**RE: Help calculating piston rod angle**

2019-09-26, 14:09 (This post was last modified: 2019-09-26, 14:31 by Philippe Hurbain.)

(2019-09-26, 13:20)N. W. Perry Wrote: Yep, that's the same selection info tool I mentioned. Trouble is, I can't figure out quite how to use its features to get the precise measurements I need, because I don't yet have all three of the points I'm interested in. Looking at my diagram, I can't just take the angle of ABC, because A and B will have moved up the Y axis to a new position, which I don't know. So the angle I need is A'B'C, and first I need to find A' (and by extension, B').Yes, you need to do a bit of trigonometry here...

Alternatively, if I knew the angle, I could get the new Y position perfectly easily by using part snapping.

We want to turn the piston arm so that its tip is at the distance between red pin and initial axis of arm (vertical here). Since I put the gear on the origin, this distance is directly pin X coordinates (13.856), but you can also derive it in the general case from LDCad measurements as sin(16.10°)*49.96. Note that the blue parts are just helpers parts to get the right measurements points.

Once we get this value, we calculate piston arm rotation angle as arcsin(13.856/60)=13.35°. Rotate the arm by this value and use snapping on red pin to correctly position the pistion arm...