This is a discussion re the bad Accel, Gyro and Baro values that we're seeing with ArduCopter-3.1.  The increase in the SPI bus speed from 500khz to 8Mhz has exposed a hardware problem on some boards.  That hardware problem is that the 3.3V regulator has been blown so all sensors are running at 5V instead of the intended 3.3V.

 

How have these regulators been burnt out?

  • Attaching a radio receiver or MinimOSD to the APM while the APM is only powered through the USB (see video below)

  • Some clone boards seem to come from the factory with blown regulators.  3DR boards might also come with blown regulators although they do a specific check of the regulator as part of the regular QA process.
  • It is not (as far as we know) actually caused by the AC3.1 software itself, it just exposes the problem.  You could prove this to yourself by checking the 3.3V regulator (see video above) before and after the upgrade.

 

How can we fix the regulator?

Option #1:  If it's a new board (so that it's less likely you burned it out yourself) you could report the problem to the retailer that sold you the board and ask for an replacement.  If it's 3DR it's called an "RMA".

Option #2: if you're handy with a soldering iron you can replace the regulator yourself.  On the APM2.5.2 (and higher) boards it's not that difficult.  On the APM2.5 it's far more difficult.

For APM2.5.2 : TPS79133DBVR

For APM 2.5: MIC5219-3.3YML TR

How can I stop it from happening again?

Do not connect any devices such as a radio receiver, MinimOSD, GPS, etc while the APM is powered especially while powered only through the USB cable.

Attaching a 100uF capacitor across any of the APM's radio input's 5V and GND pins will stop the regulator from being blown by plugging in a receiver.  video here!

There are very few reports of regulators being blown twice and no reports of it ever failing in flight.

 

Below are some graphs of the types of values that we are seeing on these boards.

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In terms of a 'software alarm' we looked for a way to detect it with the sensors we have but couldn't find a way unfortunately.  The best we have is the gyro health warning and that's not really a warning that the voltage is too high but rather than the mpu6k is producing odd values (we request the value of a register that we know should always return "1" and if it doesn't we say, 'aha!  bad health'.

I thought that using A0 eg with a wire and a voltage divider and go check this value at pre arm with the soft

and he who does not want , disable in pre arm safety check

jcfa,

    Ah, so you're saying attach a wire from the 3.3V bus to an analog pin and then check the voltage at start-up.  That would certainly work but would require everyone to make a little cable...

because I read on the mpu 6000 spec : 6.9 Absolute Maximum Ratings
Stress above those listed as “Absolute Maximum Ratings” may cause permanent damage to the device. These are stress ratings only and functional operation of the device at these conditions is not implied. Exposure to the absolute maximum ratings conditions for extended periods may affect device reliability.

it's the same on data flash and barometer , ...................

it's necessary to know the voltage , because these circuits will eventually burned

Olivier already suggested this change for future APM boards and route that 3.3V to an input as well as a pad for measurements.

http://diydrones.com/xn/detail/705844:Comment:1459461

In my opinion I would only do that if a bad 3V3 regulator turns out to be a common problem. And probably not taking Chinese boards as quality reference.

Hi Randy,

 well i just bought a new APM2.6 from 3DR and after a few days this problem happened for me as well.

I get the "Bad Gyro" message as soon as i connect and my HUD just rolls all over the place. I measured the voltage as per the video you put out and i see 4.8vdc.

This is a very worrying thing. On my last Quad with APM i had a few months of flying and it was brilliant but then i had a fly away. Using an FPV monitor it flipped upside down but was unfortunately completely lost so no logs to check. Maybe it was this regulator problem.

Now ive built a Hex in the hope if i lose an ESC or motor it might still fly.

On the new hex i installed the APM from 3DR just like i did on the Quad.

I followed all the procedures in the manual wioth calibration etc and all was fine.

Then i continued on with mounting ESC's and other things and then noticed out of the blue this Gyro problem. I am especially glad i am taking my time with the build otherwise if i had flown it, it would have been a disaster at some point.

Ive informed 3DR and they are looking into it.

Quite frankly i'm really concerned that this problem might re-appear and i'm not sure how just replacing the 3.3v reg fixes what seems to be a hardware design flaw ?

The APM is addictive but my pockets can only run so deep. I don't want to buy the clone as i'm sure the 3DR build is better but.....

Any thoughts appreciated....

So after you attached the ESCs this started happening?  I've never had it happen to me but I hear that plugging in the ESCs backwards can cause this maybe especially if you have the JP1 jumper in place.  My guess is that you blasted it somehow during the build.  I hate to say that but on the very limited evidence that's the most logical guess.  My next guess though is that it was damaged at the factory although I've heard that they test each board's regulator as part of the regular quality check.

Do you have the JP1 jumper attached?  Are you powering anything else from the APM?  Of course you have a receiver attached which draws it's power from the APM but is there anything else?

It could be a design flaw, it could be that you've got equipment that's zapping it.  Honestly, I don't know

Re the crash of your FPV copter, I've never seen a flip caused by the 3.3V regulator being blown.  We've seen twitches..and a flip is of course just a very severe twitch but still we've actually never seen that.  Most flips and crashes that we've seen are caused by much less interesting mechanical failures like props coming off, ESCs overheating or motors failing.  Also we haven't seen cases of the regulator failing in flight.  So although it's tempting to draw a line between your FPV crash and this 3.3V regulator thing, I think it's unlikely....unfortunately, as you say, we will never know.

Considering that you just bought the board, I wouldn't be surprised if 3dr replaces it for you.  If they don't, a decent number of people have managed to fix them by replacing the regulator.

Hi Randy,

 thanks for the reply.

I suppose its possible i did something wrong but i'd like to think im pretty meticulous.

Yes i use the JP1 but my esc's have + removed from the connector so they don't backfeed.

I have a D4RII connected which is powered from the APM and thats it. No servo's or anything else.

This is the way i powered the Quad. Yes the Quad is gone so it's just speculation on that part.

Ive ordered some regulators from RS Components here but would prefer 3DR to sort it out.

I'm happy with 3DR and the APM as its given me a lot of pleasure and all that.

I just wonder if the the 3.3 reg could be protected better with a design mod.

thanks again for your efforts on the FW. It's much appreciated.

regards

Matt

Some labels on the pic would really help.

May I recommend this datasheet if you need to match soldering pads on the board with the pins of the chip:

http://www.ti.com/lit/ds/symlink/tps79147.pdf

Since we were discussing this a while there was a pic indicating the 3V3 pin earlier here:

http://www.diydrones.com/xn/detail/705844:Comment:1459253

Hello
I read in a German forum that it is a layout error.
when will changed that.

look at them here: http://fpv-community.de/showthread.php?37502-APM-2-52-eine-tickende...

I myself have 3 APM all ok!

best regards

Hi Rainer,

Those 3V3 issues are discussed everywhere and you always find guys that know it all better and doom all 3DR designs. Just try RCgroups, there you find the complete group of 3DR hater. I didn't read his complete thread but he certainly has a lot of assumptions and no proof. He also says that the TPS has not internal current limiting - I guess he didn't read the data sheet. Calling it a flying time bomb?? That guy just wants attention in my opinion...

He didn't call it a short circuit in the layout. He wrote a short circuit in the regulator - means the regulator letting the full 5V through on the 3.3V side.

Anyway, I don't even own a 3DR, only clones. But unless someone measures the power consumption on the 3V3 I don't believe the TPS is too small (I was too lazy to do it). There are better designed chips and there is probably an easy way to blow the regulator up but I think if everything is under normal conditions it is working as it is.

Beside his replacement suggestion is a 950mA 3V3 regulator?? That's more than the entire APM board will draw. Its fused with 500mA on the 5V side.

In general the use of lower voltages in the microprocessor technology is to reduce current draw and the creation of heat.

I think his call for everyone to contact 3DR to bitch about it is not helping. That only ties up ppl that could do other work. Besides if you found this thread then you should realize that 3DR is already aware of this issue.

Gruss

Detlef

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