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Probably the strangest EDF question ever...

Old 07-27-2010, 03:27 AM
  #1  
Shakes_26
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Default Probably the strangest EDF question ever...

First, thank you in advance for any help possible.

I'm working on building a special project that requires an EDF for a non flying application. I've searched and the choices and specs are quite overwhelming. I do have certain parameters to respect:

1. Money isn't an issue (I have an insane boss, who wont lose)
2. I'm pretty much limited to no larger than a 65mm EDF. This is due to O.D constraints in the vehicle.
3. weight, really not an issue, but lighter is better
4. the vehicle (well call it that for lack of a better term) will not be airborne (if it is we've done something wrong, and I'll have to wear the #26 of Ricky Bobby).
5. Once 'teched in' the vehicle cannot be handled by anyone besides the tech guy. There will be 4 'heats' that last about 3 seconds each, about 45 minutes apart. We'd like a way to remotely power up/de-power the system to save battery.
6. we need to incorporate an arm (throttle on 100%) switch, when this switch closes, throttle goes to 100% if the system is powered on (by remote).
7. Must have the highest thrust possible!! See #1.

So yes its basically an EDF powered drag racer. I need recommendations for EDF unit, motor, ESC and Battery (LiPo). I'm thinking because of the way we want to do this I might have to used a fan motor with brushes...but have found nothing on those.


Mods feel free to relocate this if I've posted in the wrong forum.

I promise to reveal more details after the build and August event.


Regards,

Marc
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Old 07-27-2010, 08:46 AM
  #2  
Larry3215
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You get thrust in 2 ways from a prop or a fan unit.

The most important one is diameter. Larger diameter props or fans give more thrust. Your stuck with 65mm so you dont really have an option there.

The only other way to get more thrust is to go for more rpm. You need to get a fan unit thats capable of the maximum rpm - which means a hi quality fan.

I would go for a Schubler 65mm DS-26-DIA HDT

http://www.schuebeler-jets.com/index...=29&Itemid=112

Check the Schubler site for recomended motors for max performance. Maybe even send them an e-mail or call them up. Most likely they will be recomending a Neu motor with a Castle Creations controller.

Do you have a choice of batery packs you can use or are there limits? The Schubler will have a particular motor, battery combo they recomend but if you change the battery you need to change the motor and vise verse.

As far as I know, Schubler is in a class by itself for this size fan. There are several other hi end fan mfg's, but I dont think any of them make anything this small.

In general, Id recomend a Neu motor for what ever fan you choose and a Castle Creations ICE controller.

For the batteries, Id go with the new Hyperion G3 EX series packs for max performance. You could also use the Thunder Power ProPower 45C packs for a hair more punch.

Exactly which packs, esc and motor will depend on the fan unit, so talk to Schubler first.

If you go with a different fan, then all the details will change.
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Old 07-27-2010, 04:40 PM
  #3  
Flite-Metal
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Default Non-technical Solution For Complex Requirement...

I would address this from the least need-to-know technical attributes as possible and let proof in the pudding be the only way to judge what is appropriate....
basically you are left to observe YouTube as your resource...in light of the techno blitz that is about to decend on you.

Schubeler would be an excellent choice for top end speed after an object attached to the Schubeler reached a minimum-load-lifting state. However, you stated
you were looking for the greatest volume of air pulled through a ducted fan in the least amount of time...this would normally be considered thrust during takeoff.

Because the edf blade sweep volume (in cubic inches per revolution) determines the unattainable maximum volume at 100% effeciency (about the best % you
will achieve is 80%~85% during ramp up to forward motion)...diameter and blade pitch (angle(s) at X exhaust duct length with a given exhaust diameter to fan
sweep area ratio are critical elements of comparison.

Obviously in order to evaluate which combination of fan, motor, esc, duct length, and exhaust diameter...you can view "static" thrust evidence everyone shows
in their product performance video by viewing the screen of their edf evaluation software attached to their edf during static operation. Its as close to factual
data as you can get....facts not opinion!

Secondary, you are faced with rolling resistance which brings you to an issue equal in complexity of bearing...material, shape, composition, wheel composition
and conatact patch to a specific surface. Knowing whether this is indoors in air conditioning or out in the heat of day at X humidity and air density will help you
as well.

You failed to disclose the maximum dims and weight of the object to be moved...from the ground on which it sits... By the way, is there some requirement the plane of the
edf be parallel to plane of wheel axles @ X number of wheels?

Just a thought or two considering complexity of what your question presents...

Last edited by Flite-Metal; 07-27-2010 at 05:04 PM.
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Old 07-28-2010, 02:21 AM
  #4  
Shakes_26
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Thanks for your inputs so far.

Max width of the vehicle 69.8mm, length 177.8mm, we are designing the vehicle within these limits and around the EDF/motor/ESC/Batt combo we can fit in in there.

Weight we are shooting for something under 500grams ideally, including the propulsion.

Contact patch will be 4 wheels, about 3mm wide each,the vehicle will be run down an aluminum track, indoors under Air conditioned comfort.

I understand the concepts of thrust and blade pitch and count. My request really centers around sorting through

a. the hype
b. are there brushed motors out there we can use (avoids ESC requirement)
c. if we have to go with an ESC is there a way to make one activate as I described in the Original post.

Again thank you,
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Old 07-28-2010, 02:47 AM
  #5  
Flite-Metal
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With it only 177mm you are subject to cavitation and that is too short for exhaust duct to be a benefit. Sounds like a DYI OCD issue to me... There will not be any aerodynamic loss/gain...
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Old 07-28-2010, 08:28 AM
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Larry3215
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You can use a servo tester to drive the brushless esc. No radio system required.

You could conceivably go with a brushed motor setup but you're cutting the max power and thrust by at least 3 or 4 times. Brushed systems are not very efficient and cant handle the power you will need if you want to go fast.

On the other hand, 500 grams isnt all that much. Your battery pack will be the limiting factor in how much power you can generate in this case.

That Schubler fan is probably capable of handling over 2000 watts, but you will have a hard time fitting a pack that can handle anywhere close to that into your space. The normal power range for these fans is in the 500 to 1000 watt range.

On second thought, I think space is going to be your biggest problem.

What is the max height on the vehicle?

If its the same 69.8mm, then you are in big trouble. You're not going to be able to power that fan at anywhere near its max potential. In fact, I suspect your going to have a hard time getting your project to move at all.

The Schubler fan unit has an over all length of 148mm including the motor streamlining housing. You could do without that and get down to maybe 125 to 130mm or so depending on the motor you select.

That only leave you with about 40-50mm for batteries and that is only if you have them right up against the intake on the fan - which wont work at all.

I think you guys need to re-think your approach here.

You could maybe squeeze in some really small battery pack, but if you cant get the rpm on the fan you wont get any thrust.

These edf fans are not very efficient at best and at low rpms they produce almost no thrust at all.

In other words - they just dont work worth a darn unless you can throw a lot of power at them.

Last edited by Larry3215; 07-28-2010 at 08:47 AM.
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Old 07-28-2010, 01:44 PM
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JetPlaneFlyer
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Shakes,

If the maximum overall dimensions you mention really are absolute limits then your real challenge is finding components to fit in the space available and still provide half decent thrust.. You might have to forget the real high power systems mentioned previously, you just donít have space.
Iíd suggest to get some overall sizes of a range of components (fans/motors, batteries, ESCís) and do some layout work to see what you can fit in the space available. Bear in mind that the operate with anything like reasonable efficiency the fan needs a clear path to the inlet and unobstructed outlet.. You can't go locating your components right in front of the fan inlet for instance. Also for the fan to operate efficiently you need to provide a 'bell mouth' shape inlet with a nice curved lip, which makes the fan effectively wider than its stated dimensions. Outlet ducting is much less important, just leaving the fan outlet 'un-ducted' is fine, but not having the right inlet shape will cost you considerable loss in thrust.

I suspect that unless the vehicle is allowed to be very high then you will have to move to a smaller less powerful fan to make some space for the other components and to allow the use of a smaller battery pack.

Time to get the drawing board out...

Steve
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Old 07-28-2010, 06:14 PM
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kyleservicetech
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Originally Posted by Shakes_26 View Post
First, thank you in advance for any help possible.

I'm working on building a special project that requires an EDF for a non flying application. I've searched and the choices and specs are quite overwhelming. I do have certain parameters to respect:
5. Once 'teched in' the vehicle cannot be handled by anyone besides the tech guy. There will be 4 'heats' that last about 3 seconds each, about 45 minutes apart. We'd like a way to remotely power up/de-power the system to save battery.
6. we need to incorporate an arm (throttle on 100%) switch, when this switch closes, throttle goes to 100% if the system is powered on (by remote).
Marc
Are you located in the USA?
Making up the "Driver" for the ESC is a simple job using the modern day microcontrollers such as the units by Microchip.

I can program up a driver that will provide the 1.00 millisecond pulsewidth for motor off, then provide the 2.00 millisecond pulsewidth for the motor full power, and back to 1.00 milliseconds for motor off. If desired, a simple potentiometer can be provided to allow adjustment for how long the motor stays at full power. (With a PicChip microcontroller, the on time can be varied from anywhere from a fraction of a second, up to minutes, hours, days, or years if desired.)

If desired, the microcontroller could be programmed to delay for a specific period of time after the battery is plugged in, before it applies the 3 second run time to the motor. Something easily done with a microcontroller. Or, you can provide a pushbutton to initiate the microcontroller.

Something like this would be very small, and weigh in at a fraction of an ounce. Take a look at the example, this is 95% of the parts required! The circuit board can be cut down to not much larger than the controller chip itself. Cost of the parts is under $10.00, plus programming the chip, something I can do.

The unit would be powered by your ESC circuit that would normally power the receiver. If your ESC does not have a 5 volt output for the receiver, than the little black 5 volt regulator at the top right of the PicChip is required.

For those readers that do electric powered control line flying, yes this unit could be used to control the ESC for a control line model! Same parts, different programming. Program can be set up to delay for 15 seconds or so after plugging in the battery, give a brief blip of power to the motor to warn the flyer, apply power to the motor, until the battery voltage drops below a lower limit, set by a little potentiometer on the circuit board.

Let me know if you are interested.
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Old 07-29-2010, 03:57 AM
  #9  
Shakes_26
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Just received an update today:

rules allow a vehicle height up to 152.4mm, length up to 203.2mm, the 177mm length was from the nose to rear axle center line.

Lighter is better, smaller is better.

Kyle,

I will take you up on the Micro-controller pre-program offer, I'll PM you about more info.

For an idea of what we are aiming towards in somewhat scale

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Old 07-29-2010, 08:20 AM
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That gives you a bit more room to work with but it's still a very short wheelbase which is likely to lead to stability issues, especially if you use the full 6" height allowance; though perhaps if no corners are involved you will be ok.

Getting away from the original concept, but arent you allowed to drive the wheels?
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Old 07-29-2010, 06:06 PM
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"The 177mm length was from the nose to rear axle center line"...

Are you saying no part of the rear can over hang the rear axle? I did not read it to state that....I read it as the most rearward axle placement.

Personally, if competition is a virtual knock-off of the SAE lift comp...IMHO you need to build the entire structure as vested components.
Batteries form the duct with no additional components aside from 2 C/F axles and four waffer thin discs for wheels. The lightning rod waffer
thin "switch" and ecu would sit in the airstream to reduce the ignition source probabilities...
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Old 07-30-2010, 02:23 AM
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I agree with FM, the schubeler is made for speed where the airframe is at velocity.

I am working on our new 64mm Alloy fan, I do have a test sample now ready to run with a plastic housing, this fan runs 28mm motors and will handle 2000 watts when finished, custom 64mm GRP rotor made in Germany and it will have a crapload of static thrust!

From our recent test videos of the Extreme 70mm Alloy fan I believe this will be the most powerful 64mm fan around. I plan to do some preliminary testing later today if I can get time to finish balancing it up and plug everything up.

For what you need in duration I would not worry about big batteries, you dont need them, a 2200mah 40c cell will be more than enough for a burst of 5 seconds or so, even 6s pulling 80A will be no issue, you are drag racing not flying circuits

Kyles offer of the "microswitch" is awesome as it means a regular ESC right Kyle? You will only need a good 80A esc for the most powerful 6s setup.
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Old 07-30-2010, 03:23 AM
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Originally Posted by ExtremeRC View Post
I agree with FM, the schubeler is made for speed where the airframe is at velocity.

I am working on our new 64mm Alloy fan, I do have a test sample now ready to run with a plastic housing, this fan runs 28mm motors and will handle 2000 watts when finished, custom 64mm GRP rotor made in Germany and it will have a crapload of static thrust!

From our recent test videos of the Extreme 70mm Alloy fan I believe this will be the most powerful 64mm fan around. I plan to do some preliminary testing later today if I can get time to finish balancing it up and plug everything up.

For what you need in duration I would not worry about big batteries, you dont need them, a 2200mah 40c cell will be more than enough for a burst of 5 seconds or so, even 6s pulling 80A will be no issue, you are drag racing not flying circuits

Kyles offer of the "microswitch" is awesome as it means a regular ESC right Kyle? You will only need a good 80A esc for the most powerful 6s setup.
Yep, my little circuit would take the place of the receiver for the ESC. Some 20 years ago, I designed the software for a PicChip 16F677 that was the controller for a brush type ESC, rated for 40 Amps at 60 Volts DC. (Batteries were 38 RC2400 Nicads. Did a lot of flying with various versions of that ESC. The same software also included a servo driver, servo pulsewidth measuring, loss of signal recording, and several other things.)

Dennis V
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Old 07-30-2010, 06:13 AM
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Ok some initial testing of the high power 64mm fan unit has some reasonable results.

Running an ARC2847 inrunner and a very cold 2600mah 4s1p pack, 80A ESC, exhaust cone pulled down to approx 51mm which is 90% FSA.

Quick test got the following:
13.5v / 70A / 950W / 50,700rpm / 1380 grams thrust / 322kmh efflux

Pretty good thrust and efflux, very solid even in the plastic housing, in fact its lightweight and VERY usable in the plastic housing!

Once I can fine tune the setup and make a more uniform thrust tube and warm up the battery packs I will get some video of the testing.
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