Pong Meter

I'm pretty new to Arduino so I hope this project isn't too silly. But, I had an idea for an analog level meter using a styrofoam ball, PC fan and plastic tube.

It's still a work-in-progress. I plan to connect it tot he web and use it to visualize my web stats. But, for now this prototype is working:

http://www.youtube.com/watch?v=NKfcV2rH06k

Let me know if you have questions.

Cheers, Mike

AWESOME idea. I love it.

My only comments: Remove the tube, it won't be needed. The pingpong ball can ride an air column just fine... the column pushes the ball back to center. Remember your middle school science teachers doing this with a vacuum cleaner? If I remember right, it's bournoulli's (?sp) law in play, air rushing around the curved surface creates a pressure well or something like that; I'm sure you can find the "why" out there on these here interwebs, but skipping theory, it works in practice so the academics aren't strictly necessary.

That, and then color the balls with fluorescent paint and front-light it with either a standard black light or some high-power UV LED's.. I'm already visualizing a spectrum analyzer made with a series of these.... what's the "response time"? No matter what, the fall rate won't exceed gravity, how fast does a 0%-100%-0% cycle take?

Thanks; I really appreciate your comments. I will give it a shot without the tube and see what happens. Although I'm guessing I will still need a way to direct the air as the fan is still pretty omnidirectional.

It's hard to gauge the response time so far as I haven't quite figure out the air flow right. But, it seems to be pretty responsive on start up. It's a bit unstable right now with anything less than 100%. But, I think I just need to get the airflow right and that should help.

The ball spins at a pretty high (and consistent) rate. I wonder if there would be a way to do a led POV on the ball without adding too much weight.

Thanks again, Mike

the fan is still pretty omnidirectional.

That’s not necessarily a bad thing: the low (not really “non-”) directionality means that the pressure decreases as the ball gets farther from the fan. It’s not an inverse square, like a truly omnidirectional source, but it should decrease according to some mathematical function.

With the ball in the only-slightly-larger tube, the pressure is relatively constant until the ball reaches the top, and the leaking gets significant.

It might help to drill holes in the tube, so the higher the ball goes, the more the air leaks out.

Or it might help to set your nominal “zero” around the top of the tube. You should have a more- (but not perfectly-) directional flow coming out of the tube than out of a “naked” fan, so the change in height of the ball will be closer to a linear function of the change in fan speed.

I know this sort of thing has been done before. Some google searching might turn up some reports on their experience.

With the ball in the only-slightly-larger tube, the pressure is relatively constant until the ball reaches the top, and the leaking gets significant.

Correct, you should essentially have two levels - at the bottom and at the top. Drilling small holes at constant increments would help achieve some (albeit semi-graduated/non-linear) level control. You could also make a very shallow angle cone out of clear plastic sheet rolled up, so at the bottom it is only slightly larger than the diameter of the ball, and at the top it is maybe 1.5 or 2 times the diameter of the ball. This will give you “infinite” graduations. That is how some industrial flow meters are made. If you knew the drag characteristics of the ball, you could use your device as a flow meter! That’d be pretty neat.

Heheh.. I think I'm going to give this a try, at least a very simple version.. but on a grander scale. In the basement, I have a standard box fan (110AC), and I've got a couple of inflatable beach balls left over from the summer.. PWM to a Triac (or a pair of SCRs) for the speed control... betcha a box fan could hold a beach ball on an air column several feet high...

Heheh.. I think I'm going to give this a try, at least a very simple version.. but on a grander scale. In the basement, I have a standard box fan (110AC), and I've got a couple of inflatable beach balls left over from the summer.. PWM to a Triac (or a pair of SCRs) for the speed control... betcha a box fan could hold a beach ball on an air column several feet high...

I'd love to see that!

I've seen those balancing footballs at science museums. They're pretty cool.

I might try this too. ;)

Very cool project. What kind of control algorithm are you using? It would seem to me to be a cool application to try and play around with a PID algorithm. I might just have to try and build one myself. Are you actually sensing the height of the ball (level feedback) or just using open loop control (variable motor speed only)?

Lefty

Right now it's just a pot controlling the height, but I was thinking over the weekend that it wouldn't be that hard to put 4 photoresistors at equal distances along the tube to serve as a control mechanism (light would reflect better off the white ball).

I'd love to see it with beach balls!

http://www.youtube.com/watch?v=IhrHCmRWfno Looks like you can do it with a pretty small end on your air blower.

Right now it's just a pot controlling the height, but I was thinking over the weekend that it wouldn't be that hard to put 4 photoresistors at equal distances along the tube to serve as a control mechanism (light would reflect better off the white ball).

I was thinking of using a IR analog sensor ( http://www.hobbyengineering.com/H1060.html ) mounted on the face of the fan looking up at the ball. I have been looking for a nice useless project so that I could work with a PID control library and I think your project looks to be as useless as they come. ;D

Lefty

At any given flow rate it looks pretty stable, so I would think that varying the fan speed with PWM might be enough, without needing to use some type of feedback sensor. It would be a build-then-calibrate rather than a build-to-meet-calibration setup, but I just can't see using a ping pong or beach ball as a high-precision indicator. That being said, PWM ought to give a pretty fine degree of control...

VERY awesome project!! very unique, I love it! I could think of so many applications for this thing :D

have a twitter account with a live web cam watching it, everytime someone tweets with that hash tag it boosts the level up by 5% for 10 seconds or something, people can watch it happening and put google ads on the site.

instant money maker!

I had another idea!!!

Raise money for awareness WHILE free funding for you. Have hashtags that tweet it up the speed by 5% for 5 seconds

and then have people donate to change the color of an LED underneath and label their cause on the webcam feed.

this could be a viral explosion that will engulf the internet in one day, disappear in the other, and the only winners are the creators and the charities!

If you get child’s play charity behind it, you know Peny Arcade will talk about it, and engadget loves these kinds of projects. Be prepared to have to force a shut down from a perceived DDoS attack.

My weekend project made it onto the Make Magazine blog! :)

http://blog.makezine.com/archive/2010/11/arduino-controlled_ball_meter.html

:)