Rear Wheel Rotation Error under Full-Steer in 8×8 Wheeled Vehicle

[osman cankurtaran]

I’m simulating an 8×8 vehicle with all-wheel steering in PyChrono. Everything behaves correctly when driving straight or at moderate steering angles (up to ~15°), but as soon as I apply full lock steering and drive forward, the very last (eighth) wheel exhibits a completely unrealistic rotation—as if its joint has “snapped.”

Details:

• Vehicle: 8×8, all-wheel steer enabled on every axle

• Suspension: DoubleWishboneReplica on all four axles

• Steering: Pitman-arm linkage on front axles, mirrored geometry on rear axles

• Observed Behavior:

  • OK: Straight-line driving; steering up to ±15°

  • Fail: Full-lock steering (~±30°): rearmost wheel suddenly spins/tilts uncontrollably

What I’ve Checked:

1. Attachment points and body names in the rear suspension JSON

2. Steering index and Pitman-arm link geometry for the rear axles

3. No error messages—simulation continues but the wheel motion is clearly wrong

Questions:

1. What common mistakes cause a single wheel joint to behave “broken” only at extreme steering angles?

2. Are there known pitfalls when mirroring Pitman-arm steering linkages on rear axles?

3. Which debugging steps or visualization techniques work best for isolating axle-specific joint misconfigurations in PyChrono?

Any advice or pointers would be greatly appreciated!

[osman cankurtaran]

Does anyone have any ideas? Even a small suggestion would be a great help to me.

[Radu Serban]

Hi Osman,

 

Sorry for the very late reply.

 

My suspicion is that you have the wrong suspension/steering geometry. Note that, for an all-wheel steering vehicle, you can not simply copy the geometry of the front axle and steering mechanism from a traditional front steering vehicle and place it on the rear axle.  You’ll need to get data from an actual all-wheel steering vehicle and model that.

 

--Radu

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[osman cankurtaran]

I’ll double-check the geometry and follow up here with my findings.  Thanks again for the guidance