Beam Loading Question ?(I think)

[tonski]

I'd hate to make my first question such an easy one (especially that I can't find the answer to) but hopefully some of you folks can help me out.

When a load is applied to the end of the crank arm (going clockwise) which place on the whole set up would be ideal to place strain gauges? My initial thought was to place to the gauge in slot 1 (IE the beam pushes the gear around) but after looking at it I think slot 3 may be a better option?

The reason I don't just go try it: I have to glue the strain gauge and I don't want to chance messing it up when removing it.

 

[msquared48]

I'm straining to come up with the answer here...

Mike McCann
MMC Engineering

 

[COEngineeer]

I would think 1 just because 3 is closer to the arm and it stiffen your X section.

But really, if you are testing it anyway why not just fix the gear and apply load until it fails. See where the weak point is and put it there.

Never, but never question engineer's judgement

 

[desertfox]

HI Tonski

Best place is position 3, based on the assumption you load vertically through the crank passing between points 3 and 4 and that your crank is restrained from rotating, although if it could turn its pivot point would be the sprocket centre. I haved based this on the theory of:-

Strength of bolts withstanding torsion generated shear loading

This theory can be found at this link:-

http://www.roymech.co.uk/Useful_Tables/Screws/Bolted_Joint.html

Scroll down till you find the title I typed above the link.

My logic was if I can find which fixing see's the greatest load for the configuration then thats the rib to place the strain gauge in.
I assumed that fixing 3 was on the horizontal plane, if not then you need to calculate the forces in the fixings according to the link above.

Hope this helps

desertfox

 

[desertfox]

hi Tonski

Further to my original post you may wish to place a gauge at position 1 also, as I agree with the point COEngineer made about the change in section.

desertfox