Dubious GY-85 boards and HMC5883L fix

I ordered 3 different GY-85 boards from 3 different suppliers to find that all of them had the wrong magnetometer in them. Some even advertised their product with the HMC5883L chipset on them, but when they arrived they where the QMC5883L chipset.

After all this effort to find something without the shipping cost / time from the USA I decided to just get the HMC5883L individually and attach it to the I2C bus of the GY-85 board. The individual boards is called the GY-271. I found this supplier in Chullora in Sydney:
GY-271 HMC5883L
It worked just fine and now the head tracker is working.
You’ll see in the image below that the Honeywell HMC5883L chip is defined with the markings

Where as the 6th page of the QMC 5883L manual shows the markings something like

QMC5883L datasheet

HMC5883L datasheet

Using the GY-271 compass board by itself

(Also posted in RC groups)

Long range flying and what this dB stuff means.

The first thing to do is watch Kahn Academies video on calculating decibels

The video also points out how sensitive the human ear is.

P = power in Watts (W) = Work / time

Work is an energy measurement. What is energy? That’s a question which will stump pretty much everyone. The answer is probably another question. Why? Don’t hurt your brain with this one too much…. moving on.

J = Joules = an energy measurement.

Work(J) = Force * Distance

Force = measured in Newtons (N)

1N =  about 102grams * gravity

The actual formula being

F = m * a

Force = mass * acceleration

So 1 Newton of force is about half the mass of your house / car keys just sitting in your hand.

Lift your car keys 1 metre in one second. That is 1 Watt of energy.

You car keys have a footprint that fills the palm of your hand. You can feel it.

Spread that weight over 3 times the size of Germany, or for the Aussies reading this, a bit less than the size of the Northern Territory.  You couldn’t feel that with your hand, but your ears could hear it.

OK, It have to come back to this article to explain how it relates to long range flying.



Urban Aeronautics

A very interesting video from the Vertical Flight Society.

So I was initially thinking about 2 rotors like this for Sentach except running port / starboard rather than fore and aft. The thing is that the application is different. I’d like to take Sentach out to 300ish knots for small payloads and get 1000km range. Smaller payloads require a smaller vehicle. Thus we can stay with the wing model and use VTOL not for hovering so much as just punching off the ground and not needing a runway.

Slope test – Sentach

Took the headtracker out as I wasn’t expecting much lift today. At best 25kts (12.8m/s) at Pat Moreton. Flew perfectly, but the glide slope was not enough to keep altitude. 763g. Still waiting on props to arrive. ‘Tas heaps of drag points which could be eliminated. Could make a larger wingspan for these wind speeds.

Would be interesting to see what CFD says and how it compares to reality.

Time to have a crack at flight stabilization

Would like to get flight stabilization happening so it’s easier to fly FPV with the head tracker initially. At least if I balls it up I can throttle off, let go of the sticks and it will have some chance of landing flat. Would also be able to see compass headings, altitude and battery on screen through the OSD.

Think I’ll start here first and see if it works with that F3 board.

Some others to look at:




MWPTools for navigation to mix with the flight controller. That or the INAV software.



Sentach powered up

Put the motor in and re-balanced it. Flew at around 14:00ish under power with about a 30kt NNE (15.43m/s) for backup glideability. Flew so well. Only hit about half throttle with a 4s. Had heaps of lift, so I’d say I could max out at about 1kg payload with more throttle. Now onto a flight controller before sticking the head tracker in.

Flight weight – 1414g

New COG –  280mm from the L.E.