Ideas for steel ball detection

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mechalloy

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Hi all new here so be gentle,

We do an experiment in one of our labs that has a lot of error introduced by the students who must time a steel ball dropping in various solutions in glass tubes of various diameters. To eliminate this error we would like to create some electronic detection system that would detect the ball as it crosses a point (just after it has been release so it attains max velocity) and just before it reaches the end of the tube. We have been racking our brains trying to come up with an approach we have a few ideas but nothing that looks really promising. I would appreciate any help we could get in this matter, or ideas to pursue to achieve this.


Thanks,
Ed
 
You could use a microprocessor as the timing device, and use lasers and photo-resistors to detect were the ball was.

Just a thought....
 
Laser might work. But depending on the liquid it might not. I would think a video camera with timestamping would be best since you could just play it back in slow motion. And if it's moving really fast, a high framrate camera, though those are expensive.
 
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What is the diameter of the steel ball?

What solutions are involved? Most importantly, like dknguyen mentioned: how transparent/translucent are the solutions likely to be?

What is the diameter range of the tubes?

What is your budget?


Torben
 
I like DK's idea, that is how the Mythbusters do it. Usually have a measurement gauge and can compute cm/sec or some such. Cam speed would be an issue though.
 

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Mikebits said:
I like DK's idea, that is how the Mythbuster do it. Usually have a measurement gauge and can compute cm/sec or some such. Cam speed would be an issue though.
Click to expand...

I like that idea too, but if the solution is sufficiently opaque it might not work so well.

I was thinking about coils around the tubes, but then there's the diameter of the tubes to consider.


Torben
 
I think the original poster left out too many details to give a good answer. Maybe details will follow.
 
Torben said:
I like that idea too, but if the solution is sufficiently opaque it might not work so well.

I was thinking about coils around the tubes, but then there's the diameter of the tubes to consider.


Torben
Click to expand...


Oooooh, like a hall sensor? Good idea if you can get one sensitive enough.
 
I was thinking about coils around the tubes as well, but worried the EM might attract the steel too much. Would have to make it a really weak field.
 
The description is very vague.

- What is the ball size?
- What is the diamater of the glass tube?
- What kind of steel does the ball consist of?

According to the picture it isn't a tube, but a bottle.

The standing liquid in a bottle is never of equal temperature, not only considering height, but also concidering the air flow around the bottle which adds to errors.

So a steel ball dropped into it won't descend straight down, but also tumble sideways which will result in erroneous speed measurement.

Using soft steel (not stainless steel!) the ball can be magnetized (and maintain magetized for some months) and then use salvaged Hall sensors of a worn out DVD-burner motor drive. Depending on the magnetic field strength of the ball and the distance the sensors are arranged at the tube the position of the ball can be pinpointed.

That is a practical, cheap and accurate way.

Of course, if your budget allows you might use a high speed video camera (100,000 frames per second) which is normally used at companies developing bullet proof glass to study the destruction caused at impact and the shock wave influence.

Boncuk
 
dknguyen said:
Oooooh, like a hall sensor? Good idea if you can get one sensitive enough.
Click to expand...

Yeah, that's what I was thinking. Too many unknowns so far to really be doing anything but throwing random ideas at the wall, though.


Torben
 
According to the picture it isn't a tube, but a bottle.
Click to expand...

I did not have a clipart for a tube so I just used a bottle, just pretend the bottle is a tube. The idea was to show how one could measure speed using distance and time.

Of course, if your budget allows you might use a high speed video camera (100,000 frames per second)
Click to expand...

Since the viscosity of the solution is unknown we can only speculate on needed frame rates. Since this sounds like a college project, they may be able to access high speed cameras from another lab.

If the viscosity is high, the solution is not opaque and a cam is available I would opt for this solution as it would be the most easy way to implement. I believe in the K.I.S.S. method.
 
The simplest method would be to hack a stopwatch with start and stop buttons. Depending on the transparency of the liquid involved, you could use either optical or magnetic means of detecting the balls and triggering the stopwatch.
 
Another idea is to use a hall effect sensor to detect the ball's movement. I am working right now to have a Hall effect sensor as a sort of rotary encoder (say on a wheel).
 
Krumlink said:
Another idea is to use a hall effect sensor to detect the ball's movement. I am working right now to have a Hall effect sensor as a sort of rotary encoder (say on a wheel).
Click to expand...

Hi Krumlink,

don't you read the other replies before you post?

I described that already very clearly in mine.

Hans
 
Boncuk said:
Hi Krumlink,

don't you read the other replies before you post?

I described that already very clearly in mine.

Hans
Click to expand...

Ooh! Ooh! <Torben jumps up and down, waving his hand in the air.>

And dknguyen and I mentioned the idea (albeit briefly and in much less detail than you did, Hans) even before that.




Torben
 
If you can get a very (super high) accurate scale then the combined weight will vary with the speed of the falling ball. If the ball is falling in air it will have no effect on the combined weight, in treacle the full weight of the ball will be evident. I was going to suggest a hall effect sensor but had a quick rethink.

Mike.
 
Thanks for all the suggestions so far. Our budget is not very large so cost is an issue but I am interested in all suggestions.

More details: The liquids are all transparent. The tubes are 3' long but we only time the ball drop using 2' of the tube, the balls must reach terminal velocity before we start timing, and end timing well before the bottom. The tubes diameters are: 1/2", 1", 1.5", 2", 2.5", and 3". We currently use two ball diameters 3mm and 6mm but we can change this and they are 52100 steel and are magnetic. Anything else you may need please ask!

Thanks,
Ed
 
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