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
Joe, all I asked for is some evidence. I don't think that should illicit such a response.
Philip,
I'm not sure if you had formulated any specific test procedures yet, but I have a few ideas. Do these after you find a stimulus that causes failure.
1) Attempt to initiate failure while continually holding the reset button down. The idea being that this would power the board but disable all communication on the i2c and spi buses. Reports of regulator problems seemed to increase after the bus speed was increased. If the board still fails then data transmissions had nothing to do with it. If the board does not fail then focus more attention on data chips.
2) add diode that Joe mentioned.
3) Try triggering the failure while different firmwares are loaded. Ardurover, arduplane, prior versions of arducopter. This will partially test whether or not software plays a role.
4) set up simplified breadboard configurations with DIP pin versions of the chips and try to replicate the failure.
5) Start removing chips one by one and retesting until the problem stops.
To initiate failure, the load only needs to be powered for a split second. You should be able to just tap the load on and immediately remove it.
You can probably detect runaway before damage occurs by measuring current draw or monitoring the 5v rail voltage for increasing sag. I have been able to trigger the problem at least 5-6 times and my board is still alive.
Joe and Rob... Peace not war... we are all on the same side here....
I have boards on the way, brand new, never been used. I will compile a list of the causes and fixes, and will go through each. the object will be to kill a perfectly good board.
I will disclose all results to all.
now chill and wait for the evidence :)
So have you actually produced any evidence that confirms your theory? All you need is a capacitor, and a couple boards and/or regulators. Go ahead and try blowing that regulator by plugging caps into the 5V line. Then see if it's fixed with your diode.
There is some interesting info regarding 'hot plug in" at the bottom of the page in the link below. Scenario 1 is very familiar.
http://www.ece.drexel.edu/courses/ECE-E431/latch-up/latch-up.html
No big cap on my receiver (Wfly 7ch)
http://www.wflysz.com/en/product_detail.asp?id=60
is this a first time pug in? did you plug the connector wrong way?
First time plugin, the board was brand new, loaded Arucopter Quad rc3.2, tested gyros, baro and compass with mission planner. Everything ok!
The connector was plugged in the correct way.
In retrospect it was a stupid idea to connect the receiver to the APM board with (USB) power on, shuld have known better.
that's interesting, Does the receiver has a big cap on it?
Not sure. I am using a frsky d8r-ii plus.
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