Originally Posted by
Grumph
Stephen.....you've gone a bit too inscrutable...spell out exactly what you're getting at please. Motor swapping from one frame type to another has been done since the Hildebrand and Wolfmuller first came on the market. The practicalities of it mean that until it's done and tested the average Joe won't know if the vibes are better or worse until he tries it. If you have access to massive computer capacity and the time by all means simulate it for us.....in the meantime, adjusting the balance factor until the PERCEIVED vibration is acceptable works for me....
Tying a motor in to a frame with a larger than normal number of mounts will all else being equal raise the resonant frequency of the whole thing...whether this actually helps reduce perceived vibration or the opposite depends on many things, most of which the builder can't change...One guy here with a BSA twin read some theory on the net and turned out with what looked like an Americas Cup keel on the underside of his motor - reckoned it was smoother....but he would say that wouldn't he.
Sorry just seemed to me I was wasting my time replying , It may not have been a very well thought out reply , but its 90% there!
The second post was just a post to get people to think about a manufacturers view point if you can eliminate a part through design then you will save money such as on the CR where the design negates separate engine mounts.
As a good guide the art is to obtain a smooth running engine one must reduce or neutralize forces and couples in order to reduce the stresses in the engine and the supports.
For a single cylinder , a guesstimate would be
unbalanced forced due to inertial forces ( and couples) such as
MR/2r = m/s where MR is the unbalanced mass moment ,m is the balanced, ( primary?)
unbalanced forces and couples due to rotational parts , rod lengths, etc ( secondary )
I was going to expand a little more on this but I don't need to as if you have a smart phone it will have a free app which measures vibration ( its quite accurate and )
but if you look at the terms in a free undamped system fn = wn/2pi=1/2pi.(K/m)^1/2 = 1/2pi.(g/x)^1/2
where k = spring stiffness of material and m is mass , and X = displacement
So by changing the stiffness or mass or by changing the displacement changes the vibrations felt
A common mod is to fill the end of the handlebar with a heavy wieght , or something similar
Lets take the "tig craft" 450 in a 125 frame, the order of magnitude of magnitude of the forces As a guesstimate
450 = 125
MR/2r " 450" = MR/2r "125" while this isn't a correct formula ( I just want to show you can estimate the order of magnitude of the change in "vibration" )
Then what do you need to change in order to "reduce " those vibrations ( I would be looking at the engine first then Engine mount design next ie as you pointed out "a mount near a mass ")
The bucket that had a broken engine mount "lost engine Vibration energy " though changing the displacement value "X"
Hope all this makes sense, at the end of the day all I am really saying is I am amazed at how many people ( not just on here ) forget to " think twice cut once " and "paper is cheap " tI disagree with the make it bigger , suck it and see , or in my experience , all costs money and as an old boss once told me " thinking doesn't cost anything "
I was stunned how much that guy spent on that CBR , when a plan written on a bit of paper would have saved all that headache.
Just my Humble opinion,tis all ,,,,
Stephen
Ps as for a powerfull computer , you dont need one , I use CAElinux on a fairly reasonable desktop , and for when I really need grunt I use Amazons elastic cloud , as a fellow KB suggested ( thanks that person)
"Look, Madame, where we live, look how we live ... look at the life we have...The Republic has forgotten us."
Reply With Quote
Bookmarks