Custom fitting a steering damper

 

My Magna-sidecar rig needs a damper to stop a bad
steering wobble between 10 and 60 km/hr. I bought
a used damper with a 3" travel but am having
trouble fitting it to the bike. There's no place
anywhere I can find to locate it by direct attachment.

So after futzing around a while and making measurements
I came up with the idea of cables (like clutch cables).

One cable for each side. They would attach to the lower
triple clamp at a radius from the center of steering
rotation such that the stop-to-stop distance is slightly
less than the damper's travel.

The cable jackets would be anchored to the frame,
and the cables would lead to a location convenient
for mounting the damper (such as in front, between
the roll bars). Each cable would only pull, not push.

Actually my 1st idea was bare flexible braided wire
(like they use on sailboats) with pulleys. This could
present less frictional load on the steering than
the cables, but cables seem easier to locate around
obstacles such as the radiator and frame members.

ps. Another bright idea: If the cable mounting points
on the triple clamp result in too much travel,
I could "gear it down" with a pivoting rod
at the damper end. The cables would attach
to the end of the rod, with the damper fixed
to a point on the rod closer to its rotation axis.

Anyone have an opinion on this scheme? Especially
drawbacks: I'd rather find out them out now than
by accident.

TIA, SQ

 




I think this is a terrible idea, and you should go about creating an actual
mounting point on the frame.
Why do you want something so simple to turn into something so complex?
You're just asking for trouble.

--
Andrew
00 Speed Triple
00 Daytona
00 Squiddo

 

wrote:


I agree. He can buy a clamp for the fork end from a mail order catalog
and fabricating an anchor point for the frame end is no big deal.

Alternatively, there are *rotary* steering dampers that mount above
the handlebars.


Sometimes I think he's just trolling...

 


Generally speaking, you don't want to do this when you're dealing with what
essentially is a control system component (designed to alter the
differential equations that describe the system).  The mechanical slop
itself due to the cables may allow the oscillation to continue but with
reduced amplitude.

http://tinyurl.com/25hvzu5

http://library.wolfram.com/infocenter/Articles/5281/

http://en.wikipedia.org/wiki/Dashpot

You want rigid connections and no slop.

There used to be a rental/instructional plane at the airport that was
notorious because the autopilot would gently oscillate about the desired
heading at a very low frequency.  The cause was probably that the servo for
the thing was connected to aileron cables which themselves had some slop,
combined with the control law that the device used.  It would try to
initiate a gentle bank to remain on heading, but nothing would happen
because of the cable slop.  Then it would try harder.  So you got this
airplane that would bank about 5 degrees left until it overshot the heading,
then bank about five degrees right until it overshot the heading in the
other direction, then repeat.  It wasn't dangerous ... it was just annoying.

You don't want slop with a damper.

Datesfat

 

Datesfat Chicks wrote:


Other considerations aside, there would be no slop
in the system because I would tension the cables
such that they pulled slightly against each other.

SQ