Round tubes are back.
The goal of this build has various missions:
1) show how easy it is to build a ship on par with commercial ships.
2) stay aloft for over 30 minutes carrying a full-size camera.
3) use low Kv motors and low voltage to create an efficient ship but stable camera platform (a design that is usually contrary to the objective).
4) fly at slightly less than 200 Hz but also be able to fly at 200 Hz (the evil frequency) to test the impact of doing that when vibrations are only managed by frame stiffness and low mass.
5) test light methods to mitigate the more fragile cloth/woven carbon tubes.
6) test APM code flexibility on flying a new octa motor layout.
After a successful test using braided carbon fiber tubes that are basically indestructible, strong, stiff, light, and provide a surface that is easy to bond, this discussion will focus on using cloth or woven carbon fiber tubes. Relative to braided tubes, woven tubes have a smooth surface (not as easy to bond), have a lower resin content, and layered fibers. Braided tubes use fibers that are braided from the inside layer to the outside layer. Woven tubes stack and bond either cloth or tape layers placed in multiple directions to derive engineered stiffness and light weight. But unlike pultruded (where most all fibers in one direction), there are axial fibers to keep cracks from propagating. Why not just stay with braided? Woven carbon tubes are more available, come in more sizes, and are lighter for their stiffness.
This discussion will go from design through flight tests.
Replies
Hello! Can you share worksheet for quad? Thanks!
CAD Quad Excel Worksheet. The regular is the acro ship that I just build for my brother. The other two are for photography. But change the shapes as you like to suit your purpose. Contact me if you have any questions.
Custom Quad CAD.xlsm
thanks!
Thanks a lot for your explanation.
Eventually I got the answer! Did you try to simulate the disaster? Can the X2 or H able to recover in this situation? Actually I want to build a more reliable drones! :)
Very good thread!! Thanks Forrest.
I would like to ask which design to be provided a reliable flight if there is any one/ two props was fail during flight. I like the design of X2 and H!
For those interested, this shows the first build. A lot of good discussion on adhesives and material for a light-weight build.
http://diydrones.com/group/arducopterusergroup/forum/topics/buildin...
Installment X: Repair
Hopefully you never need to read this. But what happens if some part of the frame breaks? There are only three basic parts to the frame:
1: Electronics Platform - Secondary structure holding the central platform to the mast(s)/spar(s) and primary structure if used to maintain the locations of the mast(s) or spar(s)
2: Motor Masts - Primary structure holding the motors
3: Spars - Primary structure holding the motor masts to the electronics platform (the X2 doesn't have these).
Electronics Platform: If it breaks at a primary location, do not repair. Replace.
Motor Masts & Spars: If these break, do not repair. Replace. But if a motor mount or plate fails, those can be easily repaired.
This photo shows the failure of the adhesive bond of a motor. The reason for the close up with my macro lens is that it's also important to discern the cause.
Possible Causes:
o improper sanding of the tube - where the failure started (top of the top photo) there appears to be lack of a rough surface on the tube. This might be why a crack in the adhesive propogated at that location.
o improper sanding of the X mount - There appears to be adhesive well distributed on the X mount.
o improper mixing of the adhesive - This is a bit difficult to discern. If the adhesive is soft, then it is definitely not mixed. But this class of particular adhesive is designed to be a bit flexible so it won't fail from fatigue (being overly brittle). The adhesive when prodded with the end of a paper clip did not appear overly soft. Also, the hole in the top right quadrant of the adhesive and hole in the center indicates that the mix was good because at those points the bond did not fail, the adhesive sheared. The 3M system takes the sport out of mixing as you can use the tubes with a nozzle mixer that gets the job done right. But the downside is more waste. Not only do you discard the first bit into a small pool, but when done, all of the adhesive still in the tube is wasted.
o flying before full cure - it was not flown before 48 hours after cure.
o inadequate coverage - the adhesive coverage on both parts was beyond the area of failure, so coverage was good.
So most likely, this was poor craftsmanship on my part (not sanding the bond area completely). But it could also be that the Hardman Orange adhesive is not as good (or forgiving) as 3M Scotch-Weld EC 2216. It is this later product that was qualified by The Boeing Company and Airbus for use on the floor panels that I created to hold your seat to a stable floor structure in a "9g sudden stop" ... (called something else by passengers). So there is no doubt that the 3M product is good.
To mitigate the adhesive issue, this repair will be done using the 3M product. Doing so will tell me if it was the adhesive or my sloppy craftsmanship. I actually suspect that the two products are pretty close to being the same (both have similar specs). If no more motor mounts fail, then I'll have my answer. If only the Hardman bonds fail, I'll have my answer.
So onto repair.
1) Snip all of the zip ties: holding the wires to the affected motor mast, then the zip ties holding the motor mast to the electronics platform.
2) Remove the nylon bolts/nuts that hold the motors to the motor mounts of the affected mast.
3) Study the failure and try to come up with an approach to ensure it doesn't happen again.
4) Print off a subset of the drawing that will aid in locating the mount that needs to be reattached. In this case, the critical measurement if from motor to motor. So I printed off the two pages showing the aft-starboard outer motor mount and the aft-starboard inner motor mount that failed.
5) Tape the drawing to an even and flat floor. When taping the two pages together, hold them up to a window so see the overlap lines to help align the pages. Then use a straight edge to ensure that the motor mast lines are aligned.
6) Remove the failed adhesive from the mast and x-mount. The adhesive comes off with heat. Set the heat gun to a low setting of around 430F (220C). If you aren't sure, control heat by distance and only apply enough heat for the adhesive to be scraped off. This is a three hand job, so get someone to help or fix the heat gun and bring the part to the gun. The photo shows the part being held by a Phillips screwdriver and scraped by a flat one.
You an use a metal scraper on fiberglass or metal, but use a soft scraper (e.g., wood, plastic, or fiberglass) on carbon. Soft works great on both.
If your X mount has a center hole, drill it out. Lightly sand. When finished, the parts should look like this.
Note: Use the heat gun over cement, metal, or ceramic plate. The heat gun will warp a table/floor or ruin its finish.
7) From this point on, it's the same as the original assembly process. Tape the parts down. Build a tool to locate the mast. Get a weight to hold the parts together during cure and maintain one plane between all the plates.
There you go. Two days later, you are ready to fly hard (you can do light flying the next morning).
The current duration record is held by this build design (continuous motor masts), but with a quad.
https://www.youtube.com/watch?v=2ScZ8zDsVvk
Excellent documentation and scientific approach to your build! It's refreshing to see your focus on weight discipline and the importance of propeller balancing vs vibration isolation. I always like to run-up the motors individually to 50% after the prop is balanced and mounted. This will give a good dynamic test run and any out of balance condition is clearly felt in the frame. Some vibration can come out of the motor bearings. Do the new multi-copter motors come with axial bearings on the bottom now-days? This was problem I ran into with the cheap brushless motors on earlier builds, the bottom bearings wear out after a few hours because they cannot take the side loads in a copter set-up?
Too many copters become masterpieces but are bloated with optional weight. Every piece on a copter is taking away critical flight time that's already at a "minimum fuel" state.
Thumbs up!
Installment IX: Maintenance
A. Props - Every so often lift off, hover for two minutes, land, turn off power to the APM (necessary to end the log), then go fly for fun. When you get back, run the Hover Analysis excel worksheet to see if you are picking up more vibrations. The culprit is most likely planar prop adjustments that are needed unless you are missing a few chunks, so check your prop tip trace. After a crash, also suspect a bent shaft if prop balancing doesn't do the trick.
B. Pre-Flight, Flight, Post-Flight - My older brother, a retired NW Airlines pilot, got me into using a checklist and verbally saying out loud each item as I go through it. Out loud is critical or you will mindlessly skim. Also physically check of each box. Your list will vary depending on the type of electronics you have. See attached if you want to use it to customize for your ship. What I like about this version is:
o it is tailored to my ship. when a camera or FPV is added, then those steps will be added.
o i print off one per battery set prior to every flight; each sheet is good for up to four flights on one battery set
o it reminds me how the radio is set up for each mode (my brother also added tape with words to his radio)
o it's broken down by where i do each task (man-cave, launch site)
C. Batteries & Flight Log - My brother also got me in the habit of tracking one of your most important resources, your batteries along with other flight data (how hard did you crash, etc.). This also can make it easier to identify which APM log was for which flight and what were the payload and weather conditions during that flight.
o it keeps a track of estimated max flight time and amp usage rate for that payload.
o it tracks battery condition so you know if your battery is getting weak.
D. Bearings - Replacing bearings isn't that hard. Just don't do what I did and pop off the axle clip and let if fly where i never found it. There are some blogs on bearing that are really good that talk about sites for identifying which bearing your motor takes and how to buy them. Also, sometimes a stator might break loose from the shaft. That too is easily fixed with Loctite as long as you are careful not to get the glue on the bearings. And some motors are so cheap that it's faster and cheaper just to buy new ones and have a spare laying around.
E. Spares
- Several CCW and CW props
- An ESC
- A motor
- Other parts particular to your ship (e.g., zip ties).
Flight Check List.docx
Log Book.xlsx
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