Heave direction

Just wondering, the heave direction is the same as pitch or surge? In a 2 dof with front mount motors.

No any heave in 2dof rig

Only pitch, roll and substitutes for sway and surge

With front mounted motors, to simulate a heave-like motion, you would want the arms to move up slightly on positive heave and down for negative heave. This will be the same for positive pitch and positive surge but usually with a much smaller range of motion. The idea is to have a short and fast pitch back and forwards motion to simulate a bump. Strictly speaking it is all pitch, but the motion software will mix pitch, surge and heave to relative amounts according to the game's telemetry. It is up to you to adjust your motion profile to give as realistic a feeling for each motion individually and then hopefully they will feel good when all used together.

The limitations will be that, for example, accelerating downhill might have your rig sitting level in the same fashion as braking uphill. Racing sims should normally be tuned with surge being the most important force, with a little pitch and/or heave added in according to preference. Flight sims are better with stronger pitch forces relative to surge in general. What feels best though is down to individual taste and with a 2 DOF, you might prefer it without mixing several DOFs into just pitch and roll.

for me, in flight sims, (in most cases) pitch is perceived more visually than it is actually felt. Surge and Heave are what is felt so I use much less of the axis travel for pitch. I guess the point is you have to experiment to match your rig to your own perceptions or goals of what you want to "feel". although after reading GWiz's replay above I'm going to try the opposite and see if I still have the same opinion