Static FEA of an E-Scooter Frame under Standard Load Cases

The problem

A frame that looks strong in CAD can crack at a weld or a battery bracket once loaded on bad roads. Students often run one static load and report a colourful stress plot without checking the boundary conditions or units. A disciplined set of load cases with hand checks is the basis of every frame design review.

Objectives

• Define vertical, braking, cornering and combined load cases from an example vehicle and rider.
• Set up linear static studies with correct fixtures, connections and loads.
• Compare beam and solid mesh results and check against hand calculations.
• Report stresses, deflections and factors of safety for each case.

What you need

Key concepts

Load case

A defined combination of loads, such as a vertical bump plus braking, representing a real event the frame must survive.

Dynamic factor

A multiplier on static loads that stands in for impacts and bumps. Values are assumptions until measured data exist.

Beam vs solid elements

Beam elements are fast and give member forces and stresses along tubes; solid elements capture local stresses at joints and brackets but need more effort.

Factor of safety

The ratio of the material's yield strength to the calculated stress. A target above 1 includes allowances for uncertainty and fatigue.

Step-by-step guide

1. 1

   Define the vehicle and loads

   Take an example e-scooter frame and list the masses: rider plus pillion, an example 150 kg, battery 15 kg, motor and controller 10 kg, and body panels. Find each mass's position from the assembly. Define load cases: static, vertical bump with a stated factor such as 3 g, braking at a stated deceleration and cornering with a stated lateral acceleration. Label all factors as assumptions to be refined.

   Checkpoint: A load-case table with masses, positions and factors, and the acceptance criterion, such as factor of safety above 1.5 on yield.

2. 2

   Prepare the model

   Open the Weldments frame and create a Simulation configuration. Suppress cosmetic features, small holes and fillets that do not carry load. Make sure each structural member is a separate body so Simulation can treat it as a beam, and that joints are recognised. Assign steel such as AISI 1020 or a stated grade from the material library, and check its yield strength in the material dialog.

   Checkpoint: Simulation shows every member as a beam with joints at the right places, and material properties are set.

3. 3

   Hand-calculate the main member

   Before running the study, treat the main down tube or side rail as a simply supported beam between the steering head and swingarm pivot, with the rider and battery loads applied at their positions. Calculate reaction forces, maximum bending moment and bending stress with the section modulus of the tube. Also estimate the deflection at mid-span. Keep units consistent in newtons and millimetres.

   Checkpoint: Hand-calculated reactions, stress and deflection for the static case, with every assumption written down.

4. 4

   Set fixtures and loads

   Apply fixtures that match how the frame is supported: for example, a fixed hinge at the steering head and the swingarm pivot, or the rear shock mount, depending on the case. Apply rider and battery loads as forces at the joints or as remote loads at their centres of mass. Avoid over-constraining, which stiffens the model. Apply gravity in the static case and factored loads in the others.

   Checkpoint: The model is stable with no rigid body motion warnings, and the summed reaction forces equal the applied loads.

5. 5

   Run the beam studies

   Mesh the frame with beam elements and run each load case. Plot the upper-bound axial and bending stress, displacement and factor of safety. List the highest-stressed members and joints. Compare the static case with your hand calculation; a difference larger than about 15 per cent means checking the supports, load positions and section properties before trusting the model. Check the axial force sign in each member to make sure compression and tension match your expectation from the hand sketch.

   Checkpoint: Beam results for every load case, with the static case agreeing with the hand calculation within your stated margin.

6. 6

   Model critical joints with solids

   Pick the two most stressed joints from the beam results, such as the steering head junction and the battery bracket. Create a solid-mesh study of the frame or a sub-model of the joint with the same loads, using mesh controls at the weld region. Use bonded contact between members to represent welds, and note that real weld geometry and residual stresses are not modelled.

   Checkpoint: Solid studies of the critical joints solve and show the local stress hot spots the beam model could not.

7. 7

   Check the mesh

   For the solid model, refine mesh controls at the hot spot in two or three steps and plot peak stress against element size. Stresses that keep rising at sharp internal corners or fixtures are singularities; read stresses a short distance away or add the real fillet radius. Check mesh quality plots for aspect ratio and Jacobian. Keep the element size and location of each probe fixed so the comparison between meshes is fair.

   Checkpoint: The chosen stress value changes by less than about 5 per cent between the last two meshes, and singular points are identified.

8. 8

   Summarise factors of safety

   Build a table of maximum von Mises stress, maximum displacement and minimum factor of safety for each load case, using beam results for members and solid results for joints. Highlight any case below your target. Explain which load case governs each part of the frame. Note that a static factor of safety does not prove fatigue life, which needs a separate study.

   Checkpoint: A summary table with every case meeting the target, or a list of failing locations with proposed fixes.

9. 9

   Improve and report

   Fix failing locations by adding a gusset, increasing tube wall thickness or moving a bracket, and rerun the affected cases. Record the mass change for each fix. Write a report with the load table, hand calculation, beam and solid results, convergence evidence, factor-of-safety summary and the design changes. State the limits: linear static, assumed load factors, idealised welds. Add a one-page summary for the design review that lists each failing location, the fix and the new factor of safety.

   Checkpoint: A report showing that the final frame meets the factor-of-safety target in every load case, with mass impact and limits stated.

Testing & validation

• Reaction forces equal applied loads in every case.
• Static case agrees with hand calculations within a stated margin.
• Mesh convergence shown at critical joints.
• Factor of safety above the target in every case after design changes.

Expected results

A complete static analysis of an e-scooter frame with defined load cases, beam and solid results, hand-calculation checks, mesh convergence and a factor-of-safety summary that supports design changes.

Take it further

• Run a fatigue study using the bump load case.
• Run a frequency study to find the frame's first natural frequencies.
• Compare a steel and an aluminium frame for mass and stiffness.

Viva and review questions

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