Finite Element Analysis

Since all the models created by team P09203 are done in SolidWorks 2008, our team was able to take full advantage of COSMOSworks, a finite element analysis program built in to SolidWorks. Basic loading was first determined by hand and then feed into COSMOSworks to verify the robustness of the design.

Drive Shaft

Loading

For this study the drive bearings and drive shaft were modeled and loaded into COSMOS. The bearings were then restrained from translating and mated to the drive shaft so that the drive shaft was allowed to rotate freely but restrained from translating with respect to the bearings. The drive shaft was loaded with forces equivalent to the force that the drive shaft would see if the drive motor was stalled. Unfortunately this method of loading didn’t allow us to apply the full stall torque of the servo.

A second loading technique was attempted to apply the full stall torque of both the steering and drive motors however the resulting stress distribution was less than the distribution seen with the drive load only.

Results

Bearing, gear side

Type X-Component Y-Component Z-Component Resultant

Shear Force (N) -0.098212 -0.10089 -2.8846 2.888

Bearing, encoder side

Type X-Component Y-Component Z-Component Resultant

Shear Force (N) -0.050846 -0.083648 -1.4934 1.4966

Maximum displacement: .00005 in

Minimum FOS: 11.5

Displacement

Although we were not able to apply the steering load to the drive shaft, with a minimum factor of safety of 11.5, there is little concern that the drive shaft will fail.

Motor Coupling

Loading

The Motor coupling study includes the motor coupling and the motor coupling bearing. The motor was originally a part of this study but was removed due to meshing problems. The bearing was restrained and a pin mate was used to restrain the shaft, as well as a restrain at the end of the motor coupling to simulate the set screws connecting it to the motor. Forces equivalent to the gear reactions were then put on the motor coupling to simulate the gear train reaction when the motor is stalled.

Results

Bearing Load:

Type X-Component Y-Component Z-Component Resultant

Shear Force (N) -0.066353 5.7663 2.8709 6.4418

Maximum Displacement: .00001448 in

Minimum FOS: 15.87

Maximum Stress: 1925 psi

Displacement

A full analysis that includes the motor should be done to ensure as little radial and axial force is transferred to the motor as possible. However early indications from this study would lead us to believe that there is a limited amount of force being transferred to the motor shaft.

Lower Housing

Loading

To replicate the loading that the lower housing would see the lower housing, trust bearing, steer centering bearing and servo coupling were included in this study. The bearings were then mated to the lower housing and restrained in a manner to best mimic the presence of the upper housing. The loading conditions were based on the bearing loads seen in the drive shaft study plus the stall force equivalent of servo.

Results

Name Type Min Location Max Location

Displacement URES: Resultant Displacement

0 in

Node: 9511

(0.280442 in,

1.31164 in,

0.209734 in)

4.25876e-005 in

Node: 426

(-0.0945581 in,

-1.5205 in,

-0.102766 in)

Stress VON: von Mises Stress

0 psi

Node: 9511

(0.280442 in,

1.31164 in,

0.209734 in)

140.895 psi

Node: 562

(-0.0945581 in,

-0.55577 in,

0.195945 in)

Minimum FOS: 56.7

Displacement

Stress

FOS

Upper Housing

Loading

The upper housing proved to be quite difficult to mesh, so it was loaded by itself. To ensure a worse possible scenario the upper housing was restrained where the mounting plate would be located and full loading was placed in the bearing seats and the force equivalent of the servo torque was placed on the servo mounting tabs. Concerns that the tabs used to restrain the servo were not robust enough prompted additional loading equivalent to the maximum force seen by the bearing seat.

Results

Name Type Min Location Max Location

Displacement2 URES: Resultant Displacement

0 in

Node: 1

(-1.3123 in,

1.25711 in,

-0.575 in)

0.00049289 in

Node: 4453

(0.635417 in,

1.6698 in,

0.45 in)

Stress5 VON: von Mises Stress

0.00549785 psi

Node: 13083

(-1.54977 in,

2.05481 in,

-0.757709 in)

1083.51 psi

Node: 9381

(0.375 in,

1.6698 in,

-0.412558 in)

Minimum FOS: 7.4

Displacement

Stress

FOS

Loading this part was extremely difficult and to verify the assumptions made in this study an additional study was preformed. That said this part was modified after this study was performed to make assembly easier and add a mounting point for a wire tie. These modifications increased the amount of material used and would only increase the FOS above its current minimum value.

Lower and Upper Housing

Loading

Originally it was intended that the entire motor module would be simulated however difficulties meshing the module lead to the simplified studies. Experience from the previous studies allowed us to identify the source of the meshing problems.

Loading was a combination of the lower and upper housing studies with the addition of the servo.

Results

Name Type Min Location Max Location

Stress1 VON: von Mises Stress

0 psi

Node: 11561

(1.30259 in,

1.31164 in,

0.554367 in)

315.18 psi

Node: 24981

(1.39235 in,

0.798731 in,

1.09364 in)

Displacement1 URES: Resultant Displacement

0 in

Node: 11561

(1.30259 in,

1.31164 in,

0.554367 in)

0.000155943 in

Node: 7896

(1.04259 in,

-1.71695 in,

-0.752011 in)

Minimum FOS: 32

Stress

Displacement

FOS

This was the most complicated study preformed in COSMOS and as such it was not without its problems. The t-slot on the upper housing needed to be removed in order for the model to mesh correctly and there were difficulties outputting the results of the study at true scale. However the results seem reasonable and match the results from the previous studies.