Blogs

Our friend Warthox, which is one of the early testers of FreeIMU v0.3.5_MS on his quadcopters platforms, just published an awesome video of his tests with FreeIMU v0.3.5_MS.

The video really stress test FreeIMU on MultiWii stabilization software, doing loops, flips, acro flight, launching the quad, no stick input.. awesome. Thanks Warthox!

My friend Chris Domes from HaDi-RC.de just sent me one copy of this month Heli4Fun Magazine.. and, you know what? His EDF-Tricopter, project powered by MultiWii and FreeIMU v0.2 and v0.3 has a full 5 pages article there!

Awesome work Chris, keep the great projects coming ;-)

So, here it is.. just born.. motors, escs, distribution board and frame all assembled! Funny!

I designed FreeIMU for human-computer interaction.. but hey.. a good tool may be used in many different applications. So, it turned out that FreeIMU is actually a pretty good sensor board for using in flying machines, especially on multicopters applications.

Just one year ago, I wasn't experienced at all in all the quadcopter/multicopter stuff but as soon as I published FreeIMU, people from that world got in contact with me.. I think I now have quite some friends from the quadcopter world..

Well, it finally happened that I've been more and more interested in multicopter till almost being passionate about them even if I never flyed one of them..

But then, I went to the flying field with johnxp and I've seen and tried flying one of them.. well.. what can I say? That's awesome!

So, here I am.. two days ago, with the help of johnxp, I bought all the stuff to build my very first quad as well as the radio, battery chargers and miscellaneous stuff.

So, here is what will be my setup:

• Radio: Turnigy 9X 9Ch Transmitter 2.4Ghz Mod & 8ch Receiver UK
• Radio Battery: Transmitter Lipo Battery for Futaba Spektrum JR UK Sale
• Ubec: UBEC 5A (8-40v) SBEC Switching BEC
• Motors: XYH 28-30 750Kv 10A Brushless Outrunner
• Esc: Hobbywing Brushless Motor 25amp esc speed controller
• Motors hardware: XYH 28-XX series Spare accessory pack
• Propellers: 1045R Slow Fly Counter-Rotating Propeller and 1045 Slow Fly Non Counter-Rotating Propeller
• Batteries: HobbyKing Online R/C Hobby Store : Turnigy 2650mAh 4S 40C Lipo Pack
• Battery Charger: HobbyKing Online R/C Hobby Store : GT A-6-10 200W Balance charger & discharger

What do you expert quadcopters pilots think about it?

Just put out from their package. 100 MS5611-01B01 high resolution pressure sensor. Sexy!

This is a picture of the flight controller Tilman from microcopters.de has been able to assemble using an Arduino Pro Mini and FreeIMU v0.3.5 (version without barometer). The full article is available in German here.

Awesome work!

Bad news for those who were waiting for the MPU6000 and MPU6050 from Invensense. Macnica.eu, the Invensense's EU distributor of has just notified their customers on list for the MPU60X0 sensors, thus also myself, that:

This delays has been going on for at least 6 months now, while Invensense continue marketing their wonderful sensors but still keeping delaying them.. the question which arises, at least in my head, is.. do they really have what they are promising?

We will know.. Meanwhile, fortunately there are already very good solutions for orientation sensing.

This is one of the very first FreeIMU v0.3.5_MS I assembled during the past weekend. This is probably one of my best soldering work and PCB design.

An accelerometer is subject to dynamic (or external) and static (gravity) accelerations (see my thesis, chapter 5.1). This means that whenever you are interested in measuring dynamic accelerations rather than gravity you have to compensate for gravity.

I implemented a very simple approach for doing so, assuming that you have a 9 degrees of measurement inertial measurement unit as my FreeIMU, from which you are able to compute its orientation quaternion representing the orientation of the Earth frame with respect to the Sensor frame and that you have the readings coming from the accelerometer.

This is the code, implemented in Python:

# compensate the accelerometer readings from gravity. 
# @param q the quaternion representing the orientation of a 9DOM MARG sensor array
# @param acc the readings coming from an accelerometer expressed in g
#
# @return a 3d vector representing dinamic acceleration expressed in g
def gravity_compensate(q, acc):
  g = [0.0, 0.0, 0.0]
  
  # get expected direction of gravity
  g[0] = 2 * (q[1] * q[3] - q[0] * q[2])
  g[1] = 2 * (q[0] * q[1] + q[2] * q[3])
  g[2] = q[0] * q[0] - q[1] * q[1] - q[2] * q[2] + q[3] * q[3]
  
  # compensate accelerometer readings with the expected direction of gravity
  return [acc[0] - g[0], acc[1] - g[1], acc[2] - g[2]]

The idea behind this is pretty simple. With the quaternion we can compute the expected direction of gravity and then subtract that from the accelerometer readings. The result is the dynamic acceleration.

I'm sure that there could be a better solution but this is just the result of a 10 minutes coding and seems working pretty good.

In this video I documented how I'm using Press and Peel blue sheets for toner transfer PCB etching for an Arduino Shield PCB. The video covers all the steps in the procedure somehow explained in my awful English.