|
|
|
![]() |
|
|||||||
|
||||||||
![]() |
| Thread Tools | Rate Thread | Display Modes |
|
#46
|
|||
|
|||
|
Re: Team 665 Fan/s and More
Quote:
|
|
#47
|
|||
|
|||
|
Re: Team 665 Fan/s and More
Quote:
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:
|
|
#48
|
|||||
|
|||||
|
Re: Team 665 Fan/s and More
Quote:
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. |
|
#49
|
|||
|
|||
|
tere must be a hopper but where>?
![]() |
|
#50
|
|||
|
|||
|
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.
|
|
#51
|
|||
|
|||
|
Re: Team 665 Fan/s and More
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. |
|
#52
|
|||||
|
|||||
|
Re: Team 665 Fan/s and More
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.
|
|
#53
|
||||
|
||||
|
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:
|
|
#54
|
||||
|
||||
|
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.
|
|
#55
|
||||
|
||||
|
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. |
|
#56
|
||||
|
||||
|
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.
|
|
#57
|
||||
|
||||
|
Re: Team 665 Fan/s and More
Quote:
|
|
#58
|
||||
|
||||
|
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. |
|
#59
|
||||
|
||||
|
Re: Team 665 Fan/s and More
Quote:
|
|
#60
|
||||
|
||||
|
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. |
![]() |
| Thread Tools | |
| Display Modes | Rate This Thread |
|
|
Similar Threads
|
||||
| Thread | Thread Starter | Forum | Replies | Last Post |
| pic: Team 665 REAL Chassis, Kinda-Teaser | Greg Peshek | Extra Discussion | 13 | 25-01-2008 08:14 |
| Team 665 | TheFuhr | Robot Showcase | 13 | 23-01-2008 13:04 |
| pic: Team 66 lifted once, and will lift more | JoeXIII'007 | Extra Discussion | 4 | 11-03-2007 14:20 |
| Edit- Can we connect more than one speed controller fan per breaker? | DemonYawgmoth | Rules/Strategy | 7 | 03-02-2006 21:37 |
| Team 713 and more. | Madison | Thanks and/or Congrats | 0 | 13-04-2003 13:51 |