Monthly Archives: June 2013

Tricopter – Motor Repair

After my last crash the shaft on my rear tricopter motor was tweaked. 

Fortunately I gave each motor a spin manually before powering things on and noticed so I had opportunity to fix it. The motor was clearly rubbing and I imagine would have promptly self destructed had I turned it on.

The motor is a NTM Prop Drive Series 28-30A 750kv / 140w though I would suspect this approach would apply to other motors including those used on quadcopters y6’s octocopters and other miscellaneous multicopters.

In essence, I removed a snap ring from the base of the motor which allowed me to separate the housing from the interior. I then mounted the housing with shaft in my lathe and using a dial indicator centered it up roughly (via nocking) in the chuck.

Once reasonably centered I ran the dial indiactor on the far end of the motor shaft. It was out by nearly 10 thousandths of an inch. I located the high spot and pushed on the shaft to nock it back to 5 thousandths. The process of measuring total outage, finding high point, halving, was repeated a couple times till it was under a quarter thou out.

Remounting and replacing the snap ring I found the motor now sounded healthy. Powering it up verified all was well; disaster averted!

As an aside; the earlier part of the flight actually went quite well. Trying it in a fairly open field made flying the tricopter a bit easier and I actually managed a pretty neat steeply angled circle around 1:36 into the video.

HackRF Jawbreaker Arrived!

Welcome home HackRF Jawbreaker 305, welcome home!

To get the HackRF Jawbreaker running I:

  • Installed Ubuntu 12.04 in VMWare Fusion
  • Ran apt-get update and apt-get upgrade
  • Ran the amazing build-gnuradio script
  • Followed the instructions on the HackRF beta page to build the hack-rf tools and upgrade the firmware

The first couple times I attempted to run the build-gnuradio script it failed. This was due to a lack of ram. My VM was provisioned with 1GB of ram and 1GB of swap out of the box. Bumping it to 4GB or ram (I imagine 2 would have done it) got everything building correctly.

HackRF Jawbreaker

My Jawbreaker shipped today!

Michael Ossmann created the HackRF Jawbreaker a Software Defined Radio capable of receiving and transmitting from 30 MHz to 6 GHz. He gave away his production run of Jawbreakers (funded by the US Cyber Fast Track program) and I was lucky enough to get in on the deal.

When the unit arrives I am hoping to use it to take a closer look at some of the wireless RC gear I have been playing with of late.

Getting Ardupilot Setup for a Tricopter

To configure the ardupilot/arduflyer for a tricopter you first need to load the tricopter firmware on the board (mine came with the quad firmware out of the box).

In theory, you can use mission planner to do this but for my board at least I consistently received an error when trying to load the firmware that way. I fell back to using the Arduino IDE to compile and load the firmware. This guide covers the process nicely. Basically you:

  • Download a customized version of the Arduino IDE and a copy of the arducopter source code
  • Copy the ArduCopter and libraries folders into your Arduino sketchbook folder
  • Run Arduino set the chip, set the com port and open the arducopter sketch
  • Edit the APM_Config.h file to set the FRAME_CONFIG to TRI_FRAME
  • Compile and load the code

Once you have the board updated and configured for a tricopter you need to do a number of configuration steps before the board will allow itself to be armed. These include:

  • Use ‘Terminal’ in Mission Planner run ‘erase’ then ‘reset’ as detailed here
  • Under configuration, calibrate your receiver, calibrate your compass, calibrate accelerometer
  • Do an automatic ESC calibration

You should now be able to arm your motors. Detail instructions are here but essentially, hold the left stick to the bottom right for 4-6 seconds (the red LED switches from flashing to solid).

You can now add props and arm the tricopter. Turn on very light throttle and verify all of the props are moving air in the correct direction. If any motor is spinning the wrong direction swap two (of the three) power leads going to the motor to reverse its direction.

Now that the props spin the right way; with very light throttle try rotating the tricopter to verify the yaw servo moves the correct way. On my tricopter it didn’t so I reversed the movement by setting RC_7REV to -1 under the advanced configuration settings of mission planner.

Tricopter Maiden Flight

I have the tricopter fairly together electromechanicaly but still need to tune the firmware.

At present the main issue is arming the motors; I have to do it via a laptop, using the controller it refuses to arm. Regardless, I did manage a quick test flight and it seemed to work great. Getting it to hover only took around 70% throttle so it should be peppy and have room to carry some camera gear. Looks like I can improve my landings a fair bit though 🙂