02GF74
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| posted on 6/8/09 at 11:33 AM |
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Thursday's mathematical challenge.
Let's say I want to know the distance the piston has moved from TDC to when crank is 10 degrees BTDC.
Crank throw is 77.6mm, conrod length is 125.0 mm.
Well?
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SeaBass
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| posted on 6/8/09 at 11:39 AM |
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From wikipedia:
Where r is the offset from crank centreline. A is the angle and l is the length of the rod.
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AdrianH
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| posted on 6/8/09 at 11:41 AM |
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Or try this programme
http://www.myvirtualnetwork.com/mklotz/files/crod.zip
Adrian
Why do I have to make the tools to finish the job? More time then money.
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tegwin
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| posted on 6/8/09 at 11:42 AM |
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So to use that formula you would have to calculate r by using the crank displacement and the degrees rotated?
so = 13.48mm
[Edited on 6/8/09 by tegwin]
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SeaBass
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| posted on 6/8/09 at 11:45 AM |
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See the original article here...
http://en.wikipedia.org/wiki/Piston_motion_equations
r is the distance of the centre of rotation of the bottom of the rod from the crank centreline.
[Edited on 6/8/09 by SeaBass]
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SeaBass
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| posted on 6/8/09 at 11:47 AM |
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Can't get that to run properly sounds exactly what you need though.
quote:
Originally posted by AdrianH
Or try this programme
http://www.myvirtualnetwork.com/mklotz/files/crod.zip
Adrian
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tegwin
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| posted on 6/8/09 at 11:48 AM |
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quote:
Originally posted by SeaBass
See the original article here...
http://en.wikipedia.org/wiki/Piston_motion_equations
r is the distance of the centre of rotation of the bottom of the rod from the crank centreline.
[Edited on 6/8/09 by SeaBass]
Yup.. that works out to 13.48mm doesnt it?
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Would the last person who leaves the country please switch off the lights and close the door!
www.verticalhorizonsmedia.tv
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SeaBass
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| posted on 6/8/09 at 11:50 AM |
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Don't know what he means by throw @ 77.6 mm ? If thats the crank radius or diameter?
r would either be 77.6 or 38.8?
Or does he mean the piston throw is 77.6mm??
[Edited on 6/8/09 by SeaBass]
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tegwin
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| posted on 6/8/09 at 11:54 AM |
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Im confused... I give up!
My assumption for r is incorrect!
[Edited on 6/8/09 by tegwin]
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Would the last person who leaves the country please switch off the lights and close the door!
www.verticalhorizonsmedia.tv
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02GF74
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| posted on 6/8/09 at 11:56 AM |
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great, thanks.
i worked it out as 0.8 mm; wiki link formula is 0.77 mm so good enough-ish.
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02GF74
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| posted on 6/8/09 at 12:01 PM |
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quote:
Originally posted by SeaBass
Don't know what he means by throw @ 77.6 mm ?
ok, got that bit wrong - 2 x crank throw = stroke.... whcih would explain the 13 mm answers.
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matt_claydon
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| posted on 6/8/09 at 12:02 PM |
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r (crank radius) is half the stroke, simple.
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Project7
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| posted on 6/8/09 at 12:03 PM |
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quote:
Originally posted by 02GF74
great, thanks.
i worked it out as 0.8 mm; wiki link formula is 0.77 mm so good enough-ish.
You would be correct i worked it out at 0.7712mm - using AutoCAD
[Edited on 6/8/09 by Project7]
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mad4x4
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| posted on 6/8/09 at 12:14 PM |
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Used to do that sort of thing in Higer Teccy
Using Autocad I get 1.89mm
[img]c:\2009-08-06_131408.jpg[/img]
[Edited on 6/808/09 by mad4x4]
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MikeRJ
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| posted on 6/8/09 at 12:35 PM |
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I work it out to be 0.7712mm from using the sin rule.
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Liam
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| posted on 6/8/09 at 01:15 PM |
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0.7712mm here too from excel assuming 77.6 is the stroke (which sounds typical for a car engine). Here's the whole mess (with a few more
brackets than are probably needed just to be safe (a bit like this post  ))...
((77.6/2)+125)-(((77.6/2)*COS(10*(PI()/180)))+SQRT(125^2-((77.6/2)^2*SIN(10*(PI()/180))^2)))
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Liam
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| posted on 6/8/09 at 01:17 PM |
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Mike - would this equation also apply to the conrod in your avatar?
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MikeRJ
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| posted on 6/8/09 at 01:36 PM |
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quote:
Originally posted by Liam
Mike - would this equation also apply to the conrod in your avatar?
That is an unsolvable equation...unless you have a full wallet 
[Edited on 6/8/09 by MikeRJ]
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