I am modeling walking insects. I implement them as cuboids and use forces (including friction and drag), to control motion. However, the movement characteristics of this 'sliding box' physics don't match those due to a legged creature.

For example, legged creatures near-instantly accelerate to their top speed; whereas applying a force to a box takes time to accelerate it.

The applied force can be increased along with the counteracting drag, giving much quicker acceleration (via force) to a max speed (via drag). However, this also means the force that creatures can exert when pushing on other objects is increased.

Does anyone know of any techniques using a physics engine to cheaply model walking creatures?