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
A lesson in open Hardware..... These sellers cannot call it ArduPilot, they can't show pictures of other brands when selling a different item.
Buyer beware.... What is your plane worth? What is your time worth? What are you saving buying a clone? These Suppliers DO NOT support this community, so why support them?
Well, then get back to your studies! ;)
Thanks for the note. Another piece to the puzzle. Probably not the silver bullet, but another potential cause of problems.
unfortunately this is not solved. Please all, DO NOT TRY THIS SOLUTION YET.
We ARE investigating this very issue at the moment, and will inform you of any findings. There IS an issue with the shifter, but it is the Data lines that are wrong not the Vcc lines
the 3.3v VCC is rated to MAX 4.5v, so connecting this to the VCC 5v as suggested here could lead to an unknown situation.
Please wait for some results from our testing first.
Keep in mind, this goes back to the beginning of the APM2.5
This fault, has not caused an issue due to the fact that flash can handle the higher voltage.
This will be fixed on the next layout revision, but it is not considered a critical issue.
Not to mention, that if this was it, 100% of boards would have the problem 100% of the time.
So, I'm not sure about this one. Let's have some other people look at it before declaring anything. This is already spreading like wildfire...
But it could help to explain quite a lot of these voltage issues.
Just for your info, here is the scope trace on the Digital servo
2v per div, 50ms per div
Max voltage over 10 Volts
see my comments above regarding this.
if the servo is on ch9-10-11, then this would go straight back onto the vcc 5volt rail
I normally just use the low RF HK, but for these tests, I ran with a bench supply, direct battery, 3DR power module, and the BEC.
for info , since I put a MCP1826S I have no problem
Glad to hear some servos are good, unfortunately we have tested a few HiTec as well as HK and New-power, all create spikes that are quite nasty. they even produce these when powered directly off batteries ( cant blame a UBEC)
the fix was quite simple, we placed a 1N5339 zener diode across the servo rail, stripe end to the positive rail, the other end to gnd.
this clamped the voltage nicely.
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