Requirements for Vehicle:
1. R/C must be able to reach a speed of greater than or equal to 20mph.
2. Powertrain must contain at least one 7.2v battery.
3. Car must weigh under 8lbs.
4. Battery must sustain power to drivetrain for at least 15 minutes without a reduction in max speed.
5. The final cost of the battery and drivetrain must remain under $400.
6. The outdrive cups and rear axels must no shear when experiencing less than 30 lb-in of torque.
7. The motor and battery housings must withstand an impact from the motor/battery if the vehicle crashes at a speed of 25 mph.
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Analysis 1 was completed to identify the power output from the engine given the max current, no load current, Kv rating and battery voltage. This consisted of a max power output by the idealized motor and then an actual power output which factors in the efficiency rating. This was calculated to be 370.962 W.
(Figure1)
Figure 1
Analysis 2 was completed to identify the max RPM and Torque output of the motor. Motor RPM was calculated by multiplying the Kv rating with the voltage output of the battery. This was calculated to be 24,420 RPM. The max Torque was calculated by dividing the Power output of the motor and dividing it by the maximum RPM. This was then converted to lb-in. This was found to be 1.284 lb-in.
(Figure 2)
Figure 2
Analysis 3 was completed to identify the max speed of the vehicle. The max RPM was divided by a selected final drive ratio to calculate the RPM output to the rear axle assembly. The circumference of the wheels was then calculated to obtain how much distance is travelled in one revolution. The max speed could then be calculated by multiplying the distance travelled in one revolution by the rear axle RPM and converting this value to MPH.
(Figure 3)
Figure 3
Analysis 4 was completed to find the maximum allowable torque on the rear axle when constructed with 6061-T6 aluminum. The maximum allowable torque calculation was then compared to the actual torque the assembly is experiencing.
(Figure 4&5)
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Figure 4
Figure 5
The requirement for the battery housing stipulated that it must resist an impact from the battery if the vehicle were to crash going 25 mph. An analysis was completed to determine whether a thickness of 1mm≥ would be sufficient given the requirement. This was done by calculating the impact force from the battery, calculating the shear stress on the housing component, and comparing it to the allowable shear stress on the rear section. This resulted in the conclusion that a thickness of 1mm ≥ will be more than sufficient for the housing. This is documented in drawing 20-006 in appendix B.