[bubblefat]

maybe you could treat it as an exhaust stroke so the presure in the cylinder would be even throughout the stroke.

 

[MichaelDelaney]

more info...

another way to do it is to find the angle formed by the position of the crankshaft throw relative to TDC as shown here:

instead of the rod to crank angle.

here's the way this fella did it:

BTW there are some nice Max. Piston Speed Calculators that do this all for you and graphs the piston speeds across each crankshaft degree...

the actual formulae are:

Mean Piston Speed (ft. per min.) = 0.166 x RPM x Stroke (in in.)

Max. Piston Acceleration (in ft. per min. squared)

= ([RPM exp 2 ] x Stroke (in.) ) x ( 1 + [ 1 / (2 x Rod Ratio) ] )

(remember in algebra you do the calculation inside each bracket first and you have to convert mm to in. where 1 in. = 25.4 mm )



We had a nice application of this math in this thread on TI.net.

 

[Jacksont001]

Mike,
piston speed at any given point along it's path can be calculated as below:

plug in the numbers and you'll be rocking.

since the Peak speed of the piston alway occurs when the rod has just passed tangency (is that a word?) with the crank, you can figure out that angle for whatever you are running with this formula:

BTW correct me if I'm wrong, it's been a while since I was in highschool.

 

[TheGSRGuy]

Mike -- did I approach this correctly then? Or was I way off?

I was somewhat confused because you didn't specify any numbers. Did you just want the formula?

 

[MichaelDelaney]

Naw...I just wanted people to think and exercise their brain...you know : go for a jog, pump some weights, get on the bike, circuit train,...except it's the brain this time not the body...

 

[MichaelDelaney]

radians...can we convert that to crankshaft degrees?

remind what atan is again?

yeah it's been awhile since I was in high school too. LOL

 

[TheGSRGuy]

I think I sufficiently completed that task....not bad for an 18-year old college kid with a bit of a hangover IMHO.

 

[Jacksont001]

atan is 1/tangent

I though radian would be more fun than degrees J/K
actually it is the preferred unit of measure in trig when you are refering to something travelling in a circle, rather than describing the angle between two lines.
here is a more correct explaination

360° is equal to 2(pi) radians, so a radian is equal to 180° / (pi), or 57. 29577951°/radian.