Team 665 Fan/s and More

[Greg Peshek]

We're having fun with fans and conveyor belts, all in the same robot. Right now we've tested a 22", 3DA airplane prop. It puts out about 28 mph windspeed, and when we tried putting it on a rolling chassis alone that weighed about 90 lbs.. it started pushing it at about 3/4 speed and accelerated to a very nice speed at the end of 16ft. Here's a video of our fan testing: http://www.youtube.com/watch?v=Sw7jg...e=channel_page

Picture of our fan casing (also known as the giant cake dish):


Picture of the fan casing being held up to the robot (this picture has all the conveyor stuff off)


We tried the fan at a 1:6 ratio, we tripped the breaker before we could even get to a decent speed. We're looking at 1:1 as a very good ratio right now. We're looking at the possibility of two non-rotating fans for directional control. 2 weeks is plenty of time....

-Greg

[phr34kR]

Nice set up i like it, it seems like it has the potential to aid you in acceleration and handling good luck!

[Woodworker88]

Nice work. Out of curiosity, how much does a prop like that cost?

[EricH]

Originally Posted by Woodworker88

Nice work. Out of curiosity, how much does a prop like that cost?

If it's an R/C prop, it could be really cheap or really expensive. It depends on the type, whether it comes balanced or not, and where it's made. It varies. For example, my Aero team buys a particular brand of props. They're made in Australia, and shipping is kind of...well...not cheap. Then the props are carbon fiber. More not cheap. We do the balancing, so that saves a little money. But for your plastic, cheap type, it's not going to be nearly as expensive.

[Greg Peshek]

Originally Posted by Woodworker88

Nice work. Out of curiosity, how much does a prop like that cost?

We're using a XOAR wood laminated prop. Nothing particularly special, somewhere on the order of $30 per prop. While I'm not quite sure if they're balanced or not, it's certainly been quite smooth in all of our test runs.

-Greg

[EricH]

Originally Posted by Greg Peshek

We're using a XOAR wood laminated prop. Nothing particularly special, somewhere on the order of $30 per prop. While I'm not quite sure if they're balanced or not, it's certainly been quite smooth in all of our test runs.

-Greg

For better performance, try balancing it. If you don't have a prop balancer, all you need to make one is a couple of magnets, a steel rod, and something to stabilize the prop along the rod. Oh, and a freshman with fine sandpaper...

Find a place that is non-drafty. Set up the magnets just over a rod-length apart, and put the prop on the rod. "Hang" rod between the magnets, and give the prop a light flick. If it just turns, turns, turns, stops, it's balanced. If it stops, then reverses, then it probably isn't. lightly--very lightly sand down the heavy side for a few strokes. Repeat until the prop doesn't reverse.

Now, the motor doesn't have to fight against extra weight half the time. Overall faster prop...

[Woodworker88]

Originally Posted by Greg Peshek

We're using a XOAR wood laminated prop. Nothing particularly special, somewhere on the order of $30 per prop.
-Greg

Wow that's significantly cheaper than I would have expected. I can't wait to see how it turns out when it's all done.

[Akash Rastogi]

Now that's a propulsion system

Very nice. Good luck and may the propulsive force be with you.

[Sean Raia]

Not JUST propulsion but possibly deflecting balls.

[martin417]

I have a suggestion for measuring prop speed. The device you are using in the video looks for changes in light intensity. The room you are in has florescent lights. Florescent lights flicker 120 times per second. This flickering is picked up by the photo-tach and you will not get a good reading, if you get one at all. (try aiming the tach at the overhead lights, you should get a reading of around 3,600 RPM if you are set for a 2-bladed prop). You should make your readings outside, or turn off the overheads and use an incandescent light source like a flashlight, aimed from the far side of the prop (so the beam passes through the prop) at the tach.

On another note, you probably already know this, but static thrust (and the speeds you will be reaching in the game will be so low that static thrust is all you care about) is not affected by prop pitch, but power consumption is. So the trick is to swing the largest diameter, lowest pitch prop you can get. That will maximize the thrust you get.

For quick analysis, google thrusthp. Tis is a free program that will calculate power consumption, thrust and top speed based on prop diameter, pitch, and rotational speed.

Good luck at your regional!

[DarkFlame145]

idk why, but something about a propeller on a robot scares me =P But I like the idea

[sportzkrazzy]

One thing comes to mind when i c this. Air boat lol.
Have u guys thought about counter rotating props?

http://www.freepatentsonline.com/6821169-0-large.jpg

[gorrilla]

wow, i cant wait to see you guys at the regional

[Greg Peshek]

Originally Posted by martin417

I have a suggestion for measuring prop speed. The device you are using in the video looks for changes in light intensity. The room you are in has florescent lights. Florescent lights flicker 120 times per second. This flickering is picked up by the photo-tach and you will not get a good reading, if you get one at all. (try aiming the tach at the overhead lights, you should get a reading of around 3,600 RPM if you are set for a 2-bladed prop). You should make your readings outside, or turn off the overheads and use an incandescent light source like a flashlight, aimed from the far side of the prop (so the beam passes through the prop) at the tach.

Good luck at your regional!

The device in the video is actually a wind speed meter. It has a little (muffin-like) fan in the center that spins and then it turns that into a wind speed. So we're not actually clocking the RPMs coming out of it, just the physical speed of the wind Thanks for the advice in the rest of the post, we'll make sure to look into it.

[Tom Line]

Back of the napkin tells me that if you're putting out a uniform 28 mph across a 32 inch fan, you'll get around 340 lbf out of it. Anyone want to check my numbers? I guessed on some of my constants - been a while since I cared about air density

If my numbers are right, conservatively you may get 150 pounds of push out of it. Not too shabby!