rotating components and support emergency-stop integration
- Allow future steering, additional tire sizes, and instrumentation upgrades where practical
- Operate as a lab-grade machine for intermittent use
Process
- 1Met with the customer to reduce the original passenger-tire scope to a practical GEM e2 test machine
- 2Researched tire dynamics, flat-belt testing machines, belt tracking, machine safety, SAE J1106, and SAE J1987
- 3Established the 21.1" tire, 25 mph speed, 350-550 lbf load, space, safety, accuracy, and budget requirements
- 4Generated flat-belt, existing-dynamometer, and resistance-roller concepts
- 5Selected the flat-belt concept through a weighted Pugh matrix
- 6Compared multiple flat-belt layouts, including large drums, a compact treadmill, and a tensioned flat-belt system
- 7Developed an initial six-roller design with a vertical gantry loading carriage
- 8Replaced the vertical gantry with a lower-cost pivot arm, then replaced the pivot arm with a parallel 4-bar to maintain constant wheel camber throughout loading
- 9Replaced the three center support rollers with a continuous UHMW and steel support deck
- 10Integrated the motor, drivetrain, crowned roller, and belt tensioning into the mechanical design
- 11Completed power, speed, force, shaft, roller, lever, and structural calculations
- 12Modeled the final test stand and subsystem interfaces in Onshape
- 13Created the complete BOM and purchase list against available campus inventory
- 14Exported the CAD for teammate-run Siemens NX FEA
- 15Incorporated the final design, analysis, budget, and validation plan into the report and presentation
- 16Planned Fall 2026 manufacturing, controls integration, and physical validation
Challenges
- Reduced the original 50+ mph and 500-1,000 lbf request to a design achievable within the $1,500 budget
- Reworked the loading system after the vertical gantry was not in budget and a simple arm did not adequately maintain constant camber under braking loads
- Replaced the center support rollers with a lower-cost continuous deck
- Sized a 5 HP motor close to its service-factor capacity at the 550 lbf and 25 mph operating point
- Designed belt tracking and tensioning for a flat treadmill belt
- Integrated mechanical and controls requirements across two separate senior design teams
- Balanced structural capacity against material cost and available campus inventory
- Designed around components sourced from Kettering University, used equipment, and multiple vendors
- Deferred steering capability to a future phase
- Left physical performance and repeatability verification for the Fall 2026 build phase
Concept Selection
The mechanical team evaluated three primary approaches:
| Concept | Main Advantage | Main Limitation |
|---|---|---|
| Flat-belt machine | Flat tire contact patch and direct alignment with customer requirements | Required a complete custom machine |
| Existing SAE dynamometer | Lowest expected cost by reusing existing equipment | Curved contact surface and limited future steering clearance |
| Resistance roller | Simple tire-to-roller interaction | Unrealistic side loading, curved contact, and high custom-build cost |
The flat-belt design received the highest weighted Pugh matrix score because it best balanced customer requirements, durability, usability, and cost.
Design Evolution
The preliminary design used six rollers and a vertical gantry carriage. Three center rollers supported the belt beneath the tire, and a linear-bearing carriage moved the wheel vertically.
The final design changed both systems:
- Replaced the vertical gantry with a lower-cost pivot arm, then developed a parallel 4-bar after the pivot arm changed the wheel's camber during loading- Replaced the three center rollers with a continuous support deck to reduce cost and sourced components
- Added a fully specified motor, step-up chain drivetrain, crowned drive roller, and tensioning system
- Changed the packaging from approximately 44" x 50" x 26.5" to approximately 50" x 53" x 48"
- Retained the treadmill-sourced belt and flat tire contact patch
Belt Drive
- Selected a 5 HP, 1,800 RPM, 3-phase NAE PE184T-5-4-ODP motor
- Used the motor's 1.25 service factor for 6.25 HP of available service-factor capacity
- Calculated 4.27 HP at the typical 360 lbf tire load
- Calculated 6.11 HP at the 550 lbf upper design load
- Used a 45T motor sprocket and 32T roller sprocket for a 1.41:1 step-up
- Calculated a 2,531 RPM drive-roller speed and 26.4 mph belt speed
- Used the variable-frequency drive to limit the maximum speed to 25 mph
- Added an 18T idler sprocket on a slotted mount for chain tensioning
Crowned Drive Roller
- Used an 18" long 6061-T6 aluminum tube with a 3.5" OD and 0.1875" wall
- Added a 0.030" diametric crown to center the belt
- Added an 85A rubber cover for belt traction
- Used bolted aluminum end caps to retain sealed bearings
- Used a 3/4" solid 1018 steel dead axle
- Chose a dead axle for cleaner shaft loading, simpler frame mounting, and easier belt replacement
- Calculated a roller bending factor of safety of 37.6 with 0.0017" mid-span deflection
- Calculated a dead-axle factor of safety of 20.1 with 0.0074" deflection
Belt Support & Tensioning
- Supported the belt contact patch with a 1/2" UHMW-PE wear sheet
- Fully supported the UHMW with six butted 2" x 2" x 1/4" steel box tubes
- Created a continuous 12" steel-backed contact area beneath the tire
- Removed the preliminary center rollers and intermediate steel plate
- Kept the UHMW under compression instead of allowing unsupported bending spans
- Routed the belt around one crowned drive roller and one idler return roller
- Tensioned the belt with steel cable and turnbuckles pulling against eyebolts
- Anchored the supporting welded frame to the floor
Four-Bar Tire Loading System
- Used a parallel 4-bar to keep the tire parallel to the belt during loading
- Extended the lower link into a 38" first-class lever
- Positioned the pivot at the center for a 1:1 force ratio
- Used a bottom-mounted 900 lbf linear actuator with a 6" stroke
- Produced approximately 3" of vertical wheel travel
- Used four 1" steel pivot shafts with self-lubricating flanged bronze bushings
- Selected bronze bushings for slow oscillating motion, shock tolerance, and lower cost than ball bearings
- Installed a 1,100 lbf S-beam load cell inline with the actuator
- Used the 1:1 lever ratio so the load-cell reading directly represents wheel load
- Mounted the tire to a GEM e2 rear brake hub for future longitudinal-slip testing
Structural Verification
A mechanical team member performed Siemens NX FEA using the CAD I produced. The studies evaluated the belt frame, tire arm, and arm frame at the 550 lbf operating load and a 2,000 lbf overload condition.
| Assembly | Load | Maximum Stress | Maximum Displacement |
|---|---|---|---|
| Belt frame | 550 lbf | 3.90 MPa | 0.00036 in |
| Belt frame | 2,000 lbf | 14.2 MPa | 0.00132 in |
| Tire arm | 550 lbf | 50.32 MPa | 0.00247 in |
| Tire arm | 2,000 lbf | 182.99 MPa | 0.00898 in |
| Arm frame | 550 lbf | 13.52 MPa | 0.00118 in |
| Arm frame | 2,000 lbf | 49.16 MPa | 0.00430 in |
All three assemblies remained below the modeled steel yield strength. The tire arm was the most highly stressed assembly, while the belt frame had the lowest stress and displacement.
Budget & Purchasing
I created the project BOM and purchase-order list to compare the final design against the $1,500 mechanical budget.
The purchase list totaled $1,490.37 and included:
- Bearings, fasteners, bushings, chain, sprockets, and tensioning hardware
- Custom motor, pivot, roller, and actuator components
- 6061-T6 aluminum stock for the drive roller and end caps
- 1018 steel plate and shaft stock
- GEM rear brake hub
- Rubber roller cover
- Turnbuckles and eyebolts
The project reused a treadmill belt, return roller, tire, load cell, structural tubing, motor, and actuator available through Kettering University or the controls team.
Safety & Controls Integration
- Designed physical guarding around rotating components
- Included provisions for emergency-stop integration
- Planned floor anchoring for the welded frame
- Provided mounting and packaging space for the motor, sensors, load cell, and controls hardware
- Designed around remote or separated operation during testing
- Coordinated belt speed, motor, actuator, load-cell, and wheel-speed requirements with the controls team
- Planned control-system failure modes to prevent overheating or unsafe continued operation
Planned Validation
Physical validation is scheduled after manufacturing and controls integration.
The validation plan includes:
- Run the unloaded belt at 5, 10, 15, 20, and 25 mph
- Check belt tracking, tension, alignment, and bearing temperatures
- Apply static loads from 0 to 550 lbf in 100 lbf steps
- Test 350 and 550 lbf at both 10 and 25 mph
- Hold each combined load and speed condition for 10 minutes
- Test braking at full load and speed
- Validate the emergency stop under operating conditions
- Verify tire removal and replacement
- Measure speed and load accuracy
- Evaluate test-to-test repeatability
What I Learned
- How to develop a large mechanical test machine from customer needs through final CAD
- How to compare competing concepts with a weighted Pugh matrix
- How to revise an architecture when a preliminary concept does not meet the final requirements
- How to design a crowned roller and step-up chain drivetrain for a flat belt
- How to design a parallel 4-bar loading system around force, motion, and constant camber
- How to perform motor, drivetrain, roller, shaft, lever, and fastener calculations
- How to design within a fixed budget using existing equipment and available manufacturing resources
- How to create and maintain a detailed BOM and purchase-order list
- How to coordinate mechanical interfaces with a separate controls and instrumentation team
- How to document a design through technical reports, calculations, presentations, and drawings