F1TENTH Vehicle Parameters
I needed to know these for doing the Raceline Optimization. Getting these things nailed down is super important.
https://traxxas.com/products/models/othermodels/6807slash4x4ultimate2012?t=specs
Friction
- Asphalt: 0.6 - 0.9
- Concrete: 0.5 - 0.8
- Rubberized tracks: 0.9 - 1.1
- Gravel: 0.4 - 0.8
- Grass: 0.2 - 0.4
- Sand: 0.1 - 0.3
Personal notes:
- If Brebeuf kind of slippery → 0.3
- Concrete kind of slippery → 0.55
Daniel Chia said he used 0.8. I started with 0.53, but i think even that is too high. So I should try maybe 0.3 → No, that is too slow.
Also, now, I have a baseline of 13.66 seconds to beat on the racetrack.
- “mue”: 0.66
Tip
If your racing line does not work, like you are losing grip, then you should not try to reduce the velocity profile. Rather, in your solver, try to decrease the friction coefficient.
This is because you will lose a lot of velocity on the turns.
Vehicle Parameters
### general vehicle parameters required in several functions
# v_max: [m/s] maximal vehicle speed
# length: [m] vehicle length
# width: [m] vehicle width
# mass: [kg] vehicle mass
# dragcoeff: [kg*m2/m3] drag coefficient calculated by 0.5 * rho_air * c_w * A_front TODO:
# curvlim: [rad/m] curvature limit of the vehicle
# g: [N/kg] gravity acceleration
# See https://github.com/jainachin/bayesrace/blob/master/bayes_race/params/f110.py
veh_params = {"v_max": 15.0,
"length": 0.568,
"width": 0.296,
"mass": 3.74,
"dragcoeff": 0.075,
"curvlim": 3.0,
"g": 9.81}The length and width were obtained from the Traxxas Slash 4x4 official dimensions here.
### vehicle parameters (minimum lap time optimization)
# wheelbase_front: [m] wheelbase front
# wheelbase_rear: [m] wheelbase rear
# track_width_front: [m] track width front
# track_width_rear: [m] track width rear
# cog_z: [m] center of gravity
# I_z: [kgm^2] yaw inertia
# liftcoeff_front: [kg*m2/m3] lift coefficient front axle calculated by 0.5 * rho_air * c_l_f * A_spoiler_f
# liftcoeff_rear: [kg*m2/m3] lift coefficient rear axle calculated by 0.5 * rho_air * c_l_r * A_spoiler_r
# k_brake_front: [-] portion of braking force at the front axle of the total braking force
# k_drive_front: [-] portion of driving force at the front axle of the total driving force
# k_roll: [-] portion of roll moment at the front axle of the total roll moment
# t_delta: [s] time constant for steering dynamic
# t_drive: [s] time constant for acceleration dynamic
# t_brake: [s] time constant for braking dynamic
# power_max: [W] maximal engine power
# f_drive_max: [N] maximal drive force
# f_brake_max: [N] maximal brake force (only needed for actor dynamics)
# delta_max: [rad] maximal steer angle
vehicle_params_mintime = {"wheelbase_front": 0.128,
"wheelbase_rear": 0.137,
"track_width_front": 0.161,
"track_width_rear": 0.161,
"cog_z": 0.045,
"I_z": 0.0965,
"liftcoeff_front": 0.0,
"liftcoeff_rear": 0.0,
"k_brake_front": 0.5,
"k_drive_front": 0.5,
"k_roll": 0.5,
"t_delta": 0.1,
"t_drive": 0.05,
"t_brake": 0.05,
"power_max": 255.0,
"f_drive_max": 23.0,
"f_brake_max": 23.0,
"delta_max": 0.44}Time Constants represent the rate at which the vehicle responds to changes in steering angle, acceleration, and braking inputs, respectively.
Parameter explained:
"wheelbase_front": 0.128"wheelbase_rear": 0.137"track_width_front": 0.161"track_width_rear": 0.161"cog_z": 0.045"I_z": 0.128: More below, I INCREASED"liftcoeff_front": 0.0"liftcoeff_rear": 0.0"k_brake_front": 0.5"k_drive_front": 0.5because Traxxas Slash 4x4 is all-wheel drive, set to 0.0 if not. This makes the racing line a LOT faster"k_roll": 0.5"t_delta": 0.1"t_drive": 0.05"t_brake": 0.05"power_max": 255.0: Max amperage rating of battery is 125A (see LiPo for reasoning). Battery operates at least at 11.1V, so 125 * 11.1 = 1387.5"f_drive_max": 23.0"f_brake_max": 23.0"delta_max": 0.44- t_delta: the typical value for t_delta for 1/10 scale RC cars like the Traxxas Slash 4x4 is around 0.1 to 0.3 seconds.
- t_drive: . The typical value for t_drive for 1/10 scale RC cars like the Traxxas Slash 4x4 is around 0.2 to 0.5 seconds.
- t_brake: the typical value for t_brake for 1/10 scale RC cars like the Traxxas Slash 4x4 is around 0.2 to 0.5 seconds.
I_z (Moment of Inertia)
Apparently daniel has 0.09, i have 0.05 even though I have a bigger car.
yea, this value is definitely wayy too low. I can calculate this value making the assumption that the car is square, using the equation for a rectangular plate
\begin{aligned} I &= \frac{1}{12}m (a^2 + b^2)\\ [3pt] &=\frac{1}{12}{3.74}(0.568^2 + 0.296^2)\\ [3pt] &={0.128} \end{aligned}$$ ### Tire Parameters I have no idea about these values to be honest. ```python ### tire parameters (minimum lap time optimization) # c_roll: [-] rolling resistance coefficient # f_z0: [N] nominal normal force # B_front: [-] Coefficient B for front tire # C_front: [-] Coefficient C for front tire # eps_front: [-] load dependence of Coefficient D for front tire # E_front: [-] Coefficient E for front tire # B_rear: [-] Coefficient B for rear tire # C_rear: [-] Coefficient C for rear tire # eps_rear: [-] load dependence of Coefficient D for rear tire # E_rear: [-] Coefficient E for rear tire # Hint: The D parameter of the Magic Formula is determined by D = F_z * mue. mue can be set above in optim_opts_mintime! tire_params_mintime = {"c_roll": 0.013, "f_z0": 3000.0, "B_front": 10.0, "C_front": 2.5, "eps_front": -0.1, "E_front": 1.0, "B_rear": 10.0, "C_rear": 2.5, "eps_rear": -0.1, "E_rear": 1.0} ```