I cannot find where i last read a discussion on this, However.........I am setting up steering head on a new mini. I know the ideally the line through the povit should contact the ground at the same point as the wheel, (directly below the axle).


However............ Lets just say something has gone awry! How far from this point is still OK, lets say for arguements sake the wheel is forward of the pivot line by say 50mm..

Thanks
Glenn

It should still work, the weight of your machine will just be fighting your foot input to keep the wheel centred (and when you turn the front end of the yacht will lift a little). There are some other influences the machine will have when on two wheels but Im not exactly sure of these.

I'd try it and see

The larger the font wheel the less it will be affected.

The only fix i can think of at the moment is to bend the spine forward of the mast step. This should fix the "anti-castor" issue at the expense of reducing the layover angle.

My thinking is at the moment to leave it and see how much of a problem it is. then fix it if need be.

Which goes against the old moto.
"If it isn't broken..........Fix it until it is!"

IMHO front end will tend to slide over surface and not steer .
do it againsorry

Its not a huge job to fix it I think both my minis were done twice !!
I am a slow learner

Hiko said...


It can be tricky to get right here is one of mine with similar wheel its pretty close to right
Note the steering bush tube is set up a bit Some builders do this by putting a bend in the spine Hope this helps
Cheers Hiko

That answers why Chooks minis have the crank in the spine. Aha

Cheers Col

Yeh I buggered it up too.

I couldn't seem to get the 400mm size of the wheel to the right trail with 30 degrees on the steering shaft.

I spent hours drawing it out on cornflake packets to no avail.
Being worried about it, I did a cut with the cut off saw just in front of the seat mounting (3mm wide disc) to almost right through the pipe and a second cut beside it to 3/4's the way through and then bent it till they touched again.
It worked out to be 8mm of trail and 29.7 degrees on the steering shaft.

I have a template now and cut the spine at 1230mm long from the very rear, add my double ended fish mouth with the steering head already welded to it, I have the bushes fitted and use a long piece of 20mm shaft to line it up. Then I tack, true and weld it all up square.
The jig helps.

Paul, questioned my bend and said "the 30 degrees is just an indication" 25 will do, if I understood him properly? Just be certain the trail is correct.

Anyway I've stuck to the bend due to the jig being set up for it.

That would work too if there is enough clearance behind the tyre but would raise the front a little

All the mini chassis I have had input into, sit 90mm off and parallel to the ground without anyone in them.
The only exception is my blue coloured "Saline by" which I built and took to Lefroy last October which had 70mm clearance.
I cained it jumping the causeways and general belting around/racing and curved both rear axles 3mm upwards (when you remove them and put a straight edge along them) and this reduced it to 50mm clearance. It doesn't seem to sail/ handle any different than the other higher yachts I have. But does wear the tyres more due to the increased layover angle.
The only time this low clearance becomes a problem has been when I've been crossing hoons wheel tracks where they have got bogged on Pink Lake.

I was trying to get the mass down low as I was using a 6.2 mt sail.

I have left the axles curved.
On my older yacht I kept rebending them straight every time I removed them.
I got lazy and have left them and they never get any worse than the 3mm.

Personally I wouldn't lose too much sleep over the 120 mm, but I'm still pretty new to all this and don't fully understand the physics.

Hey! John,
When do you ever sail your machines??? Seems to me you've gone nuts on the building thing??? Ain't no good building and designing 'em if'n youz don't don't use 'em..
Ron

PS; I watched for the umpteenth time a movie out of the late sixties, early seventies the other night, "Zabriski Point" CA. Do it really exist? If so then there is an area there that should be looked at if it isn't already being sailed.. Bloody Good Movie as well

Grlynch, I wouldn't sweat over it at all. Have always built with a small amount of trail because when a high percentage of weight is carried on rear axle the machine will sag into perfect lead/trail when loaded. Or finish to point of being able to sit on, recline in proper position, etc. then check. Think it looks fine now. Looks good DesertYank but is definitely weak, especially if rough ground is involved. Steering head reinforcement was the first and only mod performed on my first version with the large wheels. Just on Weds. this week broke steering head on number two, lasted 10 months, but is definitely the weak point. For Springyacht I had a friend try to bend 1 3/4", 1/8" wall DOM tubing on exhaust tubing bender. Does not bend worth a darn, but was able to get enough of a crook to notch steering head directly to spine and weld solid. And yes, the bolts have broken at speed, but the setup provides just enough travel to really smooth out rough ground.

OK so the neck is broke!

Better, but still not great

If you have to cut and re-weld, you might be able to leave the fork hoop alone, and weld it to a thing-a-ma-jig like this. It will allow you to move the fork/wheel farther aft to make the lines line up



It's just a 'u' shaped thing that goes over the existing steering pivot tube on the chassis and rotates on a bolt. You get a lot more range of fore/aft adjustment for the front wheel. Set the chassis to where it's laying at the 30 degrees, line up your front wheel to meet the 30 degree line, then set the forks onto the 'u'; weld and brace.





Add the foot steer shaft and the foot pedals to it, center lined over the bolt, and you should be fine as frog's hair.