# Slider Crank eq. from Mark's Handbook



## BrianC (Mar 29, 2010)

Has anyone used the slider-crank equations given in Mark's Handbook? The equations are given in the Rotary and Reciprocating Elements section.

I was trying to use the slider velocity equation for problem 13 of 6MS machine design, and I can't get it to give the correct answer for the life of me. It seems that all of the variables are straight forward. I thought the equations would be quick to use for basic slider cranks, but no luck so far.

I am able to solve the problem using instantaneous centers and trig, but from I was hoping the Mark's equation would save some time. Any thoughts?


----------



## Bman (Mar 29, 2010)

I bought a cheap copy off of Amazon, but I haven't found it useful yet... I don't think I am even going to bring it with me since it is kinda bulky...


----------



## MechGuy (Mar 29, 2010)

I took a copy of Mark's with me, and it was good for all of one question on the exam. But who knows, maybe that's the one question that puts you over the top! Might be worth it...


----------



## Solar_Chris (Mar 30, 2010)

BrianC said:


> Has anyone used the slider-crank equations given in Mark's Handbook? The equations are given in the Rotary and Reciprocating Elements section.
> I was trying to use the slider velocity equation for problem 13 of 6MS machine design, and I can't get it to give the correct answer for the life of me. It seems that all of the variables are straight forward. I thought the equations would be quick to use for basic slider cranks, but no luck so far.
> 
> I am able to solve the problem using instantaneous centers and trig, but from I was hoping the Mark's equation would save some time. Any thoughts?




I believe that the solution to the slider crank problem is wrong in the 6 minute solutions book 2nd edition. It says that the arm BC rotates around its instantaneous center, point C with the same angular velocity as the crank. That is a FALSE statement. If that were true then the distance from point B to Point C would always be the same as the crank arm since point B cannot have two different velocities.

I have found so many mistakes in the 6 minute solutions for Machine Design that I double check every single solution that is presented in the book with the MERM and/or other reference materials. There are currently no Errata posted for the 2nd edition 2nd printing on PPI's website which is really bugging me.


----------



## BrianC (Mar 30, 2010)

Thanks Chris. I will have to spend some more time reviewing slider-cranks. I was able to find a simple calculator on-line that gave a result that matched Mark's equation. This makes me believe you are correct about the mistake in 6MS. Now I just have understand the details of my mistake.

Do you have a list of problems that you think may have mistakes? I will be starting the depth section of 6MS this evening.


----------



## BrianC (Mar 30, 2010)

I have found the error of my way Chris. The 6MS answer is definitely wrong. I am happy to see that proper IC technique and Mark's match up. In the end, I got ~ 6 ft/s (73 in/s) for the slider velocity.


----------

