Eachine Racer 250 - How Does Openpilot Compare to APM/Pixhawk

I saw a good deal on Banggood.com for a small ARF (Almost Ready to Fly) Quad called the Eachine Racer 250 and went ahead and purchased it.  It is a 250 sized unit with the FPV built in, includes a battery, and charger, and cost around $125.  I added a spare Orange DSMX receiver and a Spectrum DX4e transmitter and was up and running!  It sends video to my 5.8 GHz integrated receiver-monitor and works like a charm.  Build quality is good for the price, packaging was good, and it is designed well.  As usual, there are NO INSTRUCTIONS from the Chinese manufacturer in the box and you have to hunt around on the web to find out how to set it up.  I found a few good Youtube videos and they guided me through setup without a problem.

The only thing that was challenging was my lack of knowledge of the flight controller, the CC3D, an open source flight controller that is somewhat different from the APM or Pixhawk.  I again queried the web and found the ground controller for Openpilot, which supports CC3D hardware.  I downloaded the software, installed it, connected USB to the quad, and followed the instructions in the video.

The quad flew, but was very sensitive to control inputs, too much for my flying skill.  I again went to the web, found some tutorials, and tried to fix the settings.  The tutorials were out of date so I went to the wiki, which seems to be permanently down.  I then posted a question on RCgroups.com and got some information.

Unfortunately, there seems to be a schism in the Openpilot community and it has split into three factions: Taulabs, Librepilot, and Openpilot.  While Openpilot works, it does not seem to have as much support as it used to.  The other 2 options seem to be works in progress.  APM and Pixhawk/PX4 are definitely better options if you have a choice.

But I did figure out how to desensitize the quad using the current Openpilot and it flew well in a couple of outdoor test flights.  Stay tuned for more info.

Defeat Terrorist Drones Without Firing a Shot

Lots of news reports today of drones flying over the Eiffel Tower, French Nuclear Plants, and the US Embassy in Paris.  Of course this is irresponsible and dangerous behavior, and the idea of terrorists using drones is mentioned.  How could you stop a terrorist using a drone to carry a bomb or using a drone for some other evil purpose?

Here in the good old USA, we have the state of Oklahoma considering a law to allow you to shoot down drones over your land.  Shooting drones, particularly by homeowners, is not such a great idea as there is a lot of potential for innocent people to get hurt.  It may make sense for the military, who have over 100 years of experience with shooting down flying objects, but not for my neighbor Fred, who has a shotgun and last fired it when he went hunting with his brother in law 10 years ago.

There are certainly less dangerous but effective ways to deal with drones.  Commercially built or homebuilt drones rely on a few things to fly to a target and execute actions.  The loss of one or a few of these capabilities will cause a drone to crash.  Those of us who build and fly drones for fun know this all too well.

1. Sensor input - barometric pressure, accelerometers, compass, airspeed indicators..
2. GPS or GLONASS input.
3. Radio commands.  Radio telemetry back to the operator in some cases.
4. Onboard computer program.
5. Correct operation of motors, speed controls, aerodynamics, and control surfaces.

Almost all of these capabilities are needed for a drone to execute a mission, so how do you deal with an evil drone?

1. Certainly most sensors can be fooled quite easily without physically touching the drone.  I won't detail how to do this but most people with some engineering training could figure it out.
2. GPS and GLONASS can be remotely jammed.
3. Radios can certainly be  jammed.
4. Onboard computers might be hard to disable remotely but there are some techniques that will work with the unhardened commercial flight control systems.
5. Motors, control surfaces and the like are susceptible to damage with very little contact.  A piece of string or a plastic bag in the propeller will stop most drones.  There are lots of ways to stop a drone with similar low tech techniques.

So there is likely a business here for someone to make and sell drone protection systems to high profile targets like stadiums, iconic buildings and monuments, important infrastructure, and government installations.  I am sure we will hear about some startups or military contractors working in this area shortly.

Photo Credit (edited): Flickr

Test Flight Successful

Finished the basic build of the quad and was able to get a quick successful test flight in the basement after about 5 hours of messing around with the quad, my radio, and Mission Planner.

Finally worked out all the little issues and had a successful test flight:

1. The Deadcat needed to be balanced as it was naturally nose heavy.  Moving the battery allowed me to balance the quad.
2. I played around with ESC calibration and radio settings for hours because the props kept spinning when I armed the quad.  My old APM equipped quad did not do this.  Well it turns out that the default for Mission Planner with Pixhawk is to make the blades spin slowly when armed.  I did manage to program the ESCs to play tunes when they power on, but that is not much use.
3. Turning on the throttle failsafe is a waste of time as it is triggered as soon as you arm the quad, causing the arm function to fail.
4. Use loctite on all bolts, the one place that where it was skipped (landing skids), a bolt came loose.
5. Need to make up a cheat sheet with the meaning of all Pixhawk and ESC sounds and lights.  It is hard to understand failures otherwise.
6. Had to reverse all the RC channels except throttle.
7. It seems smoother than the last quad as the props are balanced but it is more twitchy on the controls, so will have to do some more tuning.

Rebuilding The Flying Flower Pot Quadcopter - The Six Million Dollar Man

Partially Rebuilt Flying Flower Pot (Pot removed for clarity)

One of the advantages of building your own quadcopter is that you know how to fix it if it breaks, and you can make improvements at the same time.  It is kind of like the Six Million Dollar Man TV series:   "We can rebuild him. We have the technology. We can make him better than he was. Better, stronger, faster."  The Flowering Flowerpot, after its last flight and crash (see previous blog post), needs this treatment.

First, I got rid of the battery monitoring module, which might be causing problems and I cannot figure out how to use it.

Second, I rewired the control module (APM) to receiver wiring to get rid of the servo extension cables and labeling.

Rewiring, receiver is on the left

Third, I repaired the damage to the quadcopter - a broken arm and a broken motor mount on the end of another arm using 5 minute epoxy, which smells like crap and gets everywhere.

Broken motor mount

Break in arm

Fourth, I got rid of the structure holding the GPS and compass and mounted them using nylon standoffs on the third level.

GPS remounted

Fifth, I removed the long landing gear and mounted the camera on top.  The long landing gear seem to cause a lot of damage in crashes.

camera mount

I also ordered a bunch of spare parts (arms, motor mounts, landing gear..).  Stay tuned for more updates as we get the Pot ready for its next adventure.

DC Area Drone User Group Meetup

I went to a "Meetup" of the DC Area Drone User Group yesterday.  It is essentially an informal meeting of like-minded individuals organized through the Meetup application.

The meeting was very useful as we had a great mix of beginners like me, experienced folks, large drones, small drones, different radio setups, etc.  I was able to ask questions of some of the experienced folks about how to set up my controller and radio, what props to use, where to buy parts, etc.  There was also an opportunity to see what other people had done with their drones - construction techniques, equipment, and so on.  You also get to meet people and exchange contact information.

If your community has a similar club or users group, I encourage you to attend as it is a great way to meet folks, get questions answered, and learn.

Evaluation of Homebuilt Quadcopter Components

I put together a table with my evaluation of the components I used to build the quadcopter and the rough cost of the quadcopter: $320.

Part	Source	Rating (1=best)	Approx cost	Comments
Hobbyking SK450 Glass Fiber Quadcopter Frame 450mm	Hobbyking	1	$20.00	Well documented, rugged
TURNIGY Plush 25amp Speed Controller	Hobbyking	1	$13.00	Well documented, works well, does not overheat, used 4
Turnigy Multistar 2216-800Kv 14Pole Multi-Rotor Outrunner	Hobbyking	1	$16.00	Works well, used 4 units
Hobby King Quadcopter Power Distribution Board	Hobbyking	2	$5.00	Works well but hard to mount
Extended Landing Skid Set for SK450 Quadcopter Frame	Hobbyking	2	$11.00	Works but a bit too flexible
Slow Fly Electric Prop 1045R SF	Hobbyking	3	$3.00	Works, inexpensive, but prone to breakage
TURNIGY BESC Programming Card	Hobbyking	1	$5.00	Well documented, works well
Turnigy 2200mAh 3S 20C Lipo Pack	Hobbyking	1	$10.00	Good power delivery, good value
OrangeRx R615X DSM2/DSMX Compatible 6Ch 2.4GHz Receiver w/CPPM	Hobbyking	1	$10.00	Works well, good value, compatible with Spektrum DX4i Transmitter
HobbyKing HKPilot Mega Mini Combo Flight Controller GPS and Power Module	Hobbyking	4	$120.00	Flimsy USB, poor documentation
5" (inch) Travel Micro USB Cable, Twin Pack Cables	Amazon	1	$10.00	Great way to protect USB on APM
Hobbypower Top Pin APM2.6 External Compass APM Flight Controller w/ UBLOX NEO-6M GPS	Amazon	2	$70.00	Works great, great value, no documentation
Tenergy 1-4 Cells Li-PO/Li-Fe Balance Airsoft Battery Charger	Amazon	1	$20.00	works great, great value
2 of NEEWER® 3.5mm Gold Plated Bullet Banana Plug Connector for RC Battery 10-Pairs	Amazon	1	$7.00	Works well, used 2 packs
Dowels, screws, glue, velcro, flower pot	Home Depot	1	$25.00	Cheaper than hobby store
Total cost of built unit (not including broken Hobbyking Controller)			$319.00

Quadcopter Build - Photos of Finished Drone

The flower pot was the best cover I could find and the bungee cords hold it to the drone

Note the hole so the Controller LEDs are visible

You can see the Vuho camera beneath the drone

Bottom view

Battery mount and USB extender connector which also protects against controller USB damage

Camera mount with battery behind

Love that flower pot!

Lessons from First Quadcopter Build

I learned a few things from building my first quadcopter drone.

1. The USB port is very fragile, attach a permanent short extender cable to connect to your PC.  Otherwise, you will be buying a new controller.
2. You need to take time to think as you assemble the drone.  There are lots of ways of attaching components and taking some time to think will yield a better result.  Spending time with the Mission Controller application will help you set up your drone, understand how it will work, and allow you to test some of the functions before flying.
3. The best places to get pieces are online stores like Amazon and Hobbyking, Home Depot, and your local hobby shop.
4. Nylon cable ties are a great way to attach things to the quadcopter frame.  Why use bolts when a simple tie will do?
5. Learn how the controller works before flying.  There are some modes like "althold" that sound useful but should only be triggered after flying.
6. Make a tethered test setup to test fly your quad.
7. Use the Wiki, google, youtube, and manufacturers sites to find solutions to problems or helpful tutorials.
8. Get a good soldering iron and learn to solder.

Building and Flying Quadcopter Part 12

Well I went back and tried to fix the problems in the last test flight, which were:

1. ESC's not properly calibrated - I was able to get them to calibrate once, but there is something weird about how these speed controls interface with the controller.
2. Poor throttle control - It turns out that you should land and take off in "stabilize mode" and I was in "Althold" mode.  It took a lot of google searching to stumble across this.
3. The receiver refused to work for a while and I don't know why.  After plugging and unplugging wires, disassembling the receiver, testing and testing, it started to work again for some unknown reason.

After fixing these issues, I tried the quadcopter with no props and it seemed better.  I then lengthened the tethers and ran another test flight shown above, which seems much better.

Building Quadcopter Part 10

Further Progress.  I reloaded Mission Planner onto my laptop and it seems to work with the controller now.  The rats' nest of wiring is somewhat tamed and the receiver and controller are mounted using double sided foam tape (get it at Home Depot where they call it "mounting tape").  The extended landing gear are installed and I found an appropriate non-metallic shell to cover the electronics.  Yes, it is a 6 inch flower pot, and it is perfect for the job.

Building Quadcopter Part 9

The build continues.  I temporarily wired up the controller, receiver, speed controls, GPS and connected to Mission Planner using my desktop PC.  It is not easy to figure out exactly how to wire it as the new controller had no documentation!  I found some useful information on the Ardupilot Wiki and found a basic pinout here.  Hooked it up by USB and it seemed to work, but...I had the controls all wrong.  After playing around with the radio calibration screens, I got the rudder, throttle, ailerons, elevator mapped correctly to the controller.  I could then calibrate the compass, accelerometers, radio, etc.

The I had a brilliant idea (uh-oh).  Since I would be programming things in the field, I should use my laptop with Mission Planner to set up the drone.  Well, for some reason the laptop did not like to calibrate the compasses so after a few hours of frustration, it was back to the desktop where everything worked.  There was also the issue of the compass being off by 90 degrees due to no markings on how to mount it, but this was easily fixed.  The compass is mounted with the GPS on the wooden tower in the photos above.

Next steps are to tidy up the wiring and mounting, calibrate speed controls, attach props, and do some testing with the unit tethered to make sure it is set up properly.  Stay tuned.

Building Quadcopter Part 3

Photo 1: Frame Top View

Photo 2: Frame bottom view

Photo 3: Frame side view

Making progress on the build.  I have assembled the basics of the SK450 frame (see the first 3 photos) and you can see that it has 3 levels for mounting electronics, sensors, battery, camera, and radio.  I am currently "dry-fitting" components to see what should go where.  Instructions are few and far between, usually a few pages written in Chinglish.  For Example: the Wiring document is called "HK Mini APM Wiring Helps".  The current plan is:

1. Top level: sensors, controller
2. Second level: receiver, maybe controller
3. Third level: power distribution
4. Hanging from bottom: battery, camera
5. Mounted on each arm: speed control

I also received the receiver, controller and sensor kit from Hobbyking, which is very small, see photo 4.  The AAA battery is just so you can judge the size.  The controller came from Hong Kong but only took about 8 days to arrive with no duty payable (gotta love the USA).

Photo 4: 6 channel receiver and Flight Controller

Building Quadcopter Part 2

Started the quadcopter build by asssembling HobbyKing SK450 frame.  Have not received the controller module but I do have the motors, battery, receiver, speed controls and miscellaneous other bits.

The frame is easy to assemble so far with a small screw driver with an allen key head.

Started My Build - Part 1

I decided to start my own build and go from the inside out.  I am going to start with the flight controller and software, get familiar with how it works, then get a frame/motor/speed controller set, then add a radio.  My first purchase is the flight controller, a HobbyKing HKPilot Mega Mini Combo.

This unit has all the smarts from the microcontroller chipset, plus GPS, gyros, compass, accelerometer, magnetometer, barometer, and ports for additional functions.  This thing will know more about where it is and what is doing than I know about myself.

Once I have the unit, I will hook it up to the mission control software, update the firmware, and start familiarization.