/// <summary>
/// Calculate the contact ratio for two gears. The gears must be
/// compatible from a meshing point of view (same module, same
/// pressure angle). The contact ratio is the average number of teeth
/// in contact with each other on the pressure-bearing faces as
/// the gears are rotating. Ideally this should be > 1.1, but the
/// absolute minimum is 1 for the gears to not 'click' as they turn.
/// Note that this is the ideal figure, valid for no backlash, no
/// profile offset, and no undercut. It is the theoretical maximum
/// value that is never achieved!
/// </summary>
/// <param name="g1">The first gear being meshed</param>
/// <param name="g2">The second gear being meshed</param>
/// <returns>The contact ratio</returns>
public static double IdealContactRatio(GearParameters g1, GearParameters g2)
{
if (g1 == null || !g1.CanMeshWith(g2))
{
throw new ArgumentException("Gears have differing modules or pressure angles");
}
double gear1 = 0.5 * RootDiffOfSquares
(g1.PitchCircleDiameter + 2 * g1.Module, g1.BaseCircleDiameter);
double gear2 = 0.5 * RootDiffOfSquares
(g2.PitchCircleDiameter + 2 * g2.Module, g2.BaseCircleDiameter);
return((gear1 + gear2 - Math.Sin(g1.PressureAngle)
* (g1.PitchCircleDiameter + g2.PitchCircleDiameter) / 2)
/ g1.BaseCirclePitch);
}
/// <summary>
/// Given we are meshed with another gear where this and
/// the other gear might have a profile shift, calculate
/// the contact length for the two gears
/// </summary>
/// <param name="meshedGear">The gear with which we are
/// meshed</param>
/// <returns>The length of the path along which the two
/// gears are in contact before breaking apart</returns>
public double ContactDistanceWithGear(GearParameters meshedGear)
{
if (!CanMeshWith(meshedGear))
{
Information = "Gears have differing modules or pressure angles";
return(0);
}
double distanceBetweenCentres
= PitchCircleDiameter / 2
+ meshedGear.PitchCircleDiameter / 2
+ Module * (ProfileShift + meshedGear.ProfileShift);
double distToPitchPoint = distanceBetweenCentres
* BaseCircleDiameter / (BaseCircleDiameter + meshedGear.BaseCircleDiameter);
double meshedDistToPitchPoint = distanceBetweenCentres - distToPitchPoint;
double contactLength
= Math.Sqrt(Involutes.DiffOfSquares(distToPitchPoint, BaseCircleDiameter / 2))
- Math.Sqrt(SquaredUndercutRadius - Involutes.Square(BaseCircleDiameter / 2));
double meshedContactLength
= Math.Sqrt(Involutes.DiffOfSquares(meshedDistToPitchPoint, meshedGear.BaseCircleDiameter / 2))
- Math.Sqrt(meshedGear.SquaredUndercutRadius - Involutes.Square(meshedGear.BaseCircleDiameter / 2));
return(contactLength + meshedContactLength);
}
/// <summary>
/// Calculate the sequence of cutout point sequences that make
/// the spokes in the gear. Used to try and reduce the inertia
/// of larger gears.
/// </summary>
/// <param name="spokes">The number of spokes to put between
/// the gear hub and the teeth-bearing perimeter</param>
/// <returns>The point lists that each make up the
/// outline of the cutouts</returns>
private List <List <PointF> > CalculateCutouts(int spokes)
{
List <List <PointF> > cutouts = new List <List <PointF> >();
if (spokes < 3)
{
return(cutouts);
}
// Set some design constants
double cornerRadius = Gear.Module;
double spokeThickness = 2.0 * Gear.Module;
double minHubDiameter = 8 * Gear.Module;
// Calculate the minimum hub diameter for a given number of
// spokes, a specified spoke thickness and corner radius.
double hubDiameter = (spokeThickness + 2 * cornerRadius)
/ Math.Sin(Math.PI / spokes) - cornerRadius;
if (hubDiameter < minHubDiameter)
{
hubDiameter = minHubDiameter;
}
// Calculate the corner at the outer end of one side of a spoke.
// For this reference spoke we assume the spoke runs along the
// positive X axis. We shall rotate it for other spokes.
double rimDiameter = Gear.InnerDiameter - 2.0 * spokeThickness;
if (rimDiameter < hubDiameter + 4 * cornerRadius)
{
return(cutouts);
}
double cornerCentreY = spokeThickness / 2 + cornerRadius;
double rimCornerCentreX = Math.Sqrt
(Involutes.DiffOfSquares(rimDiameter / 2 - cornerRadius, cornerCentreY));
PointF rimCornerCentre = Involutes.CreatePt(rimCornerCentreX, cornerCentreY);
double angleAtRim = Math.Atan2(cornerCentreY, rimCornerCentreX);
IEnumerable <PointF> outerCorner = Involutes.CirclePoints
(-Math.PI / 2, angleAtRim, Involutes.AngleStep, cornerRadius, rimCornerCentre);
// Calculate the corner at the inner end of a spoke.
//double hubCornerCentreX = Math.Sqrt(Square(hubDiameter / 2 + cornerRadius)
// - Square(cornerCentreY));
double hubCornerCentreX = Math.Sqrt
(Involutes.DiffOfSquares(hubDiameter / 2 + cornerRadius, cornerCentreY));
PointF hubCornerCentre = Involutes.CreatePt(hubCornerCentreX, cornerCentreY);
double angleAtHub = Math.Atan2(cornerCentreY, hubCornerCentreX);
IEnumerable <PointF> innerCorner = Involutes.CirclePoints
(Math.PI + angleAtHub, 3.0 * Math.PI / 2, Involutes.AngleStep, cornerRadius, hubCornerCentre);
// Calculate the outer rim circle segment
IEnumerable <PointF> outerRimSegment = Involutes.CirclePoints
(angleAtRim, 2 * Math.PI / spokes - angleAtRim, Involutes.AngleStep, rimDiameter / 2);
// Calculate the hub circle segment
IEnumerable <PointF> hubSegment = Involutes.CirclePoints
(angleAtHub, 2 * Math.PI / spokes - angleAtHub, Involutes.AngleStep, hubDiameter / 2);
// Calculate the far side of the cutout. Reflect the inner spoke
// across the X axis, and reverse its points. Then rotate it round the gear
// by the angle between adjacent spokes. This gives us the correct
// list of points.
IEnumerable <PointF> nearSide = innerCorner.Concat(outerCorner);
IEnumerable <PointF> farSide = GearParameters.ReflectY(nearSide)
.Select(p => Involutes.RotateAboutOrigin(2 * Math.PI / spokes, p))
.Reverse();
// Now create the lists of points for each of the cut outs
List <PointF> cutout = new List <PointF>();
cutout.AddRange(nearSide);
cutout.AddRange(outerRimSegment);
cutout.AddRange(farSide);
cutout.AddRange(hubSegment.Reverse());
cutout = Involutes.LinearReduction(cutout, (float)Gear.MaxError);
cutouts.Add(cutout);
for (int i = 1; i < spokes; i++)
{
cutouts.Add(new List <PointF>(cutout.Select
(p => Involutes.RotateAboutOrigin(2 * Math.PI * i / spokes, p))));
}
return(cutouts);
}
/// <summary>
/// Contact ratio between two gears, allowing
/// also for possible profile shift. Contact
/// ratio is defined as the average number of
/// teeth in contact between two gears as they
/// rotate. If this is less than 1.0, there are
/// times at which no teeth are meshing on the
/// involute surfaces and the gears will
/// vibrate or lock up.
/// </summary>
/// <param name="meshedGear">The other gear we
/// are meshing with</param>
/// <returns>The contact ratio. Must be greater
/// than one for gears to mesh correctly.</returns>
public double ContactRatioWith(GearParameters meshedGear)
=> ContactDistanceWithGear(meshedGear) / BaseCirclePitch;
/// <summary>
/// Check that the two gears are compatible for meshing
/// </summary>
/// <param name="meshedGear">The other gear with which
/// we are trying to mesh</param>
/// <returns>True if the gears are compatible</returns>
public bool CanMeshWith(GearParameters meshedGear)
=> meshedGear != null &&
PressureAngle == meshedGear.PressureAngle &&
Module == meshedGear.Module;
