Mike Pass
Supporter
You are correct that the hub moves in an arc, however...
The suspension geometry is set with a short top arm at a steeper angle up than the lower arm which is longer and at a shallower angle down. ( the arm being the distance between the ball joint or pivots - not the metal tubes). This is what increases camber in bump and reduces it in droop. In bump the top balljoint moves towards the car centre line whilst the lower balljoint moves outward - thus increasing camber). Over the "normal" range of movement of 2" bump and 1' droop they tend to cancel each other out. The actual arc followed by the hub can be measured by tracking it against a fixed vertical bar placed next to the hub centre. If this arc is considered to be significant then this arc can be used as the guide for the laser pointer rather than a vertical straight line.
The main advantage of using a laser pointer is that when the wall or card is placed say 4m away, the beam is effectively an "optical lever". A very small change in hub angle results in a big movement of the laser spot on the wall or card. The longer this optical lever is the more sensitive the system is to the hub movement. This effect can be magnified further by using a mirror on the hub and aiming the beam from a fixed laser pointer at the mirror.This effectively doubles the angle change in the laser beam.This setup is used in very sensitive galvanometers which use a light pointer rather than a solid pointer as the light beam is weightless. As the optical lever is so long the movement of the laser dot is far greater than the movement of the dot from the hub moving in an arc. The distance to the wall or screen must be as large as possible.
The hub must be clamped to prevent rotation as it is raised and lowered.
The easiest way to attach the laser pointer or mirror is to glue them firmly to a strong magnet. I buy cheap laser pointers from Ebay.
A set of steel plates with a range of thicknesses can be mixed and matched to get the best rack height position re. bumpsteer.
Cheers
Mike
The suspension geometry is set with a short top arm at a steeper angle up than the lower arm which is longer and at a shallower angle down. ( the arm being the distance between the ball joint or pivots - not the metal tubes). This is what increases camber in bump and reduces it in droop. In bump the top balljoint moves towards the car centre line whilst the lower balljoint moves outward - thus increasing camber). Over the "normal" range of movement of 2" bump and 1' droop they tend to cancel each other out. The actual arc followed by the hub can be measured by tracking it against a fixed vertical bar placed next to the hub centre. If this arc is considered to be significant then this arc can be used as the guide for the laser pointer rather than a vertical straight line.
The main advantage of using a laser pointer is that when the wall or card is placed say 4m away, the beam is effectively an "optical lever". A very small change in hub angle results in a big movement of the laser spot on the wall or card. The longer this optical lever is the more sensitive the system is to the hub movement. This effect can be magnified further by using a mirror on the hub and aiming the beam from a fixed laser pointer at the mirror.This effectively doubles the angle change in the laser beam.This setup is used in very sensitive galvanometers which use a light pointer rather than a solid pointer as the light beam is weightless. As the optical lever is so long the movement of the laser dot is far greater than the movement of the dot from the hub moving in an arc. The distance to the wall or screen must be as large as possible.
The hub must be clamped to prevent rotation as it is raised and lowered.
The easiest way to attach the laser pointer or mirror is to glue them firmly to a strong magnet. I buy cheap laser pointers from Ebay.
A set of steel plates with a range of thicknesses can be mixed and matched to get the best rack height position re. bumpsteer.
Cheers
Mike
