Tilt Bed With Screw Actuator

phoenix911

Do you understand how to apply force vectors? I have to log off when I came across this, if its there when I back, I'll see what I can do, I would solve it, but i'll set it up for you to solve. . . . if it did'nt get solved aready.

phoenix911

Just out of curiosity, why don't you want to use hydraulics??

There is a reason that hydraulics are the "standard" equipment for such a task, they are simple and quite effective. Not that it can't be done as you state, it just seems more problematic to use the screw actuator.

Well if the max load is 900lb its probably just a small tilt-bed trailer. In which case its probably much easier to find electrical power (aka truck's 12v system) than it is to find hydraulic power. With hydraulic power you would need a pump, reservoir, valves, filter, etc. I'm guessing the added cost is what is stopping the use of hydraulics despite the fact that they are generally superior in uses like this.

I would help you figure out the force required but I really can't understand the picture. Get a clearer picture and you might find more help.

here is a link to a pdf of that drawing,

http://www.mwt.net/~spyder/C15061_00-00.pdf

Joe

In actuality the screw is a lot less trouble than all the hydraulics involved. in addition, less than 50% of the cost of a similar hydraulic system.

We think we have the load figured out. but wanted to try here for a blind test to see if the numbrs we came up with match what someone else does. Then for sure we will know if we are close or not.

Thanks everyone ..

I just naturally lean towards hydraulics for similar applications, I like the precise control and available power. I agree that a hydraulic system would cost more up front, but as the saying goes "you get what you pay for".

I'll be the first to admit I'm biased, as I design and build hydraulic systems for a living.

I can`t tell where the two attachment points are, where is the CG of load. that picture makes no sense to me.

The Piviot Point is at the lower left,

the bottom of the screw is at the lower right,

the attachment point is of course under the top bed via the angled line that is the path/angle of the screw.

I take it there is another pivot attaching the end of the screw actuator to the bottom of the bed...

Yes, the lower right is the lower attachment point of the screw, and it slopes up and left till it hits the underside of the bed.

Then at the lower left is the piviot point.

Thanks For Trying.

Joe

If you want help instead of posting up the same picture why don't you draw up a *good* diagram of what you have where can see all attachment points, dimensions, and geometry.

I hope I understood your drawing the right way, please correct if necessary following sketch:

In the assumption that the drawing is correct you can use following equations to determine your loads at every position of the bed. You should verify if the actuator has the right stability at ALL positions. Definitions for the equations are:

A= tilting angle from initial position considered horizontal

B= angle P-O1-O2 measured in O1 = A+Ao

Ao= angle P-O1-O2 in initial position = 32.78°

D= angle P-O2-O1 in initial position = 21°

Point "P" describes a circle with the radius "r" = 21.769

load is always vertical ( I assume) = 900 at b= 53.407

a= on the vertical distance point of load application to rotating center = 11.787

c= distance between rotating points= 49.007

La= actuator length=( r^2+c^2-2*r*c*Cos(B))^0.5

e = distance load to rotating center = b*Cos(B)-a*sin(B)

D= asin(sin(B)*r/La)

e'= lever arm of actuator = c*sin(D)

Force on actuator= N= F*e/e'

For A=0° the maximal force is Nmax= 2737

It is as mentioned above never the less important to verify that for all length the load is not over the stability limit considering a safety factor which I would estimate around 2...3.

In above computation the weight of the bed structure was NOT considered. you can implement after you define the weight and the COG position and use same approach with a different "r" and Ao and sum the loading moment to F*e.

If you need other explanations you will be welcome.

The equations you can use easily in a spread sheet as EXCEL or open office.