Replies to This Discussion

Permalink Reply by Coby on March 28, 2011 at 12:04pm

Hey Bill,

You may not be getting a bunch of responses since most of us are using fixed pitch/direct drive electric power trains in our multi-copters.  Which BTW, can scale to carry the kind of weight you spec'd.

 

I wish I could help you out more.  There are similar issues to work through with fixed pitch/direct drive setups such as prop size and RPM's, but you are adding a few more variables with variable pitch, constant speed rotors.

 

Keep safe in AFG.

 

 

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Permalink Reply by William Bishop on March 28, 2011 at 7:09pm

Thanks Coby,

I realize that the majority are using the BLDCs but I would like to design reliability into this monster.

If a BLDC motor dies can the other three carry the acft back to the helipad?  Maybe the code can convert to a Y airframe config. I would buy four of the monster Hacker A50s if I thought I could get enough power on board to keep it afloat for more than a few minutes. I even looked into putting a IC engine onboard to run alternators that would help with power but everyone treats me like I'm trying to turn a turd into a snickers bar.    I have asked unanswered questions that I am apparently too dumb to figure out for myself.  I wish it were that easy so I could plug in a target weight and get answers on Motors, props, ESCs and batteries.  I appreciate any tidbits of knowledge at this point.

Saludos

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Permalink Reply by Christof Schmid on March 29, 2011 at 12:02pm

Hi William

Many things are based on trial and error in this hobby. I usually try to calculate as much as possible but then I make a sample for proof of concept. If that works I build the project. Usually I make the adjustments needed and then reconstruct the project based on the experience made,

I try to give some more answers to you catalog.

 

1. total airframe weight.  I think that 25 - 30lbs should be the target. Thats up to you.

1. 
2. Motor selection - would the Titan ZG 45SL work OK rotated with the shaft facing down/vertical? Yes. It runs in all positions. Shaft up is good to start it.
3. Rotor blade characteristics - length and variable pitch. 430mm but what material?  Wider= better? Start with a standard Align blade. They are not to expensive and good balanced blades (I think its CFK)
4. What would be the optimal necessary RPMs for hover, flight and maneuver operation? Why dont you start with 2800 - 3000RPM as I mentioned above.
5. Weight of each rotor head/blades - power requirements total for each rotor assembly. Have a look in my post above +- 300W for hover per head. The weight is "lightweight" when you use a trex 450 head. If you dont mind I do not take apart a 450 to take the weight. You should find the weights on aligns website. There is a ready flybarless 450 head available.
6. Gearbox selection -high efficiency, high RPMs, Speed Increasing gearing Please calculate the gearing. You have the data ready at hand. Guess some 1:2.3 or 1:2.5 might be fine
7. Shaft selection - straight fixed or with universal joints (slight alignment tolerances friendly) Use 2 8mm ID bearings. I think the 450 mainshaft is 8mm.
8. All outputs on the gearboxes and shafts should be between 8mm and 12mm? Up to you calculations and layout.
9. Total power efficiency robbed by gearboxes, shafts, bearings and rotor heads/blades Thats something you should calculate or guess
10. Motor selection - based on power - RPMs and HPs needed?? I gave you an idea above.

Everyone please help adding to the list and putting ideas on the comments.

Questions:

1. Does anyone know where to find quality pitch only rotor heads that will accommodate 430mm blades? Again, check align T-Rex 450 flybarless
2. Does anyone know where to find variable pitch 3-blade props that have 430mm sized blades? What would you need that for?
3. Does anyone know any companies that produce high RPM (up to 10,000 RPM) gearboxes?  TEAUSA and DieQue only have stuff for 1000 to maybe 3000 RPMs.  Size needs to be <4" square. Why dont you use a beltdrive to start? As you will fly positive pitch only, the play is not so important. 

 

Good luck

Christof

 

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Permalink Reply by William Bishop on March 29, 2011 at 12:23pm

Thanks again Christof,

I wouldn't have any control, on the four rotors at constant speeds with fixed pitch blades with belts or gearboxes.  I haven't seen any development or discussion on any posts about the ArduCopter code dealing with quad variable pitch systems.  Way beyond my scope to write code...  maybe one day.

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Permalink Reply by Christof Schmid on March 29, 2011 at 12:56pm

William

No I do not think so. You would use as governor on the engine side to keep your rpm constant. The PID System of the ACM code should allow you to adjust your system with collective pitch over swashplate (I guess). Just your servos have to be fast enough. You can supress the vibrations to a certain degree. I would give it a try.

The other solution is using 4 big eMotors in gov mode and still go with collective pitch.

 

Christof    

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Permalink Reply by William Bishop on March 29, 2011 at 2:43pm

Here is a more structured question.  I have been looking at some of the Hacker motor combos and am thinking about going that route to get started and practiced with all of the stuff on DIYDrones.

I won't give up my gas powered dream, but have to get my hands on now.  I'm good at soldering, even surface mount by hand, and good with wires and cabling, mechanically inclined.

If I were to use one of the TRex 500 combo sets x 4:

http://www.aero-model.com/300-450mm-Blade-Class-Heli-Combos.aspx

Would one of the three blade props 14 - 16 inches x 10 pitch found here work OK on a quad? 

http://www.hobbyking.com/hobbyking/store/uh_listCategoriesAndProduc...

 

I am asssuming, probably wrong, that with a stronger motor and a higher pitch, I could calibrate/program the ESCs at a lower RPM rate to use the power to my advantage with more weight on board.

If this is totally wrong, which prop would be better for a 500 sized motor and do three bladed props give more power?  No sweat if not, I'm just hoping for more lift power at lower power consumption.  The three blades are heavier than two....so maybe not.

Thanks man,

BB

 

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Permalink Reply by Christof Schmid on March 29, 2011 at 9:42pm

Hi William

You can do some calcs here.

attached is the answer to your question.

 

Christof

 

Attachments:

• 16x10 3blatt.pdf, 157 KB

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Permalink Reply by William Bishop on March 30, 2011 at 6:55pm

Christof

I came up with two possibilities for the 5 lb per motor.

A whoppinhg 6 - 8 minutes of flight time!  LOL

Should I be calculating for 7.5 lbs per motor to factor in the extra 50% for maneuver?

Thanks for all the advice/mentoring.

Attachments:

• 5 lb Motors.pdf, 61 KB

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Permalink Reply by Christof Schmid on March 30, 2011 at 9:47pm

William

Recalc with propeller airplane when you intend to use airscrews. Best is to use an APC airscrew, they are very efficient. Yes, add the extra 40-50%.

Lets say you want to lift 5Kg, system weight is 10Kg then look for 6-7Kg thrust per motor.

Permalink Reply by William Bishop on April 6, 2011 at 10:53am

Christof,

Please check this post and tell me what you ideas and comments are appreciated if you would...

ESCs & DCBM vs Pitch controlled stabilization

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Permalink Reply by Greg Fletcher on March 28, 2011 at 7:42pm

William, I am sorry, I went to far. If I saw you face to face I would not talk like that.

I deleted that comment.

The technical part I stand by. Helo rotors are geared down from the engine a lot. If I were you I would look into single rotor heli crafts and use their numbers as a guide *4.

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Permalink Reply by William Bishop on March 28, 2011 at 8:09pm

Greg,

I am here to learn.  I know that many of you have spent years in this craft and science.  I was a tech for a while in the mil but I only built electronic surveillance devices and antennas, etc..

I really am excited to get started and I am studying daily.  I will reach out to all that I can in search of answers and help.  If the rotors don't have to be at 10,000 RPM maybe I can go straight 1:1 on the gearboxes.  The speed increasers have been the stumbling block.   I still am stuck on the notion that a gas engine can last and turn radial rotors.

I found variable pitch props...only 9,000 per!  That was just an idea that I thought would bring flexibility to a heavy hard to manage stability craft.

Take a deep breathe and give a brother a chance!

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