Frame Design

The thing I run into is you can't add compression damping to aid with bottom out without negatively impacting small bump. You could have a high shaft speed because you hucked it to flat or a high shaft speed because you're flying over roots. The shock knows no different. With something pretty linear it's hard, or in some cases impossible, to strike a balance between the two.

Thats why I'm confused that position sensitive damping isn't really a thing in mountain biking. I guess HBO is becoming mainstream now. 

If you have a progressive leverage curve you effectively get position sensitive damping as you'd feel it at the wheel. HBO makes a ton of sense beyond that when you look at rebound speeds too.

Any amount of progression will do it. The million Dollar question is what's the optimal amount? Damping force produced by the shock is proportional to shaft speed. Shaft speed is wheel speed (in terms of displacement from an impact) divided by the leverage ratio. Then damping force as you feel it at the wheel is damping force at the shock divided by leverage ratio. So damping force as you feel it at the wheel is inversely proportional to the leverage ratio squared. Interestingly, this means a perfectly linear (in the sense of in the from mx+b) leverage curve does not cause the damping to ramp linearly through travel. A slightly concave leverage curve, on the other hand, creates a linear ramp in damping force. Below is an arbitrary example where the initial leverage ratio is 3 and the final leverage ratio is 2. Damping factor is normalized to 1 at shock stroke=0.

I guess no one has experience with Marino frames around here....

Are there any designers here that would like to help me with a project in fusion? Front triangles are fine, but getting the rear triangles working is a whole other thing and I'm suffering, I'm not entirely sure I have the skills for this stuff. 

I locked in.

Changes may be made in future (so that it doesn't need to be made from one colossal block of Aluminium)

Why a machined chainstay vs tube and machined bits?

Easier to clear the tyre and crank like this. 

Next model I work on I'm doing the rear end first and working back to front. It seems like a sensible idea.

Watch this space. In a few years you'll see this bad boy on bike of the day!

Is it a high pivot? Looks like it, but there’s no idler…

There's a hole to mount one... 

Yea, there's a hole for one to mount to, but I never got round to actually modelling the pulley wheel. I was just gonna buy a jank components x-sync chainring thingy for it, cause my brother can get me them cheap.

I've just designed a simpler version of the concept too, designed to be made from 3dp steel as it's more accessible to me than machined alloy. 

It's got a yoke to reduce the eye to eye, it either does 225x75 203mm Mx or 205x65 180mm 29"/Mx. I wanted to do the 6-bar, but the machining on the links would cost a load of money so I've kept it cheap to print, with only the rocker needing machining.

You can see the hole I've made for the idler in this pic of the main pivot section.

Horst link with an idler? I-Track will have their lawyer send you a passive-agressive letter. 

Do they care that much about one-offs? I'm not trying to start a brand hahaha

Yes

I'll send them a letter back telling them I look forward to cooperating with them when I intend to take the bike to market, which is never. If they want to get between me and my hobby I'm more than happy just ignoring them 😂

All prototype one offs not for sale ended up carrying their sticker. Apparently the letter includes that. So you're good for a one off but still expect the letter. 

If the letter has a cool I-track sticker in it I'll take it

Is it a derailment of the thread if I mention how much I hate our patent system, both in the US and internationally? 

I've heard the pro-side of the arguement, but its aways presented as a given with no data. "But it helps the little guy" the vast majorities of patents are held by large firms, not small ones. "Patents protect you against predatory companies" it seems to me patents are wielded by companies who typically have more lawyers than engineers. "Patents are the only way to protect your ideas" patent law is enforced by judges who are not engineers. 

The "benefit" of patents is always presented as self evident, but its not. 

The benefit of patents is that you can piledrive the opposition (regardless of whether it is someone holding the patent and you want to use it or you have the patent and someone else is using it) into the ground with enough money for either lawyers, to make a deal or both. The bigger the money difference is between the sides, the more driving the pile does. 

Patents in no way protect the little guy as the little guy does not have the finances to fight infringement.

I've often heard it say to just innovate and be faster than the competition instead of dealing with patents and/or that keeping things secret (if possible) is better than patenting them which just makes things public. 

In light of the new Santa Cruz Vala and everyone hating on the single shear bolts, I will be changing some things so that I also do not have single shear bolts 🤣

There are quite a few bikes with single shear bolts, is it really such a problem? 

My friend who just recently started following this thread doesn't know what single shear bolts are. Can you help him out?

This will probably be best:

The thing is that bolts are usually used to clamp down two parts in the axis of the bolt itself. By squeezing the two parts together, enough friction is generated to prevent any movement side to side so the bolt technically shouldn't be loaded at all. If a bolt is loaded perpendicularly to the stem, it's not tightened enough or the design isn't good enough. In general. 

With mtb pivots it's a bit different, I'm quite sure the bolts are used as the load carrying elements and sized appropriately so this part goes out the window. 

Another detail about single vs double shear is, if you pull the two types apart, the double shear layout is "in balance", you have all the loads going in and out of the structure balanced across the mid plane. With a single shear layout one side is pulling above the midplane, the other on the bottom which means you also get a moment (torque) trying to twist the structure out of plane or at least bend the two plates. So besides having a single shear plane in the bolt (higher load), you also have some twisting applied to the bolt, which is a further load to it. 

In practice for bike pivots this means the frame is likely to twist more in the case of a single shear bolt if it is not made strong or stiff enough vs having a double shear layout. On the other hand it is much, MUCH easier to manufacture the parts in a way where they fit reliably. With a double shear variant (a U "cup" for the other part to slide in) you need to have the gap just wide enough for the other part to slide into, but not too wide where you're then squeezing it together too much.

EDIT: thought it through a bit more... Technically any through frame bolt, connecting both sides of the frame part (rocker, chainstay) should be considered single shear. Yeah, it's double, but it's so far apart that it doesn't really affect things. Replacing that single bolt with two separate ones won't change a thing. Qed, Santa Cruz frame pivot of the upper link. Hell a trunion shock is mounted in this way while a rocker right next to it is likely mounted with either two separate bolts (threaded into the frame) or with a through the frame bolt. Let's ignore the nuance of having a threaded part (smaller effective diameter) carrying the load vs. a threaded bolt just axialy preloading the assembly and the thicker shank of the through axle carrying the load and at the same time the nuance of how hard it is to make one or the other on the frame side (threaded holes vs. a through hole you can just ream to size) 

Where we could talk about a single shear application is a chainstay/seatstay pivot or the rocker link pivot for the seatstay where you have two separate short bolts assembling the two sides of the frame. Single shear bolts there are rare, but are also used. Commencal for example used it on V4 Meta platform. I think the biggest issues with actual single shear bolts is fixing everything in place axialy. We're talking about pivots, which means bearings, which means it can't just be clamped together like with steel plates in the ai preview above. You have to fix the bearing in place in both parts of the frame. The ID is simple, the bolt itself does this. But you also have to fix it in place on the OD. Commencal for example uses a nut with the cassette lockring interface that screws in over the bearing. The problem is you can't rely on friction of the bearing being pressed into the bore alone, you really need to fix it in place to prevent it from moving. 

Jezus the amount of rambling... 

 No, but the way I've been doing things is clearly not the way things are done in the industry, and if I want to work in the industry I'll have to adapt. It's things like having the bearing in the chainstay-seatstay pivot in the chainstay, when everyone else puts it in the seatstay. I'll probably be able to make the lugs smaller if I change that, and the more tube I get compared to lugs, the better, as the tubes are the cheap bit. 

Um... It doesn't mean the industry is doing it better the way it is or the way the industry does it that it's the best way for you and your one off prototype. Doing hundreds or thousands of frames opens up production methods that are not available to one off projects and vice versa.

When talking about Horst links, the bearings are in the seatstay because that's where the forging is for the brake mount, axle, derailleur hanger and the pivot. My Bird frame has it this way, but GFs Meta TR, which is a single pivot, has the bearing in the chainstay, again, in the dropout forging. It's not a game of where the industry puts it, it's a game of which part makes more sense to put it in. 

It made sense, as I can drop in the hardware from my Vitus now, and it's made it over 300g lighter even after adding a brake mount and shock mount. 

And then, I painted it

Definitely avoid single shear bolts as much as you can - I'm sure the vorsprung best practises document has already been mentioned here but he specifically singles them out-

8. Do not use single-shear bolts under bending loads unless absolutely necessary.
These see much higher stresses than double-shear (ie through-bolt) type loads, and are
more prone to coming loose and/or breaking, because as soon as they come loose, the
bending stresses go through the roof. Through-bolts (double shear) are much stronger
and have greater tolerance to load when loose.

If you ever have pivot bolts that work loose or wear too fast they are almost always either single shear or wildly undersized (6802 or smaller etc). This is why Trunnion bolts are prone to coming loose if they are even slightly under torqued