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
Cala
I know how you feel!
I like the bit about the ice skater. Very slowly the mist is clearing.
Release changes that were done:
-Cutting unecessary carbon masts length on both pitch and roll axis
-Cutting unecessary servo cables length (keeping the standard end connectors)
-Cutting unecessary portions of the camera plate (was over-dimensioned)
I'm planning some more weight removal for an even lighter version 3. In the next release, will come:
-replace the servo wires (heavy wires) by lighter servo thinner servo wires
-replace the over-dimensioned 3D printed parts by lighter ones (size and infill ratio currently at 100% which is unecessarily (too) strong)
Impressive!!!, only ideas thinking how to ligther, it's necesary the motor cup? and another thing, how mobius box weight? it's usefull to change for a sandwich ligther box?
GLUP!!!, mine weigths 180grs I bougth as the ligthest that I found, that's substract me 1 min flying time than yours, I didn't use yet and I'm thinking that I have to rebuild it, thank's for share all building details, wait anxious the field tests :)
As a follow up of my previous posts, these last months in this thread, about building the lightest brushless gimbal able to carry a full HD camera, here are some build pictures and comments:
Assembly of the cf masts.
First they are cut and sanded to shape, to fit together at a right angle (see above method described by Forrest):
It is tricky to get everything perfectly (or as perfectly as possible) aligned and/or at right angles:
Another advantage of this glue, it start to harden in 10 minutes (while the 3M starts to harden in 90 minutes) and cures in 24h (while the 3M cures in a week).
Then the question is how to fix the two roll/pitch motors on these carbon fiber masts ? Answer : glue and 3D printing.
There are two 3D printed parts , one for the stator, one for the rotor. The stator piece is either glued on if you never need to use the motor for anything else later, or could be even screwed on if you need to get your motor back for antoher application later on.
The stator 3D printed mount is only used on the pitch motor. Indeed the stator of the roll motor will be screwed to the frame hilding the whole brushless gimbal ( a drone's frame for example or a handheld pole).
This piece was custom designed for the particular 1806 motors that are used and fixes itself by three little clips:
Then fitted on the motors:
After that , the full HD camera mount plate for the Mobius camera is glued on the rotor of the pitch motor:
Although screw holes were drilled, I did not use them as it is simply glued on the 3D printed cover, capping the motor's bell.
Now the tirickiest part of all, gluing the roll motor. This is difficult to achieve because , once again, you need to be perfectly at right angles and find the right tangent on the round roll mast. You also need to find the center of gravity on the roll mast. So extensive use of squares are required, using gravity for perfect verticals:
And the final result:
Weight measurements:
Without the camera:
With the camera:
The weight here includes the motors, the servo cables, the velcro strips to hold the camera on ist mount plate. So it is a real all-in weight.
I wish I could build with such precision.
To be able to get the precise balance correct and then join the parts without anything going out of alignment takes real skill.
Jon
Hi Hugues,
you stated in the other thread that you are using of-the-shelf brushless gimbal motors (in opposite to the rewound, repurposed CD Drive Motors used in some other Gimbal Builds)
Do you have a link where i can get some of these 1806 gimbal motors?
i have searched a lot some time ago, but the smallest ones i was able to find were 2208 with ~29g
Thanks
(Jo)hannes
Hi Johannes
http://www.ebay.com/itm/Micro-2-pieces-20-g-Brushless-Gimbal-Motor-...
The link is above they are Maytech MTGBM 1806 with 180mm of cable and plug weigh in at 20.3g
Jon
Thanks Jon!
Good to see that the manufacturers are finally selling small gimbal motors.
Just an idea. If you can get the battery out of the Mobius and add a female connector you could run it off the esc's BEC. I think these cameras will run on 5V??? Could save you some more weight as long as the voltage is right and clean enough. Very good ideas in this thread, you guys are real crafts men.