The purpose of this posting will be to document the building of a video capable low vibration quad with FPV/OSD that flies for 1.5 hours.
- flight path range > 15 km (2km radius)
- max speed > 30 kph (capable of handling moderate winds)
- GoPro camera/video on gimbal
- optimal designed vibration dampened electronics platform
- fits in a suitcase
- quiet (will not disturb animal life)
It will document the following in installments:
- design validation
- frame+motor mount build
- propulsion system build
- vibration optimization method, test, and analysis
- vibration dampened EP build
- electronics build
- gimbal build
- battery optimization & build
- propulsion system optimization
- flight tuning
- flight & FPV test
- video test
Step I: Design Validation (does design satisfy the criteria)
1) Fits in suitcase - This is a plan view CAD drawing of the ship frame and VDEP support base along with approximate location of the forward GoPro and aft GPS. The ship was made as wide as possible to fit into a standard 19" wide x 26" tall suitcase.
The white area is the inside of the suitcase. With motors (or props) removed and safely placed in foam pockets, the ship can flex under high load enough to survive luggage handling. The size of the quad (between motor axles) is rectangular at 24" wide x 17.437" long.
2) Quiet - With 17.25" or 16" props (the two contenders), the spacing between props is 0.187"/6.75" and 1.437"/8" respectively. The motors are either 268KV or 380KV. The 16" props will be the quieter of the two sets, but either set produces low db at the above stated spacing.
3) Flight Path Range of > 15 km - This was demonstrated while breaking the world duration record. The most efficient flight is at approximately 10 kph. Props/motors to be similar to Rufous (the duration ship).
4) Max Speed > 30 kph - The battery chosen in the Preliminary Design Review was a 6S6P LiIon. At 5 amps max per series, the 6P battery allows about 30 amps for the ship without chemical collapse. This puts about 7 amps to each motor. Hover is at 1.8 amps per motor. So the ship will be able to accelerate at about 3 x gravity until drag overcomes the acceleration. From prior knowledge, 2g acceleration is enough to counter moderate winds.
5) GoPro Camera on Gimbal w/ 90 degree FOV - GoPro gimbals are less than 4" wide x 4" long. The worst case forward spacing between props has 2.75" to spare. According to the calculations in the Excel Custom Quad CAD, with the camera 9" in front of center as shown, the FOV = 90.8 degrees (the GoPro has an approximate 90 degree FOV).
6) Optimal Tuned Vibration Dampened Electronics Platform (VDEP) - After the frame is built, motors mounted, electronics attached, one Pixhawk will be mounted on the VDEP base and and a second Pixhawk mounted on the VDEP. Different dampeners and quantities will be placed between the two levels, brought up to different flight vibrations, with the vibrations compared for a variety of weights. The VDEP will contain the mass of the battery, gimbal, and other electronics (mass being the best damper). The optimal set/quantity of dampers will be chosen from the tests. The test will focus on 3D offset-compression (conventional and proven) style dampers. 3D Trampoline style dampers may or may not be tried. Thus while tuning will be optimal, design may or may not be optimal.
7) Other Design Criteria
- GPS/Mag located more than 2" aft of the battery to minimize magnetic interference (see box in back of drawing); longer wire cables needed between Pixhawk and GPS/Mag.
- Total ship weight less battery < 1026g (not easy but doable)
- Stiff frame (using .6" diameter carbon tubes; same as duration ship; has proved to be quite stiff/light and crash resistant)
- PixHawk bonded to frame for precise control (the area in the center of the drawing is the pocket for the PixHawk).
Very interesting proyect Forrest I'm follow it. I'm in about 25 min yet but very happy, I like your proyects because they really fly not only hover as many long fly videos in you tube.
Excellent Cala. I'm hoping to convince a friend to create a post where he lightens, in steps, a video platform he operates from a proven QAV400 to increase flight time to over 40 minutes without sacrificing his 60mph top speeds or the basic QAV400 design. The the discussion would show for the QAV400:
- weight and duration impact
If you are ever interested in doing the same, I'll be glad to help.
That's good, thank's Forrest, now I limited for customer laws to import things but slowly I'm trying to make some adjustments to the setup to improve my cuads, I find a Tmotors sale for my first cuad (the vibration one) but I have to wait to february that a friend travel to here and bring it to me UFF! , then I have to choose props if 10*4.7 that I have aren't adecuate for that motors and find another caritative friend that's travel to here, now i'm working in my Tarot I'm going to share it's vibration results in few days, I learn a lot with your lessons, Thank's
What will be your objective of two pixhawks (one Pixhawk will be mounted on the VDEP base and and a second Pixhawk mounted on the VDEP)? To compare vibrations on both ?
to tune the mass of the VDEP (Vibration Dampened Electronics Platform) to the dampers, i need simultaneous reading on the frame and VDEP. In this way, i can figure out the change in vibration at the VDEP. the types of dampers will be swapped out, the quantities of each will be changed (3 to 6), the mass of the VDEP varied, all done at various throttle levels. hopefully the result will be a table for how to choose the best dampers for your VDEP given the mass of the VDEP.
the Pixhawk offers the advantage of dual accelerometers running at different input rates resulting in more reliable vibration data..
once the VDEP is tuned for its mass, the second Pixhawk (the one on the VDEP) will be removed so the final build can continue.
the other approach would have been to buy a second Extech Vibration Meter. But at over $1,000, going with a second Pixhawk seemed the more miserly approach.
Results of these analysis will be interesting. I use a cheap xcam vibration !easurememt device to tune the dampening of my gimbal. So far I had best result with the secraft silicon rings damping system.
put one on order. i'll test it too.
really liked your post on your test. will have to take a longer look and see how it was done.
You suggest to open an especific post for each cuad and post there the evolution?
friend me and i can help you create the forum for your ship. the place to start is the baseline flight. what is the ship type. how long does it fly (keep one battery for the sole purpose of the duration tests). and what you plan to do to improve it. but only if you are interested and have the time.
Step II: Frame + Motor Mount Build
Tape the frame design to a flat surface
- For a flat surface, you can use the floor, a table, but not your wife’s dinner table, please. On floors watch out for joist waves and not all tables are flat. Check for gaps and ridges under a long straight edge. I created a flat table made from ¾” plywood screwed into 1” and 2” extruded aluminum framing. The table doesn’t have to be level, just flat (planar) in x & y.
- Print out a full scale drawing of the frame, motor mounts, and other key elements.
- When you tape the drawing to the table, be aware that tape has a thickness. So if tape goes over one end of the drawing of the motor mast, even up the middle and other end using the same tape.
Prepare the Motor Mounts
- Buy or cut out motor mounts.
- The best material is 1/8” (3mm) single ply carbon / balsa core sandwich panel (Nomex core is lighter but doesn’t have the required peel strength needed with motor mounts).
- Consider airflow to the motor from the bottom (but only cut air holes in the mount away from where the tube will be bonded to the mount).
- Consider the size of the protruding axle and keeper and ensure the center hole accommodates free rotation.
- Maximize the bond area for the adhesive that will go against the mast. Try for 0.5 square inches of area (about 300 sq mm), which will deliver about 1000 lbs of shear load and 10 lbs of peel if 3M 2216 adhesive is used.
- Weigh and record the total weight of the motor mounts.
Size and Prepare the Motor Masts
- Lay the motor mast tubes over the drawing of the motor mast.
- Put masking tape around the tube where it gets cut.
- Carefully align the tube to the drawing and mark where it gets cut and which side of the line the cut goes.
- Mark where the bisected tube is cut (at the middle of the continuous mast), the approximate angled line, and the exact angle per your calculations if you are using a table saw or other saw with controlled cutting angles.
- Cut the tube (3 cuts; two end cuts and one middle cut). Keep the blade thickness of the saw that cuts the middle cut to less than 3/16” wide or about 4mm. You don’t want to remove too much material from the center of the bisected tube.
- Remove the tape
- Lightly sand the tube ends to remove stubborn end fibers and clean.
- Lightly sand and clean the tube outer surface to within 2ish inches of the ends (where the motor mounts will be bonded.
- Lightly sand the middle of the continuous mast where the tubes cross
Miter the Ends of the Bisected Motor Masts
- Tape a piece of 80 to 200 grit sand paper around the middle of the continuous motor mast.
- The sand paper can only be one layer thick.
- Use one piece of the sand paper under the bisected mast to act as a spacer to align the end of the bisected mast correctly against the continuous mast. This aligns both masts at the same elevation off of the table.
- Align the bisected motor mast to the drawing.
- Align the continuous motor mast to the drawing.
- Work the masts back and forth against each other sanding off the end of the bisected motor mast until it takes on the exact shape to fit around the continuous mast tube, at the correct angle, centered, and of the correct length.
- The angle is best checked by pressing the mitered end of the bisected mast against the bare side of the continuous motor mast. You will feel where it seats firmly. Check the resulting angles against the drawing.
- Do both bisected masts.
- Remove the sandpaper from the continuous tube.
- Clean all of the masts.
- Weigh and record the total weight of the masts.
Prepare the Mast Gusset
- Support the bisected masts with shims the same thickness of the motor mounts to make the masts are planar.
- Make the gusset from extruded rectangular solid carbon/epoxy. The end dimension of the rectangular extrusion should be about mast [OD / 2] wide by [mast tube wall thickness x 3] thick.
- Cut the mast gusset length to > 6 diameters of the mast. In this case, the mast OD = 0.6” so > 6 x .6 > 3.6” long so the gusset was cut to 4”.
- Lightly sanded the ends.
- Lightly sanded both of the flats (only need to sand the flat that will be adhered to the bisected mast, but you don’t want to be asking yourself after the adhesive goes on as to which side was actually sanded).
- Mark the center of the gusset (used later to align).
- Weigh the gusset and record it weight.
- The adhesive to use is 3M EC 2216. It has a long room temperature cure (about a week) but can be handled in 24 hours. It can be accelerated by oven temps down to a 30 minute cure. It is the only adhesive tested so far that appears to have the required peal and shear strength. It is expensive, especially if used via a dispenser gun and throw away nozzles. The dispenser gun is nearly $100 and each nozzle costs nearly a buck. The adhesive can be purchased in cans and hand mixed at a ratio of 2 (base):3 (accel) by volume or 5:7 by weight. It has a 90 minute work life so plenty of time to bond and adjust.
- If using a nozzle, waist 1" of bead (where the mixing isn't great).
- Tape the motor mounts to the drawing.
- Apply a bead to the two motor mounts on the singular mast (see photo).
- Carefully place the mast onto the motor mounts and roll the mast slightly back and forth to spread the adhesive slightly around the mast to increase bonded surface area on the mast to > the mast diameter/2 (in this case about 3/8” or 10mm).
- Tape the mast to the table so it doesn’t move easily; taping blocks on the sides also help.
- Repeat for the bisected masts, except, also put a bead of adhesive on the end of the bisected masts that will be bonded to the singular mast. Spread the end adhesive about 1/8” (4mm) on the outer or inner surface (the adhesive strength comes from surface area, not thickness)
- Tape the bisected masts down to the table so they are pressed tight against the continuous mast.
- Put weights on the masts over the motor mounts; these weights need to span two motor mounts to ensure that they are keeping the masts parallel to the table surface.
- Apply a bead down the center of the mast gusset.
- Align the gusset evenly over the bisected masts.
- Roll it side to side to get the adhesive to spread out.
- Add a thin layer of adhesive to the side of the continuous mast around the motor mast joint to increase surface area.
- Wipe off the top of the gusset.
- Put a piece of paper over the top of the gusset.
- Put a weight over that to press the gusset onto the masts (the paper prevents the weight from bonding to the gusset).
- Use the tongue depressor to wipe away excess adhesive from the crevices between the motor mounts and motor masts.
- Put the adhesive away (nozzle, cap, etc.)
- Let cure overnight at room temperature (cures fully in one week). Or accelerate the cure in an oven.
Weigh the Frame
- Subtract the weight of the masts, motor mounts, and gusset.
- Record the weight of the adhesive.
58.2 g Masts
6.9 g Motor Mounts
0.8 g Mast Gusset
2.1 g Adhesive
68.0 g For a frame that can take 17.25" propellers.
I'm building one following your technique. I ordered:
-For the masts, 16mm OD - 14mm ID, 71 g for 1 m 3K CF:
-For the motor mounts I will be trying either my Hugues's plate (3mm balsa core, CF skin) or this that is heavier but will serve for a coaxial config:
Weight : 4g per arm (available http://www.pitlab.com/pitlabshop/accesories-for-multirotors/boom-bl...)
with these :
(4g each, 1.5mm GF10)
-I ordered your famous 3M2216 and I broke my bank account; this is orageously expensive! Better be good glue. I compared the specs with what I used so far UHU strong expoxy and the 3M one is two times stronger in shear and peel. Plus it is slightly elastic which will resist vibrations better (fatigue).
-I ordered this glass sheet/nomex core platform for electronics :
Weight : 28g
-For the masts gusset I ordered this at the same place:
(1mm thick, so i will have to glue three strips together)
weight : unkonwn
So my total expected frame weight will be:
Masts (90cm x 2) : 128g
Motor mounts (x4): 32 g
Adhesive : like you probably : 2.1g
Gussets : ?
Total : est. 162g
(this is almost three times your weight! are you sure you counted your two masts weight or just one mast?)