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I was already crazy...DIYDRONES made it worst ! The story...part 2

Posted by Mario on September 30, 2010 at 5:10pm


This is part 2. To avoid ending up trapped in the twilight zone read Part 1


Hey Guys! First, I have to confess. I lied... It did not started by looking and drawing on an autocad 2009 computer screen.


It started with some delirium about designing a different kind of quad. I talked about it to my partner and we both agree that variable pitch quad was something to consider. Before many of you start screaming about complexity I would like to give you my position about it.


The venerable 4 motors / 4 ecs quad is the way to go for simplicity, affordability and quick fun.

It is the perfect platform for what it is intended for. Some are dreaming about a quad entering a contest like the outback challenge but we all know that autonomy is not what a quad is made for.


Also, redundancy is null in a traditional quad. Loose one motor and zap it goes. Loose a prop and zap it goes again. Lets pushed it further, what would it be like to have a quad to do 3D flying like a TREX 450 helo? And maybe a very different kind of 3D flying? What would it be like to have a quad flying with the speed and the autonomy of a plane? What would it be like to have that kind of quad doing it with absolute redundancy and also with total safety to surrounding peoples and infrastructure?


That is where you will say I have got crazy. My friend and I have the intention of proving you right about this craziness by proving you wrong about the limitations of a quad.


One last word, this one about KISS (keep it stupid simple). It is my opinion that you can KISS a simple design by design, OR, you can KISS a complex system by a simple design. Both result should be targeting a different mission and be good at it. DIY does not keep one from making it a complex but efficient system. Alright, money can do that so that is why we also added that requirement to our project.


You can now see that we are indeed crazy and some of you probably are to. Those one will understand that a guy can't sleep over some crazy ideas and some times find the solution in the middle of the night. That is what happen to me when at 2 o'clock in the morning I saw 4 penny's standing side by side on the night table. ZLAMM ! Here is the simplest way to have 4 rotors turning by opposite rotation pairs. You all know that it is a requirement for yaw control of a quad. Many have tried to figure it all and it was there, costing only 4 cents.


So now, talking about affordability... What looks just like a quad arm but with a variable pitch head? Many of you again thought about that but a few tried it. You are right, an helo tail boom seems to fit the profile. And what is the most common helo with easily available, affordable parts? The trex / clones family. Just check on eBay, it is crazy what our Chinese friends can do for almost nothing. If you want some quality, you guys from the US are pretty good at it although a little bit expensive. But hey ! you get what you need for the place you need it.


Ok now for my Fans Club, here some more details... Please understand that the next video clip is showing an hand drilled crude prototype never intended to fly. It was merely a proof of concept for a gear train and also maybe a dream catcher. If this is bothering you and your are disappointed, I will stop right here, just let me know...


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Comments

  • Mario October 1, 2010 at 7:33pm
    @ Joe

    Your concern are very valid and believe me we are seriously anticipating them. We are starting the development with stock trex 450 gears set. If you look how a 450 is doing when flying #D, I would say that the gear train is pretty tough. Any ways, a bigger gears set like the trex 500 and / or a torque shaft drive instead of a strap is part of our contingency plan.

    And what if I tell you that aerobatic could be carried out very, very slow?

    Thanks for the support !
  • Mario October 1, 2010 at 7:20pm
    @ Ted

    I like you Ted !

    Two motors, around Tex 450 / 500 series ratings hooked up via Trex 450 power gears and one way bearings. That is our first redundant system. One motor can drive all four rotors heads and if this is just to bring back the quad safely to ground, it is still redundancy to me.

    A Trex 450 weight is about 700 to 780 g with a motor rated around 3800KV and a 3s battery at around 2200mA/h. A trex 250 has a flying weight of about 350-380 g with a rotor diameter of roughly 430 mm. That means that a trex 250 rotor would require to produce at least 350g of thrust just to stay in the air, but as you can see here, it is doing way more than that. And we are not even considering the lost power that is used just for yaw control via the tail rotor.

    If I tell you that so far, the expected flying weight of our quad will be around 1200-1400 g and that it may have 4 sets of trex 250 blades (205mm per blade), would you reconsider your concerns?

    As you can see in the latest pics, everything is fully symmetrical so weight distribution is under control.

    Ted , I like you because you speak up your mind... please keep it that way.

    Any time my friend!
  • Moderator
    John Church October 1, 2010 at 6:46pm
    I think this is going to be a nice machine. If I were putting my own together, I'd use the Arducopter code almost right out of the package, later defining two more outputs for independent ESC control/power management etc..
  • Mario October 1, 2010 at 6:23pm
    @ Sebastian Gralla

    I know who your talking about. It is the HG3 from FoxTeam. We have to raise them our hat for being the first one to have posted a video of a flying variable pitch quad.

    A few questions for you: How long your quad could fly at a 100km before battery depletion?

    To me, autonomy is how long you can stay in the air. Range is how far you can go and come back. So if your quad can fly for 10 minutes at 100km/h and mine let say hypothetically, can fly for 45 minutes at 50 km/h, wich one has the best autonomy?

    How much cost your hecta or octo? because for me a quad is not an hecta or octo so why compare oranges and apples? Any way, if your octa or octo cost less than a quad I will by a dozen.

    Here, I am talking about a quad with 2 motors coupled with one way bearings / gears ( Oh cheez ! now you know!) and only one could rotate all four rotors heads.

    So the reasons ... just plain fun of proving you wrong my friend.

    With all due respect!
  • Mario October 1, 2010 at 6:06pm
    Whoa Guys ! You are getting pretty aggressive... I like that ! I guess I will have to start to answer to all of you soon but before, just for the pleasure, a few more pics. For the ones who wants to know what the rollers are for? please be patient, we are not there yet.

  • Wil S October 1, 2010 at 5:29pm
    I hope it works and I am very interested to see if it runs out of collective vs RPM. If it does I think you could still make it work in this configuration but the mixing is going to be complex without four motors.
  • Moderator
    John Church October 1, 2010 at 5:14pm
    Luckily, I don't think this will be the case since the individual heads won't be articulated and used for control. This looks like it will use the same control principles as a fixed pitch quad, substituting pitch for RPM to impose a torque.
  • Wil S October 1, 2010 at 4:39pm
    I may be wrong but I think the system will work great in a hover with no wind. Problems may occur as you transition through ETL if the rotors aren’t hinged or allowed to droop and flap. Typically in a variable pitch design the blades can articulate or the Rotor Head can see-saw. This allows the retreating blade to provide as much or slightly less amount of lift as the advancing blade. It is far easier to mix the throttle settings to accommodate for this effect when each rotor has its own motor in a fixed pitch design. To take advantage of the variable pitch the motor or motors should stay at a fairly constant RPM and the control surfaces (rotors) will need three inputs.
  • Joe Bloeski October 1, 2010 at 12:03pm
    There are two motor so there is some level of redundancy. My bigger concern especially if any sort of aerobatics are expected is how the gear train will respond to four quickly changing loads as the rotor piitches are quickly changed. Level flight when all rotors are pulling at about the same load should be fine but there maybe problems when the four have sudden changes.
  • Ted October 1, 2010 at 11:54am
    This is a really cool project for sure, and not to be a nay sayer, but I also see a few issues, it will be interesting to see how you guys resolve them.

    -To start, there is no safety/redudancy since there is now as far as I can see, only one motor. (A typical 4 motor quad actually can fly with one motor down, not well admittedly, but it can do it well enough to land)

    - You are going to need a big (heavy) powerful motor, specially if you want to do aerobatics. Now all four props instead of having their own motor, all need to pull from 1. The single motor will have to now do the work of 4, plus make up for all the drag and resistance created from all the belts and pulleys.

    -Big motors need big ESC's and big batteries, and with the draw this is going to want on the batteries, your going to need some serious battery firepower, 40+C packs, and I would imagine at least 4-6s packs.

    -It also appears the motor is offset, I think this will cause issues since you now have a weight bias that is off center. A bigger heavier motor will compound that issue, and then trying to trim each individual variable pitch prop will become a nightmare, so you will probably need to either center the motor, or throw some balast on to counter it, but that would be yet MORE weight.

    I still think its a very cool project, and I hope you have plans to solve these issues. I look forward to your next installment.
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