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Unread 01-02-2009, 01:37
Woodworker88 Woodworker88 is offline
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Re: Team 665 Fan/s and More

Quote:
Originally Posted by Greg Peshek View Post
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.
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Unread 01-02-2009, 03:01
Akash Rastogi Akash Rastogi is offline
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Re: Team 665 Fan/s and More

Now that's a propulsion system

Very nice. Good luck and may the propulsive force be with you.
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Unread 01-02-2009, 10:15
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Re: Team 665 Fan/s and More

Not JUST propulsion but possibly deflecting balls.
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Unread 01-02-2009, 10:55
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Re: Team 665 Fan/s and More

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!
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Last edited by martin417 : 01-02-2009 at 15:37.
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Unread 01-02-2009, 11:22
DarkFlame145 DarkFlame145 is offline
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Re: Team 665 Fan/s and More

idk why, but something about a propeller on a robot scares me =P But I like the idea
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Unread 01-02-2009, 14:46
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Re: Team 665 Fan/s and More

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
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Last edited by sportzkrazzy : 01-02-2009 at 14:52.
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Unread 01-02-2009, 14:50
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Re: Team 665 Fan/s and More

wow, i cant wait to see you guys at the regional
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Unread 02-02-2009, 10:01
Greg Peshek Greg Peshek is offline
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Re: Team 665 Fan/s and More

Quote:
Originally Posted by martin417 View Post
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.
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Unread 02-02-2009, 11:03
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Re: Team 665 Fan/s and More

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!
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Unread 02-02-2009, 11:37
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Re: Team 665 Fan/s and More

Quote:
Originally Posted by Tom Line View Post
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!
How much power would be consumed, in order to generate that? I don't think that airspeed is anywhere close to uniform over the propeller disc.

Anecdotally, I've dealt with a propeller-based system: a 100 lb model aircraft with a pair of 1 250 W (mechanical output) motors and Ø20 in two-bladed propellers with 12 in pitch. In long-duration maximum-power static thrust tests on the ground (there was resistance at the wheels, but not much), it had between 30 lb and 40 lb of thrust. The blades were spinning at over 6 000 rev/min, and the motors were drawing over 40 A each at 40 V. (The aircraft had a conservative flight duration of around 8 minutes at maximum power. When cruising, it needed far less power than that to sustain estimated airspeeds of 100 km/h.)

Incidentally, it's the experience on that project (everyone stayed safe), that fuels my healthy distaste for propeller systems in crowded spaces.
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Unread 02-02-2009, 12:15
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Re: Team 665 Fan/s and More

Quote:
Originally Posted by Tristan Lall View Post
How much power would be consumed, in order to generate that? I don't think that airspeed is anywhere close to uniform over the propeller disc.

Anecdotally, I've dealt with a propeller-based system: a 100 lb model aircraft with a pair of 1 250 W (mechanical output) motors and Ø20 in two-bladed propellers with 12 in pitch. In long-duration maximum-power static thrust tests on the ground (there was resistance at the wheels, but not much), it had between 30 lb and 40 lb of thrust. The blades were spinning at over 6 000 rev/min, and the motors were drawing over 40 A each at 40 V. (The aircraft had a conservative flight duration of around 8 minutes at maximum power. When cruising, it needed far less power than that to sustain estimated airspeeds of 100 km/h.)

Incidentally, it's the experience on that project (everyone stayed safe), that fuels my healthy distaste for propeller systems in crowded spaces.
Like I said - 320 pounds if uniform. Assume it's not, so I halved the value to 150. Even if you want to cut it 80%, they're going to get similar drive from that fan as they do from the wheels, so they'll accelerate twice as fast as a non-ducted bot.

They better not have the air-intake on the bottom of the robot though.....
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Unread 02-02-2009, 12:25
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Re: Team 665 Fan/s and More

I'm a big fan of 665...tee hee. Actually I think this is going to be really fun to watch
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Unread 02-02-2009, 12:45
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Re: Team 665 Fan/s and More

I like how no one is really that concerned about safety here when the guy has his hand REALLY close to the prop, yet when our team posts anything about prop testing, we are continually nominated for the Darwin award XDD
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Unread 02-02-2009, 13:11
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Re: Team 665 Fan/s and More

his hand is close to the blade but not in the plane of rotation like you guys were. Also there protection around the fan is far superior to the one you have currently proposed. I think people are becoming tired of your blatant disregard for safety. It's ok if you want to hurt yourself, but by not shielding the fans properly you will be putting hundreds of people at risk.
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Unread 02-02-2009, 13:56
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Re: Team 665 Fan/s and More

I think the safety officails will have fun with this team
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