Engineering Problem Help

[RyanbabZ71]

Ok we have this project to design a scale (to weigh objects 0-5 lbs to an accuracy of +/- 1 ounce) not using any commercial scale or scale parts (No springs)

 

I (my partner agreed) came up with a pretty good idea

 

Small plastic tub.  Cut a hole in the side.  Ran a plastic 90 degree piece out of the side.  Connected clear vinyl tubing to it.  First i used (Inside dia) 1/2".  Then I used 1/4".  

 

What i am doing is placing an object (heavy) into a smaller tub which is floating on the surface.  This causes the water to displace thus going into the tubing and from there we can mark off measurements of various weights we test.  

 

Well my problem is the water is barely rising up the tubing.  I need it to rise a good amount to see small changes in weight

 

Any ideas?  My brain is fried tonight and i could use any help

 

Thanks

[Jpshostr]

If you can, just place the object itself into the water.  Since you are using a tub, I assume you can't.  It appears that your small tub is way too bouyant (sp?).  Make it as small as you can, so the object just barely fits in it.  Also size the tub its floating in to just be slightly bigger, enough that water can flow around it, but no more than .25" or so.  You will want to make as much vertical displacement as you can, I'm thinking you have too much surface area, so its getting distributed out way too much.  

 

Another idea, no spring, but why not a chunk of rubber?  See how much it stretches when the weight is added.  Calibration of this would be the hardest part, but it could be done.

 

Another idea, use something like a see-saw, putting the weight on one end and on the other having a piston running into something like a syringe.  The more compression you get, the more it weighs.

[RyanbabZ71]

basically our options are beam deflection or displacement of water.

 

Beam deflection is to easy and everyone is doing it.  I wanted to do something different

 

So far the write up is good and in theory it should work.

 

I still have till april 17th at 5pm to get it working  

[Jpshostr]

I still have till april 17th at 5pm to get it working  

####, what are you so worried about?

[RyanbabZ71]

i want it done so i dont have to worry about it.  To much other stuff to work on

[ekonk]

I'm assuming the tub and the tube are both open to the atmosphere.  If that's the case, then the height of the water in both should be equal, so you wouldn't see much change.

 

My suggestion is that if the smaller tub will float level with and without the weight in it, measure the distance from the surface of the water to the bottom of the tub.  Calculate the volume of water displaced by the tub empty, and the volume displaced when loaded.  Take the difference of these two volumes, multiply it by the density of water, and you should have the mass of the weight.

[siume99]

BTW GREAT IDEA :exclaim: :exclaim: :exclaim: Hydraulics have a lot of potential in society.

 

Think CONSTANT VOLUME:

 

(looking from the top of the apparatus)  Increase the x-sectional area of where you put you "unknown weight" and decrease the diameter of the tubing.  The bigger the difference, the more accurate your scale.  Of course you still need to calculate the displaced volume and use density of water and such.    

 

I have a pic at webshots....I hope  

 

http://community.webshots.com/photo/27767223/34249254EcjKWg

 

Drop me a line if this doesn't gel with you.

[RyanbabZ71]

The link doesnt work

 

JP and I discussed a few things last night

 

I stayed up till like 2am.  I cut down (quick) a piece of styrafoam to fit inside the tank (didnt quite fit the sides to good).  I put that in there and hooked up the 1/4" tubing.  I pushed down on the styrafoam and the increase was much more than with the floating "boat" apparatus.  However to much water was getting by on the sides.  I hope a small dia tube and a better cut piece of styrafoam will work much better

[siume99]

well, try this link:

http://community.webshots.com/photo/27767223/34249254EcjKWg

[CityTruck]

Try a lighter liquid (alcohol or something) and bend the tube at a 45 degree angle instead of 90.