I have spent a few interesting days going through the posts for building a Mini. It is nice to see an active group of creative builders and the resulting evolution of the design.

I am still developing my approach to putting it together. Today's challenge is trying to account for tire and axle deflection when attaching the steering tube to the main beam. Setting the beam level will result in an inclination when the pilot is onboard deflecting the non rigid bits. This may not be critical but I'm interested in accounting for it.

Would it be possible for someone with a relatively standard Mini to measure the ground clearance at the following locations and weights?

Three weights, empty and with two sizes of pilot

Ground clearance at the rear face of the axle
Ground clearance at the bottom edge of the front wheel (shouldn't change much as the CG is well aft)
Ground clearance at the inboard bottom edge of the rear wheel (checking for camber change)

Distance between inboard bottom edge of the rear wheels
Distance between axles (wheelbase)
Tire pressure 20 psi


Thanks for your help.

Welcome to the forum.

My yachts are all set up with my actual body weight in them prior to completely welding them up.
I feel that's the way we sail them with us on-board, so that's the way they must be setup or all your efforts are for nothing.

This low friction approach was well proven in very light wind racing conditions last month at Lefroy.
Otherwise you climb into it and it all changes. Just like if you own a truck, why on earth would you get a wheel alignment done on it without the truck in it's loaded state. I always smile when I hear truckies whingeing about their poor "tyre life" on the front steerers.


My yachts are first just tack welded together, then I load the mini with 108kgs of exercise weights to the layout of my body mass, then adjust all the parameters of ground clearance= 45mm clearance both front and rear on hard packed salt and 70mm on soft ground back and front. This is very easy to do with spacers underneath.
I usually add an extra 10mm of packer height to allow for sagging/distortion over the total width of the rear axle with the final welding process.
Even with fully welding the main chassis of the whole yacht in my really solid (75mm x 75mm x 8mm wall) jig, it still distorts sags down a bit. (This is using the process where the square tubing for the rear T frame is only cut on the top and down the 2 sides and the bottom left un-cut to keep it in position. Of course the uncut area wont shrink. Hence the sag.)

My axle camber is also done with the yacht loaded at this time too, along with the neutral toe-in/out. I have the 2 axles tack welded up into position and the wheels fitted to make sure the settings/ground clearances are correct and only then are the axles fully welded up.

If final minor adjustments are needed later after fully welding them, I shrink it back into alignment using a oxy/acetylene torch to heat it red hot and quenching it with a damp towel held over the heated area to shrink it straight. A bead of weld (if you don't have an oxy setup) will also shrink it back into position. It can then be normalized with more heat all round this area afterwards so it's not brittle. Not very often this is required if enough care is taken with the initial alignment before welding.

Welding in the correct order will also minimize distortion. Don't fully weld a complete single joint all at once, as it will shrink it a hell of a lot. On square hollow section tube weld opposite sides first and then the top where it's tacked last and that will minimize the shrinkage. Steel can shrink up to .9 to 1% and the frame will distort as you go. High yielding steels, (High tensile) will shrink much more than this.

Anyone can learn to weld in a few hours. It takes the 4 years plus, of an apprenticeship to learn how to minimize these distortions and to weld out of position well.


I run 20psi on soft ground in the barrow tyres and 35-40psi on hard packed salt.

Hope this help you. The mini's are by far my favourite form of sailing and are a hell of a lot of cheap fun.

Chook

Thanks for the welding tips. I anticipate a fair bit of experimentation on scrap before committing to something that I wish to keep.

The change in rolling radius (ground clearance 45 to 70 mm) when going from 20 to 35 psi is impressive.

My cross-member has a cut at 50 mm and extends a further 655 mm to the center-line of the wheel. The angle at the cut is 4 degrees placing the wheel center some 46 mm above the cross-member vertical center. If the 35 mm cross-member is mounted flush with the top of the 60 mm beam that itself has a 45 mm clearance below, the wheel center is 133 mm above the ground. The unladen rolling radius of a 4 X 8 wheel and tire combination is 203 mm. The 70 mm difference is split between tire and frame flex. I am looking to quantify this so that I can jig, tack and weld the frame accurately.

I chose 4 degrees camber as a starting point. The camber increase by 1 degree per 11.4 mm of frame flex.

Would you happen to know the the angle of camber as well as the ground clearance fore and aft with the seat empty?

Thanks

Where in Canada.

Select to expand quote

CGZDF said..
The change in rolling radius (ground clearance 45 to 70 mm) when going from 20 to 35 psi is impressive.

My cross-member has a cut at 50 mm and extends a further 655 mm to the center-line of the wheel. The angle at the cut is 4 degrees placing the wheel center some 46 mm above the cross-member vertical center. If the 35 mm cross-member is mounted flush with the top of the 60 mm beam that itself has a 45 mm clearance below, the wheel center is 133 mm above the ground. The unladen rolling radius of a 4 X 8 wheel and tire combination is 203 mm. The 70 mm difference is split between tire and frame flex. I am looking to quantify this so that I can jig, tack and weld the frame accurately.

I chose 4 degrees camber as a starting point. The camber increase by 1 degree per 11.4 mm of frame flex.

Would you happen to know the the angle of camber as well as the ground clearance fore and aft with the seat empty?

Thanks

I wasn't very clear CGZDF. Sorry about that......
The differences in the heights are completely different setups on the same yacht chassis, for the sailing surfaces that I use. I just change the front end and axles for the different surfaces.

I fit different rear axles and front ends to lift the yacht for more clearance on our local soft gypsum covered lake.
It gets quite boggy in places so that's why the greater ground clearance. Nothing to do with the actual tyre pressures.

The front end also has more trail for sailing on the softer soil from 10mm of trail to 40mm. (as the wheel is climbing a small hill all the time and this reduces the trail significantly.)

I'm using 1 degree of camber with me in it. It's very close to zero degrees unloaded. (0.1 degrees) Your camber difference with chassis flex is very similar to mine around the 1 degree more mark when loaded up. I also use internal 25mm x 25mm x 1.6 wall doublers inside my rear axles, as I kept bending them on our very rough surfaces. I'm too fat!!!! They are about 300mm long and start just outboard at the attachment bolt hole in the axle and extend out towards the wheel.

Next time I'm sailing I will measure the unladen static chassis height/clearance. I really don't think that it's important though. Better to set it up so it works with you in it.

I use one of these Digital protractors, almost on every job I do in my shed (not just yachts) and they are absolutely brilliant. They can be zeroed/calibrated at any angle and read to 0.1 of a degree. I just don't know how I got on without it. It even holds the reading so you can pick it up and see what the angle is. Just lift the component till the angle is correct and tack it with the welder.

If you then need too, a hit on the welding tack with a cold chisel stretches it slightly to adjust the angle to get it spot on. Or a slice with an "ultra fine" 1mm cutting disc to let it sag a little.
See the "arrowed bar graph" on the sides of the display, it tells you up or down to get it level or the degrees that you require. It automatically turns the display off after 5 mins of inactivity, to save the flat cell batteries.

This little device saves a LOT of heart ache.

From here.

http://www.ebay.com.au/itm/Digital-Bevel-Box-Inclinometer-Angle-Gauge-Meter-Protractor-360-Magnets-Base-/321664398281?hash=item4ae4b133c9:g:PQoAAMXQaBtRAkWb

From Sabydent: Where in Canada.

The forum profile is not working very well, I couldn't edit the State and Suburb.

Near Toronto, also far from the ocean and very new to this sport. I have seen your mini topics and will have another look.

Thanks

Select to expand quote

Chook2 said..

The differences in the heights are completely different setups on the same yacht chassis, for the sailing surfaces that I use. I just change the front end and axles for the different surfaces.

I fit different rear axles and front ends to lift the yacht for more clearance on our local soft gypsum covered lake.
It gets quite boggy in places so that's why the greater ground clearance. Nothing to do with the actual tyre pressures.

The front end also has more trail for sailing on the softer soil from 10mm of trail to 40mm. (as the wheel is climbing a small hill all the time and this reduces the trail significantly.)

I'm using 1 degree of camber with me in it. It's very close to zero degrees unloaded. (0.1 degrees) Your camber difference with chassis flex is very similar to mine around the 1 degree more mark when loaded up. I also use internal 25mm x 25mm x 1.6 wall doublers inside my rear axles, as I kept bending them on our very rough surfaces. I'm too fat!!!! They are about 300mm long and start just outboard at the attachment bolt hole in the axle and extend out towards the wheel.

I had a look at your Fowl-Play-another-LLM topic and now understand how how you put it together. Many interesting details, I may borrow a few of your ideas.

I think that for now I will design the rear cross-member flat and allow deflection to provide wheel camber. I am hoping that a degree will result, I am close to 100 kg so there will be some flex. As you said, I will have to test as I build. Same goes for tire deflections.

A kink in the frame will help lower the CG.

Again, thanks for the building tip. Good stuff, might be worth a topic of it's own.

Select to expand quote

CGZDF said..


I had a look at your Fowl-Play-another-LLM topic and now understand how how you put it together. Many interesting details, I may borrow a few of your ideas.

I think that for now I will design the rear cross-member flat and allow deflection to provide wheel camber. I am hoping that a degree will result, I am close to 100 kg so there will be some flex. As you said, I will have to test as I build. Same goes for tire deflections.

A kink in the frame will help lower the CG.

Again, thanks for the building tip. Good stuff, might be worth a topic of it's own.

That is what this forum is about. Lots of great designers and build information on here. They are only too happy to share ideas, or save people running into the same mistakes they have made..
It helped me out immensely when I first found out what a land yacht actually was.

The kink in the front of my mini chassis was an error originally, as I worked out the steering head angle. But the positive offshoot of it was that it lifted my steering pedals up higher from the body for my larger foot size.
It meant I could have my steering pedals right up the front, pretty close to the steering head (as I'm fairly tall 183cm) and they were then high enough to make contact with roughly the balls of my feet. Pure fluke!!!!

I use my jig to make all my font ends with this same kink now, for that reason.

You can see my latest yacht at the bottom of here.

www.seabreeze.com.au/forums/Land-Yacht-Sailing/Construction/The-evolution-of-my-Lake-Lefroy-Minis/

I'm positive the other contributors to this forum will help you out if you have any more questions as I'm relatively new to this game.

Please post some photos to let us see your construction and also your part of the world.