Wheelie of a car coming out of a ditch: what is the correct model?

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The discussion centers on understanding the dynamics of a car's motion as it exits a ditch, particularly why the front wheels lift off the ground while the rear wheels remain in contact. Key points include the influence of the car's velocity vector and center of mass on its trajectory, as well as the role of angular momentum in the motion. Participants debate the correct equations of motion, emphasizing the need to account for the car's suspension and the physical characteristics of the vehicle. The conversation highlights the complexities of modeling real-world scenarios, suggesting a gradual approach to increasing model complexity based on validation. Overall, the aim is to accurately interpret the car's behavior during this specific maneuver.
  • #121
haruspex said:
Ah, yes, I see my mistake. In post #92 I omitted an "h+" at the start of the formula. It's in my spreadsheet, but I missed it.
So you confirm that the 3rd element in the wheels coordinate expressions is neessary. I'll reflect a bit more on this.

My expressions in #114 are ok?
 
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  • #122
alex33 said:
Before starting the simulation of phase 2 (free fall), I ask you to confirm the starting data:

##V_0x = V = 2,52 m/s ## (Chord length / 18 frames ...I think it is the most reliable data)

##V_0z = \frac {1}{2}V* \tan(α)##

##ω_0 = \frac {1}{2L}V* \tan(α) - (\frac {3g*L}{h^2+4L^2}*4/24)##

##X_0c= \frac {chord-length}{2}-L##

##Z_0c = \frac {(ω_0 + \frac {1}{2L}V* \tan(α))}{2} * L * 4/24##

##θ_0 = \frac {V * \tan(α)}{2L}*4/24##

Thanks
##V_0z## should be ##=ω_0 L##.
##Z_0c ## needs "h+", as discussed.
For ##θ_0## I use the average rotation rate during del t:
##(\frac {V * \tan(α)}{2L}+ω_0)/2*4/24##
 
  • #123
alex33 said:
Thanks Tony !
we went from theory to numbers just to verify the first proposed solution to the problem, with respect to a real event, but identifying the correct physical model is always the main objective of the question I asked in this thread. So thank you for your comments on which I and the other friends who have made themselves available will reflect for sure.
The first model is the absorption of sharp edges of the tires, then the spring mass shock model. Otherwise this buggycar will drive anyone buggy without more assumptions being defined or become just a wooden car with no suspension and solid rubber tires with an extremely rough ride.
 
  • #124
haruspex said:
##V_0z## should be ##=ω_0 L##.
##Z_0c ## needs "h+", as discussed.
For ##θ_0## I use the average rotation rate during del t:
##(\frac {V * \tan(α)}{2L}+ω_0)/2*4/24##
Dear Haruspex, do you check the values I send you? Please take a look at last calculations we shared. Thanks
 
  • #125
alex33 said:
Dear Haruspex, do you check the values I send you? Please take a look at last calculations we shared. Thanks
I will do, but did not get a chance today.
 
  • #126
Ok, thanks... don't worry
 

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