I'm building a mount for a small IR sensor which will look very similar to this, minus the large camera.

enter image description here

I am wondering whether or not it would be necessary to do calculations to ensure that the structure is safe and will not collapse.

The potential problems I see are the bending moment due to the weight of the top motor. Would I calculate this and compare to the yield stresses in the bolts of the bracket? Potential buckling? Would it be worthwhile to use a software such as Ansys to run a stress simulation? The weight of the camera is very small and would not effect any calculations. I am using aluminium. Thanks


If it’s not just a hobby project, you should at least hand check the major stresses/forces.

While doing that instead of using the weight of the motor, the mass times max expected max acceleration must be considered.

Acceleration depends on your operational limit cases, I.e. drop, touchdown, or crash scenarios.

If you do not foresee any reasonable scenarios, still, you could take rough factors to weight, (the more serious it is, the higher the factor).

And finally a 1.25 or 1.5 for safety must be considered.

Without any checks, if it’s a hobby project, you can of course go ahead and experience the world, and tweak the design in time.

  • $\begingroup$ Thanks. I'm currently trying to calculate the amount of weight a set screw can take. I'm using a aluminium hub attached to a motor shaft. It is an m3 set screw. There is a weight of 4.53N which the set screw is preventing the hub from sliding down. I can't seem to find much information online about the amount of force it can take. $\endgroup$ – Yogi12 Mar 19 '18 at 22:18
  • $\begingroup$ If you really need a correct figure I’d suggest to make an experiment, applying a known force and increasing it until you notice a change in the set screw mount (unacceptable displacement or shear) $\endgroup$ – Gürkan Çetin Mar 20 '18 at 5:31

In this sport of situation requirement for stiffness tend to dominate so for any halfway acceptable design actual yield probably won't be an issue as a design which is acceptably stiff will be fairly lightly stressed.

FE analysis may help you to optimise a design but its not foolproof and you still need a reasonable degree of knowledge and experience to set up the model properly and interpret the results.

Just by eyeballing the example image I would make a couple of points.

  • The corner joints will tend to be the limiting factor, you're probably better off using short lengths of equal angle extrusion a L shaped brackets than the small blocks shown.
  • With aluminium is it generally better to bolt through with a nut and bolt then to drill and tap the aluminium itself.
  • Putting four bolts per side rather than two will greatly improve stiffness, you want to avoid putting any bending load on bolts.
  • Adjust the dimensions of the structure to keep cantilever lengths to a minimum, for a beam supported at one end only the maximum deflection is proportional to the cube of the unsupported length.

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