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Report FourPost anti on the wheel-center path beside the contact patch - #157
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FourPost reported anti-dive and anti-squat only for an Fx that the upright reacts. That is right for an outboard brake or a hub motor. An inboard drive or brake reacts its torque on the chassis, so its anti comes from the wheel-center path. The BobSim default car has an inboard motor and a differential. FourPost now exports the CP and wheel-center x positions and computes, per axle at the design pose, the kinematic dFz/dFx on both paths and the anti percent with the same h/L and signs as the avg_ keys. The new keys name their force path. The avg_ keys keep their names and values.
rhorvath02
approved these changes
Oct 29, 2026
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What
FourPost reports anti-dive and anti-squat only for a longitudinal force that the upright reacts (the contact-patch path). That suits an outboard brake or a hub motor. With an inboard motor and differential, the chassis reacts the drive torque, and the anti comes from the wheel-center path. BobSim's default car (
EVBatInvMotDiff) is inboard-driven, so its reported rear anti-squat uses the wrong path.Changes
longitudinal_jacking_coeff_<axle>_{contact_patch,wheel_center}_path(N/N, fromc = -(dx/ds)/(dz_cp/ds)) andanti_{dive,squat}_{contact_patch,wheel_center}_path_pct, with the same h/L and signs as theavg_keys.avg_keys keep their names and values. The report and docs label the force path.How to check
c_cp = z_p/x_p,c_wc = (z_p - R)/x_p.The contact-patch values agree with the existing force-pulse averages (+0.00525 and -0.00881) within about 2 %.
Notes
Limits
This fixes the FourPost report only. VehicleSim still reacts every drive and brake torque at the upright: BobDyn/BobLib#59.
Stack
6 of 7. It depends on the BobLib frame names surviving #151's BobLib bump.