Steering linkages

Sunday, 11^th August 2013, noon

Managed to get a bit of work done and my skin’s holding up well. Connected the two front wheels, a tricky job involving a bit of 3D trigonometry.

These are the components for the steering linkages –

One end of the arms with the rod ends connects to the kingpins, the other end connects to the square section brackets which mount to the chassis. The arms are made from some more bits of that hang-glider and I have used some tiny 16x6x8mm ball bearings that I had lying around.

These are the templates I used to mount the brackets –

Getting the rod ends positioned accurately is critical, otherwise the toe-in will alter as the suspension compresses. The motion of the inner rod end must parallel the movement of the outer rod end precisely. It’s axis of rotation has to be the same as the kingpin, with the inclination and caster the same as the kingpin. As well as that, both the inner and outer rod ends have to be centred between the inner and outer wishbone pivots.

This is the bracket riveted in place, showing the linkages attached –

To find the length of the connecting rod between the two sets of linkages, I set up a makeshift trammel for the front wheels, setting the toe-in to zero for minimum drag and clamping the wheels in place –

I was then able to make the rod (chromed shower curtain rail) incorporating two bushes at the ends to allow a bit of vertical travel, install it and connect the linkages–

These pix show the effect of the Ackerman angle on the front wheels as the machine corners –

As can be seen, the inside wheels are turning much tighter than the outside wheels. The turning centres of both front wheels pivot about the same point on the projected axis of the rear wheels, ensuring that the wheels travel without scrubbing or drag. The inner wheel is also leaning into the corner more than the outer wheel, due to caster and kingpin inclination.

Glad to have that out of the way, it was a bitch of a job to get right.