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Operational forces on the pin were found for a lower bound on the pin diameters. The operational force was found by using 600N 1200N transferred to the pinion from the steering system (see FEA of rack extension), the torque transferred to the steering column would be 7500 15000 N*mm with a pinion radius of 12.5mm. The inner diameter of the steering column is 19.05mm, therefore the operational force on the pin would be 787 1575 N.
The minimum diameter for the pin to operate in each material using a safety factor of 2, and F=787N1575N:
Material | τallow (MPa) | Diameter (mm) |
|---|---|---|
Nylon | 70 | 35.7835 |
Aluminum (6061-T6) | 207 | 23.2011 |
Steel (ASTM - A36) | 400 | 12.5824 |
Previous on MSXII, the shear pin used was (believed) to be 4-5mm nylon pin, therefore, it would be suitable for MSXIV to also use a nylon pin, from calculations above, the nylon pin should be between 4 5.35 to 6mm in diameter. A diameter of 5.5 mm was chosen and the pin will be machined out of 1/4” OTS nylon rod.
Verification
Scenarios | Force (N) |
|---|---|
Pulling on steering wheel | 225 |
Average body weight of 20+ year male | 890 |
Average torque generated by steering (500ms) | 2100 |
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All three forces are below 1575N with SF of 2, therefore the pin is not expected to fail with normal handling.
References:
Steering Torque study
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