Discussion Overview
The discussion revolves around calculating the required wheel thrust to accelerate a vehicle from a given speed to another within a specified time frame. Participants explore the relationship between force, acceleration, and vehicle specifications, including weight and torque, while considering practical applications in electric vehicle design.
Discussion Character
- Exploratory
- Technical explanation
- Mathematical reasoning
- Debate/contested
Main Points Raised
- One participant seeks a formula to calculate wheel thrust needed to accelerate a 5000 lb vehicle to 75 mph in 15 seconds.
- Another participant references the formula f = dp/dt, suggesting that 'f' represents force, while seeking clarification on the terms dp and dt.
- A participant calculates that to reach 75 mph in 15 seconds, the vehicle must generate an average thrust of 1140 lbs and torque of 950 ft lbs at the axle shaft.
- One participant mentions that if acceleration were constant at .72 g, the vehicle would reach 75 mph in approximately 4.74 seconds.
- A participant discusses the design of an electric truck with multiple motors, indicating that torque generation is not an issue, but battery and power system design is a concern.
- Another participant questions how the calculations would change if starting from 25 mph instead of 0 mph, while considering the same parameters.
- One participant notes that while applying the same force is necessary for constant acceleration, factors like air resistance and rolling friction become significant at higher speeds.
- Another participant acknowledges that the change in speed is now 50 mph instead of 75 mph and suggests that acceleration will not remain constant due to various factors.
- A participant confirms that while acceleration may not be constant, torque can remain constant due to variable frequency drives (VFDs), indicating a focus on general trends rather than precise calculations.
Areas of Agreement / Disagreement
Participants express varying viewpoints on the calculations and factors affecting acceleration, with no consensus reached on a definitive formula or approach. The discussion remains exploratory with multiple competing ideas presented.
Contextual Notes
Participants acknowledge that air resistance and rolling friction may affect calculations, particularly at higher speeds, but do not resolve how these factors quantitatively influence the thrust required. The discussion also highlights the dependence on vehicle design and specifications.