Electric Rickshaw (L5) Ladder Chassis Design and Load Check

The problem

Many electric rickshaws are built on chassis that have grown by trial and error and crack at cross members or the rear axle mounts after months on rough roads. A chassis designed from a load model, with each cross member justified, can be lighter and more durable and is easier to take through type approval.

Objectives

• Package the battery, motor, rear axle, driver and passengers on a ladder frame layout.
• Model the chassis in Weldments with channel and box sections, cross members and brackets.
• Analyse static, bump, braking and diagonal twist load cases.
• Compare two cross-member layouts for mass and stiffness.
• Produce a drawing pack with cut list and bracket details.

What you need

Key concepts

Ladder chassis

Two long side members joined by cross members. It is simple to fabricate and strong in bending but relatively weak in torsion unless cross members are well placed.

Axle load split

How the total laden weight divides between front and rear wheels, found from the centre of gravity position. It sets the reaction forces in the load cases.

Diagonal twist case

One front wheel and the diagonally opposite rear wheel lifted, as when crossing a kerb at an angle. It tests the torsional behaviour of the frame.

L5 category

The Indian vehicle category for three-wheelers above a certain speed and power. Check the current AIS requirements for the category before claiming compliance.

Step-by-step guide

1. 1

   Set requirements and example masses

   Collect example inputs: kerb mass target, a driver plus four passengers at an example 70 kg each, a 150 kg lead-acid or 80 kg lithium battery, motor and differential mass, wheelbase around 2000 mm and rear track around 1000 mm. Define load cases: static at 1 g, vertical bump at 2.5 g, braking at 0.6 g and a diagonal twist. Choose an example steel such as IS 2062 grade and record its yield strength.

   Checkpoint: A requirement sheet listing masses, positions, load cases and a target factor of safety of at least 2.

2. 2

   Lay out the packaging

   Sketch a top view and a side view of the vehicle: front wheel, rear axle with differential, battery boxes under the passenger seat, driver seat, footboard and cabin pillars. Dimension positions from the rear axle and link wheelbase and track to Global Variables. Build an assembly with simple block parts for each major component to visualise space and access for battery removal.

   Checkpoint: Layout sketches are fully defined and the block assembly shows a removable battery path.

3. 3

   Compute axle loads

   Use Mass Properties on the block assembly, with correct masses assigned, to find the laden centre of gravity. Calculate front and rear axle loads by taking moments about the rear axle, and check them in Excel. These reactions become the support forces in the Simulation study, so record them for each loading condition, including driver only and fully laden. Note how much the rear axle load rises when all passengers board, because the rear mounts and leaf spring hangers must carry it.

   Checkpoint: Axle loads computed by hand and by Mass Properties agree, and front axle load stays within an example target share for stable steering.

4. 4

   Model the ladder frame

   Create a 3D Sketch for two side members, cross members at the front steering mount, under the driver seat, at the battery boxes and at the rear axle mounts. Place Structural Members, for example 75 × 40 mm C-channel for side rails and 40 × 40 × 2 mm box tube for cross members. Use Trim/Extend at every joint and add Gussets at the rear axle mounts and the front steering head junction.

   Checkpoint: The cut list shows each member and the chassis mass is in a believable range for the example design.

5. 5

   Add brackets and mounts

   Model leaf spring or suspension hangers, the motor and differential mounting plates, battery tray supports and cabin pillar sockets as plates merged into the weldment. Use the Hole Wizard for bolt patterns matching the component blocks. Re-run Interference Detection in the assembly with the real chassis and fix clashes with the battery boxes or axle. Keep bracket plates at a thickness the fabricator can cut and weld easily, and place bolt holes clear of weld toes so welds and holes do not overlap.

   Checkpoint: Interference Detection passes and every bracket has a bolt pattern that matches its mating component.

6. 6

   Set up the static study

   Create a Static study with members as beams and check joints with Edit Joints. Support the chassis at the axle mounts using Fixed Hinge and Roller/Slider restraints so only rigid-body motion is prevented. Apply passengers, driver and battery as distributed forces on their support members and the motor as a Remote Mass. Add Gravity. Check reaction forces against the hand-calculated axle loads.

   Checkpoint: Reaction forces at the supports match the hand-calculated axle loads within a few per cent.

7. 7

   Run bump, braking and twist cases

   Copy the study for each case: scale vertical loads for bump, add longitudinal inertia loads for braking, and for twist apply an enforced vertical displacement at one front and one diagonally opposite rear mount while restraining the others. Plot Upper Bound Axial and Bending stress, displacement and Factor of Safety. Compute the torsional stiffness from the twist case as applied moment divided by twist angle.

   Checkpoint: Every case is run, the minimum factor of safety is recorded, and a torsional stiffness value in N·m per degree is calculated.

8. 8

   Hand-check a side member

   Treat one side member as a simply supported beam between axle mounts with the passenger and battery loads as point loads. Calculate the bending moment, stress (M·y/I using the channel section properties from the section property tool) and mid-span deflection. Compare these with the Simulation result for the static case. A large mismatch usually means a wrong restraint or load.

   Checkpoint: Hand and Simulation bending stress agree within about 15 per cent for the static case.

9. 9

   Compare two cross-member layouts

   Create a second configuration with a different cross-member layout, for example an X-brace under the passenger area instead of two straight members. Run the same four cases on both. Tabulate mass, maximum stress in each case, bump deflection and torsional stiffness. Choose the layout that meets the factor of safety target with the best stiffness-to-mass ratio and explain why. Keep fixtures and loads identical between configurations so the comparison reflects the layout change only.

   Checkpoint: A comparison table for two layouts with a reasoned choice.

10. 10

    Drawings and report

    Produce a chassis drawing with a Weldment Cut List table, bracket detail drawings and weld symbols, with general tolerances to ISO 2768. The report covers packaging, axle loads, load cases, results, the hand check and the layout comparison. Note that beam models miss local weld stresses, that fatigue under rough-road loads needs separate study, and that the current AIS requirements for the L5 category must be checked before approval.

    Checkpoint: A complete drawing pack and a report with all load cases, the comparison and stated limitations.

Testing & validation

• Reaction forces match hand-calculated axle loads.
• Hand bending check of a side member agrees with Simulation.
• All four load cases meet the factor of safety target.
• Torsional stiffness is reported and compared between layouts.
• Interference Detection passes with all packaged components.

Expected results

A packaged ladder chassis for an example L5 electric rickshaw with verified static, bump, braking and twist results, a torsional stiffness figure, a two-layout comparison and a fabrication drawing pack.

Take it further

• Add a Frequency study and compare the first chassis modes with motor and road excitation.
• Run a fatigue study on the rear axle mounts from a repeated bump load.
• Design the cabin roll frame and check it under a roof-load case.
• Compare lead-acid and lithium battery layouts for axle loads and chassis mass.

Viva and review questions

Learn it at DIYguru

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