A bit of illustration for torsion bars spring:

On the left, torsion spring is in the relaxed state and is effected only by gravity which we ignore for simplicity. On the right, torsion spring holds a portion of mass of the tank. So how do we get to this:

We can set angular limit to 90 degrees, so handle can turn up to M1 and M2. M1 and M2 would be the points where maximum force of the spring is generated. So spring force will go from -Angular Position Strength at M1, to 0 at A and to +Angular Position Strength in M2.

We want force of the spring to be equal "Mass of tank in kg * acceleration due gravity / amount of wheels " at 15 degrees (point B), which is 70% from point A. Which means that we should set Angular Position Strength to:

(Mass of tank in kg * acceleration due gravity / amount of wheels) * 1.3

to add 30% of force that we should have at M1 and M2.

We can take different angle. For example default position is 30 degrees and we allow freedom of 60, it means that lever can travel from 0 to 60 degrees and if our desired position under tank load is 15 degrees then we need to set Angular Position Strength as:

(Mass of tank in kg * acceleration due gravity / amount of wheels) * 2

as 15 degrees is a half way between relaxed position and fully compressed.

On the left, torsion spring is in the relaxed state and is effected only by gravity which we ignore for simplicity. On the right, torsion spring holds a portion of mass of the tank. So how do we get to this:

We can set angular limit to 90 degrees, so handle can turn up to M1 and M2. M1 and M2 would be the points where maximum force of the spring is generated. So spring force will go from -Angular Position Strength at M1, to 0 at A and to +Angular Position Strength in M2.

We want force of the spring to be equal "Mass of tank in kg * acceleration due gravity / amount of wheels " at 15 degrees (point B), which is 70% from point A. Which means that we should set Angular Position Strength to:

(Mass of tank in kg * acceleration due gravity / amount of wheels) * 1.3

to add 30% of force that we should have at M1 and M2.

We can take different angle. For example default position is 30 degrees and we allow freedom of 60, it means that lever can travel from 0 to 60 degrees and if our desired position under tank load is 15 degrees then we need to set Angular Position Strength as:

(Mass of tank in kg * acceleration due gravity / amount of wheels) * 2

as 15 degrees is a half way between relaxed position and fully compressed.

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