How to measure force/pressure

Thread Starter

JDR04

Joined May 5, 2011
356
Hello, I hope somebody can help me with this;

I have an electric motor for a rc boat and would like to measure just what sort of "push" power it has.

I also need to measure what force/pressure is required to push a camera shutter button down to activate the shutter.

I'd like to make it a small electronics project so any guidance or suggestions will be appreciated.

Thanks a lot.
 

WBahn

Joined Mar 31, 2012
24,970
Hello, I hope somebody can help me with this;

I have an electric motor for a rc boat and would like to measure just what sort of "push" power it has.

I also need to measure what force/pressure is required to push a camera shutter button down to activate the shutter.

I'd like to make it a small electronics project so any guidance or suggestions will be appreciated.

Thanks a lot.
The basic approach in metrology (essentially the science of measurement) is to figure out a way to convert what you want to measure into something you already know how to measure.

There are lots of ways to do this. For instance, for the boat you can tie a string from the boat to the dock and now if you can measure the tension in the string you have the thrust of the boat. So how can we measure tension in the string? We can convert that into a displacement of some kind. Perhaps put a spring between the string and the dock and measure the elongation of the spring. Or mount it using a leaf spring and measure the strain on the spring. I did this to measure model rocket engine thrust using a little jig made from small aluminum U channel from Home Depot and the sensing element stripped out of an electronic bathroom scale.

For the camera shutter you could possibly use the same rig as for the boat, if the forces are comparable. If you just want a rough number quickly then fashion a little beam that balances across a fulcrum of some kind such that the end of the beam is barely resting on the camera button. Now hang weights from the beam at some well defined position until the camera clicks. You'll want to them repeat this several times until you find a weight that never causes it to click and a weight that always causes it to click. Using the dimensions involved, you can calculate the force that was applied to the button.

If you really wanted to make this electronic, you could replace the weight with just a string that is pulled downward manually in a smooth motion until the camera clicks and then you just have to figure out how to measure the tension in a string, which we've already figured out how to do.
 

cmartinez

Joined Jan 17, 2007
6,621
Hello, I hope somebody can help me with this;

I have an electric motor for a rc boat and would like to measure just what sort of "push" power it has.

I also need to measure what force/pressure is required to push a camera shutter button down to activate the shutter.

I'd like to make it a small electronics project so any guidance or suggestions will be appreciated.

Thanks a lot.
In the past, what I've done is use a small scale with peak detection to measure said forces. In the case of the boat, I'd attach it to the scale using strings, making sure that everything is properly aligned before applying power. For the button, it would be much easier, just use a stick and use it to press the button against the scale until the camera activates.

EDIT: Bahn beat me to it... :rolleyes:
 

Thread Starter

JDR04

Joined May 5, 2011
356
Thanks folks, certainly food for thought.

Is there a type of potentiometer I could use which will be read with a microcontroller?
 

LesJones

Joined Jan 8, 2017
2,414
You can measure the voltage from the slider of any potentiometer with any microcontroller that has analogue inputs. Potentiometers can only measure position not force. Most potentiometers would not give very accurate conversion of position to voltage. Force and pressure are not the same thing. Pressure is force per unit area. The units could be pounds per square inch, grams per square centimetre or Pascals etc. You could consider using a load cell such as this one. It would probably be easier to buy a cheap digital kitchen scale.

Les.
 
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