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Unread 06-02-2009, 19:05
jwkelly jwkelly is offline
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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!
I'd have to say your estimate is quite generous. We have run a fan test on a 28 inch prop with it directly connected to a CIM motor (1:1). Xoar 28x10 prop gives us approximately 8lb static thrust, whilst a 28x12 gives approx 7lb of static thrust.
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Unread 07-02-2009, 12:56
Urban Hawk Urban Hawk is offline
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Re: Team 665 Fan/s and More

Quote:
sorry, but Q&A got to that one pretty quickly when it was brought up. http://forums.usfirst.org/showthread.php?t=11025

Yeah, it's intended to deflect incoming moon rocks. But I can almost guarantee you that at least one inspector per event will not allow the up-angle. (Most likely the lead inspector, but could be another one.) It's going to be really hard to build a deflection system that works using air jets, because it has to be horizontal. That said, anyone who does a fully legal one deserves at least a Xerox Creativity Award.
well i looked at the thread you gave me but id rather have to dissagree with it. There are 2 main arguments in there against it. The first being the vaccume will damage the floor and the second being it goes against <R06>.

For the first of the 2 I'd have to say that the main argument there is merely about suction such as a vacuum cleaner would provide. How ever if you have it so that the fan draws the air from a large area around it then it shouldn't create a vacuum and should dispel that particular argument.

As for the second with it breaking rule <R06> from what i see of the rule it isn't breaking it.
Quote:
<R06> ROBOTs must use ROVER WHEELS (as supplied in the 2009 Kit Of Parts and/or their equivalent as provided by the supplying vendor) to provide traction between the ROBOT and the ARENA. Any number of ROVER WHEELS may be used. The ROVER WHEELS must be used in a “normal” orientation (i.e. with the tread of the wheel in contact with the ground, with the axis of rotation parallel to the ground and penetrating the wheel hub). No other forms of traction devices (wheels, tracks, legs, or other devices intended to provide traction) are permitted. The surface tread of the ROVER WHEELS may not be modified except through normal wear-and-tear. Specifically, the addition of cleats, studs, carved treads, alterations to the wheel profile, high-traction surface treatments, adhesive coatings, abrasive materials, and/or other attachments are prohibited. The intent of this rule is that the ROVER WHEELS be used in as close to their “out of the box” condition
The fan is not a traction device because it doesn't provide traction. It merely causes an increase of the force caused by frame of the robot (and the components of the robot) in pushing/pulling downward on the wheels. The robot already naturally does this through gravity but the fan just increases it further and so increases the wheels natural friction without any form of modification to the wheels.
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Unread 07-02-2009, 15:18
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Re: Team 665 Fan/s and More

Quote:
Originally Posted by Urban Hawk View Post
As for the second with it breaking rule <R06> from what i see of the rule it isn't breaking it.


The fan is not a traction device because it doesn't provide traction. It merely causes an increase of the force caused by frame of the robot (and the components of the robot) in pushing/pulling downward on the wheels. The robot already naturally does this through gravity but the fan just increases it further and so increases the wheels natural friction without any form of modification to the wheels.
Let's not start that debate again. It came up early in the season when someone first suggested fans for propulsion. I don't remember the exact thread, but a quick search should turn it up.

I will simply say that the apparent intent of <R06> is that you cannot increase your traction by any means other than a heavier robot, and getting a heavier robot by adding a fan to increase your normal force is illegal according to the Q&A. I just wish that they'd make that clear as glass and end all these debates.

Incidentally, your physics is wrong. µ (the coefficient of friction) never changes, so you can't say that friction increases. However, Ff (the frictional force) = µ*N, where N is the normal force. Because µ is constant, if you increase N, you increase Ff. Friction never increases; frictional force does.
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Unread 07-02-2009, 15:30
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Smile Re: Team 665 Fan/s and More

tere must be a hopper but where>?
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Unread 07-02-2009, 17:16
Urban Hawk Urban Hawk is offline
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Re: Team 665 Fan/s and More

I think i know which thread you were talking about. The one i found was:Team 2526 - Propeller Propulsion Prototype. As well as that post on the Q&A. i guess that you are right about not being able to use it to provide a downward force.
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Unread 07-02-2009, 18:43
Greg Peshek Greg Peshek is offline
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Re: Team 665 Fan/s and More

Quote:
Originally Posted by robert2.0 View Post
tere must be a hopper but where>?
You can see in this more recent picture that the balls are stored in the conveyor, we run into people, and dump them out into the trailer. We can store 8 balls and dump them all in 1-2 seconds. We can also eat people's bumpers, it's fun. The design is very similar to the design that 1712 posted on here. We just plan on having two separate towers, so instead of running into the problems where the balls get all jumbled and stuck in the conveyors, there is a constant column of them.



There is now dividing lexan to keep the balls separate that isn't shown in that picture. The fan/s is/are going right behind that tower, over the electronics.

We've tried multiple pulley setups/ one versus two CIMs and at this blade size and weight the pulleys actually start becoming inefficient from the vibrations and loss in the pulleys. We have found a way to increase thrust (not windspeed) by 20-30% on only one CIM with no gear ratio. I'll post more pictures and videos on the whole setup near the end of build season.

The idea is to be able to get all 8 balls in, turn on the fan to zip across the field, violently run into someone (with the aid of the fan), dump, repeat. We're hoping the space lost in the manipulator design to the fan will be made up for by the advantage of the fan. If we can use the fan to catch people/ push easier.. we believe we'll have an advantage over hopper dumpers/ power dumpers that may have a harder time of pinning.

We'll see..it'll be an interesting year for us to say the least.

-Greg

Last edited by Greg Peshek : 07-02-2009 at 18:49.
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Unread 07-02-2009, 22:14
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Re: Team 665 Fan/s and More

Quote:
Originally Posted by Urban Hawk View Post
I think i know which thread you were talking about. The one i found was:Team 2526 - Propeller Propulsion Prototype. As well as that post on the Q&A. i guess that you are right about not being able to use it to provide a downward force.
Actually, I was referring to one from even earlier, something about propulsion without using wheels. There was a big debate until the above referenced Q&A came out.
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  #53   Spotlight this post!  
Unread 15-03-2009, 23:56
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Re: Team 665 Fan/s and More

We were also experimenting with props direct drive off the FP motors. We tried APC 11x3 spinning at 7800-8000 RPM and it produced under 2 lbs in our static thrust test. When we tried the 11x6, it produced about the same thrust at a lower RPM but the same power. ThrustHp indicated that the 11x3 should produce a 50% better thrust than the 11x6. We've found other analysis tools (http://www.mvvs.nl/prop-power-calculator.xls) that indicate that as RPMs go up that the hp to thrust ratio goes down and tends to cancel the finer pitch to thrust ratio improvement. This "prop-power-calculator" seems to match our test results closer than the ThrustHp program. I'm curious if anyone have found that the ThrustHp is seemingly too optimistic for pitches under 10 degrees.

We are still searching for the "optimum" 11" prop: either off the shelf or fabricating ourselves (Ooooh, the mental energy we expend to eek out extra pounds of thrust...).
It's probably too late to study to become an airfoil designer- I'd settle for trying to be an airfoil hack.

Quote:
Originally Posted by writchie View Post
The no load RPM spec on the CIM is 5310 @ 12V. Trying to remain 1:1 is the basic problem. I don't see how you can do it without a much larger dia. At a torque load and RPM that will give you the required shaft horsepower for this prop at 8500 RPM you would need to gear it up about 1:2.75. But those numbers are really for a normal prop, not a slow fly. SF props at this size are not safe at this RPM even for airplanes. When you add the likelihood of shock induced tip flutter from collisions it's a bit scary.

We are using direct drive FP motors and our thruster is still optional. We were originally planning to machine a custom prop but are now planning on off-the-shelf adjustable pitch props with a custom machined 3 blade hub to get us a 1 - 2 pitch in a pusher configuration.

As another poster pointed out, careful attention to the shroud will help.

I suspect we may see both geared up CIM's and Direct Drive FP's with total thrusts approaching 10 lbf (at the start of the match).
  #54   Spotlight this post!  
Unread 16-03-2009, 07:18
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Re: Team 665 Fan/s and More

We did a lot of experimentation and comparison with ThrustHP. While the program was a little optimistic, it was not found to be overly so. Regardless of program or testing, static thrust is completely independent of pitch. Use the lowest pitch prop you can get for a given diameter (power is affected, so lower pitches turn faster, giving more thrust) We used two APC 10 x 3.75 Slow-Flyer props, mounted in a custom fiberglass shroud and direct driven with Fisher Price motors. When measured with a fish scale, the setup produced 6-8 LB.s of thrust on average. The fans were an optional "booster", activated by the joystick trigger (only if the joystick output was greater than .4) They were some help in a pushing match, but the real boost came when chasing a robot for the score. When the driver hit props, you could see the bot accelerate down the field. We called it "turbo boost" mode.
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Unread 16-03-2009, 12:04
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Re: Team 665 Fan/s and More

Thanks for your analysis. I had the idea from reading your previous posting (http://www.chiefdelphi.com/forums/sh...7&postcount=38) that if you ran both fans at the same time that you were getting less than 2 pounds of thrust each due to battery loading. Your previous analysis seems to correspond to the numbers we were getting with a pair of 11x3s.

If you don't mind me asking, how did you achieve jump from under 4 pounds to the 6 to 8 pound range?

We will likely try some experiments with a 10x3.8 SF and a more optimal shroud. We were also experimenting with "javaprop" to understand what the optimal airfoil shape would be.
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Unread 16-03-2009, 12:08
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Re: Team 665 Fan/s and More

I don't know all the details but I believe our shrouds increase our thrust by about 150%. I know that we greatly out accelerated everyone and could push multiple robots at once at will.
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Unread 16-03-2009, 20:15
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Re: Team 665 Fan/s and More

Quote:
Originally Posted by boomergeek View Post
Thanks for your analysis. I had the idea from reading your previous posting (http://www.chiefdelphi.com/forums/sh...7&postcount=38) that if you ran both fans at the same time that you were getting less than 2 pounds of thrust each due to battery loading. Your previous analysis seems to correspond to the numbers we were getting with a pair of 11x3s.

If you don't mind me asking, how did you achieve jump from under 4 pounds to the 6 to 8 pound range?

We will likely try some experiments with a 10x3.8 SF and a more optimal shroud. We were also experimenting with "javaprop" to understand what the optimal airfoil shape would be.
In the previous post, I mentioned the "very unscientific (and dangerous) testing" and the "bare props" In the more recent post, I was talking about the same props, mounted in a custom fiberglass shroud, designed upon a paper written by NACA (see this thread for details) and testing on the bot with accurate fish scales. The shroud can theoretically give a 50% to 75% boost in thrust. So, in answer to your question, The first numbers may have been off by good bit due to the resolution of the bathroom scale, the shroud may have done the trick, or some other unforeseen factor. At any rate, I am confidant in the latest data due to much more rigorous, scientific methods of test.
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Unread 17-03-2009, 00:12
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Re: Team 665 Fan/s and More

Thanks for clarifying. . .I'll also boost our Ae to be closer to 1.6 of Ad. The first test shroud (cut from a 5 gallon pickle bucket and with a garden hose for the radius of the lip) had Ae about 1.2 of Ad.

We are working to improve the rigorousness of our testing methods.
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Unread 17-03-2009, 07:04
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Re: Team 665 Fan/s and More

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Originally Posted by boomergeek View Post
Thanks for clarifying. . .I'll also boost our Ae to be closer to 1.6 of Ad. The first test shroud (cut from a 5 gallon pickle bucket and with a garden hose for the radius of the lip) had Ae about 1.2 of Ad.

We are working to improve the rigorousness of our testing methods.
According to the NACA paper, the parameter that had the most effect on thrust was inlet radius. The radius should be at least 6% of prop diameter, more is better (ours is 15%, or 1.5" radius on a 10"prop) Ae and Ai had some effect, as did shroud length (we had to cut about 1.5" off our shroud in order to get it to fit on the bot, and noticed no reduction in thrust). These effects were small in comparison to inlet radius. For more info, the paper can be found here.
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Unread 17-03-2009, 09:49
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Re: Team 665 Fan/s and More

We did try to understand the paper (reading it several times) but we did not do enough fabrication and experimentation. From the discussion associated with Figure 5 and 6, we thought that the advantage of larger lip radius beyond .06 toward .15 would not provide a significant advantage. The paper did not indicate the effects of the size of the lip radius AFTER reaching 90 degrees from the general thrust direction: I.e., how large surface plane (i.e., what the paper describes as the simulated upper surface in figure 1)needs to be after the radius reaches 90 degrees to achieve the lip radius benefit. On our inital tests, we assumed we could extend the lip radius to 180 degrees(basically following the curve of the hose): I think that is probably our larger problem.

We are limited in how big we can make the "simulated upper surface" to about a 12" to 13" square for each shroud.

Thank you for your continued expert advice for trying to help us to a more optimal configuration.

The amount of team energy to work on upgrades for our second and last regional is not as strong as the enthusiasm back before the first regional.

We will definitely let you know how it turns out.
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