Guess what these are for!!!

OK Aussiejester and all. My package arrived from Tenn. We have zero snow down here, except in movies! What part of my trike are these gonna be? For Tricruiser 5.0 I hope!
otherDoc

- Novel form of suspension?

- Support for a canopy?

Da*n engineers! Yes, it will be an attempt at a front suspension. My idol, Aussie engineer Julian Edgar mentioned trying skis in his quest for a trike front suspension, but bypassed them because of length vs springrate. His trike would have to be 6 feet wide to get 1 hz he wanted. I am not so fussy! I also saw an article a while back on the successful use of skis for suspension, but now I cant find it. At the very least(if it works !) it will reduce some weight from the front and give some flex. Camber issues may be present! Another windmill joust coming up!
otherDoc

I built a paramotor trike a year or so ago using a home made carbon fibre beam rear suspension. Here's a few pics to give you an idea of what I did:



The half finished trike showing the rear spring bonded into place.




The completed trike with PPg unit fixed in place, ready to fly.




Cross section through the composite spring.


It might give you food for thought. Effectively you are building a swing axle, which is sort of OK except for it's tendency to jack the vehicle up when cornering. I raced a Clan Crusader years ago (lightweight composite monocoque sports car, based on the Hillman Imp Sport running gear). That was pretty grim when cornering hard as it had a swing axle front end. It would sail round corners with one front wheel 6" off the ground, which was a bit disconcerting. You may find that the combination of a semi swing axle and a solid central location (which a conventional swing axle doesn't have) removes much of this trait. I'd be keen to see if it works for you, as I've had it in mind to do something similar for a while, mainly as it's both nice and easy to do and fairly aerodynamically clean.

Jeremy

Cross country skis, they can be easy to break. If really old, count on the glue delaminating pretty easy. Just depends on the load, silly me I could break any ski jumping too far. If you bust these, try goodwill for downhill skis that will be stronger. Amazing how you can find skis and skates in the junk stores in warm climates.

Something like this, Doc?
http://www.maxwellrender.com/img/gallery/engineering/vehicle/pics/fumitake_suzuki01.jpg

Wow! Thanks for the response!
Jeremy: Thats moulding beyond my abilities. I may try to laminate layers with epoxy and some glass, but my plan is to make either a cross like on the bike now or try semi-leading arms and a very obtuse angle facing forward.I used to drive "vw based dune buggies" in autocross till they were banned! The swing axles were controlled by a limiter strap to prevent jacking and I may use a limiter if it seems necessary. Julian Edgar says not!

Miles: I can barely tell which is the front of that gorgeous sculpture It seems to use leading arms that look like skis with a thickened shaft at the back. Probably tooooooo sophisticated for my abilities. The 2 skis together weigh about 2.5 lbs, and my super reinforced alloy crossbar weighs 12 lbs! Ill do some crude drawings to show u all what Im thinking!
Dogman: This here is the deep South. Goodwill only has bicycles and waterskis! The waterski blanks seem way too heavy and non flex. Also these skis were 20 bucks!
OtherDoc

docnjoj said:

Also these skis were 20 bucks!

Click to expand...

And they say "EPOKE" on them. Deals don't get any better than that.

Yeah Link. Made in Norway and still have the wax on! I think carbon and glass/wood core!
otherDoc

Subscribed!! this looks very interesting Doc shall be watching closely

Best of luck

Kim

In the snowy areas, skiis are a fashion item: they get tossed almost seasonally. I've seen dumpsterloads go to the landfill.

I've been toying with making bents from em... I hadn't got a concept for shape until I saw Marty L.'s "linear". 8)

Doc, IIRC the '64 Corvair had a swing axle with transverse leafspring:
(Later years had nice lower links in the rear. )


Got Sketches?

Miles said:

Something like this, Doc?
http://www.maxwellrender.com/img/gallery/engineering/vehicle/pics/fumitake_suzuki01.jpg

Click to expand...

NICE!!!
Love the frame design !!!


Back to topic, docnjoj:
I have made several suspensions in my life but this "ski suspensions" open for me some new frontiers. Just thinking of something like double flexible wishbone front suspension. With different spring rate and dimensions it can be solved lots of problems that "conventional" design have. Bump steer, Ackerman angle change over bumps, etc...
With your post my latest vehicle idea just become past...hmm?
Even my in-hub-steer can be lighter...hmmm^n...

Let me know you ideas on ski suspensions, folks. I'll try to come up with some sketches if my life gets a little less hectic. We may have to evacuate for the da*m hurricane Gustav!!
otherDoc

docnjoj said:

Let me know you ideas on ski suspensions, folks. I'll try to come up with some sketches if my life gets a little less hectic. We may have to evacuate for the da*m hurricane Gustav!!
otherDoc

Click to expand...

Fingers crossed for you and your familiy and friends safety as far as the the hurricane situation goes Doc...thankfully im far enough south in Western Australia not to have the threat, we have handful of BIG hurricanes up North of W.A each year Thankfully down in Perth we only get the "tail end" lot of rain and 40-50knot winds. Very scary stuff them Hurricanes. Wish i had something to offer on the ski/suspension but that has totally bamboozled me i would NEVER have thought of using them...not in the least suggesting it isnt a fantastic idea either! very much look forward to the ideas you come up with Doc.

Kim

One of the best things about this forum is the great way ideas bounce around and become better than the sum of their parts.

I've seen at least one ultralight with a ski used as landing gear, by all accounts it worked well.

The really neat idea is to use TWO skis, one above the other, as a double wishbone system. This gets around the problems of a swing axle, saves the weight and complexity of a conventional double wishbone with springs system and has a great deal of elegance to boot.

Jeremy

Yes! I have given that some thought, but I first have to do some spring rate testing. Even though i wont get near the preferred 1-2 hz, I dont want to make it too stiff, although the weight savings alone might still be worth it. It would capture the axle boxes quite firmly with upper/lower "skiing" arms!
otherDoc

My experience when I built my trike semi-elliptic carbon spring was that it was easy to make the spring plenty strong enough, but hard to make it stiff enough. My first two attempts were far too soft and the final version looked ridiculously beefy just to get it to be stiff enough. One thing's for sure, it is unlikely to break, as there's enough uni carbon in the thing to hold up a small road bridge!

I found the key to getting enough stiffness, but keeping the weight (and cost of carbon fibre) down was to use a balsa wood core, pre-laminated into a curve. I wrapped that with biaxial glass, then laid up the unidirectional carbon on the top and bottom. Were I to do it again for a "proper" suspension system, then I'd be inclined to use a slighter harder wood core, as this would provide a bit more damping. As it is, the balsa works pretty well at damping that spring down, I don't think additional dampers would be needed if the thickness of core and spring rate could be adjusted to work well together.

Wood core skis may well be pretty close to what's needed already and would certainly be cheaper and quicker to build with if they can be bought at the right sort of surplus price.

I may do some more digging around to see if there's an easy way to work out the spring rate and damping coefficient for this stuff, just to save all the trial and error (and cost of wasted carbon fibre). Luckily, I still have around 80 or 90 metres of 2" unidirectional carbon left, probably enough for another couple of springs...........

Jeremy

Thats a lot of carbon! I dont believe that it would need separate "dampers" (shocks here in Americadia) cause that is usually developed in the ski chatter rate testing. The problem is that much of the flex is on the tips and tails, and that meand U need a 6foot wide trike. I will have to test sections of the skis and find the parts closest to my needs, then possibly cut and rejoin with alloy plates and epoxy/glass. I think too that breakage wont be a factor, but it will spread the load between both front wheels, approx 100 lbs per. At a 1 gravity bump, thats 200 lbs on the wheel and it could occur at the same time (speedbump). Luckily this amount of weight is easy to obtain to provide the test! Stay tuned and if I crack one, it will definitely be photographed!
otherDoc

Last year I bought new skies and they have on upper side some kind of damper. It reduces all resonant vibration that are common when you go fast downhill on ice or hard snow. It works perfect.

Jeremy Harris said:

...I found the key to getting enough stiffness, but keeping the weight (and cost of carbon fibre) down was to use a balsa wood core, pre-laminated into a curve. I wrapped that with biaxial glass, then laid up the unidirectional carbon on the top and bottom.

Click to expand...

Just to compare, It will be nice to see similar suspension with carbon wrapped around some rubber band (like 5 x 50 mm).
But carbon have "stress memory". On a plane it works only few minutes, and on the bike it will work all the time.

If carbon has "stress memory" then does that make it more prone to fracture? What about carbon bike frames??? and aircraft spars?
OtherDoc

I made an aircraft spar with unidirectional carbon spar caps once. The max stress in the carbon was very low, for the same reason as with the trike springs, as you end up using a thicker layup than is needed for strength just to get the stiffness up.

I agree that if the carbon fibre was being cycled to fairly high stress levels then it could effectively fatigue (although it's not true fatigue, but the propagation of micro-cracks from localised individual fibre failures that's the problem, I believe). If you keep the stuff working at low max stress levels, as it would for a practical road trike spring, then I'm sure it's be fine.

I like the idea of a high hysteresis elastomer layer on the outside as a high frequency vibration damper. I don't know whether or not it's be needed with a trike though, as the added mass of the wheel and upright at the end of the moment arm would lower the natural frequency a great deal.

Jeremy

Yes! I used to build model glider spars with carbon tow caps on spruce and even balsa spars and rarely cracked from flutter in a dive. They would, however crack on impact
otherDoc