Help Needed to Derive a Formula

Here' a stab (with a few gross approximations):

Static:

Torque_s = M x g x d

where M = mass of bridge.

Dynamic:

Average acceleration (lowest point to half-way up),

A = (2 x d)/(t²)

where t is the time to move.

Torque_d ≈ (d/2) x M x A

Total Torque = Torque_s + Torque_d

How does that compare with your figures?

Thanks John.

I was looking at the static case and hadn't done any calcs with the dynamic. I will absorb this and let you know.

You should consider the instant acceleration which is the secdfond derivative of the vertical coordinate z= R*cos(α) with α = ω*t. In the ascending stroke the inertial force adds to the weight.

Friction forces on the columns depend on the friction force between pin and window and thus of the vertical TOTAL load.

If the verical bearings are not preloaded only one column will take the horizontal forces. If the bearing length is small there is a force amplification since the vertical force genrates a moment with respect to the sliding bearing on the carying side.

The model you should use for the analysis is much more complex and there is a risk of blocking if not all factors have been considerd. Be VERY careful.

Best is to make the full model for computation and show it for comments and corrections if required.

Nickname,

Thanks. I am starting to understand why my formulas didn't make any sense.

Hello, ddk, What your got there is called a Scotch yoke. These links may or may not help but may give you some insight.

K-MODDL great graphics D08 looks like what you want to do.

Scotch yoke

Piston motion equations

and Prototype Fish Robot has a formula that may be the best fit for you to figure out your project. Unlike the piston driving crank.

Thanks. Some good sites

Free Body Diagrams...

One part at a time...

Slow and steady takes the race...

Measure twice, cut once...

Double check each step before moving to the next free body diagram...

Might be an idea to have a look at the cranking moment on the lineal bearing, while you're there.

thanks,

We're looking at longer bearings for to ensure parallelism.