Watts linkage ratios?

[rlukens]

Hello forum.
In designing my second model... a beam engine. I'm considering Watts linkage versus an external piston rod guide. I like the aesthetics of the Watts linkage, it's more "blingy". While I've found many examples of this set-up, I've found no formulae for the ratio or relationships of the actual links. Can someone enlighten me?
TIA, this forum has been most invaluable and entertaining to me.
Russ

 

[crueby]

Check this page - it tells which parts of the linkage need to be same length, etc.

https://en.wikipedia.org/wiki/Parallel_motion

 

[stragenmitsuko]

how about a paucellier-lipkin linkage instead .
https://en.wikipedia.org/wiki/Peaucellier%E2%80%93Lipkin_linkage

Don't know if it was ever used , but it does offer true straight line motion .

Just a thought ...........
http://www.homemodelenginemachinist.com/showthread.php?t=3693&highlight=peaucellier-lipkin
Pat

 

[rlukens]

Crueby, I found that page. Took a few re-reads but I got it.
Stargen, that is blingy. I'm going to bone up on it too.

Thanks guys for your input.