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:
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
Using the GY-271 compass board by itself
(Also posted in RC groups)
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.
Sentach glider version
The Sentach glider worked well today at the Pat Moreton park in about 15-20kts NNE. Videos to be posted shortly.
Flight weight 680g.
COG 310mm from the L.E.
Beautifully smooth flat landings. Some wobbles as expected. The’s alot of drag points. Especially with the flat sides of the nose. Don’t think anhedral would totally fix it because of the nose as it’s obvioualy turbulating when a crosswind happens.
Crashes it once and the wing popped off nicely dispursing the impact force. Plugged it back together and went again.
The angled wingtips wouldn’t stop the tip vortex as XFLR5 shows in the sim.s. would be better to round into them like Gemot. The difference they made to Gemot was nothing short of impressive. Holding Gemots wing in one hand whilst spinning around, with and without wingtips gives a tactile feeling of the drag differnce involved.
More to come soon.
The current tip foil for Sentach
Being a bit too fried to do a proper stability analysis for Sentach, but having enough mind to sketch out the dimensions for the tip twist foil, the above shape emerged.
Designed to fit into the 50mm thick EPS sheet at 7degrees. It should kill the lift and thus tip vortex nicely. Same as Gemot, however Gemot is 7degrees and a far slower and more tolerant foil.
After watching all of the tutorial videos on XFLR5 yesterday I might do a stabilty analysis first…. Hmm maybe…. I also just want to test the head tracker and Sentach is a rough wing, not a refined design.
Something to put the head tracker in.
I wanted to put the head tracker in some thing. Gemot would only just allow for the head tracker in it and it only had 35mm maximum air flow distortion (i.e. the thickness of the centre foil). The EPS sheets I’ve been buying are 50mm thick which is plenty of air distortion to create heaps of lift. This wing above will also have the fuselage as part of the lifting surface. It will be the same proportions as the wings. Thus making it about 70ish mm thick.
It’s about the same wingspan as Gemot coming it at just a touch over a metre. I’ve learnt that the little 0.25N torque servos (2.5kg/cm) are straining on almost everything when the wing span is over a metre.
This wing also allows for the GRP (Glass Reinforced Plastic) chassis to be pushed inside to convert it to powered flight later. It can be tested gliding and then step across to powered later by sliding in the engine. The V- shaped EPS frame inside should spread the load on impacts with the ground during testing.
About the head tracker. The HMC5883L chip arrived in the post on Friday and I couldn’t wait. Put it together that night. Added the chip into the I2C bus, Added Dennis Frie’s code and away it went. It worked through the Turnigy i10 using the trainer cable and a 10channel RX.
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.
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.
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.