[Closed] Engineers - CAD/FEA for a complete beginner/non-engineer

I made a new linkage for my old Intense as they were no longer available.
Just used the hole centres/sizes and worked around that. Ended up with a stiffer/lighter linkage than the original 🙂
Had a lot of help with the CAD side of things from a very kind soul on here..
Old:
[img] [/img]
New:
[img] [/img]

Awesome, it's just that I want to change the design quite considerably to make it more progressive, decrease the leverage ratio and accommodate metric sizing, like Transition have done. Maybe I can get away with no doing a stress analysis? Or perhaps I can convince an engineer mate of mine in GE to do that side of it - but he does 65 odd hour weeks so I'm not so sure.

Lovely bit of work there.

FEA is probably not required. Just err on the side of caution and put some radiuses on it like Steve's linkage

make it similar, but a different shape. IE, use similar wall thickness, in similar places. If it's currently 5mm use 5 mm.

Pretty rough, but i think it'd do.

Awesome, this is giving me the confidence that I can actually pull this off. Cheers guys. Time to tear down the rear linkage this weekend.

I would like to learn some of the theoretical side as well - I figure I don't want to be 45-50 living in a world where the economy is based on bots and cottage industries. I'd like to be able to be creative outside of my work environment just to make me a little bit more able to cope with change over my lifetime.

Won't be able to put a CAT 2/3 lab in my garden shed to supplement the inevitable basic income. 😆

Tom_W1987 - Member
Maybe I can get away with no doing a stress analysis?

definitely.

To copy the basic geometry of the exisitng link you'll need a vernier for accurate measurements especially of the bearing sockets.

I'd reccomend Solidworks over Creo as its easier to learn IME. I've never used any free CAD software like Sketchup so not sure if that'd be any good.

And to get one made without the hassle of producing an engineering drawing I recommend a company called Firstcut as they take 3d CAD data and have a good website that'll give you a quote.

Got a vernier 8)

Cheers mlbaker

How would you guys go about getting the correct dimension for a one piece upper rocker link, when the original is a two piece? Measure some of the dimensions when it is on the bike?

Doubt you'll need FEA. As above, just err on the side of caution & keep an eye it; smooth radius' & don't worry too much about making it a bit bulky.
You could always do some simple hand calcs assuming each side of the rocker acts as a point loaded cantilever beam, but even doing this approximation, you'd need to know the kind of loading it'll see.
(To do FEA you'd need to understand the input forces that the link would see when the bike is being ridden & without those you'll just be pissing in the wind).

You probably need to understand the current set-up to know how you want to change it. Do you have that information? I imagine you'll need to model the rear end of the bike & look at the kinematics of that before you can change anything...I imagine it would be pretty easy to design something that completely buggers it up, if you aren't careful.

The easiest way to do it might be to come up with a rocker link with multiple hole mounting options from something like laser-cut folded steel that can just be welded into a box-section or whatever to make it rigid; like a test mule component. You can then use this to try out different mounting positions for the rocker link; presumably a multitude of holes for pivot, shock & rear-end of frame?
You could then try variations that you think will work & once you have those hole positions more or less right, design a 'finished article' from those positions & get it machined up & anodised.

It was me that did the CAD stuff for stevied's new link. It was mainly just a case of plugging in the dims that he gave me with a bit of iteration via back & forth e-mail to make sure I'd got things how he wanted it.

Have fun with it!!

You probably need to understand the current set-up to know how you want to change it. Do you have that information? I imagine you'll need to model the rear end of the bike & look at the kinematics of that before you can change anything...I imagine it would be pretty easy to design something that completely buggers it up, if you aren't careful.

I have the kinematics information from linkagedesign, I'm going to talk to the guy who runs the site about the software he's using to do the modelling. I'm not going to be making any drastic changes but I want to see if I can make the rear end more suitable to using a coil, without having to resort to loads of compression. Basically, add a little more progression at the end if I can.

And of course, adapt the bike to a metric design.

Speaking of software, I've heard of Inventor Fusion, which is free?

For 2D only, there's Draftsight, which is also free for home use.

If you were to use pirated software you must absolutely not distribute any files created with it as there's anti-piracy stuff embedded in the files, which could cause a lot of trouble if opened with a properly licensed installation.

Regarding the CAD side of things, there is a cloud based 3D CAD package that I keep meaning to try called OnShape.

You can sign-up for a free subscription that will let you have 10 private documents and unlimited public ones.
It will also run on tablets.

I really should sign up & give it a try....

Autodesk Fusion 360 is free for personal use. They have 100's of official tutorials on YT to get you going. They even had a tutorial using a swing arm for a mountain bike, I have just spent 5 minutes looking for it, but couldn't find it.

If you had a 3D printer you could print a prototype for mockup. 😉

Looking on the autodesk website, it looks like the 'free' Fusion 360 is for students; or can anyone use it? It's not like one of these bits of software where you have to prove you are a student to activate??

I found this link:

http://www.autodesk.com/products/fusion-360/students-teachers-educators

otherwise it seems to be a subscription at around £250/yr which is still pretty good value if you use it a lot.

I have a feeling the RS do a free 3D cad modeling package.

As above, I made two for my carbon frame. Didn't use FEA, just some 'better' grade of Al (and that was from ebay so could have been anything)
Not sure if the photo link works:

[img] https://richmars.smugmug.com/Hobbies/Bikes/Full-Suspension-MTB/i-wBxhFt3/A [/img]

if not try here:
[url= https://richmars.smugmug.com/Hobbies/Bikes/Full-Suspension-MTB/i-wBxhFt3/A ]link photo[/url]

Edit: and it was milled by hand, no fancy CNC.

Stumpy01 - I use Fusion 360 for personal use and have never had to pay for it. Make sure you are not signed into a Business Autodesk Account when you open it.

I would second OnShape.
I am a mechanical designer and I have used many CAD softwares (currently Catia and Inventor) for my job.
At home, I use OnShape, it is free, parametric and actually very good for part design.
I am not too keen when modelling an assembly.
All you need is a web browser, works on Windows, Mac and Linux.
There is also an iPad app.

The other half is also worth considering, what stress are you putting on the frame and the mounting points? If you are going to extend the leverage in places keep an eye out for weak spots and of course pop the warranty in the bin 😉