Start Ramps

Replies to This Discussion

Permalink Reply by Mark Gorman on December 16, 2012 at 21:37

Hey guys this plan will do your head in,  and my math was never that good, can anyone tell me , but dont you need a base measurment to get a centre point  for r = 3 m, or a distance of the line between the two elliptical r (X) to calculate the base (Y),,

So is (X)  1500mm ?? and (Y) 3000mm, i could never work out this diagram , The r =160 centre point cant work off the 150 mark ( It would have to be 140 or 160 )  Arrrrr

The r = 160 m looks a bit more of a easy drop in then Pauls :) for the oldies , i can drop into bowls, but start ramps have always freaked me out  Have some old drawings will post up this week some time that are a lot more easy then the above

LOL

Premium MemberPermalink Reply by Marek on December 17, 2012 at 17:40

Geez Mark now your making my head hurt. But from what I can tell it is likely a typo or a missing decimal point in the 160, ie its really 1.60 mtrs. And I think that is just the radius of the circle if that curve was continued for a full 360 deg. A radius of 160 mtrs would be effectively flat (much easier for us with ramp nerves, and I can't drop into a bowl).

So even though that diagram doesn't look it. It would be tighter over the top and gentler coming out the bottom.

ASRA AdminPermalink Reply by bernie on December 17, 2012 at 18:06

The decimal points are there, but they are really really hard to see.

Height is 1.5m, so radii would have to be 1.6m, and 3m.

That would give a fast short kick from the top, and a manageable transition to the road at the bottom.

Of course I could be wrong.....

PC has been building bigger and better ramps, so this could actually be the design for his latest 150 metre high "warp-drive special" ramp, for when the "road to nowhere" is opened to traffic at freeway speeds!

Permalink Reply by Mark Gorman on December 17, 2012 at 20:26

 I could tell it was 1.6 m or 160mm ,, But R = 160mm is wrong at the centre point shown, The centre point for R to = 160 would have to be at -10  You can do it at R160 from the centre point shown and have a unknown freehand flatish trasition to the top of the start ramp, but it looks nothing like there diagram, Have a go at drawing a R160 from  a 150 centre point to meet at a height of 150 

.I will post some  Drawings this week i have rm some place of a ramp that anyone can use basic 1,2,4 triangulation to get a perfect outline for a cut, no freehand dodgey flat transitions and crazy bullshit math that dont add up :)  

ASRA AdminPermalink Reply by Bugs on December 17, 2012 at 21:58

I think the way PC designed his ramps is so that the top radius meets the bottom radius when they're both at a 45 degree angle. He's then experimented with adding a straight section of ramp at 45 degrees between the two radii to effectively add height (and length) to the whole thing.

But there's no reason (?) the two radii couldn't meet at a different angle - even 90 degrees (ie vertical). If they did meet at vert then adding a straight section between the radii would be creating some free-fall. I think that ultimately it wouldn't matter too much how steep that straight section was as long as the bottom radii was mellow enough to deal with the speed created by the height. The higher the ramp, the mellower the bottom radius needs to be, or else you risk face-planting the asphalt. The top radius can stay tight - rolling over is the easy part, landing on the ground right-side up is the hard part.

Permalink Reply by Mark Gorman on December 18, 2012 at 10:21

This is the 124 Triangulation Ramp

It is easy to do and reduces timber waste,and cost as you can get both sides of the ramp with one cut. Having both R the same dose have a slingshot  type feel

To use larger R is a great concept for a mellow exit but no 2 ramps would be the same as you need to have a hand drawn curve to meet the ellips of the radii , and if you dont know what you doing or have beter diagrams then above , can lead to fuck ups, ( Please post some plans if there functional )

The 124 was pushed for in the uk back in the 80s so when skaters went for country to country all the ramps would be much the same uniform standard,

Cheers

Mark 

 

Premium MemberPermalink Reply by PC on December 18, 2012 at 10:39

Just forget that diagram above all together. That's just wack.

Don't confuse yourself with all that maths either.

Best thing to do is draw your own design or copy something that works already.

Dimensions for my 915 mm high start ramp are - 2100 mm radius at base to 45 degs, with a 1000 mm radius roll over. Good for short WB boards only.

Dimensions for my 1650 mm high start ramp are - 2500 mm radius at base to 45 degs,with a 700 mm section of straight at 45 degs to meet a 1600 mm radius roll over to meet the platform.

The larger radius roll top on this 1 allows for longboards, top mount & drop thru to roll in without scraping the bottom of your deck, & get a nice clean pump thru the base radius. You don't want to be hanging up at the top of a 1650 drop.

The secret to getting a nice smooth junction where the ramp meets the road, is to design & start the cut of your base radius at 5 degrees off vertical.

The 2 to 3 layers of  7mm ply surface overlap & extend beyond this so you end up meeting the road surface at about 3 degrees. Which is nothing.

I always build modular & bolt sections together. Pull in handles, steps, all separate pieces.

The 45 deg angle is keeping with ISSA standards for slalom start ramps maximum angle.

No reason you can't make it stepper or mellower.

I'll try get my design drawings up soon.

It's all about radii & tangents. Get out the geometry kit & see what you come up with.

I just designed a 3.6 metre high roll in, not sure if I'll be building anytime soon though.

Hit me up with any questions, glad to help out.

Premium MemberPermalink Reply by PC on December 18, 2012 at 11:15

Hey Mark.

Didn't mean your diagram. Must of posted at the same time.

I was talking about the 1 at the top of the page. which would work ok I guess.

Definitely a larger radius at the base is the way to go.

Angle below 45 degrees don't give you much transition length to get a good pump through the radius.

Permalink Reply by Mark Gorman on December 18, 2012 at 11:19

Thank Paul can i stop crying now LOL :)

 

Permalink Reply by Mark Gorman on December 18, 2012 at 11:45

 Thats the best thing about Triangulation kids, you dont need a tape or to know why x = r cos(t) to find centre points for radious, a bit of string & chalk you cant go wrong.

Looking forward to seeing you drawings PC Having someone do the hard stuff makes the the final construction for  the builder a lot more simple   3.6 m  Thats huge ,i get the shakes on the 915