Stepper driver 17DNSWF ULN2003A

Why am I looking at stepper motors?

Well with pretty much all planes we alter the shape of the airfoils to move the centre of lift (COL) relative to the centre of gravity (COG). In this I hope to do the reverse and change the COG relative to the COL. Much like a hang glider or windsurfer does. Thus we can try many more wing types more quickly as we won’t have to deal with making flaps, inserting control horns, mounting servos etc.

Let’s see how we go.

I bought this stepper and hardware driver off Ebay for about $AUD4-.

Chip marking


which appears to be a regular Darlington array. This is the data sheet link


Playing with the GY-85

I am trying to make a head tracker for the FPV setup on our slope soaring gliders, as we need to be able to look around to find the cliff edge when gliding. If you’re more than about 30m out, you can be falling out of the sky. With a camera just facing forward, there is no way of telling where you are in the sky relative to the cliff edge and thus the air currents.

From the RCgroups forum post link:

Head Tracker forum post

This link points out that the GY-85 which I ordered from DX.comĀ  based on Dennis’ initial forum post is not the same as it was some 6 years later. The GY-85 I bought does not have the same magnetometer chip on it. So the headtracker code from this forum does not work on the yaw axis.

The PCB I bought has the QMC5883L chip setĀ  instead of the HMC5883L chip set by Honeywell.

I dug up the data sheet and some code for the QMC and the code seems to work well enough in all axis’ . It doesn’t seem to isolate any particular axis fully, but I’m sure with some filtering I could make it more accurate. However it was getting on midnight so I stopped playing with the board and software and decideed to focus on what I was doing.

The i2C bus address was obviously incorrect in Dennis’ code for the QMC chip set. –> Fixed that.. good.

But the QMC works slightly differently and has a different library to the original head tracker code. For the sake of $AUD15- and the fact I could get an IMU board out of Melbourne, I took the time efficient path and ordered the GY-85 board with the HMC chip set below. You can see the



Markings of the HMC5883L chip in the image below.


I ended up ordering this GY-85 from ebay and the images show the Honeywell chip comes with it. Fingers crossed it’s the correct one.

More on this later. Soon we’ll be slope soaring FPV with a head tracker.

Back to it.

It’s been a while without flying, but a recent revival of enthusiasm has put Gemot back in the sky. 30knots or so at Lennox about a week ago. Awesone flying. Then of course a throng of overconfidence about low passes caused a meeting with the ground cracking the top laminate on the starboard wing and a snapped servo horn on the flap.

Some repairs this morning and we’ll be back in the air in the coming days.

Gemot Yellow
Repairs for a snspped wing.

INAV F3 Flight controller arrived

Will have to make some time to put this one into action. Hopefully the telemetry going to the OSD will overcome the issue of knowing where the horizon is in flight when staring up into the big blue. The altitude feedback will be good also. Wouldn’t mind fitting an angle of attack indicator to the OSD, ,,, well one thing at a time.

Zamten – Flying wing with a quad chassis

Prototype from fibre glass panel either side. Joiner tubes –> Tapped some 6.2mm alloy tube with an M5 thread. Joined with M5 (thread length 17mm). Carved wing quickly with 50mm thick EPS foam (12kg/m^3) using 60 grit sand paper.

Nano Talon weight test

Have been testing the ZOHD Nano Talon slope soaring without the prop. We did a weight test yesterday. At a flight weight of 590 grams it flew just fine slope soaring in about 25knots of wind. This was 70 grams heavier than the flight weight with the 1500mAh 4S and the FPV gear. (Runcam eagle rpo 2, BEC, eachine ATX03) which clocked in at 520grams.

Releasing designs and mill files.


Still waiting on parts to make the EPP moulding machine. It will probably be some time away before I can mould these wings.
In the meantime I have put the original designs in this torrent file.

They include the 3D model with the foil sections and twist angles. The 3D’s of the plane and packaging are organised into 1200 * 600 * 50mm EPS sheets ready to mill.

I have also included the .tap mill files to work with a Mach3 controller in mm. There is a text file at the top of the mill folder with the details of what tools to use when and how to go about it. I had not intended it to be released to the public, so if it’s a bit confusing then let me know and I’ll try clean it up to be more machinist friendly.