Clamp player thrust influence

Question

How to: clamp influence of thrust, while allowing other forces to be infinite.

Example: A rocket can thrust in its rotated direction. Only explosions can push it past its top-speed. I'm looking for a theory more than code.

Any help would be appreciated.

SOLVED

EDIT: top-speed is determined by thrust speed and friction.

Thrust can stack onto velocity, but top-speed can be reached when friction is stronger than thrust speed.

vx = (vx + fx) *fr -- velocity = (velocity + force) *friction
vy = (vy + fy) *fr

When the velocity is high enough, addition of force will be deducted by friction.

fr = .9 : hard to see top speed

fr = .6 : easy to see top-speed

Answer 1

Controls: left, right and thrust

The top speed of thrust can be adjusted with friction.

-- VARIABLES
player = {
    frc = .95, -- friction
    acc = .05, -- acceleration
    max = .5, -- acceleration max
    deg = 0, -- rotation in degree
    rad = 0 -- rotation in radian
    -- rotation is CW and 0 points to the right
}

-- MAIN UPDATE
function love.update()
    control(player)
    applyVelocity(player)
end

-- UPDATE
function control(a)
    if  L then addRotation(a,-5) end
    if  R then addRotation(a, 5) end
    if  U then thrustOn(a) else thrustOff(a) end
end
function applyVelocity(a)
    -- velocity + force
    a.vx = (a.vx + a.fx) *a.fr
    a.vy = (a.vy + a.fy) *a.fr
    -- position + velocity
    a.x = a.x + a.vx
    a.y = a.y + a.vy
end

-- OTHER
function thrustOn(a)
    accelerate(a)
    rotateDist(a)
end
function thrustOff(a)
    a.f = 0 -- integer of force is used to convert to point (x,y) with (rad)
    a.fx = 0
    a.fy = 0
end
function addRotation(a,deg)
    a.deg = a.deg + deg
    a.rad = math.rad(a.deg) -- math.sin/cos functions use radian instead of degree
end
function accelerate(a)
    a.f = a.f + a.acc
    if a.f > a.max then a.f = a.max end
end
function rotateDist(a)
    -- end point of force rotated from player
    a.fx = a.f *math.sin(a.rad)
    a.fy = a.f *math.cos(a.rad)
end