New bike design unleashed...
- Thread starter Pslide
- Start date
pin-tube construction is term used for the "space-frame" style steel construction you see on some older motorcycles and Sunn Radical ++'s
FTW and Jimmy used it when they designed the hood, and I can certainly say that those Hood Mussels are the stiffest bikes I have ever felt. With lighter tubing (instead of leftover FBM Angel of Death parts)it would still be equally stiff yet sub 10 pounds
The weird aluminum thing is a frame for an electric MX bike that was designed by Neal Saiki from Haro. Foes has done the same sort of thing with their swingarms in the past. Lahar may be correct that the structure is sufficently triangulated as to be stiff. But cutting and chopping some straight tubing instead of the hassle of bending tubing to fit would really appeal to my laziness....
FTW and Jimmy used it when they designed the hood, and I can certainly say that those Hood Mussels are the stiffest bikes I have ever felt. With lighter tubing (instead of leftover FBM Angel of Death parts)it would still be equally stiff yet sub 10 pounds
The weird aluminum thing is a frame for an electric MX bike that was designed by Neal Saiki from Haro. Foes has done the same sort of thing with their swingarms in the past. Lahar may be correct that the structure is sufficently triangulated as to be stiff. But cutting and chopping some straight tubing instead of the hassle of bending tubing to fit would really appeal to my laziness....
Ah, I see what you're talking about. The Ducati was one of my inspirations for choosing steel, and you'd probably call that a pinned construction. And at one stage in my design, it resembled a Hood (or a Duc I'd like to think) a lot more than it does now. Inevitably, you end up using more metal in that type of straight tube to pin type of design. I think it's a heavier way to do things in steel. Sometimes all you need is a little bend to save a lot of metal.
And not to dis the design further (because I love the look of the Hood) but I think too much stiffness can be a bad thing. One of the reasons I chose steel was for compliance. Did you know that when Honda builds Moto GP style bikes they've had to actually reduce the stiffness at the headtube junction? Too stiff and the chassis can loose traction and become skittish at severe lean angles because there's not enough "give". I'd like to think it's one of the reasons Ducatis have that special "feel".
So, to make a long story short, I don't mind some compliance, so long is it's in the right place and in the right direction. For instance you want the BB and rear axle relationship very stiff for maximum power transfer and good tracking. But a little compliance in the front triangle probably doesn't hurt much... There are probably a lot of people here that would completely disagree, but that's my theory!
-Aaron
PS: Vrock - we'll see about the chain flex issue. I'll be able to build in a lot of overshoot into the shifting action and with the shifting aids on good chain rings I think it will work. Hope I don't have to eat my words!
And not to dis the design further (because I love the look of the Hood) but I think too much stiffness can be a bad thing. One of the reasons I chose steel was for compliance. Did you know that when Honda builds Moto GP style bikes they've had to actually reduce the stiffness at the headtube junction? Too stiff and the chassis can loose traction and become skittish at severe lean angles because there's not enough "give". I'd like to think it's one of the reasons Ducatis have that special "feel".
So, to make a long story short, I don't mind some compliance, so long is it's in the right place and in the right direction. For instance you want the BB and rear axle relationship very stiff for maximum power transfer and good tracking. But a little compliance in the front triangle probably doesn't hurt much... There are probably a lot of people here that would completely disagree, but that's my theory!
-Aaron
PS: Vrock - we'll see about the chain flex issue. I'll be able to build in a lot of overshoot into the shifting action and with the shifting aids on good chain rings I think it will work. Hope I don't have to eat my words!
Hey pslide, what size of shaft were you planing on making the shaft for the front shifting mech? just wondering?
I tend to leave the complicated stuff until last...so that parts not quite done. Right now I have it drawn as an 18 mm shaft (with hollow bore) running through a 7/8" steel tube w/ a fairly thick wall for strength and stiffness. It might change when I work out all of the dimensions and what's available out there...
-Aaron
-Aaron
That should work my design uses a .750 shaft that is stepped down to .500 made out of 4130 solid bar drilled and tapped both end idler side preloads the bearings, the non drive side adjusts the chain line
OG - Sorry if I flaked it, but I didn't even realize you were working on something... Got any pics? Is there a thread out there somewhere with it?
I absolutely love seeing home designed stuff. I wish I had the skills to do what you have done.
One question though. As the shock goes through its travel, will the link extend down such that it could present a clearance problem going over say a downed log?
One question though. As the shock goes through its travel, will the link extend down such that it could present a clearance problem going over say a downed log?
thaflyinfatman said:
Draw an unmitered tube, then create planes at the angles of the miters. Draw a sketch for the miter cut and you're there. The hard part is getting the distance right so the tube is exactly the right length. If, it's off, it won't assemble cleanly.
Ahh crap. I was hoping there would be a more fundamental way of doing it, so that it referenced the tube to other geometry (eg reference the down tube to the head tube) rather than having to re-calculate and re-do the miter if I wanted to change it. Bugger.buildyourown said:
This is how I do it, from the start:
I make a 2D sketch of the main tubes, including all important geometric dimensions and angles (HA, TT length, CS length, BB height, etc.). This is a constrained sketch, so you can change things and everything will rebuild around it.
Next, put in a reference plane perpindicular to the line for which you want to draw a tube on. Sketch your tube and I usually do a blind extrusion up to and through the middle of the finishing tube. There is an option box for "Merge Result", unclick it so the tubes don't become one object.
Do this for your entire frame, with all the tubes overlapped and unmerged. Then, just go through and do a extrude cuts using the existing tube sketches to delete all of the overlapping parts. Obviously, you need to apply the extrude cut to only selected items (another option) so you don't delete the primary tube, just the joining tube.
This is pretty hard to describe...hope it helps! One thing I haven't bothered with is tapering or squashing larger tubes which intersect with narrower ones so that there is no gap...it's not really necessary though, except for aesthetics.
Good luck!
-Aaron
PS - To the guy wondering about the rocker link coming down and potentially hitting objects - it's not really a problem because it is guarded by the big ring of the crankset.
I make a 2D sketch of the main tubes, including all important geometric dimensions and angles (HA, TT length, CS length, BB height, etc.). This is a constrained sketch, so you can change things and everything will rebuild around it.
Next, put in a reference plane perpindicular to the line for which you want to draw a tube on. Sketch your tube and I usually do a blind extrusion up to and through the middle of the finishing tube. There is an option box for "Merge Result", unclick it so the tubes don't become one object.
Do this for your entire frame, with all the tubes overlapped and unmerged. Then, just go through and do a extrude cuts using the existing tube sketches to delete all of the overlapping parts. Obviously, you need to apply the extrude cut to only selected items (another option) so you don't delete the primary tube, just the joining tube.
This is pretty hard to describe...hope it helps! One thing I haven't bothered with is tapering or squashing larger tubes which intersect with narrower ones so that there is no gap...it's not really necessary though, except for aesthetics.
Good luck!
-Aaron
PS - To the guy wondering about the rocker link coming down and potentially hitting objects - it's not really a problem because it is guarded by the big ring of the crankset.
Ahh sick, thanks Pslide. Yeah that's how I was hoping it could be done! Doing it with that way would be easy enough to use variable cross-section tubes too, just use the loft function and it's all good.