Measuring force on a working face

[shawc01]

I have been asked to design a system to measure the force being applied to the working face of a system. Basicly it is a class two lever and i want to measure the force being applied at the load point.

 

The image below shows the object where the load is being applied. The load is applied to the inner face on the left hand side.

 

 

Can someone suggest a location where I can find information on how and where to attach strain gauges to measure force on such a face?

[forufes]

simplify please.

 

i wanna help but it seems i can't without at least 5 trips to wikipedia..

[shawc01]

Ok basicly a load is being applied to the flat surface on the inside of the device on the left. The device is mounted via a pin that goes through the hollow section on the left. I need some way of placing gauges on this to measure the applied force. Any ideas?

[foodchain]

Maybe you can see if the force applied produces vibrations?

[InigoMontoya]

I'm not 100% sure I follow your description of the system in question (a free body diagram or similar would have been nice!) but...

 

If I understand you correctly, the force will be transmitted through a single pin that goes through the hole in the upper left? If so, then this sounds like a perfect application for a strainsert. I'm not sure if that's a brand name or a generic name, but a strainsert is basically a pin with strain gages built into it to measure forces placed on the pin in shear. They're pretty expensive, but they do a remarkable job if used correctly.

 

Hmmm... A bit of Googling tells me that Strainsert is a brand name. In any event...

http://www.strainsert.com/pages/load-pins-overview.php

[forufes]

i'm sorry i'm totally lost, couldn't find nor come up with anything..

 

this is the link to the image of the device you provided, in case someone else can be more useful..

 

http://www.concept2.com/us/oars/related_products/Oarlocks.asp

[InigoMontoya]

Oooooooh!

 

So what the OP wants to know is how hard his man is rowing!

 

I'm thinking that rather than track it by force at his flat surface (oar/oarlock interface), it might be a lot easier to track it by force at the oarlock/boat interface. IE, in the shaft that the oarlock slips over NOT in the oar itself.

 

Unless, that is, he's doing structural analysis on the oar?

 

Need more data!

[shawc01]

Yes it is for measuring power output in a rowing application. I am guessing the device is not going to be cheap to build (given component cost) so I wanted it to be easily transferable between boats/seats so it can be used by multiple athletes, hence using the oarlock.

 

It seems the logical point to measure force as it is the load point of the boat and hence unaffected by rigging changes. The added benefit is a rigging change can be analysed for whether it effects athletes effeciency.

 

Perhaps a redesign of the typical oarlock shape could allow force to measured more easily?

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Merged post follows:

Consecutive posts merged

 

I have quickly drawn a picture of the two parts of the system.

 

1) The top image shows the oarlock from above (the red dot represents the pivot point).

 

2) The bottom image is the oar. The yellow part sits in the oarlock with a flat surface of it against the flat surface of the oarlock.

 

Hope this helps people better understand the problem.

[InigoMontoya]

How are the triangular parts (gray stuff in top view) of the oarlock held on to the boat? It seems like some sort of load measurement in that structural element would give you a pretty damned good measurement. It's not as direct, but a bit of math will solve that problem with reasonable accuracy. If that piece could be swapped out easily....??

 

...I guess what I'm envisioning is a button load cell screwed into the end of that piece. The button could measure push/pull. Voila. THey're off the shelf and reasonably inexpensive.

 

But that approach requires that the structural element be reasonably simple to remove/replace.

[shawc01]

Several problems with that approach:

1) Hull shape differs from sat to seat within a boat and hence moving the out-rigger is not an option as a unique out-rigger is used per position.

2) Such a system would require recalibration when rigging changes are made (ie oarlock is actually able to be located anywhere between about 88cm and 82cm from the middle of the boat)

 

My original theory was that by making the force measurement at the oarlock (where the force is being appilied) there would be minimal need for calibration by the user and the oarlock can be easily transferred to other positions.

 

Any thoughts on how to strain gauge the oarlock?

[InigoMontoya]

Any thoughts on how to strain gauge the oarlock?

Well, I was thinking of using a strainsert on your vertical pin.

 

Baring that, I'm not aware of any off the shelf solution. A custom made oarlock with a button load cell embedded in it comes to mind, but obviously that's not off the shelf. Similarly, strain gages laid on the oar sound like they'd work (with some sort of calibration) but I'm gonna guess that you'll tell me different guys like different oars.

Edited October 7, 2009 by InigoMontoya