QuadCopter Week 2-6: The Build

Posted: November 10, 2012 in Projects, quadcopter
Tags: , , , , , , ,

Completed QuadCopter BuildI spent all week prepping for my build. I read and re-read the terrible assembly instructions (more on that later), did a good deal of research to fill in the gaps, and spent time prepping my workspace. I bought a beat up stainless steel table that came out of a restaurant kitchen to use as my main work table. It was pretty ugly, I don’t think anyone washed it before throwing into storage, but after a good scrubbing and an hour or so of rust removal work, it looks like new. My multimeter and some other bits a pieces arrived at the beginning of the week, and I ordered 4 Turnigy LiPo batteries (3x 3300mAh and 1x 5000mAh) and a Venom Pro Plus Charger charger.

I meant to post about the copter build weekly, but quite a number of things got in the way, including not having any free time to build. I did finally find the time, and once I did I didn’t want to stop to blog about it! The result is this one big blog post that brings us through the (somewhat successful) first flight and up to today. I’ll try to keep it as short as possible without missing anything important. Let’s get started!


A Note About Tools

In the last QuadCopter post I outlined all the tools and associated tech I had to purchase to undertake this project. The cost of entry in terms of tools is a bit daunting at first glance, but after undertaking the project I can’t imagine accomplishing the project without them. I found constant use of every tool I purchased. Additionally, I found that not having a simple but somewhat costly tool (that I considered not purchasing at first) would have caused me a lot of grief. For example, I purchased 3 sizes of soldering tips for my soldering iron, a small tip that allowed very fine soldering work on the ArduPilot board, and a much larger tip for faster heating of heavy gauge wires. If I had to do both those things with the standard tip I’d find both tasks difficult.

When choosing to buy or not to buy certain tools, consider that you’ll be more likely to be successful with the proper tools for the job. Additionally, you’ll always have them for the next project. I’ve calculated the cost of my first quadcopter was x, but the cost of the next quadcopter will be .125(x).

The Kit

As you might recall, I ordered a 3d Robotics 3DR QuadCopter kit. The kit includes the frame, 880kv motors, Electronic Speed Controllers (ESCs), ArduCopter autopilot, GPS unit, power distribution board, and all the associated wiring. The kit comes in a nicely compact box. All the components were bubble wrapped and well protected. Purchasing the kit, you’re expected to provide your own RC receiver and batteries. Additionally, I purchased deans connectors for all my batteries to have consistent connections for all my batteries (more about that later).

Here’s the unassembled kit:

The Build

The assembly instructions for the 3DR kit are incomplete at best, at worst actively thwarting success. I’ll call out specifics as we go, but be aware that if you choose to purchase a 3DR kit you should be prepared to do a lot of googling to find answers to simple questions. Right, let’s start building!

The Build: The Quad Frame

The frame is constructed from 4 3/4″ square aluminum tubes, 4 cnc cut 2mm fiberglass plates, 4 2-piece fiberglass landing legs, and an assortment of machine screws and nylon standoffs.

3dr Frame Parts

The main frame construction is the clearest part of the documentation, so assembly was quick. You start by attaching motors to each of the four arms with small mating screws and lock washers, (it doesn’t matter which), threading the 3 motor leads through the arm, and finally assembling the landing gear and attaching them to the arms:

3dr Leg Assembly

The arms have holes drilled for the motor mount screws as well as holes in the opposite side of the arm to push the screws through. It’s a smart design choice, it means the screws are flush in the inside surface of the arm directly under the motor. I’m told previous generations of this kit have the screws pass through both sides of the arm, causing warping if they were over-tightened.

After all four arms are assembled it’s a simple matter to attach them to the two main center plates using 8 machine screws:

3dr Assembled Frame

Next, soldering! Lots and lots of soldering…

The Build: Power Distribution Board

The Power Distribution Board (PCB) distributes power from the battery to the motors by way of the Electronic Speed Controllers (ESCs). This particular board also distributes the 5v output from the ESC’s to power the Arducopter Autopilot board and the RC receiver, and routes the ESC signal wires to the autopilot as well. Slick.

The PDB comes unassembled, requiring soldering. We have to solder female Deans connectors to the 4 DC outputs first:

Power Distribution Board

The Deans connectors solder to the positive and negative pads on the PCB. This is one of the few places where you could make a disastrous mistake. Make sure you’re soldering the + side of the connectors to the + pad on the PDB and vise-versus.

One other note at this stage: Deans connectors come pre-soldered to many batteries, but not all. It’s a good idea to purchase a few extra sets of connectors to solder to batteries and other connections. Standardizing your connectors will save time and annoyance later.

After the connectors, you have to solder on the wiring to connect the signal wires and 5v power to the autopilot, and the main power from the battery. The battery cable also needs a male deans connector soldered prior to soldering to the PDB. The main thing to remember when doing the signal wiring is to get them in the right order! If you mismatch any of these wires the autopilot will think it’s connected to a different motor than it actually is, and you’ll quickly crash on your first flight.

PDB Soldered

The final step for the PDB is to mount it in the frame. Make sure the arrows on the board are pointing forward so your motors all map to the correct inputs. Once the PDB is built and mounted, it’s time for the last big soldering effort: The ArduPilot board.

PDB Installed
The Build: ArduPilot Board

The ArduPilot board comes unassembled, with your choice of angled or straight pins. You have to solder connection pins to 3 tracks on the board, one set for input, one set for outputs, and a third set for accessory board connections.

ArduPilot Unassembled

It’s worth noting at this point that there are absolutely no instructions included for how or what needs to be soldered on this board. You have to infer what goes where based on the connection instructions on the DIY Drones wiki. It’s a wasteful time consumer that could easily be headed off by a few lines describing what goes where.

Soldering pins is mostly time consuming, and not terribly difficult. If you’ve never done any soldering before, practice on some junk electronics first. Also, be sure to carefully ground yourself while working on this part of the project. The electronics on ArduPilot are delicate and can be ruined by a stray static shock.

ArduPilot Soldered
The Build: Final Assembly

The final assembly is pretty straight forward once you spend a few 10s of hours online decoding all the mismatched documentation. I had to send a few e-mails to 3d Robotics to get some simple questions answered, which can be frustrating since it often takes 2 or more days to get a response. I found my way through it finally, and here is the result:

Completed QuadCopter Build

So, ready for configuration! I’ll go into more detail about configuration later if anyone is interested, but here is a quick overview. First, the firmware has to be installed through a windows client application connected to the board via USB. Once firmware is installed you use the same utility to configure it for flight.

Next you have to use your radio control and a slightly confusing set of on and off sequences to calibrate the ESCs for flight. If I had had more experience, this would be where a major warning flag would have gone up. When calibrating the ESCs the first time one of my motors was twitching instead of spinning as it should. I thought I had gotten confused in the calibration sequence, so I reread and did the calibration again. The motor spun as it was supposed to, so I assumed I had solved the problem.

I hadn’t.

The First Flight

I finally completed the build on my birthday weekend, and boy was I excited! It was a beautiful day and I was anxious to fly, so we packed up and went over to my girlfriends’ mom’s house where they have a huge open yard. I went through my preflight and took off, trying to keep it low and in control, and somewhat succeeding. And then…

CRASH.

I got really lucky. The quad was low to the ground when the motor failed, and I reacted by dumping the throttle. The result was it flipped over twice and landed dead in the grass on it’s legs.

After some reading on the forums and confirmation testing by connecting the suspect motor with other ESC’s, I was certain the motor was bad. There was info online about some of those motors having cold solder joins that crack loose. That’s what happened to me.

After some frustrating back and forth (and the 1-2+ day wait between e-mail responses) I arranged to send the motor back. They wanted to test it first and confirm my diagnosis before sending me a new motor, which is understandable, but annoying with a company that takes it’s sweet time with customer service. Long story short, it took a month from when I sent off the motor for them to confirm the problem and send me a new one, which brings us to today. I have now received a new motor, installed, tested, and reassembled my quad, and now I just need a nice day to fly it!

I’ll post again after my first sustained flight.

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