[trikes] more suspension trike touring and testing

[Julian Edgar]

I am currently experimenting with the air springs being used as fluid
displacers. In this approach the miniature Firestone airsprings are filled
with water. The displaced water moves through tubes to an accumulator tank
where the water bears against a rubber diaphragm pressurised by air. 

This approach allows suspension interconnection and also allows damping
valves to be placed in the interconnection lines. It is very similar to the
1970s BMC Hydragas system, except using air pressure rather than nitrogen
pressure. 

Damping can be very easily driver adjusted, ride height can be easily
adjusted, and damping can be configured to remain constant in rate with
differing loads. 

I have chosen to interconnect the front wheels, reducing roll stiffness
(roll stiffness is provided only by a leading arm torsion bar) but giving
potentially soft one-wheel bump performance. When going hard, the damping is
manually adjusted upwards to provide a 'sports' suspension performance.
After experimenting with a variety of approaches, I am using simple taps in
the fluid lines to allow simultaneous adjustment of bump and rebound
damping. 

I am using commercially available accumulators, normally used on boat
pressurised water systems. In my machine the max air pressure is only 30
psi; the accumulators are rated to 120 psi. Each accumulator weighs about
400g; including water the total weight of the suspension springing/damping
system is about 3kg. 

So my system comprises two front air springs filled with water,
interconnected and then joined to a pressure tank with adjustable taps on
these interconnecting pipes. At the rear, a single accumulator tank and
displacer are used, again with an interconnecting tube with adjustable tap. 

My problems now are in getting my lash-up plumbing to seal properly, but
first results look promising. At least there are no sliding seals in this
system!


Regards,

Julian Edgar


-----Original Message-----
From: trikes-bounces at bikelist.org [mailto:trikes-bounces at bikelist.org] On
Behalf Of Colin Bryant
Sent: Friday, 1 January 2010 11:39 AM
To: trikes at bikelist.org
Subject: Re: [trikes] more suspension trike touring and testing

Hi Julian,

Are the damper seals replaceable?  If you want to stick with the 16" rear
wheel, maybe an internal hub would suite better.

 -- 
Colin Bryant
Vancouver, Canada




________________________________
From: Julian Edgar <g.edgar at bigpond.com>
To: trikes at bikelist.org
Sent: Sun, December 20, 2009 12:45:28 PM
Subject: [trikes] more suspension trike touring and testing

Hi Folks,

Went for a ride the other day on prototype suspension trike. 

A last minute change of plans (a major bushfire in the area I'd intended to
go to) meant I went straight over the Great Dividing Range on what turned
out for much of the distance to be a fire trail through a national park.
(From Hoskinstown to Braidwood, New South Wales.) 

With the longer trip in mind I was packed for 4 days of self-supported
touring, including 15 litres of water, food, spares, etc - 39kg of stuff. 

Was very tough - only about 20 kilometres for this section but very steep,
rough, and often wet and slippery dirt. Camped overnight. 

I didn't expect the road to turn out to be a fire trail (had poor map and no
phone reception for nav) and I certainly didn't expect it to be so deserted
- no one passed me for 18 hours or so. So I was a bit disconcerted by the
difficulty and lack of other people. Knowing what I now know, I would do it
again, either in the company of others or with an epirb (even a sprained
ankle would have been very dangerous). 

Blew seals in all three suspension dampers (need to do more work on the
damping) but had no punctures and no other failures. With 16 inch wheels,
the rear derailleur was at times dragging in the mud - not good. Am now
developing new damping system. 

For low qual pics taken with i-phone, see first seven pics at
http://s638.photobucket.com/albums/uu102/JulianEdgar/


Regards,

Julian Edgar


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