Why won't my C++ template vehicle move?

I’m at my wits end trying to make my UE4 vehicle actually move.

Essentially, if I use any of the sample-FBX files, the vehicle moves fine (my code is the exact same as the sample vehicle template c++ code, with renamed joints and meshes in the *Pawn.cpp file.

My model is just a cube with some spheres attached:

As far as I can tell the parent hierarchy is correct for a jointless mesh (I’ve tried joints too).

When I press play, and press the ‘W’ key, the ‘wheels’ spin, but the model doesn’t move. The only hint I have is that the model sinks into the floor to the body depth, like so: (And yes, I have tried increasing the wheel radius)

The model looks normal in the mesh viewer (the wheels aren’t below the 0-line):

My physics asset also behaves a bit oddly - when I press simulate, the model flies off into space. I have it setup like this:

And the physics settings for the wheels is:

If I move the body bounding box down, then the wheels don’t sink, but there’s still no forward movement.

I can only imagine I’m doing something wrong with the physics… but I can’t understand what. If I import the sample FBX files, and don’t even touch the physics, they work fine. Help? I’m at my wits end.

Hey it’s exactly what was happening to me, have you solved it yet?