Up Up and Awaaaay (slowly)

Discussion in 'Build Logs' started by Jerry Ginn, Dec 14, 2017.

  1. Jerry Ginn

    Jerry Ginn Member

    As a new member and a very inexperienced quad pilot, I may be getting over my head by starting to build my own quad from scratch, or as Tommy Smothers used to say, "made outa scratch!" I have a few ideas to get out of my head so please feel free to tell me if I'm headed into trouble or worse. My feelings are not all that fragile.

    I will start with the frame. I don't want a small fast racer and I'm not ready for a really big quad. I want something big enough to be stable in light winds and to be able to carry a reasonable payload and with a 15-25 minute flight time. I think something in the 300-400 mm range to start.

    I'm going to start with an "H" style because the larger central body gives me more freedom of mounting points, and until I have proven my structural method, I think will be more rigid. I am going to start with a wooden structure because metal, even aluminum is too heavy, plastics are too flexible, and composites to complicated for a start. I don't want to buy parts and just assemble someone elses design.

    Wood offers some challenges of weight and strength but they can be overcome with good design. Just ask Howard Hughes, but don't expect him to answer. Wood has fallen out of favor as a general construction material mostly because of life span, but even more stable materials gain strength by using internal stress to advantage and to reduce weight. Pre-stressed concrete lets us build longer and lighter bridges and taller buildings.

    I thought about using spruce but it is hard to come by in small quantities so I am using pressed basswood. Here is a look at progress so far:

    Vcontrl0001.jpg Vcontrl0002.jpg Vcontrl0003.jpg Vcontrl0001.jpg
     
    Last edited: Dec 14, 2017
  2. Jerry Ginn

    Jerry Ginn Member

    Okay, so I haven't got photo posting quite worked out but I'm working on it.

    The above pics show the current status of the project. Three pieces, (two cross arms and one center plate. By bending the outer frame members ( basswood - 1/4" x 3/16" ) and balancing that against the stress imparted to the 1/32" 3 ply birch skin produces a very stiff and light frame member. These three pieces weigh about 40 grams. There are a few more pieces to add and some fasteners but I see no problem bringing this in under 150 grams. It will be just a bit over 325 mm
     
  3. holtneil

    holtneil Well-Known Member Moderator

    Hi Jerry it's looking very nice , and you can hide any wires in the recess under the frame and arms
    You may have the make the arms a bit wider at the ends to mount the motors ,you can always make motor mounts and then bolt these to the arms
     
  4. mozquito1

    mozquito1 Well-Known Member

    I think you will struggle with the 25min flight time unless you use a car battery sized 8S lipo lol . I got a tweaker with all the kit that weighs 182g only 14cm shorter Base than yours. I ain't getting that to fly for 20 min no matter what battery I use, never mind 25.
    For that kind of flight time you should be looking at a hex or octo. Around 22xx or bigger 900kv motors & somthing like a 30,000mah or two 20,000 evenly distributed. More flight time = more battery = more weight. I would say the size of battery for that frame is around a 4 or 5000mah but you ain't racing. You gotta have a balance & that frame doesn't equal 25min. & if you do, go see Elon musk I'm sure he will give you a position.
     
  5. Jerry Ginn

    Jerry Ginn Member

    Thanks. I'm still working on moving from theory to practice. I just like the feel and look of wood and I'm aiming for a light weight appearance as well as actual light weight. My intention has always been to fabricate separate motor mounts for several reasons but the main reason that I haven't done that yet is because I wanted to see what level of strength and stiffness I could achieve with the prestressed concept. The second reason is that I want to investigate some kind of isolation mounting for the motors. I see isolation mounts for cameras and I have seen some comments that vibration can have an effect on flight controllers with recommendation to mount them to a rubber isolation pad. It seems to me that the vibration should be damped as close to its source as possible and that cameras and controllers would benefit from the inertia of the frame, and other weighty components such as battery, and that it would be easier to isolate the relatively low inertia of the individual motors. In automotive design you might compare this concept with the sprung to un-sprung ratio. If there has been any work in that area, I would like to hear about it.
     
  6. Jerry Ginn

    Jerry Ginn Member

    You are obviously right about that. And I have no experience to contradict you. But 25 min flight is only a long range upper goal. I May never get there but that is the direction I am headed rather than zippy turns and other acrobatics. There might have been a time when I would have gone the other way. I have very good reaction times but I have very poor fine motor control. Due to an error in my original forum registration, my actual age is 79 rather than the 69 that shows up. I don't have the shakes, but I do have the yipps.
     
    mozquito1 likes this.
  7. dragger201

    dragger201 If it ain't broke, don't fix it??? You kidding?

    Hey Jerry.................one of the things I recommend(and use myself) is something called "eCalc" for a fairly good idea of what will work and what won't. It takes a bit of getting used to, but it's actually been fairly accurate in the results.

    https://www.ecalc.ch/
     
  8. mozquito1

    mozquito1 Well-Known Member

    You can learn new tricks. 79 is young,
    I seen a bloke in yesterday's rag that was 113. Maybe that 20,000mah is a bit excessive but you gotta go big for them flight times.
     
  9. Jackson

    Jackson USA member at large

    Since you like to tinker, look into using packs assembled using 18650 Li-Ion type batterries. Lotsa vids on YouTube. You often see folks using Panasonic cells (low C rates, ~4.8A rated) , but these days you can get many higher discharge rate and mAh cells. And note unlike LiPos these cells can can be discharged to 2.5V with no problems.

    Good place to shop.
    https://www.imrbatteries.com/18650-batteries/
    These look good, and are rated @ 10A.
    https://www.imrbatteries.com/lg-mj1-18650-3500mah-10a-flat-top-battery/

    Worth a peek.


    This guy uses them all the time.

     
  10. Jerry Ginn

    Jerry Ginn Member

    Thanks for that link. I was sure that there had to be something like that but had not been able to locate it. I have joined and have spent a few informative hours playing with the possibilities. There are critical design considerations that I had never even considered, mostly because I'm not sure that the raw data to make the calculation is easily available elsewhere. Motor temperature as a function of prop pitch is a good example of that. This design tool will certainly save a lot of time and disappointment as I get into the choice of components. Thanks again
     
  11. Jerry Ginn

    Jerry Ginn Member

    That dangling battery packs makes me think about some kind of mid-air refueling capability! Whadaya think?
     
  12. dragger201

    dragger201 If it ain't broke, don't fix it??? You kidding?

    Hey Jerry......if the 18650 batteries is the way to go.......I would stay away from Panasonic batteries. As someone who vapes and built my own boxes........that is the place to look for info on 18650 batteries..........

    https://ecigarettereviewed.com/best-high-drain-batteries-for-sub-ohm-vaping-2015
     
  13. Jackson

    Jackson USA member at large

    I think fmkit is just a wild and crazy guy, but I do like his style. :)
     
  14. Jackson

    Jackson USA member at large

  15. T.C.

    T.C. Active Member

    Good work so far.... I think 40 grams is pretty darn light. Wouldn't exceed the 150 though.
     

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