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› Designing an RC hover bot. Can anyone help?
02-11-2003 07:25 PM  14 years agoPost 1
Uncletimmy

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Okay, First Post here. Guess I better explain myself.

I'm an Aeronautical engineering student studying at Glasgow University.
I've beeen given a project to do with my team, the brief being to design and build an executive toy model air craft for use both indoors and outdoors.

We're in our third week of development and have become very stuck.

Information on specific details of components is very hard to find; The department subscribes to all kinds of journals and has a library etc... But very little information on smaller Aircraft. (For anyone interested, Reynolds numbers are a big problem).

Can anyone supply any links/information relating to small scale aerodynamics? Specifically propeller thrust (I say propeller as we are proposing a contra-rotating blade design - No cyclic or collective pitch, more of a sort of tilt rotor idea.)

Yeah, Any response, at all would be most useful. We're really quite stuck.

I am more than willing to discuss any relevant matter what so ever.

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02-11-2003 07:43 PM  14 years agoPost 2
Doug

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Port Saint Luice Florida....

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My suggestion is to do your own testing at your chosen scale. Use electric motors so that you can use the Current/Voltage along with the thrust to provide your curves. It sounds like you have bitten off a lot and unless it is stupid simple (like a 10/6 prop on a pencil spun between your palms) control and stability will be a big problem.

First member of Member of Bearings Anonymous

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02-11-2003 08:41 PM  14 years agoPost 3
Uncletimmy

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He he... We have been fed more than we can chew I'm afraid is the case...

The Control has not yet being examined, as the project is still in very early development; We're supposed to prove to our co-ordinator that the project is viable by thursday. Ie; For Steady hover, Thrust = weight, so We're just gathering data of weight and propeller efficiency.

One major problem that we have is Static Conditions: Propellers are designed to move through the air not sit in it; rotor's are designed for hover. Also, our aim is to produce a very small craft (Blade Diameter of say 18"), so there are no rotor's available for our purpose [Or I haven't found any.]

Also, We needed propellers / Rotor's For both Clockwise and Counter-Clockwise Rotation.

One more question What are the dimensions on the propeller's short for? Diamerter and what? [I could tell you all about Naca aerofoils but haven't got a clue about models. ]

I have a weekly meeting with our Project Co-ordinator, And The group have discussed that we are going to ask for funds for testing etc...

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02-11-2003 08:55 PM  14 years agoPost 4
Indrid

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Hamburg, NY

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you can always look at the designs of piccolos and hornets, those are very small helicopters that seem to match your requirements.

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02-11-2003 09:15 PM  14 years agoPost 5
midwestpilot

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Crystal Lake, IL

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props...

you are right about the diameter...say a 10-6 prop does have a diameter of 10"...the 6 Refers to pitch...specificaly it means that in one revolution of the prop the craft would move 6"...this distance is in theory not reality...but anyway larger second number = more pitch to the blade

In life there is no spacebar!

Rich Erikson AMA 6175

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02-11-2003 09:16 PM  14 years agoPost 6
Uncletimmy

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The specifaction is that it has to be able to fly outside, without a tether, and must lift it's own power supply.

I've had a look at the piccolo, it was the first thing we came across. Anyone know how much it weighs.

Our preliminary calculations so far look like 600g model, with 1kg thrust or there abouts....

Any recommendations for motor's by the way guys?

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02-12-2003 01:07 AM  14 years agoPost 7
Mad Scientist

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Boston

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I'll give you a big headstart by recommending you buy 6 Kokam or E-tech Li-Poly 1020mah battery cells to use for a power source.This alone will save several hunderd grams from your project. You also need a charger.
Wire the battery packs in several different ways until you get the power you need. Start by testing 2cells in series(7.4V-4A), 4cells 2s2p (7.4V-8A), 3cell 3S (11V-4A), 6cell 3S3P (11V-8A)
Have fun, I could tell you the rest, but what would you learn from that?

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02-12-2003 01:46 AM  14 years agoPost 8
Dave_D

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Philippines

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I say take a gander at http://www.rcgroups.com for all your electric powerplant queries as the crowd there is more attuned for electric flight.

You might also take a look at the Vectron Blackhawk, the Draganfly and Hoverfly helicopters for some ideas how to get it to work.

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02-12-2003 02:03 AM  14 years agoPost 9
KeithA

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Friendswood, TX

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Uncletimmy,

I think that you will find that a tilt rotor counter-rotating design will be more challenging to design and difficult to control than a collective/cyclic system. Why? Mainly because I haven't seen one in RC modelling yet, and some people are ONLY in modelling to do the "undoable". I hate that word because I am a mechanical engineer myself. I think that your team will realize that coming up with a tilt rotor design that is "controllable", light enough to fly, and within your project budget will be very challenging.

However, anything is possible with the right brainpower!

While you are biting off more than you can chew, how about a model Hovercraft! Now that would be Way Cool!

p.s. If you continue to be stumped, may I suggest a mini electric flying wing design (similar to the Zagi, but smaller, slower and with landing gear). Not nearly as interesting, but will probably allow you to pass this class PLUS all your other classes! Been there, done that!

Good Luck!

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02-12-2003 12:14 PM  14 years agoPost 10
Uncletimmy

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We can still pass the course by not getting anywhere.

Also, we are trying to do things that haven't already been done. It would be very easy to build a model plane for us, as we built gliders last year, and they're a lot easier. Unfortunatly the hovercraft idea doesn't meet our design specifaction, and a model plane has much too high a stall speed for use in an office.

Also, we know that the control will be a major issue, but the principle of our project is okay.

We currently need a relationship between pitch, rotor diameter, Angular Velocity/RPM speeds, to thrust... That's our stumbling block. I'm pretty confident that we can produce a lightweight model, as we can make it out of almost any material.

If anyone knows of anything to do with motor thrust, I'd appreciate it.

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02-12-2003 12:19 PM  14 years agoPost 11
Indrid

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Hamburg, NY

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well you have come to the right place... i have seen people spout off complex problems when i simply asked them how i can make my heli go faster

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02-12-2003 07:17 PM  14 years agoPost 12
HELI ADDIC

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USA Illinois

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How about keeping it simple and use some kind of helium container for lift?

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02-12-2003 09:24 PM  14 years agoPost 13
Jeff H

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Cincinnati, OH

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a heck of a lot of research has been done on low renoylds no. airfoils.

Go here and see a ton of Dr Seligs work.
http://www.aae.uiuc.edu/m-selig/


Also download a demo of motocalc @ http://www.motocalc.com/
It doesn't completely apply to you but it does have some neat relationships with prop dia, thrust, speed, pitch. You may find it useful.

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02-13-2003 12:24 AM  14 years agoPost 14
Barjam

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Olathe Kansas

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http://www.rctoys.com/draganflyer3.php

Check that out.

We actually designed something very similar (even speced out the parts/wrote the software) but never finished it. Basically we felt the flight times would suck (we calculated about 5 minutes).

It sounds like your toy will require gyroscopes. If you dig a little bit you can find people who will sell the primary gyro component that Telebee uses. I believe this is an analog device, but with some trivial circuitry and a PiC it would be easy to interface with. The price for this component is 20 bucks (Yea, Telebee makes a killing, considering they don't spend a dime on QC).

You will more than likely need servos, these too are trivial to interface with using a digital circuit. There is tons of PIC source code out there that already does this.

You will find that simple propeller thrust formulas won't be adequate for use in a hovering craft, you will probably want to familiarize with helicopter theory. There are plenty of books/websites on the topic just do a search on "helicopter theory".

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02-13-2003 12:25 AM  14 years agoPost 15
ncostes

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Va, US

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Do you have access to something like theTwin Rotor MIMO system trainer?

http://www.fbk.com/

Click on Products->Control and Instrumentation->Matlab Applications->Twin Rotor MIMO

This is a system used by some universities in their control classes.

Feedback is a British Company I believe.

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02-13-2003 02:29 AM  14 years agoPost 16
KeithA

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Friendswood, TX

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"It would be very easy to build a model plane for us, as we built gliders last year, and they're a lot easier."

Ah yes, but:

"... a model plane has much too high a stall speed for use in an office."

sounds like a challenge to me if your facts are correct.

Don't get me wrong, rotory aircraft are much more interesting than fixed wing without a doubt!

Best of Luck!

p.s. I've got it - a model Harrier!!!

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02-13-2003 05:28 AM  14 years agoPost 17
Ace4

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Chandler, AZ

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If you want it to hover with hands off control, you are going to need some active control mechanism on both pitch and roll axes. If you are only going to hover, you may be able to get away with fast response tilt sensors, but more than likely you are going to need a gyro on each axis. For $20 that Telebee gyro sounds interesting, I don't know anything about it, though, like how it drifts,etc. I know Analog Devices has 2 new gyros out (or will be out any day), they're supposed to be $33 each and have temperature sensing circuitry onboard the gyro unit already. I think you really should shy away from tilt-rotors, unless you have a thorough understanding of dynamics & control systems, or can learn really fast. You're going to need to be able to come up with and implement a controller anyway to maintain pitch and roll while hovering, however it will be much easier if you don't have your rotors tilting.

You can check out this hovering experiment. The company makes control system experiments for universities, and that one has some documentation about controlling the 4 rotor hovering machine, however theirs is fixed to the stand so it doesn't actually fly. It also can use rotary encoders since its fixed. They may have some more papers online related to some of the other experiments, you can probably get some info from them too. Heck you could even email them asking if they would be willing to provide any info about propeller thrust etc.

As for thrust, just go out and get an electric motor, an adjustable power supply, a couple of different props, and a postal scale, and you can set it up so you can measure static thrust (lift in your case) vs power required for each prop and figure out which is most efficient for your purposes. Efficiency is key for small electric VTOLs, since you don't want battery weight to kill you.

Ace4

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