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
Ok, I just did the power up with both the UBEC and the 3DR power module (see below). I didn't see that overshot that Andrew was measuring and I repeated it a couple times. Pretty much the same curve each time for both power supplies. The UBEC goes straight to the 5.2V and the 3DR module does it even more straight :)
HobbyKing UBEC 3/5A Low RF Noise Power-Up
http://www.hobbyking.com/hobbyking/store/uh_viewItem.asp?idProduct=...
3DR APM Power Module Power-Up ... (Yes, I am not only Chinese ;)
http://store.3drobotics.com/products/apm-power-module-with-xt60-con...
Hi, yep mine was doing the same, only would boot with UBEC already powered then plugging into APM, that's why I looked to see if the UBEC had a spike as that was the only reason I could think of being the problem.
I am using this;
http://www.hobbyking.com/hobbyking/store/uh_viewItem.asp?idProduct=...
Maybe I can check the 5V with my scope and see how it comes up during startup. What kind of UBEC do you use? I use currently the 3A low noise UBEC from HK.
Both mine were bought a month or apart and worked fine for a few weeks before the symptoms.
I would think HK has sold a bucket load of these by now and alot are powering the same as me so we'll see if the reports start rolling in as people migrate to the newer firmwares.
Hi Randy yes it's only milliseconds and my multimeter is a cheap one so it would be good if someone with some good gear to confirm the spike, for what it's worth all my ubecs in parts box did it.
Ok thanks Randy, I repaired the 3.3v reg like Detlef and all is good, but that is the 2nd HKpilot board with same problem, so obviously it's whatever I'm doing or the board doesn't like the turnigy 3a ubec in the input side with JP removed...
Maybe the the reg doesn't like the 8-9v startup spike of the Ubec?
Hi Randy, which release will eventually have the new check and change bus speed code?
Bruce, Detlef or anyone else suffering from the problems on this thread,
I was wondering if you could give this modified version of -rc6 a try? It's -rc6 (or maybe closer to -rc7) and includes some extra logging of the MPU6k spi bus errors in the dataflash's PM message in a new "INSErr" column.
Like -rc5 & -rc6, this version runs the MPU6k at 8MHz but will reduce it to 500kHz after it detects 4 errors. On a broken board this should happen almost immediately. If you connect with the mission planner you will probably see:
1. "Bad Gyro" appears on the HUD and you can never make it go away (sorry!)
2. "PreArm: INS not healthy" appears when you try to arm
Despite these problems the MPU6k should work as well as it did in AC3.0.1 and you can force it to arm by going to the CONFIG/TUNING > Standard Params screen and set ARMING_CHECK to "Skip INS" and press the "Write Params" button. If the "Skip INS" option is not there go to the Full Parameter List and set it to "-17". That may seem like a weird number but that's because ARMING_CHECK is now an 8 digit bitmap so when the highest bit is set it becomes negative when viewed as a signed byte.
By the way, there's probably no need to actually fly it (although I think it will fly fine) a bench test should be fine.
so I'll order a new board !
What's the good way to power the board (with Lipo and USB in the same time) to avoid this kind of problem ?
I have an Attopilot 180A sensor and 3A 5.3V ubec plugged in one of the outputs with the JP1 plugged
Can I plug the ubec on the PM port on only 2 wires ?
Thanks
Ok, I am back in business! Seems like the APM did not mind the birth defect of 5V on the 3.3V rail. I loaded Randy's test firmware with the error counter and SPI0 stays at high-speed "1" and counts "0" errors:
Double checking my power during USB power-up looks good this time - the 3.3V stay at 3.3V:
I know there are concerns of 5V on the 3.3V rail damaging components but so far it flew for 2 months with Arducopter 3.0.1 without any problems and now with the 3.3V fixed it will go as ArduPlane into a Bixler :)
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