Saturday, June 6, 2015

F450 Quadcopter Build and Flight Testing


This is my F450 quadcopter. There are many like it, but this one is mine.

I have a lot of experience with RC airplanes, but I'm new to quadcopters, so I want to document the build in case it is useful to others. I learned on the excellent and incredibly affordable Syma X1, which is serious fun for the money and a perfect trainer when flying indoors. I put a number of flights on an ARDrone, until it went berzerk and parked itself in a very tall tree. At that point. I decided something with a real, proper RC system was in order.

A few abbreviations:

ESC - electronic speed control. Converts control inputs from you (through the flight controller) into a throttle output to one of the motors.

FC - Flight controller - a small microprocessor board with gyros and accelerometers that stabilize your quadcopter in flight. It handles the mechanics of keeping the machine in the air by making small adjustments to the motor power many times a second, and turns your stick input into your desired motion.

BEC - battery eliminator circuit. Steps down the main flight pack's 12.6 volts to the 5V the receiver and flight controller needs. A regulator.

3S - a 3 cell lithium polymer battery.

Here's what I selected for parts:

A combo containing the frame, motors, ESCs, and propellors. 

This contained:

1 x F450 frame kit
1 x F450 Landing gear( 4pcs/set)
4 x Sunnysky X2212 980KV Brushless motor
4 x HP SimonK 30A Speed Controller
2 x 1045(CW+CCW) Black Propeller
2 x 1045(CW+CCW) Red Propeller

Knowing what I do now, I'd not have bought this as a kit. I would have bought the components individually. More on that later - live and learn.

KK2.1 Flight Controller (FC)

FlySky FS-T6 radio system

Turnigy 2200 mah 3S Lipo pack

That covered the obvious stuff. Then as I examined the kit I determined I needed some less obvious stuff.

Heavy silicone wire to connect the quad's power distribution to the battery

XT60 connectors. You need at least one on the end of those nice wires you just bought. The other end gets soldered to the power input on the frame's power distribution system.

A set of 5 male to male JR style servo connectors. These go between the flight controller and the receiver outputs.

A 5V switching regulator, because I don't trust the linear regulators on the ESCs.

A dedicated low voltage alarm. I never got the low voltage cutoff on the flight controller to work right. This one works great. You need one or the other, since quadcopter ESCs don't have a low voltage cutoff like airplanes do. Set to 10.8V, you have 30-60 seconds to get it on the ground before you lose power.

A pack of 3S balancing wires, to connect the battery to the low voltage alarm.

Whew. OK. Once you have the stuff, building it is actually quite easy. You need a higher power soldering tool - I used a soldering gun - since you need to solder heavy wires to the copper traces on the frame. There is an extremely helpful build video from Legend RC here:



Other very useful links if you are new to quadcopters:

Identifying the props and their locations

Connectors and Plugs for Quadcopter Newbies

A great guide to quadcopter wiring. This goes over how to connect the various boards.

Be sure to read the KK2.1 manual section on powering the board carefully. I chose to cut the red wire from all 4 ESCs that connects to the FC motor outputs and power it with a dedicated switching Battery Eliminator Circuit (BEC). The switching regulator runs cooler and more efficiently that the linear regulators on the ESCs.





One of my ESCs was dead on arrival. I didn't find it until the kit was 90% built. I couldn't return the whole kit, and even returning the dead ESC to China would have a been a serious pain. I tracked down the same part on Amazon and bought a replacement, along with a spare. This is a serious drawback to buying the kit.

After very carefully checking propellor rotation direction, as well as making sure the correct prop was on the correct motor, I did a quick test flight, and was surprised to find that it flew fine with stock settings on the KK 2.1. I did make some PID adjustments, but it was quite controllable. 

There were bugs to work out. My KK 2.1's low voltage alarm, set to 10.8V, would howl continuously in flight, and cease on landing. I never figured out why. I turned it off and installed a dedicated low voltage alarm, listed above, and it works superbly. 

On the first few flights, I have trouble with split second instances where the motors would just STOP. All at once, for a fraction of a second. It would fall abruptly, and then recover, unless I happened to be low. I first blamed the linear regulator on my BEC.I tested with a dedicated receiver pack, did a quick test flight, and presto, it was fixed. Victory! I installed a nice dedicated switching BEC, went flying, and SMACK, it fell out of the sky again. It finally dawned on me to range test it. On the ground, with the motors spinning just above idle, I started walking backwards. At 40 feet or so, the receiver light blinked out. A few steps forward, it came back on.

Argh. Radio trouble. Gambled. Ordered new receiver. Got lucky - that fixed the problem. No way to return cheap dead receiver, at least not economically, so into the trash it went and I ate the $15. But it passed a range test and works fine farther than I can see the quadcopter.

ALWAYS RANGE CHECK YOUR MODELS. I have known this for years, and got lazy, and it bit me.

Several more flights, and a new problem cropped up. Propellor blades started randomly separating from the hubs. Once in flight, causing a crash from 30 feet, and once on takeoff, narrowly missing me. Cheap plastic props that came with the kit are absolute garbage - to the point that they are dangerous. Into the trash they went. Ordered some 10x4.5 carbon fiber props, which are absolutely superb. My flight time immediately improved from 7 minutes to 9. I'm not sure if they would fail before the bones in my finger would, so... respect. 

One final note about propellors - they aren't perfectly balanced from the factory. Take the time to balance them - mine flew much more smoothly and quietly than before they were balanced. My video quality dramatically improved too, since it eliminated the jello/rolling shutter artifacts I was getting.

I borrowed a friend's Dubro prop balancer and used scotch tape on the back of the blades to balance them. Went surprisingly quickly. I intend to buy a balancer and add it to the periodic maintenance list. I never bothered with planes, but it matters a lot for multicopters.

I now have perhaps two dozen flights, and the bugs are worked out. It is a reliable machine, climbs well, and has plenty of lifting power. I printed a camera mount for an ancient Canon point and shoot camera and it hauled it around just fine - all 1/2 lb of it. I have since upgraded camera and added a gimbal - more on that soon.

Knowing what I know now, I would not have bought the kit - I would have bought the same components, with decent propellors. That way, if I got a bad speed control, I could return it, rather than the entire kit.  Other than that, I am pretty pleased with it. 

2 comments:

  1. Hey great write up well done. I done the low voltage mod to my kk2 and I only had to run one wire from the battery to the kk2 set its alarm trigger and it works really well. My build is Here
    Thanks for the idea on carbon props that's my next purchase cheers

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  2. The thrill of flying a quadcopter is certainly exciting. However, it will be even more fun to fly a quadcopter that you’ve made on your own. By making your own DIY quadcopter, you will not only have something to fly in the air but also a model that is truly unique (since the model is totally your own). See more http://mydronelab.com/blog/diy-quadcopter.html

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