hey atul, hope you see the amount of welds and cutting in this project. need your help for the fabrication man...

A noob question.
Looking at the Chasis design i have a doubt. How will the engine be bolted to the chasis? There isnt any support underneath to hold the engine in place. What if the engine falls down?

But a wonderful job you are doing Sir. I respect your attitude of why not build myself!

i have not drawn the two thin members coming down from the frame, supporting the front of the engine. will draw them soon but they are not a major structural consideration.

the engine does not need tubing under the engine. it just needs to be supported on its mounting points... two in front and two at the back. the lower rear mount (the most important one) can be seen as an extension of the footpeg plate.

the front mounts only need to support the ~22kg weight of the engine in static condition and to prevent the lifting of the front of the engine under acceleration. most of the forces the engine generates around the sprocket will be absorbed by the rear mounts.

thankfully, because the rd engine is pretty smooth because of the 180 deg crank on a twin, the vibrations and the rocking couple is not a major consideration.

will draw it up tomorrow. thanks for reminding me

you are building this bike in pune??? can i get a test ride if i come once its done??? The frame is freakingly beautiful!!! What welding technique you intend using on this??

@ sling - yes baba, im keeping a watch here. dont you worry fabbing wont be an issue mind you

did some rough number counting today. and had to do the calculations thrice.

the weight of the frame including the front and rear ends, if you exclude the axles, bearings and fasteners is about 14kg!

thats less than a sbk frame and structurally, it is just as strong.
all this because the frame is triangulated in 3d.

for the welding will probably do the spotwelds on an arc welder on the jig at home. then go MIG.

but from what i am learning, it is hard to get full weld penetration in the first 15mm or so of the weld. (till the heat accumulates in the workpiece) and due to the complexity of the frame, i dont think its possible to weld more than 20mm at a stretch.
maybe will try welding at a higher amperage trying not to blow holes in the metal.

that also means there will be more heat in the work area and subsequently, more warping. which means i need to have the frame in the jig for the final welds. that would cause access problems for the welder and may result in bad welds.

under any circumstance, this frame has no gussets and only tubing to tubing joints. that means there will no be major warping by the time you finish welding. but i jig will still be needed to keep control of everything.

still looking for a way to get full weld penetration from the beginning of the weld.



and btw

jd666, thanks a ton for the r15 manual. was looking for it too long.

^^ anytime.

Brilliant effort man!! I liked the way you have brought the spring damper units close to the centre. I also liked the stiffness test result. I am absolutely a non-expert in motorcycle chassis design but I have some thoughts about the frame design.
First of all, the front wheel subframe design as everyone has pointed out seems to be heavy in nature and to get the right damping and spring rate, you would have to go with stiffer springs and dampers which will be heavier. Also, steering linkages and the issue regarding bump steer comes into the design consideration too. Is the variable rake and trail function worth all that additional dry weight? Why not have the spring/damper between the longest laterally horizontal tube on front wheel subframe and the laterally horizontal tube below the handlebar? The A arms could get a lot lighter if you do that.

good to have you in the discussion man...


the bump steer is whats causing me to take so long to come up with a design of the steering linkages. the thing i have in mind (something similar to an aircraft nosegear) will minimise bump steer.

under any circumstance, the bump steer will make itself felt only at higher steering angles and it wont matter too much as you are going too slow when your steering is turned more than ~5 deg.


the R&T control has never been done on a motorcycle and in my opinion, its worth the extra unsprung weight to investigate the system. and control over R&T is not the only reaon for choosing this arrangement. there is fork sticktion, decrease in load on the front wheel when brakes are applied, longitudinal stiffness as other issues this system overcomes.


as for your suggested position of the front suspension unit, there are two problems:
1. the suspension units i intend to use are the r15 rear suspensions with stiffer custom springs and they wont fit the space. i cant increase the spacing of the transverse tubes because that will change the suspension geometry.
2. this control of R&T needs a 'very' progressive springing, which (for now) i feel is only possible by using a linkage... and that needs space.


about the weight of tubing, i am using 3/4 inch 14 gauge(about 2.1mm) tubing. that comes to about 200 gm/ft. its very light. the fatter tubing is about 420 gm/ft.
i dont remember exactly how heavy the rd forks are but there might be a chance that this front end is equal or lesser in weight. the reason i can get away by using such tiny tubing is that i have taken care to triangulate everything in 3d.


rohit, if you can, please tell me any flaws and problem areas you see in this frame...
cheers

I would love to see some results for forces and moments at the A arm joints for lateral force on the front tire contact patch.

give me a couple of days. been taking a couple of days off.

Hey dude, I'll be in Thailand from the 21st to the 30th of November. But if you need anything from my place or need access to the cobra, feel free to drop in. Someone or the other should be there to help you out.

Hey braindead,

Are you using the Hossack Style front end for the motorbike because the design looked like Hossack. Try going to eurospares for Hossack fork details. I too am trying out a different front end.

I need help from you as to where are you fabricating the parts and what are the costs.

Please do let me know

Mayur

atulastro is helping me find the right guys for all the machining needs... cnc or otherwise.

getting hold of an arc welder to weld the jig and tack-weld the frame at home. gotta get the hands dirty.

for the fabrication, the more you let others do for you, especially welding, lesser control you have over quality and budget.

best to learn welding and do it yourself. being educated and 'understanding' welding and warpage in metal, you can do a better job than the average weld monkey you find by the road.