Fried the QX90C mosfet

Yes, by the 4th flight it was baked. The mosfet labelled A08K 77 overheated. I think possibly because we are NoObs at Quad flying and so hovering around indoors on and off the ground without much air movement over the mosfets doesn’t give much of a chance for heat dissipation.

We ordered some mosfets off Ali Express. They should arrive in a couple of months and then we can test our micro soldering skills. Util then we’ve ordered some more QX90C’s and will also order a spare flight control board.

Maybe it’s worth sticking a baby heat sink on these mosfets.

Testing the weight shifter.

Just tested the weight shifter at skenners. Flew perfectly … in a straight line. Flight weight 836g. Too much lift on these wings. Also the lift goes all the way to the tips rather than being laterally centralised. Thus the weight shift makes bugger all difference in this wing.Using 50mm thick foam sheets as wings is great as you don’t have to laminate them, but then they’re heavy, cause way more lift and require more power, torque, mass movement to drive rhem.

QX90C from Banggood

We flew this for the first time on the weekend. We can’t fly quad to save our lives, but it resisted all our crashes. Shows what a lack of mass does for your survival rate. Quads are great FPV practice as a transition to wings. Get’s you used to floating in space and moving around through the goggles without the device moving away from you at a million miles an hour.

The 2 versions of the GY-85 9DOF PCB

This one has the HoneyWell Magneto chip on it.

Chip markings:

And this one has the QMC magneto chip on it:

Chip markings:

It’s difficult to confirm which one you’re going to get from any given online seller as they look very similar.

Mass shifter attempt 3

Attempt 2 was quickly cannobalised by attempt 3. Rather than trying to figure out a complete answrr to the universe by thinking about it, just start building.And by just building this the possibility of fore and aft mass shift becomea more apparent.This time the weight shift is only port and starboard. AOA set by a trailing wing.

Another dud GY-85

This is the 4th order of the GY-85 and it has the QMC magneto in it again even though the photos on ebay showed the Honeywell chip. Hmm, bit of a fail. RC groups was saying the Honeywell chip is not manufactured any more.

I got the QMC chip working on all 3 axis’, but it uses a totally different code library and thus Dennis Frie’s code doesn’t work with it. Might be time to write some code??

Weight shifter concept attempt


Shift the weight around in the plane, rather than shifting the lift point around using control surfaces (ailerons, elevators, etc).


  1. Save time on making control surfaces for every wing designed.
  2. Control the stall point like a hang glider or bird does, to enable controlled stall landings.
  3. Give the ability to shape and switch wings quickly.
  4. Reduce the number of weak points caused by embedded servos and control surfaces.


In this attempt on making a flying object which uses weight shift, I decided to use standard servos to see what I could get away with. The stepper motors I want to use would take time to get here and I am impatient on this one.

Definitely the conclusion on the DS939MG servos is that they are not really made for aircraft much bigger than a 1m wingspan. After that the mass just steps up too much and they don’t handle it. Even though I kind of know this when smashing tests together, I do them anyway just to prove concepts.

This case was no different. It flew!! The weight shifting worked, but the servos were under powered.

It’s a 1950mm wide wing. The mass is just too much for the hardware. It was not the intention to make the central fuselage so thick (130mm) , I wanted enough swing from the servos to shift the weight far enough during flight. I didn’t want the weight shifting gear hanging out in the air stream. Hence the thickness to enclose the weight shift system.

The 2.5metre wingspan plane I made over 6 months ago had the same problem with hardware. It glud (Yes, glud is now a real word) down the local hill perfectly with no electrical control system mounted. However, upon installing the control system, the 0.25Nm (2.5kg/cm)  servos were seriously outgunned.

I wanted this to be a easy rebuild wing. By that I mean to have a decent weight shifting fuselage whereby I could just slam on a couple of roughly shaped 50mm thick EPS foam wings.  If I destroy them I can just go put on another couple of sheets of foam. A quick general testing platform. If I could control stall, then very slow landings are possible.

The tail plane you see here is to control AOA (Angle of Attack) as there’s not reflex or tip twist. I prefer this method to putting reflex or tip twist in the wing as both involve complex shaping which would contravene the Purpose.

In conclusion. A successful test. I’ll scratch my chin on making a sub 1m wing which can use the small servos. A small wing also fits in the car more easily.