Part 2: Finishing the rest of the arms

Just finished the four arms, which feels like I've done a lot, but I still need to do ALL THE REST -_-

Part 1: Intro + Getting the parts + First steps

Intro

This is my build log/guide of me building a medium-sized quadcopter. After visiting the awesome emfcamp and seeing a couple flying around, I had to build one, for as little money as possible. I'll be including as much detail as possible, I'm new to RC but not to tinkering, and didn't find enough clear instructions beginning to end. This is a long post, catching up to where I am as of when I'm writing this.

My plan/aims is/are:

four carbon fibre tubes sticking out of a central hub, with a propeller on each side.

3d printing all of the plastic parts on my prusa 2 (I may consider selling parts, email me at james.n.glanville@gmail.com if you're interested)

the ability to carry about 1kg of payload

eventual FPV capability
Publishing all my source code/designs at https://github.com/JamesGlanville/quadcopter

Anyway, here goes:

Shopping List

I'll try and keep this up to date as I go along, it does already list all of the expensive parts though.

From HobbyKing:

Code Description 387000001 MultiWii 328P Flight Controller w/FTDI & DSM 1 Reserved TR2217/20 Turnigy 2217 20turn 860kv 22A Outrunner 4 Reserved TR_P25A TURNIGY Plush 25amp Speed Controller 4 Reserved 017000063 10x4.5 SF Props 2pc Standard Rotation/2 pc R 4 Reserved Z50003S-20 ZIPPY Flightmax 5000mAh 3S1P 20C 1 Reserved ACC6 Turnigy Accucel-6 50W 6A Balancer/Charger w/ 1 Reserved DL-Volt-Alarm On Board Lipoly Low Voltage Alarm (2s~4s) 1 Reserved FS-L001 Hobby King 2.4Ghz 6Ch Tx USB Cable 1 Reserved HK-T6A-M2 Hobby King 2.4Ghz 6Ch Tx & Rx V2 (Mode 2) 1 Reserved 258000011 10CM Male to Male Servo Lead (JR) 26AWG (10p 1 Reserved WHS2MM-Yelow Turnigy 2mm Heat Shrink Tube Yellow (1mtr) 4 Reserved WHS3MM-Yelow Turnigy 3mm Heat Shrink Tube Yellow (1mtr) 3 Reserved WHS5MM-Yelow Turnigy 5mm Heat Shrink Tube Yellow (1mtr) 2 Reserved OR009-00506 M3 x 20mm Nylon Screws (10pcs/bag) 1 Reserved

Total:  £193 including delivery

From ebay:

carbon fibre tubes http://www.ebay.co.uk/itm/150766369446 £11
XT60 power connectors http://www.ebay.co.uk/itm/120983871463 £4

Odds and ends I already had:

A few metres of high current wire for connecting between the battery/ESCs/motors.
Solder/flux/etc
a few m3 bolts of various lengths

Designing the motor holders:

I'm going to be 3d printing all the plastic parts, so I thought I'd start with the motor holders since they're quite simple. I'm using openscad to design the parts, slic3r to slice them, and my prusa2 to print them. My code is:


$fn=100;
difference()
{
union()
{
cylinder(r=36/2,h=18,$fn=100);
translate([0,-12,9])rotate([90,0,0])cylinder(r=9,h=25,$fn=100);
translate([0,-20,4.5])cube([18,34,9],center=true);

}
translate([0,0,9-4])cylinder(r=29.2/2,h=10,$fn=100);
translate([0,0,5+6.5])cylinder(r=30/2,h=10,$fn=100);
translate([0,-12,9])rotate([90,0,0])cylinder(r=12.3/2,h=50);
rotate([0,0,0])translate([0,3+3.5,-1])cube([4,6.5,30],center=true);

rotate([0,0,45]){
rotate([0,0,0])translate([0,3+5.5,-1])cube([3,6.5,30],center=true);
rotate([0,0,90])translate([0,3+5.5,-1])cube([3,6.5,30],center=true);
rotate([0,0,-90])translate([0,3+5.5,-1])cube([3,6.5,30],center=true);
rotate([0,0,180])translate([0,3+5.5,-1])cube([3,6.5,30],center=true);
}
translate([0,0,-1])cylinder(r=7.5/2,h=10);


}


which produces:

I love how quickly I can go from measurements and ideas to holding a real part in my hand. This part is my second attempt, since I managed to get the holes slightly too small, and the motor screw holes in the wrong places. Here it is all attached:



















To assemble, I just sanded the hole for the tube until it was a very tight friction fit (easier than gluing), then screwed the motor from underneath with short m3 bolts, being careful that the bolts were not so long that they'd damage the motor windings. As a quick test of motor power, I lifted 1kg with this setup, holding the other end of the tube loosely. This will mean I get 4kg of max lift when done, so even if the whole quadcopter weighs 1kg I've got plenty of spare for accelerating and carrying payload.



Here's what I have so far:

The hub in the centre is just a test piece to check how strong the printed parts are. I'm printing at 0.2mm layer heights, with cheap chinese PLA at 204C. The piece as shown is very strong, I couldn't break it by hand. The weight of the rods + hub is about 100g, which I think is reasonable, though I'll try and reduce the hub weight a little more.






This is the end of the post for now, I'm all caught up to now. Next time, I'll have finished the four arms, and will start thinking about the rest.