Contact US

Log In

Come Join Us!

Are you an
Engineering professional?
Join Eng-Tips Forums!
  • Talk With Other Members
  • Be Notified Of Responses
    To Your Posts
  • Keyword Search
  • One-Click Access To Your
    Favorite Forums
  • Automated Signatures
    On Your Posts
  • Best Of All, It's Free!

*Eng-Tips's functionality depends on members receiving e-mail. By joining you are opting in to receive e-mail.

Posting Guidelines

Promoting, selling, recruiting, coursework and thesis posting is forbidden.

Students Click Here

Mechanical design/Math rotating bars

Mechanical design/Math rotating bars

Mechanical design/Math rotating bars

Hello all,

I can't find the ralation between the movement of 2 bars that go in opposite directions that I need to find for a mechanism. I need to find the distance that the bar B will travel if I pull from the hole on bar A (see image).

Thank you!

RE: Mechanical design/Math rotating bars

There are entire books on mechanical linkages.
This is simple geometry.
You are actually interested in the movement of the hole in the end of "B" aren't you?

= = = = = = = = = = = = = = = = = = = =
P.E. Metallurgy, consulting work welcomed

RE: Mechanical design/Math rotating bars

Hint: It's not a linear relationship for more than infinitesimal travel.

RE: Mechanical design/Math rotating bars

EdStainless yes I am interested in the movement in the hole in B

RE: Mechanical design/Math rotating bars

Did you have a class in trigonometry?

RE: Mechanical design/Math rotating bars

3DDave Yes

RE: Mechanical design/Math rotating bars

This is not unlike some of the mechanisms that I worked with when I was a machine designer. The primary purpose was to convert a constant input motion into a variable output motion. In fact, we patented a mechanism which we called the 'variator' that used this principle, that is a cam follower, attached to the crank arm on one rotating shaft, retained in a slot on a second crank arm attached to a parallel rotating shaft. The distance between the centerlines of the two parallel shafts determined the profile of the curve which represented the rotational speed of the output shaft relative to the rotational speed of the input shaft. Note that the length of the slot in the second arm was long enough that the shafts were able to rotate a full 360 degrees . This was used when we needed a portion of a mechanism to start slow, speed-up and then slow down again before the end of a cycle. The input shaft was driven through a single rotation clutch, which when activated only allowed the shaft to make one rotation. The clutch was cycled for each desired output cycle (I wish I had a picture).

John R. Baker, P.E. (ret)
Irvine, CA
Siemens PLM:

The secret of life is not finding someone to live with
It's finding someone you can't live without

RE: Mechanical design/Math rotating bars

You should know the distance between the pivots and the distance from the one pivot to the pin marked B. You know the angle of the slot relative to the baseline between the two pivots.

So, recalling that C^2 = A^2 + B^2 - 2 ABcos(theta) and you know C, you know A, you know theta you can calculate "B", the distance from the first pivot to the place along the slot the pin is. Knowing all three lenghts you can calculate all three angles; in this case the remaining 2 of which you are interested in only one.

Red Flag This Post

Please let us know here why this post is inappropriate. Reasons such as off-topic, duplicates, flames, illegal, vulgar, or students posting their homework.

Red Flag Submitted

Thank you for helping keep Eng-Tips Forums free from inappropriate posts.
The Eng-Tips staff will check this out and take appropriate action.

Reply To This Thread

Posting in the Eng-Tips forums is a member-only feature.

Click Here to join Eng-Tips and talk with other members! Already a Member? Login


Close Box

Join Eng-Tips® Today!

Join your peers on the Internet's largest technical engineering professional community.
It's easy to join and it's free.

Here's Why Members Love Eng-Tips Forums:

Register now while it's still free!

Already a member? Close this window and log in.

Join Us             Close