Velomobil steering
 

This question is for any of the forum members.
On several velo designs they use a center pivot steering shaft/column/stick. my question is thus. Is the pivot design similar to a cv joint on a car and if so, do/are they made small enough to use in a velo design?


thank you in advance
beckie

PS: i have asked a a some what similar question in a different forumhttp://www.bikeforums.net/showthread...g-carbon-fiber

Due to the low rotational velocities involved, a constant-velocity joint design is unnecessary. A simple universal joint (cross-and-trunnion type) will be fine. They are commonly used in auto steering systems. Probably something similar to the universal joint used on (say) 1/2 inch socket wrench drives should be sufficient.

thank you
beckie

I'm pretty sure the Quest velomobiles use a plastic block for their universal joint. It's a wear-prone part. If you buy a used Quest, replace it.

http://en.velomobiel.nl/quest/img/quest_drawing.png

thank you , the pick is a huge help.

beckie

Hi,

http://www.2jsautomotive.com/wp-cont...1/CV-joint.jpg

The CV joints used in most front wheel drive cars are more complicated
than is needed, and there are no miniature versions AFAIK - there is no
suitable low power application I can think of for them to be made.

They elegantly fix problems you simply don't have with a steering joint,
e.g. the response doesn't need to be linear and the joint doesn't need
to to be able to fully rotate I assume.

Steering design is quite complicated - but I reckon go-kart designs
are probably the best place to look for relatively simple solutions.

rgds, sreten.

thank you, we will look in to go carts. we may also look in to having a local machine shop fab us one.

beckie

a rack and pinion substitute can be as simple as winding a cable up around a drum
as you turn the steering control post.
and unwind the cable to the opposite side.
, and the tie rod between the wheels controls them both

Having crashed a 3 wheel HPV in testing prior to a competition, I can also say that a center-pivot steering design with a shared center shaft going through both hubs may not be the best design for stability and intuitive feel. The front steering may need some camber and toe in adjustments for stability and straight line tracking that may not be achievable with a straight axle. Our initial design was a simple center-pivot design but with a single center horizontal axle and relatively short wheelbase. It allowed us to attack the obstacle course with greater ability to steer. Only problem was the trike was never stable going straight and extremely twitchy. One moment too long without a correction and the ride would be heading off the course. We took some time with some machining and trial-error to get the stability worked out and reach compromise.

So then would a control set up with the grips located near the wheels( like on green speed, tera trike,etc,etc) be a more pratciable design then?
regards
beckie

I'm not sure it would make a difference. Stability and steering feel have more to do with the geometry of the steering knuckles- caster, camber, offset, toe-in, etc. Velomobiles tend to have center-stick steering in order to keep the body shell narrow and the hands from interfering with the wheel wells. Un-shelled trikes can have the steering handles virtually anywhere.

The exception would be the Borealis velomobile, which is a shell placed on an ICE trike chassis:

http://velomobiles.ca/Borealis.html

http://3.bp.blogspot.com/-Z4WpycG8Za...is-cutaway.jpg

Hi,

The most critical angle is the trail, and the most often one
got wrong, as people tend to try to center the bearing over
the load of a front axle, whilst the axle should pivot forward
of the axle to give some self centering to the steering.

Only then do you look at camber and toe-in adjustments.

rgds, sreten.