Leaf Suspension using Skis

[amberwolf]

I got these as a random find a few days ago:

http://www.endless-sphere.com/forums/viewtopic.php?p=306463#p306463
and took them home because I have been pondering whether sections of skis could be used as leaf springs, either single- or double-ended, for at least a trailer if not a bike or trike, for a pretty long time. It just wasnt' worth actually buying any of the sets I see at thrift stores, because they are usually either beat up pretty bad if they're in the $5 range, or else they are $15-$50, sometimes *each*.

Plus almost all of them have holes drilled thru for the boot mounts. These don't have any holes yet. And they're hot pink, if I need visibility from them for some reason. :lol:

I know they can take a lot of abuse and flex in general, as I've seen some skiers take bad flips, falls, and rolls, as well as some horrendously bad landings from jumps that started with the point of the ski and bending it up nearly into a J without breaking. Haven't actually tried bending these very far yet, because I want to preserve them for the actual experiments of suspension.

I'm thinking the first place to try them is on the kennel trailer, which would be the easiest one to modify. I'd just need to make a wooden block or bar across the center of the leaves left and right, to bolt the wheel-mount plates to. Then secure the leaves to that block, and to the trailer flatbed and/or frame.

If everything works as expected, I could then fabricate steel or aluminum parts to replace the wood, but I don't want to do all that work unless it at least seems to function as desired.

I assume I will have to fix the ends so the ski section I'd be using goes into the curve of a bow, pointed upward at the ends and down at the middle, so that the bow is in compression and acts like a spring by bowing out the curve on either side of the center while the center travels upward?

This ought to be fairly simple to do. I'm not sure if I would be better off using the thinner front end of the ski or the thicker middle or so-so rear. I am thinking that it should be the thinner part, so it has more give as a bow shape. I then could try the thicker part later as a half-leaf shape, with the axle near it's lowest end. That one I don't expect to work. The first *should* but depends on teh springiness and strength of the ski.

I'm hoping it works well enough that I can try making a leaf suspension for the rear of a bike, although I expect that could get complicated, the way I am visualizing it.


Anybody ever tried this before, with skis?

 

[Jeremy Harris]

They should work. Someone built an ultralight (aircraft) trike using skis as the landing gear springs years ago and they worked fine. My paramotor trike uses a homemade carbon fibre leaf spring and bit like a thick ski, see a pic in this thread: http://endless-sphere.com/forums/viewtopic.php?f=38&t=19614#p287261

Jeremy

 

[AussieJester]

Pretty sure otherdoc had some ski suspension on the drawing board awhile back dunno if anything came from it?


KiM

 

[docnjoj]

Good memory, AJ. I was going to use the skis as a horizontal leaf spring on the front of my old tadpole. Unfortunately for them I decided after the home made trike threw me off at 20mph and broke a bunch of ribs I would treat myself to a storebought trike. No regrets and no more broken ribs. I ain't rich but I am old!
otherDoc
Edit: There are several examples of trikes with ski leaf springs both tadpole and delta on the net.

 

[spinningmagnets]

Michael pogue drew a cad pic of an E-motorcycle with a carbon-fiber leaf spring that doubled as the rear fender...

http://endless-sphere.com/forums/viewtopic.php?f=10&t=17733&start=15#p260621

 

[AussieJester]

Leafs spring is upside down in his CAD drawing i do believe?...smaller springs should be on the outside not the inside
if they're all clamped together like he has then they would form a solid unit, if you look at any car
suspension leaf springs, shorter springs are always on the outside of the larger springs ...

KiM

 

[amberwolf]

I did some sketching while at lunch at work today, as a concept for the kennel trailer. Still thinking about this, so it could be a while before I get anything done with it. If possible I want to assemble them onto the trailer without actually drilling any holes thru them, which will weaken them. Instead I just want to clamp them down, so ignore all the bolts I drew in the sketches.

 

[docnjoj]

Hey AW. From your drawing it looks like both ends are fixed. That won't work well as a spring, particularly if they are under compression from the bend. Did I miss something? One end has to slide or be on a rotating spindle like car leafs. The trailer that was shown a while back use half leaves which would work well IMO.
otherDoc

 

[torker]

Aw, Just leave the extra length hang out the back. Maybe keep the tailgators farther back

 

[amberwolf]

HA! I actually considered that, given their color, but I don't think I can make them work the way I want if they're still the full length.

From your drawing it looks like both ends are fixed. That won't work well as a spring, particularly if they are under compression from the bend. Did I miss something? One end has to slide or be on a rotating spindle like car leafs.

Ah; I guess I am misremembering how the leaf springs worked that our shop class took apart to make the crossbow back in early highschool (which *was* like 25 years ago, and my memory isn't perfect even for yesterday!). I thought they were fixed at the ends, and the bow of the leaves simply bent upward, dimpling out the portion of the bow between the center and the ends. (kinda like the way a balloon expands the area around your finger poking it even if you restrict the expansion of all the rest of the surface). I guess not.

Well, I'll be clamping all the stuff together anyway, so maybe I'll just try it and see what happens. Wo

The trailer that was shown a while back use half leaves which would work well IMO.

I considered half-leaves, but I need to haul things like 100lb dogs, 200lbs+ of dog food, 200-300lbs of various stuff I find, etc. I'm not sure the half-leaves would survive that very long, at least with my engineering skills.

I studied the pics I could find of it and am not sure that I can do the same thing with what I have here, especially not being able to do whatever math is needed to figure out lengths, angles, etc. I might experiment with it, but I want to try the full leaf first, unless anyone here would like to help me with that math thing.

 

[texaspyro]

I guess I am misremembering how the leaf springs worked that our shop class took apart to make the crossbow back in early highschool

What! Making weapons in school!!! Go to jail, go directly to jail, throw away the key!

Ok, we made long bows in our metal shop... And every semester the principal made the standard announcement that if you brought your gun to school, stop by the office and have it locked up in his gun rack.. you can pick it up at lunch or after school. And our high school ROTC drill rifles started out as fully functioning 03A3's. Next year they took out the firing pins. Next year they brined pins into the barrel . Our rifle team shot real bullets (and we were damn good at it). And the school had a fully functioning cannon and used it at football games. See how that would go down these days. I think that they now consider asparagus spears deadly weapons. And heaven forbid... Metal Shop! We Can't Have That! You might get a paper cut drawing those plans!

 

[amberwolf]

This was rural Texas, back in the early 80s. Technically we weren't "in school" doing it, as it was after school hours, though it was using school tools/etc., with occasional guidance (don't do that, it's stupid!) from the shop teacher (and a couple of other interested parties).

It was a success, though it took 3 (sometimes four, depending on who) people to cock it. :lol: Put metal rods thru cars at close range, though accuracy sucked. Lodged a piece of rebar in a stone wall after it went thru the 1/2" plywood and the hay bale.

I'd like to say I had some hand in it, but all I did was pass parts and tools to people, as I wasn't really interested in much of the whole building things idea at the time. I did kitbash spaceship and other plastic models at the time, as well as sort of begin scratchbuilding some, but I wasnt' all that interested in functional stuff, just stuff that looked the way I wanted it to.

 

[texaspyro]

Sounds fun... perhaps you could make a dual purpose leaf spring suspension/cross bow. Useful for teaching idiot drivers about the rules of the road.

Our shop class was in a public school with about 3000 students. The standard projects you could build included the longbow or a rather formidable bowie knife. Most people chose the bow... they already had large knives (and knife sharpening lessons were a standard part of the class that you were tested on) . Dems wuz da days...

 

[amberwolf]

I'm not sure the whole school had 300 students (the entire town barely had 500 people), including K-12! Most of them got bused in from around the local area of the county just to do that many. :lol: I think the bus I often rode on had more total kids than any of my classes.

The most interesting thing we ever did as a class was to build the new Ag/FFA barn, which included cutting and stick-welding the I-beams and whatnot, and riveting in the sheetmetal covering, running the electrical/lights/etc. All doublechecked and frequently redone by the adults.

 

[will_newton]

Hey AW. From your drawing it looks like both ends are fixed. That won't work well as a spring, particularly if they are under compression from the bend. Did I miss something? One end has to slide or be on a rotating spindle like car leafs. The trailer that was shown a while back use half leaves which would work well IMO.
otherDoc

the idea of a half leaf attached at one end only is a good one, but is a ski strong enough? it reminded me of the Softride bikes that used a carbon beam suspension. http://www.softride.com/bikes/bikes/650cLE.html

the other solution would be to mold the spring yourself from carbon and epoxy. If you look up techniques for homebuilding laminated recurve archery bows, you will be seeing the fabrication of some potential leaf springs.

one more for you, snowmobile skis! mount them upside down. http://www.wahlracing.com/product.php?productid=19801

nice thread, very creative use of materials

 

[rkosiorek]

i've been looking to try and find the pictures i took of a fully suspended tadpole trike that used sections of skis as the springs for the front suspension. the guy even had a website and plans available for his design. so far no luck finding the pics though.

his front suspension had upper and lower "A" arms with short rods connecting the lower arms to a single transversly mounted leaf spring. layout was similar to a F1 car with inboard mounted suspension. he claimed to have over 1000km's of riding on the trike without suspension problems.

rick

 

[amberwolf]

That sounds reasonably doable once I get back to the cargo tadpole again. I could definitely use the pics if you do find them eventually. I'll do some web searches too, once I have time (whenever that is).

the idea of a half leaf attached at one end only is a good one, but is a ski strong enough?

That's the question, indeed. I'm pretty sure that for the trailer's own weight it'd be fine, and probalby even for most of my grocery runs. But I don't really need suspension for those things; I really need it for the dogs, and for the heavy loads (to keep the unavoidable potholes and road debris from breaking the trailer itself).

the other solution would be to mold the spring yourself from carbon and epoxy. If you look up techniques for homebuilding laminated recurve archery bows, you will be seeing the fabrication of some potential leaf springs.

Oh, I'd love to make my own, but your'e talking about spending money there, and that I don't have. Tossed-out skis, on the other hand, I can get for a few bucks at thrift stores if I wait and keep an eye out, and sometimes like these I can get them for nothing if I'm at the right place at the right time. (Or I guess I could post a wanted on Freecycle or CL, if it comes to that).

(also, besides the money, there is the adventure of repurposing! )

one more for you, snowmobile skis! mount them upside down. http://www.wahlracing.com/product.php?productid=19801

Ah, perhaps those would work but I dont' have any ready source for discarded ones.

Another potential option is snowbaords and similar, some of which appear to be made to flex significantly when necessary. But they rarely show up in thrift stores (last one I saw was $50, and in pretty poor shape externally, internal condition unknown but suspect).