A simple simulated gearbox

simulated_gearbox.lua

--@name Simulated Gearbox
--@author Cheezus
--@shared

local crankAxis = Vector(0, 0, 1) -- Rotation axis of the crankshaft
local flywheelAxis = Vector(0, 0, 1) -- Rotation axis of the flywheel
crankAxis:normalize()
flywheelAxis:normalize()

if SERVER then
    local ratios = {
        -8,
        0,
        8,
        5,
        2.5,
        1
    }

    local finalDrive = 1 -- All ratios get multiplied by this number
    local gear = 1 -- Gear to start in
    local holdingForce = 0 -- Force for holding the crank and flywheel angles EXACTLY together
                            -- 0 will essentially act as a centrifugal clutch (and is more stable)

    local angVelMatchForce = 0.2 -- Force for matching the angular velocity between crank and flywheel
                                -- This allows some slipping between the two linked entities

    wire.adjustPorts({
        GearUp = "number",
        GearDown = "number",
        Crank = "entity",
        Flywheel = "entity"
    }, {
        CrankRPM = "number",
        FlywheelRPM = "number",
        Ratio = "number",
        Gear = "number"
    })

    local crank = wire.ports.Crank
    local flywheel = wire.ports.Flywheel
    local abs = math.abs
    local min = math.min

    local function sendEnts()
        net.start("send")
        net.writeEntity(crank)
        net.writeEntity(flywheel)
        net.send(owner())
    end

    hook.add("input", "ports", function(name, value)
        if name == "GearUp" and value > 0 and gear < #ratios then
            gear = gear + 1
            wire.ports.Gear = gear
        end

        if name == "GearDown" and value > 0 and gear > 1 then
            gear = gear - 1
            wire.ports.Gear = gear
        end

        if name == "Crank" and value:isValid() then
            crank = value
            if isValid(flywheel) then sendEnts() end
        end

        if name == "Flywheel" and value:isValid() then
            flywheel = value
            if isValid(crank) then sendEnts() end
        end
    end)

    -- No negative axes or everything breaks
    for k, v in ipairs(crankAxis) do
        crankAxis[k] = abs(v)
    end

    for k, v in ipairs(flywheelAxis) do
        flywheelAxis[k] = abs(v)
    end

    local angularError = 0
    hook.add("tick", "simulate", function()
        if not isValid(crank) or not isValid(flywheel) then return end

        local crankAngVel = crank:getAngleVelocity():dot(crankAxis)
        local flywheelAngVel = flywheel:getAngleVelocity():dot(flywheelAxis)
        wire.ports.CrankRPM = abs(crankAngVel / 6)
        wire.ports.FlywheelRPM = abs(flywheelAngVel / 6)

        local ratio = ratios[gear] * finalDrive
        wire.ports.Ratio = ratio

        if ratio == 0 then return end

        -- This should only be calculated on gear changes, not every tick
        local lowestInertia = min(
            crank:getInertia():dot(crankAxis),
            flywheel:getInertia():dot(flywheelAxis) / (ratio ^ 2)
        )

        local angVelDifference = flywheelAngVel * ratio - crankAngVel
        angularError = angularError + angVelDifference

        wire.ports.AngVelDiff = angVelDifference
        wire.ports.AngError = angularError

        local force = Vector((holdingForce * angularError + angVelDifference * angVelMatchForce) * lowestInertia)

        crank:applyTorque(crank:localToWorldVector(force * crankAxis))
        flywheel:applyTorque(flywheel:localToWorldVector(-force * flywheelAxis * ratio))
    end)

    net.receive("request", function()
        if not isValid(crank) or not isValid(flywheel) then return end

        sendEnts()
    end)
elseif player() == owner() then
    timer.create("requestEnts", 1, 0, function()
        net.start("request")
        net.send()
    end)

    local crank
    local flywheel

    net.receive("send", function()
        crank = net.readEntity()
        flywheel = net.readEntity()
        timer.remove("requestEnts")
    end)

    enableHud(owner(), true)

    hook.add("drawhud", "hud", function()
        if not isValid(crank) or not isValid(flywheel) then return end
        if not owner():isAlive() then return end
        if owner():getActiveWeapon():getClass() ~= "gmod_tool" then return end

        render.pushViewMatrix({
            type = "3D"
        })

        local t = owner():getEyeTrace()
        if t.Entity and (t.Entity == crank or t.Entity == flywheel) then
            local size = crank:obbMaxs():dot(crankAxis)
            render.setColor(Color(255, 255, 255))
            render.draw3DLine(crank:localToWorld(crankAxis * -size), crank:getPos())
            render.setColor(Color(255, 0, 0))
            render.draw3DLine(crank:getPos(), crank:localToWorld(crankAxis * size))

            size = flywheel:obbMaxs():dot(flywheelAxis)
            render.setColor(Color(255, 255, 255))
            render.draw3DLine(flywheel:localToWorld(flywheelAxis * -size), flywheel:getPos())
            render.setColor(Color(255, 0, 0))
            render.draw3DLine(flywheel:getPos(), flywheel:localToWorld(flywheelAxis * size))
        end

        render.popViewMatrix()
    end)
end