MaxTBehrens Posted October 1, 2015 Posted October 1, 2015 I've been MTB'ing for quite some time, and all bike I have ever known was a hardtail. And being considered still a green leaf by my old man, the hard-on-the-rear steed has served me well. Starting out on a 24 ton 24" mongoose working my way up to the now owned Silverback Syncra 27.5". My aim of MTB'ing is solely for fun, and the funny tan you get on you arms and legs that define a tan line. What I deem as the most fun style of riding is trails, at a place like Groenkloof. Hence the 650b wheel size suits me perfectly, no wagon-wheel 29ers nor slow-poke bumpy 26ers. At the awakening of spring I decided, after trying out and building some bikes, to upgrade my steed to a dual-suspension mid-travel 650b trail eating machine! This decision has lead me to tons of research concerning dually bikes, different types of suspension, and also to the three main problems of duallys which are brake jacking, pedal bob, and small bump compliance. Having time on my hands to kill and having a desire for creating my own things, I started learning how to use a CAD program to design, and maybe build one day, my own dual suspension frame. Starting with a few doodles I decided on a few basics, minimal chain growth, solid rear triangle, and as simple as possible. I was also playing around with the idea of having a single pivot design that pivots around your crankset. Keeping this in mind I started with Generation One. Which went well... Firstly I had NO idea how to do anything on this program, and I am still in the process of learning. I only got as far as deciding on the geometry, and molding creating some sort of tube for the seat and a odd looking head tube with bearing cups(I was quite impressed with myself there). I settled on a fair length, but on the shorter side chain stays and wheel base while maintaining a slack-ish head tube angle of 69deg, and a far reach. Soon I realized this was going nowhere extremely fast, as my geometry was well... to put it softly, absolute rubbish. Giving my impetuous design some more thought I dreamed up a chameleon styled frame that can take anything you throw at it. Any wheel size, and any travel up to 160mm, front and rear, and suiting to nearly any riding style. With that I moved on to Generation Two, which might be a tad bit better. Generation Two proved much more promising that its predecessor, and I felt I might have something good here. Being more well versed in the language and usage of the CAD program, I set out with a sketch deciding on the geometry. Sticking to the slacker head angle of now 68.5 and keeping the chainstays and wheelbase short but the reach long. I considered the change of the geometry more with the change of wheel sizes and travel when designing Gen Two This one I actually finished with a simulation of what the shock would do during the travel. As much as I liked the simplicity of the design, the angle at which the shock changes was too great, which will give poor small bump compliance and will promote bottoming out, rather than resisting it.So I finally had a design, but improvements still needed to be made. Thus I press onward to Generation Three. I threw everything I had at this model, and I toyed around a bit with the CAD program just to learn the ropes. The geometry I gave another whack and fine-tuned it even further to accommodate the changes the different wheel sizes will bring as well as the changing travel. The result was quite satisfying. To be continued...
MaxTBehrens Posted October 1, 2015 Author Posted October 1, 2015 I should maybe add how I can to the single pivot concentric to the crank axle. Well The front triangle has a narrower width but with PF30 sizing in diameter, to you insert a PF bottom bracket into the front triangle. The rear triangle has a width of 14mm on the area where the pivot is, and has a hole with also PF30 diameter sizing, in which you insert another PF bottom bracket. In between the front and rear triangles there are thrust needle bearings with a 30mm inside diameter. Placing your crankset straight through both bottom brackets and installing as one normally would, it will act as a pivot and keep everything together.
Pulse Posted October 2, 2015 Posted October 2, 2015 Hmmm... I don't know what to think about this, but will be following your adventure
MaxTBehrens Posted October 2, 2015 Author Posted October 2, 2015 I should maybe add how I can to the single pivot concentric to the crank axle. Well The front triangle has a narrower width but with PF30 sizing in diameter, to you insert a PF bottom bracket into the front triangle. The rear triangle has a width of 14mm on the area where the pivot is, and has a hole with also PF30 diameter sizing, in which you insert another PF bottom bracket. In between the front and rear triangles there are thrust needle bearings with a 30mm inside diameter. Placing your crankset straight through both bottom brackets and installing as one normally would, it will act as a pivot and keep everything together. Reason for using PF30 bottom brackets is that they are readily available, and quite easy to install
PeterF Posted October 2, 2015 Posted October 2, 2015 I think Dave Weagle pretty much solved all your concerns years ago.
Paulst12 Posted October 2, 2015 Posted October 2, 2015 Having ur rear shock placed there eliminates your water bottle attatchment?I recently built a softail. Here is the frame.
rudi-h Posted October 2, 2015 Posted October 2, 2015 cool project. just asking, how and with what are you planning on building that? looks like a too difficult geometry for steel or ally, are you thinking carbon? If so, how would you get around the issue of molds etc.?
rudi-h Posted October 2, 2015 Posted October 2, 2015 Having ur rear shock placed there eliminates your water bottle attatchment?I recently built a softail. Here is the frame. nice job! how did you get the down-tube formed, and what material is the flat section just behind the BB? That area would see quite a bit of flex in your design, is it a spring steel of some sort?
_im_from_earth Posted October 2, 2015 Posted October 2, 2015 Hey Max Nice fun journey, I hope you enjoy Just one note regarding your pivot placement is to take into account anti-squat / pro-squat. This is the biggest reason that no mainstream MFGs use concentric BB / main pivot designs. I would suggest reading up on this, how its calculated, and how it can be used in your design to ensure efficient pedalling and maintain less dynamic stability of the rider under acceleration / braking. These are probably the most important fundamentals to understand when it comes to suspension design and layout. There are plenty of resources online for these, but Tony Foale is probably the leader in this field [on the moto side of things].
MaxTBehrens Posted October 2, 2015 Author Posted October 2, 2015 Having ur rear shock placed there eliminates your water bottle attatchment?I recently built a softail. Here is the frame. Jeah, but that's gen 2. bottle mount issues are far down on the list of improvements. You have an interesting frame. Seems like it utilizes the flex of the metal?cool project. just asking, how and with what are you planning on building that? looks like a too difficult geometry for steel or ally, are you thinking carbon? If so, how would you get around the issue of molds etc.?Still deciding. The curves and shapes of the tubing doesn't have to be as it is, as long as the important things are where they should be. They can be straight, I'm' only playing around with the curves to learn how to use the CAD program.I would very much like to build such a frame in carbon. One day.
Dieter ( ͡° ͜ʖ ͡°) Posted October 2, 2015 Posted October 2, 2015 I've been MTB'ing for quite some time, and all bike I have ever known was a hardtail. And being considered still a green leaf by my old man, the hard-on-the-rear steed has served me well. Starting out on a 24 ton 24" mongoose working my way up to the now owned Silverback Syncra 27.5". My aim of MTB'ing is solely for fun, and the funny tan you get on you arms and legs that define a tan line. What I deem as the most fun style of riding is trails, at a place like Groenkloof. Hence the 650b wheel size suits me perfectly, no wagon-wheel 29ers nor slow-poke bumpy 26ers. At the awakening of spring I decided, after trying out and building some bikes, to upgrade my steed to a dual-suspension mid-travel 650b trail eating machine! This decision has lead me to tons of research concerning dually bikes, different types of suspension, and also to the three main problems of duallys which are brake jacking, pedal bob, and small bump compliance. Having time on my hands to kill and having a desire for creating my own things, I started learning how to use a CAD program to design, and maybe build one day, my own dual suspension frame. Starting with a few doodles I decided on a few basics, minimal chain growth, solid rear triangle, and as simple as possible. I was also playing around with the idea of having a single pivot design that pivots around your crankset. Keeping this in mind I started with Generation One. Which went well...Gen01 sketch.PNG Firstly I had NO idea how to do anything on this program, and I am still in the process of learning. I only got as far as deciding on the geometry, and molding creating some sort of tube for the seat and a odd looking head tube with bearing cups(I was quite impressed with myself there). I settled on a fair length, but on the shorter side chain stays and wheel base while maintaining a slack-ish head tube angle of 69deg, and a far reach. Gen01 SBs.PNG Soon I realized this was going nowhere extremely fast, as my geometry was well... to put it softly, absolute rubbish. Giving my impetuous design some more thought I dreamed up a chameleon styled frame that can take anything you throw at it. Any wheel size, and any travel up to 160mm, front and rear, and suiting to nearly any riding style. With that I moved on to Generation Two, which might be a tad bit better. Generation Two proved much more promising that its predecessor, and I felt I might have something good here. Being more well versed in the language and usage of the CAD program, I set out with a sketch deciding on the geometry. Sticking to the slacker head angle of now 68.5 and keeping the chainstays and wheelbase short but the reach long. I considered the change of the geometry more with the change of wheel sizes and travel when designing Gen TwoGen02- shape.PNG This one I actually finished with a simulation of what the shock would do during the travel. As much as I liked the simplicity of the design, the angle at which the shock changes was too great, which will give poor small bump compliance and will promote bottoming out, rather than resisting it.gen02-down.PNGgen02-Down01.PNGGen-02Down01.PNGSo I finally had a design, but improvements still needed to be made. Thus I press onward to Generation Three. I threw everything I had at this model, and I toyed around a bit with the CAD program just to learn the ropes. The geometry I gave another whack and fine-tuned it even further to accommodate the changes the different wheel sizes will bring as well as the changing travel. The result was quite satisfying. To be continued...Great job on the CAD! Are you using SW? Try 'pick up' Keyshot for your renderings No learning curve for amazing results!
MaxTBehrens Posted October 2, 2015 Author Posted October 2, 2015 Hey Max Nice fun journey, I hope you enjoy Just one note regarding your pivot placement is to take into account anti-squat / pro-squat. This is the biggest reason that no mainstream MFGs use concentric BB / main pivot designs. I would suggest reading up on this, how its calculated, and how it can be used in your design to ensure efficient pedalling and maintain less dynamic stability of the rider under acceleration / braking. These are probably the most important fundamentals to understand when it comes to suspension design and layout. There are plenty of resources online for these, but Tony Foale is probably the leader in this field [on the moto side of things].Thanx, I'll read up on it more. It's all about your center of gravity on the bike, is it not? and how it gets thrown back with acceleration and pushed forward with braking, and the effects it has on the suspension. I will look up on how it is calculated.
_im_from_earth Posted October 2, 2015 Posted October 2, 2015 Another good resource, a little long in the tooth now is this piece: http://downhill-rangers.com/frame/infos/mechanik_physik/path_analysis/Path%20Analysis.pdf
MaxTBehrens Posted October 2, 2015 Author Posted October 2, 2015 Great job on the CAD! Are you using SW? Try 'pick up' Keyshot for your renderings No learning curve for amazing results!Using the student version of inventor pro. But I also have some exposure to SW. Googles is my dear friend when it comes to an all too familiar question, "Hooowww do you do this!?". Thinking I should give google more credit...
MaxTBehrens Posted October 2, 2015 Author Posted October 2, 2015 Another good resource, a little long in the tooth now is this piece: http://downhill-rangers.com/frame/infos/mechanik_physik/path_analysis/Path%20Analysis.pdfHey, Thank you very much for this! will put it to good use.
ALLMTB Posted October 2, 2015 Posted October 2, 2015 Here is another bike which uses the BB as the pivot for the rear suspension, sortof..http://www.pinkbike.com/news/pole-rinne-yla-review-2015.html From the article:" is the heart of the bike, a concentric pivot that rotates on cartridge bearings that also double as the bottom bracket"
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