DJI Zenmuse H3-3D – repair (Part 1?)

Big Drama…

I had a pretty horrible crash with my DJI F550. There was a catastrophic resonance which made the copter unstable and uncotrollable. The Gimbal, defektDrama was, that my beloved DJI Zenmuse H3-3H Gimbal was underneath, when it crashed on the roof. This is how the gimbal looked… (Thank god, the GoPro was OK)

The first problem was a sticking ‘roll’-axis. It was easily fixable. The axis of the roll axis has an easily reachable screw which claps the motor to the axis. The arm squeesed onto the regulator PCB due to the crash. Fixing was as easy as loosening the screw and tightening it again.

But, at a close look, I found a defect halleffect sensor on the ‘nick’-motor of my gimbal. Normally this is a death-sentence. Googling A search online yielded that the DJI motors are sold and made nowhere. Not even Alibaba.

After I tore down the gimbal and removed the motor, halleffect sensor crumbs fell out of it. The other sensor were labelled ‘1432’, which yielded exactly no results, aside from some analog Sensors from Allegro. Important to note was that Pins 1 and 3 of the 3 remaining sensors were connected to each other. Also, Pin 2 of these SOT23 sensors were connected to something what seemed to be a ground pour. Some cross-referencing later it turned out that the pinout 1: VCC, 2: OUT, 3: GND i a pretty usual pinout for halleffect sensors in SOT23 package. Conveniently, there also was a small ceramic cap on the flex-PCB which was connected to Pins 3 and 1 respectively GND and VCC. I traced one of the remaining sensor outputs to the flex-connector, where I removed the kapton and connected a wire (please re-check the pinout on the picture). I set a current limit of 5mA and slowly raised the voltage to 4.5V. But, unfortunately, there was no recation to stimulation with a neodymium magnet. It was not before i connected my scope and found some interesting spikes. The sensors on the motor have open-drain outputs.

But which kind of halleffect sensors are they?

There are several types of hall effect sensor. Bipolar, unipolar, latching, analog, … luckily, there are very nice videos on Micronas’ Youtube Channel [1] [2], which neatly explain the behavior of bi- and unipolar hall effect sensors. In our case, the output of the sensors was consistent with unipolar halleffect sensors. Quickly checking out Farnell I found the SS360xT (x for North or South) from Honeywell as up to the job. The only thing still unknown was the polarity of the sensor (north-on or south-on). So I ordered both categories…

After testing which polarity was the right one (magnets!) (NORTH in our case – so it’s SS360NT) I mounted the sensor in the motor, which was not quite easy duue to some kind of melting plastic, and attached a wire to it’s output in the usual way.

I mounted ‘freestyle’ pullups for open-drainability and hooked everything up for a test….

Actually looks pretty nice. Yelloow is our new sensor. Interestingly, our new sensor seems to be ‘high’ on power-on, which the others aren’t.

Apart from that the signal looks as we would imagine such a signal, showing magnet position in a imaginary circle, measuring always 120° apart.

Now of course it is on to putting it all back together. It’s important to note that the notch in the little gear which turns the pot on the controller PCB must be aligned with the notch on the motor axle. Otherwise, the closed-loop-control isn’t working right. Apart from that, always align the screws with the notches in the axles…

Tada – The gimbal is working again! :)

The (absolute) angle of the ‘roll’ axis is still off because it’s mount is bent. But that maybe is

part of part 2… :)

Wouxun KG-818 VHF Teardown


On the Hamradio Friedrichshafen I got myself a Wouxun KG-818 VHF (5W, 136-174.995 MHz). I plan to realize a small APRS transmitter for my car.

“The Wouxun…”

…whithout batteries. You have to remove the screws on the bottom left and right…

…as well as the nut around the antenna connector …

…to slide-wedge the whole assembly bottomwards-out. The dials will come off as well as some plastic thingy. Beware of the ribbon!

The two modules. On the left the processor/TRX-board, on the right, the LCD/speaker/kexs section with part of the case.

And once again the TRX/Chinagirl-module. Unfortunately the PCB is soldered to the RF-connector, which prevented me from further teardown, because I had no soldering iron at hand. Underneath the firmwaresticker it reads “M64X802”.

Great!” The TRX works even without its keys/speaker etc attached!

Well and that’s about it. I will mod this further so stay tuned.

HamRadio 2012

It was once a gain HamRadio Friedrichshafen-time. I was there – unfortunately on sunday. So.. Here are the pics.

eZ430-Chronos unboxing

This was in my mail today…

It’s from Digi-Key! Let’s crack this sucker open…

Ok, I’ll see what I can do… 😉

Look!!! I found an eZ430-Chronos! :)

The Chronos was on sale on tiDeals for $25 or so, so I bought one…

Little extra: The CHronos RF modem and a MSP-eZ430U Debugger (epic win!!)

As Dave would say: “Don’t turn it on, take it apart” (actually with the supplied screwdriver..), this is what you cet; the Chronos watch module (with debugging connector).

Unfortunately the Chronos is a little ugly (even more than on the website – so I think I won’t wear it.. :( ). Also it consistently measures the altitude 500m too high (haven’t found barometer setup yet). But it sure is a great toy and the MSP-eZ430U Debugger/Programmer is worth it’s money.

So.. Stay tuned!

Magmount refurbishment

I do (of course) have an antenna on my car, which was to date mounted with a pretty rusty old magmount. I don’t know; our local marten didn’t like that at all, the RG-58 which was unprotected ~20cm was completely torn to peices.

To cut it short; I didn’t document the process. I could only reuse the magnet from the original magmount, the connector was completely encased in PVC and thus irretrievable. So i turned a new connector holder out of delrin (POM) and milled the fitting for the connector with my CNC. After I de-rusted the magnet, drilled matching holes, applied a base coat and some layers of laquer I screwed on the holder with V4A INOX screws.

Tada…. (click for larger..)


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