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Feb 15, 2004, 10:31 PM
Registered User

Need advice for a college prototype project using Ducted Fans...

I'm a college student working on a seinor project involving ducted fans. My project is getting a set (4) of ducted fans to levitate a platform. I'm not worried about powering them because my project will be teathered for power.

I don't know much about these fans, so this is where I need your advice. We've done a test with one ducted fan that we got a hold of, and we are sure that the fan will thrust a platform in the air.. the problem is balancing it so it stays stationary.

We plan on using 4 ducted fans layed out in a square formation. Each pair of fans NEED to spin opposite directions to counter blanace the torque produced by each fan. This will keep our platform from spinning. We'll be doing our balancing control by with a microcontroler and accelerometers. This will in turn control the servo's for each of the fan motors.

What we need advice on is what fans and motors to use. Keep in mind we're on a limited budget and time frame (5 weeks to gather our parts). We need ducted fans that can spin in either direction (so they can counter torque each other). We're hoping to find something at around $400 US for all 4 fans/motors. Our main problem is finding fans that can have the propeller reversed so they can spin in either direction.

Please help us in finding our fan/motor combo's. We need brands, models anything that will point us to right direction. We'll post updates of our project as we develop it.

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Feb 15, 2004, 11:47 PM
cawink's Avatar
Hey Michael, what college?

how much weight does the platform have to support?

in reading your post, using servos to control motors sounds like something glow-powered, so maybe you will get more replies in the glow section.

If you want a ready made EDF, maybe the wattage one found at or other similar sites would do. They are only about 25 dollars each, and the speed400 motors can easily run in reverse if you just reverse the 2 wires going into them.

the whole unit is at

though I think you are thinking of a gas powered DF.

Feb 15, 2004, 11:51 PM
Registered User
Reversing the motor wires won't work for the rotor is designed to spin in one direction only.
Feb 16, 2004, 12:19 AM
Registered User
I'm at University of California Santa Cruz.

This project is actually for a computer engineering class. Main goal is to get the microcontroler setup to sample data to control the fans to keep the platform level. We're not too knowledgeable with these fans but we believe we can get it to work (should be fun trying to also).

We are looking for electric power. And like dw1122 said we need more than just reversing the motor's rotation. Our biggest problem is finding rotors that are ment for the opposite rotation.

I mentioned servo controlled because thats what my TA suggested. Its some item that takes a electronic pulse width and relays power according to the pulse it recieves. He thinks this is better than a speed controler because we will instead run the motors at a percentage of duty cycle, rather than speed up or speed down to keep the platform balanced.

Our weight requirement isn't too tremendous. We're hoping to keep weights not including fans/motors to about a pound to two pounds. Just enough for a lightweight frame and the weight of our prototype micro chips. Unless we can find a battery source to power 4 fans and keep weight down we're going to have to do this teathered to a powersupply. Like I said before our main goal (and learning) is to electronically and autonomously get the platform to hover stationary. If we have enough time we'll try to write up some code to possibly move the platform around with a remote control.

I know this project sounds kind of extreem to try, but if it works it could lead to some interesting hovering models.

Thanks cawink for the link I'll check it out and do more research.

What directions do fans usually spin (clockwise or counter clockwise)? I'm hoping that there is some manufacture out there does make rotors that spin the opposite way.

Feb 16, 2004, 01:05 AM
Registered User
I don't think you understand what a servo is....its a proportional actuator and cannot act like a speed control. A speed control is what you runs off the same signals (1-2ms or something like that) and it adjusts the motor speed according to it.

I am just learning about ducted fans, but I do fly helis so I know a little about getting something to hover. If you will use counter rotating fans, then to control yaw you will have to change the fan speeds to increase power on one set of fans and decrease on the other to keep the total thrust the same. I am pretty sure you won't find a fan that runs "backwards". normal engines and motors run counter clockwise when looked at from the front. I guess you have your heart set on ducted fans intead of props which have more thrust and are not too hard to find reversed?(the more diameter, the more thrust). If you really want fans I would recommend that you just mount the fans to where they can be rotated (with servos) to "twist" the thrust.

Here are some links to some stuff similar to what your making.

Good Luck,
Feb 16, 2004, 01:09 AM
high-speed freak
opualuan's Avatar
edf's are meant for high rpm, high pitch speed... not really for a ton of static thrust at near zero air speed.

I'd try to find left and right hand props, and use a geared or outrunner motor system sized around the props you can find. you can build them into ducts if you need to.
Feb 16, 2004, 01:23 AM
smug in granny panties
monkamarm2000's Avatar
op is right, your better off playing with ducted props. that way you can find matching ones with reverse rotation. And check out some stuff they did at I think Texas A&M, they found ducted props were not only more efficient at low speeds, but also found enhanced thrust, and more importantly stability, in making square outlets. Square outlets reduce tumble there by enhancing stability. These were tests's were for VTOL also.

Feb 16, 2004, 04:43 AM
Registered User
Doc Watson's Avatar
look at, Ducted props will be more efficient but the Kool factor of ducted fans is worth it...........

You need 3 gyros and a control system from

Doc Watson
Feb 16, 2004, 05:32 PM
Senior Member
sguty's Avatar
I'd have to question whether you really need contra-rotating fans--the stators on a properly designed fan take a lot of the 'swirl' out of the efflux, and the torque factor on EDFs is negligible compared to propped planes. With the fans placed any distance away from the center of mass, I don't see a high likelihood of fan-induced rotation.
Also, if you're planning on gimbaling the fan units, you could take out any residual torque component there, or use a vane coupled to a gyro to offset any torque effects.
It sounds like your TA wants to see you manage the platform hover purely through the power modulation to the fans? It would still be possible to null out any rotation component by having each fan in a pair canted slightly toward the other to allow some differential thrust around the yaw axis if needed/desired.

Good luck with the project, and post some pictures so we can see how it turns out!

Steve G.
Feb 16, 2004, 06:50 PM
Registered User
There is a unit on the market that uses four props instead of fans,
with a micro contoller that maitains yaw and rotation. I can't remember what this unit is called, but is suppossed to be very stable and controllable. I have seen it in several R/C magazines, but the price kind of put me off from any inrerest.anyhow it may be worth a look.

Feb 16, 2004, 07:27 PM
Registered User
Ed Waldrep's Avatar
Maybe Cliff is talking about the Roswell Flyer? It's a four motor geared prop electric hovering platform. The geared props are supported on the ends of carbon fiber booms in a X configuration. The avionics/gyros are in the center of the platform. I don't believe there is any gimbaling, control is achieved by differential throttle to the individual motors. There is a "tail" attached to help with orientation I believe (there's no fuselage so seeing which way the "fuselage" is pointed can be difficult).

A cheap platform could be built by using some of the geared electric prop drive units sold by GWS. These units come in a variety of sizes with different motors. For example the EPS 300C units have something like 9 in props. You can get a fairly high thrust to weight ratio with geared props. The efficiency of a geared prop will be higher than a ducted fan, especially when you compare a 9 inch diameter disk area to say a 2.5" ducted fan. Even if you use the stock brushed motors, you'll still probably get more lift per watt vs a ducted fan. You could use brushless motors for their higher efficiency, but for your purposes the cheap brushed stuff should be fine. You'll have to worry more about prop strikes if the vehicle tips over, so if that's a worry then ducted fans might server you better.
Feb 16, 2004, 07:30 PM
Registered User
Sounds like an interesting project. I second Monkamarm on using ducted props. This will allow you to use left & right hand props (3 or 4 blades) available readily at your local hobby shop.

I can see having opposing fans along pitch and roll axes. Then you only need 2 gyros. 2-Geared brushless (B/L) motors might do as masters on each axis & balanced by a slave via gyros.

You might be able to cut down diameter of prop pairs to suit power (torque) required. Of course, thrust from the df units is what you need. You can test each df unit for thrust; just remember to give each round inlet rings. As Monkamarm mentioned, larger diameter gives more thrust & gearing will allow you to use larger diameter. B/L motors rotation can be easily reversed by swapping 2 of 3 leads.

Vectors & vanes can be made to work, but keeping it simple will probably cost less in the end.

Have fun with your project & post any progress or update if you can.
Last edited by PhilLin; Feb 16, 2004 at 07:33 PM.
Feb 16, 2004, 08:07 PM
Registered User
Hi Ed,
That's the one I was referring to. Don't know much about it though. When I saw the 6 or $700 price tag, I instantly thought about all the cool jets I could do for that kind of dough and quickly went to the next page.LOL

Feb 16, 2004, 08:30 PM
Registered User

yeah, use gyros!

I agree with an earlier post...just get three gyros to lock out rotation on all axis, and then control throttle for vertical height.

You'd have to make two or more of your DF units able to turn on a horizontal axis to counteract the torque. But the gyros could conceivably control the servos attached to each DF rotating unit, similar to two helicopter tail rotors.

Sounds like a fun project, especially with someone else's money.