Round tubes offer the following pros:
- handle twist better than square tubes. Thus for the strength, are far lighter.
- are more readily available (pipes, tubes, arrows, kite frames, golf clubs and sticks of all materials).
- easier to cut (square tubing can twist and be damaged by cutting forces)
- easier to peg (fits into a drilled hole and easy to find extenders)
- less expensive
Round tubes are thought to have the following cons:
- difficult to mount motors
- difficult to join
None of the cons are real if you know how to work with tubes. Mounting round tubes to motors is easier and faster than with square tubing. Round tubes are also faster and easier to join together. The resulting joins are also far lighter and better.
In the H-frame forum, I was asked to share these build techniques so have decided to demonstrate the methods on the most complex multi-copter one can build, an Octa-V. I'll do this step by step. The result will be a multi-copter that reduces frame, screw, gusset, and motor mount weights by more than 40%.
The steps will be Design, Assembly, Charmin Test, and Flight Test
Installment 1: Design
First, both simple and complex multi-copters share something in common. When using round tubes for arms, there is no reason to cut a perfectly good tube in half for each arm. And then add a bunch of weight and fasteners to hold the halves together. How this is done will become evident in the third installment, the Charmin Test. For now, just know that each tube is continuous (no breaks, no joins). Opposite rotors share the same boom in a quad, hexa, or octa. All of those fasteners are gone. The cross beams on a V or H are also continuous. Assembly and disassembly is quick.
Most quads are so simple that one grabs two pieces of wood the same size and slap them together. Done. If the angle of view isn't good, just move the camera forward a bit. But, if you want to know the exact length of a quad boom based on prop diameter and platform size so you can minimize weight to get longer flights, then I've attached a worksheet that does the math.
An Octa V is a bit more complex. It is specifically used for camera work. So you need to optimize the motor boom angle and aspect ratio of the frame to achieve the desired Field-of-View for the camera (void of propellers), It also uses 8 motors so that if one dies, the copter can return to the ground with the $12K of camera/lens in tact. You also need to minimize platform vibration, so the platform needs to be large enough for the electronics, gimbal mount, and at least 1.2" (30mm) from the prop radius.
I've attached an Excel worksheet that does all of the calculations for optimizing weight. There is an instruction sheet if you want to ever build one and calculations for a Quad X, Quad +, Quad Spider, and Octa V.
The next installment will be Assembly.
P.S. I'm not experienced nor am I an expert. I'm just a tinkerer like many of you. There are builders out there with far more experience and wisdom. I'm hoping that this blog will allow us all to share ideas on building strong, fast, and light not only for initial build, but also for crash repair.
Replies
I didn't read the whole thread. I assume you're aware of Rusty's frames that use round tubes. Even if you want to build your own frame he has motor mounts for tubes etc.
http://www.shop.aglhobbiesllc.com/Rusty-s-UAP1-Frame-Kit/
http://www.shop.aglhobbiesllc.com/Motor-Mounts/
etc
I've just finished mk II of this frame. I extended the central platform to 38cm, and increased the length of the arms to 44cm, so now the motors are closer to equal distance apart, and there's more clearance from the frame.
The weight of the foam/fibreglass is 90g, and the arms are 60g. The all up weight including gimbal, gopro and 4500 4s battery is 1.5kg.
First test flight looked good. I flew for 20 minutes and took the battery down to 12v under load. Unfortunately I'm pretty sure my current monitor has the wrong setting for apms per volt. It was indicating 10A at hover, but the batt % showed 25% when I landed at 12v, so I'm guessing the true value was 12-13A, which I am still plenty happy with! It's also very very quiet.
There was no jello in the video and the gimbal is just zip tied to the frame with a latex foam pad between to stop it sliding around.
Next up I'm going to try a different central foam piece with carbon fiber on both sides to see if there's much of a difference in handling. It seemed to fly fine as it is though. Also it would benefit from a couple of cut up pool noodles as feet under each motor so that it doesn't sit on the battery.
Nice simple build. I was ticked by the small diameter of the props you use with such powerful low KV motors. Do you know you could put 12 inches props at least on those ? It would be even more powerful !
I finally got around to putting an H-frame together, and so far it goes well! It's ridiculously overpowered, and fun.
The central part of the frame is made from a sheet of stiff foam that has been fiberglassed only on one side. I just got it as a scrap from a friend who builds boats, but may get another one made up that uses thinner foam, and has carbon on both sides. I haven't weighed the current build.
The arms are two lengths of 40cm long 12mm square pine. Distance between front and rear motors is 30cm, and left and right is 36cm.
It's running 620kv nx4008 motors with apc 10x4.7 props on 4s. The 4500mah battery is kind of heavy and overkill but it's all I've got, and it still seems to climb at 20+m/s. I plan to make a brushless gimbal for the front, and replace the multiwii board with an apm clone next week.
So Steve, did you get your ABS sheet yet ? Some results ?
We are impatient to know....
Can anyone recommend a substitute for this? It comes from Thailand and can take a month to arrive.
http://www.amazon.com/epoxy-resin-adhesive-Double-syringe/dp/B000WG...
So I'm intrigued in this build design and am currently working on my design. I'm going to build a quad X. My question would be in regards to the motor mounts and the use of the Hughes Plate, great design by the way. I wanted everyone's opinion on using ABS plastic. I have a 3D printer and making theses would take almost no effort and time on my part. I can design them to be as thick as needed and have the holes for zip ties and mounting hardware already in place when made. Just wondering if they would be strong enough for this, and weight wise they would be next to nothing.
I'd quite like to build a quad using uncut round cf bar like you have done. I'm thinking if I build the central part exactly the same as yours, and just shorten the bars on the outside so that they only extend to the ends of the asymmetrical X
I guess just running different pitch/roll PIDs should make it fly well using the standard quad X mix?
Hello,
I have finished yesterday a new prototype Quad "H" but with carbon tubes crossing.
The plates are built with a home made laminated balsa wood :
-took a first 2.5mm thick balsa plank. Covered it with slow cure epoxy (the UHU epoxy about which i posted earlier)
-As I did not have fiber glass or carbon sheets, I took some simple strong cotton fabric (that my wife was using for covering a chair, shuuut don't tell her). This layer of fabric was layed down onto the balsa covered with epoxy
-I recovered a second layer of epoxy on the top of the cotton layer
-I covered on top a second layer of 2.5 mm balsa
-Everything was pressed down with a clamp for 24h
Result : a ultra rigid and solid 6mm plate that I used for this quad. I compared a 20cm x 10 cm rectangle of this stuff with the same size poplar plywood (5mm) and it is twice lighter ! (30g instaed of 60gr for plywood).
I guess this could be called the high tech laminated sheet of the poor...
For the carbon tubes I unfortunately did not have nor find easily long 60cm tubes. I found easier even if not optimal to purchase a talon frame kit on hobby king providing just the 4 carbon tubes and holding aluminium brackets for plates and motors. One big negative point of this is the approximate plane alignment of the motors : you have to judge by the eye..certainly not optimal and this could lead to yaw problems during flight. The method explained by Frantz is much more better, to use a flat surface to glue your motor mounts. You are then sure all motors will be aligned in same plane. This method was not applicable with this HK kit as the mount sdo not allow to lay then down flat on a surface. I might use later today a laser projecting a leveled line to align my four motor mounts...we'll see.
Back on the frame: this is how it looks,
On the picture you notice four spacers sticking out. Thes will be used to fix the APM. It is a suspension system : rubber dampening spacers are used. The top plate does not touch these four spacers. The top plate is only attached by the four aluminium spacers between the bottom and top plates. The bottom plate is fixed on the frame by double sided adhesive.
better view of the rubber dampeners.
I placed the powr distibution board and 3DR power module in the frame center between the four tubes. All motor wires passes through the tubes. The ESCs are placed in between the bottom and top plates.
I might move the GPS in the same plane as the top plate to have a better aerodynamic profile.
I did a short test flight with it and it seems quite stable.
The total weight as show on the picture is 1,2 Kg (3110-700Kv tiger motors, 11x4.7 props, 20A Esc) ! Extremely light , two times lighter than my first quad based on the stock 3DR frame kit. I might have to modify my PIDs to account for this.
If I am happy with this, I will look for a CNC supplier to have my wood plates converted into perfectly cut carbon plates.
The advantage of prototyping with wood is that we can drill, try , correct until everything is optimal. Then industrialize with more expensive material.
What I'm not yet happy with : plane alignment of motors. All of the aluminium brackets of this kit makes it heavier than it could be.
What is also nice with it is that it sticks well on carbon (versus fast cure epoxy that does not stick at all on carbon, even after sanding and degreasing)
-
40
-
41
-
42
-
43
-
44
of 44 Next