Machine Kinematics
solved, then drawn
Concept

Camber — where it appears

How far a wheel leans from vertical, which for an independent suspension is the rotation of the link its upright is part of. It is a coupler angle rather than a design parameter: once the link lengths are chosen the camber curve follows, and it can only be changed by changing the linkage.

Named by 2 essays across one field — each of them below, with the objects they name alongside it.

The wheel is the coupler — double wishbone. The suspension solved at 0 mm of bump, with the whole travel ghosted behind it. The two arms are the cranks and the upright between them is the coupler; the wheel is bolted to that coupler, so camber is the coupler's rotation and nothing else. Camber here is 0.00° and the contact patch has moved 0.0 mm across the road. The cross is the instantaneous centre of the upright, found from the solved velocity field; the roll centre is where the line from it to the contact patch crosses the car's centreline, and it is at 73 mm here.

The wheel is the coupler

A double wishbone is a four-bar standing on end whose coupler carries a wheel, so camber is coupler rotation and scrub is a coupler point's path. Both are computable, and the second one comes out with the opposite sign from the model every suspension book uses — by more than the whole scrub.

applied · Fourbar The roll centre through the travel — double wishbone. The roll centre is a construction: the instantaneous centre of the upright, joined to the contact patch, extended to the car's centreline. It is quoted as a height. Over 160 mm of travel it moves 54 mm — 52 mm to 106 mm — The number in a specification is the value at one position of a curve, and the curve is steeper than the thing it is a property of.

A roll centre is not a point

The roll centre is a construction on the instantaneous centre of the wheel's upright, and every step of it is exact. What it is not is a height: over eighty millimetres of bump and droop it moves 54 mm on a wishbone and 131 mm on a strut, and on the strut it goes below the road.

applied · Fourbar

Named alongside it

The objects these essays reach for when they reach for this one.

CouplerFour-barScrubSuspensionConstraintCoupler curveInstantaneous centreKennedy's theoremPin in slotPrismaticRoll centreSensitivity

All concepts