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Three Wheel Bike Car

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Step 7: Steering Issues

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The steering design is "underseat steering," a term you'll hear a lot in reference to trikes. I like a cleaner cockpit without a bulky steering setup over my lap. (this latter often is called "OSS" for short, meaning "overseat steering.")

Something different that I did: I engineered a system of cables to pull on the steering arms, with a T bar up front as a pulling point.  Being a section of headset bearing, it is smooth and has decent leverage.  It keeps steering hardware clear of the cargo deck. My main concern was to be able to tidy up the hardware that runs from the front to the underseat steering bar.  Many setups use a one-sided bell crank that runs off to one side, this can be a space problem depending on cockpit design. For me it would have crowded the pedaling leg space. My arrangement hides the pulling device (the cables) underneath the center fore and aft tube.  Clean, quiet, light, effective.  I needed to make custom brass pulley towers to reverse the cable action, as well as give them a narrow line up. Works pretty well.
In much shorter trikes, often the steering is direct, with the rider pulling on handles rising out of the steering knuckles. This wouldn't work on a long-wheelbase trike, too far to reach. Those steering handles can crowd the cockpit sometimes, anyway. 

 I used established principles for laying out the angle of the steering arms on the knuckles. (See sketch about Center Point steering.) You can research Ackermann steering for more about all this. Basically it's best practice to have the steering arms pulling on the steering knuckles in a controlled way that helps keep the inner wheel in a turn from fighting the outer wheel so much.  There still is some disparity owing to the tighter circle the inbound wheel cuts compared to the greater distance the outer wheel has to cover in executing the same turn event. But the way that the steering arm points to the rear of the "car" is germane. 

Other parameters, like caster and camber, deserve some study on your part, if only to enrich your knowledge base. For a slow-speed vehicle, there are differing opinions. Some say too much emphasis is given to the need for these angular dimensions to wheel mountings when you're not talking about a motorized vehicle.  Camber, especially if set to splay the bottom of the wheels out, can enhance stability in cornering. But it enforces a weird tire wear pattern, not landing on the centermost and thickest part of a cycle tire. It loads the spokes laterally. If a frame design is pretty narrow (and therefore more tippy left to right) a bit of camber can make some sense. Short, narrow sport trikes more often have camber.

Caster is a fore and aft angle, affecting the "trail" of a wheel from its pivot point as it steers. In a two wheel bike, the head tube angle and the bend or rake in a fork combine to make "trail" that produces stable steering results if done right. It's very noticable if done wrong. A bike steers poorly "no hands" if this dimension is off. (note that steering also suffers during "no hands" if steering bearings are too tight.)  Some say caster is less important on a 3 wheeler, but sloppy steering connections or poor weight distribution can introduce chatter if trail is non-existent or backwards.  (Think shopping cart wheel, rabbiting wildly at high speed, or when you push the cart backwards. On a shopping cart there is a large amount of caster, plus sloppy axles.)

Anyway, after much study, I incorporated very mild caster, and used NO camber. For my wide front end, long wheelbase, and loaded cargo platform, much that I read said that this could be the way to go. Some folks are hung up on this as they see visible camber on most all sport trikes they encounter, and assume it is de rigeur.  But I try to keep my designs in context and don't just blindly follow similar bikes if they aren't truly parallel to what I'm building.  In practice handling is very good.
 
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