Best Strain Gauge for Biomechanical Application?

Hi, all I am looking for suggestions of the best strain gauge or force snsor to be used in meauring the reaction force between the hand and wheelchair wheel when propelling a wheelchair. I looking for the Reaction force Ft to be meaured.

The strain gauge will be mounted in the circled points in the image below between the psuhrim and wheel. My design has 4 strain gauages at each mount.It will interface using a module with an# arduino uno or nano. All help is whelcome! :grinning:

eugo pic mount

Getting the desired force measurement from strain gauge readings in the manner suggested is probably not going to be a trivial matter.

For one, strain gauges measure strain (elongation) rather than force; translating strain measurements into a force measurement requires accurate knowledge of the mechanical properties of the system, which in the case of an item like that pictured might not be as well-defined as one might imagine. Aside from the matter of measured strains being dependent on precisely where on the structural member one chooses to take the measurement, you probably don’t have a very good handle on the precise dimensions of the structure, what it’s made of, the effects of any heat treatment (e.g. welding), work hardening, etc. All of which will factor into the relationship between force and measured strains.

Second, there are a lot more forces acting on those members than the ones indicated above. By virtue of being structurally conjoined, both the push rim and wheel rim will be taking up forces due to loading on the wheel, which of course would be dependent on the weight of the person in the chair, what direction they’re leaning, and probably even what their uncle ate for lunch last Thursday…

If the ultimate goal is to measure the tangential force applied to the pushrim, your best bet would probably be to investigate ways of modifying the structure so as to focus that force along a linear vector, allowing it it to be measured with a single, well-calibrated load cell or two. Otherwise, the risk of acute hair loss come data analysis time is likely to be quite high.

Yes the basis of this project is extremely complex, as this is a personal one I am making many simplifications and assumptions hence my force diagram.

My ultimate goal is to measure the reaction force between the hand and the wheel using load cells and force transducers. The outcome doesn’t need to be force but a value that represents the force such as voltage or resistance. How do you suggest modifying the structure to calcite this reaction force? Thanks

Good question. The first idea that comes to mind would be to extend the axle, mount the pushrim to it using a separate hub of its own, and connect the pushrim to the wheel rim through a pair of load cells such as the FX293X-100A-0100-L, one each for forward/back motion.

It might take some creativity from a fabrication standpoint, but in terms of getting the data you’re looking for, it would seem to be a much cleaner approach than trying to make sense of readings from a pile of strain gauges that are picking up all sorts of unrelated information.

Thanks sounds like a feasible good idea! The only problem that comes to mind how I can extend the axle and create the pushrims own hub. I am on a budget of £200 so creating this is seeming quite difficult.