# Automotive Calculate the position for a linear acutator

1. Mar 6, 2017

### Apple&Orange

Hi everyone!

So I'm working on project where I have to design a hinge system for a hard lid that is fitted onto the back of a pickup truck.
In this system, I will be using 2x linear actuator(s) that will need to lift a total weight of roughly 95kg.
At the moment, I've got a selection of 600N, 900N, and 1200N single actuators to choose from.

In the past, I would figure the ideal position for the actuator via experimentation. However, I would like to tackle this problem through a more calculative approach. Having said this though...it has been a while since I've done any form of engineering calculation, and would greatly appreciate it if someone could point me in the right direction.

From memory though, it seems like I would need to calculate the shear force and bending moment?

Cheers

2. Mar 11, 2017

### PF_Help_Bot

Thanks for the thread! This is an automated courtesy bump. Sorry you aren't generating responses at the moment. Do you have any further information, come to any new conclusions or is it possible to reword the post? The more details the better.

3. Mar 12, 2017

### Nidum

Just imagine that you were in the box and wanted to raise the lid . Where would be best place to push and at what angle would you push ?

4. Mar 13, 2017

### Apple&Orange

Thanks Nidum

Would the best place to push the lid be at the very end of the lid?
As for the angle, would the ideal place be perpendicular to the surface of the lid?

5. Mar 14, 2017

### Nidum

In a practical design you will probably have to come a good way back towards the hinge when actually locating the actuator but keeping the line of action of the actuator as near as possible perpendicular to lid surface is definitely a good idea .

6. Mar 14, 2017

### Apple&Orange

Hey Nidum
Thanks for the feedback. Just so I am on the right track...

From a practical point of view, it would be best to have the actuator closer to the hinge the as shown below?

I am guessing this is more practical for the following reasons:
• Less intrusive for people to load things at the back.
• Less stroke length required for the actuator.
• Less wire length required to connect the actuator to the car battery.
However, with the ideal position...

A lower force rating actuator can be used, but it turn, it has the opposite effects as having the actuator in the 'practical location'.

Would this be correct?

Additionally, I did a bit of revision regarding the physics behind this, and it seems like it has something to do with the Centre of Mass.
When the COM of the lid is the left hand side of the actuator (i.e. the ideal location), there is no opposing rotation when the person and/or the actuator attempts to lift the lid.
However, when the COM is on the right hand side of the actuator, (i.e. the practical location), there is opposing rotation, which will require more effort to lift the lid.

Is that a correct assumption to make?