Calculate the position for a linear acutator

  • Context: Automotive 
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Discussion Overview

The discussion revolves around the design considerations for positioning linear actuators in a hinge system for a hard lid on a pickup truck. Participants explore the balance between practical placement and theoretical calculations related to forces and moments involved in lifting the lid.

Discussion Character

  • Exploratory
  • Technical explanation
  • Conceptual clarification
  • Debate/contested

Main Points Raised

  • One participant suggests using a calculative approach to determine the actuator's position, mentioning the need to calculate shear force and bending moment.
  • Another participant proposes imagining the action of lifting the lid to determine the best angle and position for the actuator.
  • A question is raised about whether the actuator should be placed at the end of the lid and if the angle should be perpendicular to the lid's surface.
  • It is noted that while practical design may require positioning the actuator closer to the hinge, maintaining a near-perpendicular line of action is beneficial.
  • A participant discusses the trade-offs of placing the actuator closer to the hinge, including reduced intrusion for loading, shorter stroke length, and less wiring, while also considering the implications for actuator force ratings.
  • The concept of the Centre of Mass (COM) is introduced, with a participant suggesting that the position of the COM relative to the actuator affects the effort required to lift the lid.

Areas of Agreement / Disagreement

Participants express varying views on the ideal positioning of the actuator, balancing practical considerations against theoretical implications. There is no consensus on the best approach, and the discussion remains unresolved.

Contextual Notes

Participants reference assumptions related to force distribution and the mechanics of lifting, but these assumptions are not fully explored or agreed upon. The discussion includes various perspectives on the implications of actuator placement without definitive conclusions.

Apple&Orange
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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.

upload_2017-3-7_8-32-34.png


upload_2017-3-7_8-34-6.png


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
 
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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 ?
 
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?
 
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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 .
 
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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?

upload_2017-3-15_9-21-16.png


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...

upload_2017-3-15_9-28-47.png


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?
 

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