Recumbent trike front wheels

The fit-up and welding for the front wheels was the most taxing process in the build of the trike  by far. There are multiple factors to take into account when creating the front steering geometry.  The pivot point for the front wheels should be under the contact patch of the wheels. For the axles I had made this meant that the steering tubes had to be at a 15.5 degree angle with respect to the plane of the wheel. If this was not enough, the same steering geometry had to lead the tire patch by about 10 degrees to make the wheels (caster) to naturally track.

The instructions said to fit the steering tubes directly to the struts.  Then adjust the strut angles with the rest of the frame to get the correct geometry.  I think the plan authors must have been rolling on the ground laughing at how much fun this would be.

Problem 1:  The tires need to pivot on the contact patch as you turn the front wheels. If this is mis-aligned you scrub of tire and lose cornering control. So, you need to fit the axle to the steering tube and held it in place at an obscure angle so that the projected line through the tube lands under the center of the contact patch of the tire.  Check.  With my axle configuration and hubs this as about  a 15.5 degree angle.

Problem 2: Now that the wheel can turn without scrubbing, you need to set the forward angle of the pivot such that the trike will track on its own. On a car, this is referred to as the Caster.  Think of the fact that hands free steering is “really nice”. So how do you accomplish this? It requires that the steering tube be inclined at about 10 degrees forward such that the imaginary line through the tube lands in FRONT of the tire contact patch. The tire is then automatically following the steering direction and tracks nicely in the forward direction (not so much in reverse) .

To achieve this , there was a lot of measuring, template making, cutting, grinding, cutting and grinding again and cussing. Making all of this fit, is a 3 dimensional puzzle with pieces that keep turning, throwing off the angles,  as you play with them.  The plans are basically saying “make it fit” rather than giving good guidance for the angles which may be hard given all of the variables in play. On top of this, as you dig into the AZ website you see  the slogan on the of:  “weld, cuss, grind, repeat” —  I did a few cycles of this …

Eventually I ended up with a reasonable facsimile of the angles and arms that are needed and they even fit the bearings I had purchased. The FSA ” the PIG” bearings have so far worked out well  (but I am still worrying about losing pieces).

So now, I have front wheels for the trike.  I have also tacked on the pieces to connect the wheels so they turn as a single unit. The Ackerman geometry seems to be working with the inside wheel turning more sharply than the outside wheel. However my testing in the shop is limited by available space.

Next, will come the brakes and the rest of the steering components.