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.
Replies
I just went through the reviews of the HKmega on HK's site and a few people have mentioned dead 3.3v regs, I'm wondering if it's feasible to rig a 3.3v ubec in there for durability?
Thanks Detlef I'm powering from inputs with JP removed.
Am careful using a UBEC with sub 5.3 voltage.
Although it does fly fine on pre RC3 firmware so....
:) No worries, I had advice over at the other forum that all the 3.3v sensors and chips would be damaged by the 5v, and to get a new board, that might be prudent advice...
This is my second board and before my first board died prematurely (pilot error) it was have the boot problems also so may have had a faulty reg also, would love to find out what is causing it.
On this 2nd board I was very careful not have usb and ubec powering at the same time, although the advice is it is fine to do so, but I forgot one time and it may be purely coincidental but it seen to develop the boot problem after that, has there been any discussion on that?
Hi Detlef, thanks I'll order one,I didn't havn't any arming issues, just booting the board requires an already powered ubec, I suspect the startup voltage spike in the ubec is doing something to make the board not arm.
RC5 is looking good on my APM 2.6. My first attempt at Autotune ended in a crash - Looks like 3 meters is not a good starting altitude. 10 - 15 worked much better. Definitely need a nice big open area. Altitude hold and loiter are great! Stab mode is sweet also!
Thanks guys!
Hi Randy, it's definitely not normal behavior, on the pre rc's it corrects immediately and is perfectly flyable.
So did we deduce it is a blown 3.3v reg that needs to be replaced?
Hi fellows, I joined to say I have similar problems to Detlef.
My board will only arm if UBEC is powered first, then plugged into board.
I checked the 3.3v line today and yes it is 5v also.
I also noticed after a certain rc3-4 firmware my ACC was "sticking" as in I could lift off and hover fine, but once a few heavy inputs in pitch or roll were applied the acc would stick in one direction and slowly go back to level after approx 8 seconds.
You could see this in MP by shaking board when armed and immediately setting down still on the ground and watch the HUD slowly steadily go to level.
Hud would immediately go to level on disarm.
So I didn't have the revolving hud like others but the behavior described above.
is this noticeable and happening as well in rc4? What behavior is noticeable in flight? I have rc4 loaded and on occasion I get a weird jump on one motor as if the bearing jammed for a 10th of second or so. I checked the motors and swapped them and teh ESCs around, but it still happens off and on so it cant be a faulty motor or ESC. It might not happens at all for a whole flight so its weird.
Well i need to step back and redo my measurements. But definitely something wrong. Stay tuned....
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