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
Would be really nice but I seriously doubt you will get reliable answer to your question.
Simply nobody knows the answer exactly...
Thomas,
Really, nobody's been able to reliably reproduce how the 3.3V regulator is being blown. People have been trying but it's really not that easy to do. Many (mostly clone) boards come from the factory already blown. Some people do blow them somehow but it's not clear exactly how it's happening.
Well after replacing them, board simply worked so I'm assuming regulator is blown, no need to check
Yes, I think this is necessary. And not only for the defective reg. also for the new one so we make sure it is good before installing it.
It will be a tough job and will have to be done under a magnifier. But it can be done...
Could someone provide the procedures to do this test?
The reg. has five legs. Which ones to be used and how?
I think mostly clones are blown because most people have clones not the original. I think scenario goes same for both original and the clone except the part that clones have bad product quality checks. If clones works well then its the same as the original. Nothing seems to be different from each other. I cant even tell whats what
I will be setting up some brand new Genuine 2.5.2's in nasty ways to try and Isolate this issue, but so far, no one has come up with a good reason as to why these would blow. AFAIK, I could count on one hand the number of genuine 3DR boards that have the issue. and in the case of my board, it has had a LOT of abuse.
If used with the Power module and no servos with JP1 removed (copter) I can see no possible way to damage this part. add servos, and there is some (unproven) potential that the digital servo spikes may play a part. to protect against that, run your servos off a BEC, and don't connect JP1.
Its all about risk. The Power module was designed to reduce the risk from unknown power supplies, but if you choose to fly without it, then make sure you have set up s system that matches its specifications,
Philip, I am really starting to think that we will never find one single silver bullet. It's probably a random confluence of user error and production tolerance. The fact that you were able to put power on the SPI pins, effectively reverse-voltage on the board, without blowing that regulator, demonstrates that the regulator on YOUR board over-performs the spec. But that does not mean they all do. I'm quite sure his is why my board failed.
Again, not that that scenario is the one single possibility either. It's just one of many. Some may have defective regulators right from the factory. Some might have been overheated on assembly. Some might be killed by voltage spikes from BECs that don't behave typically. etc. etc. There's simply too many variables. Seems like we've tested most of the potential easy silver-bullets already.
As I understand it
You can connect USB with battery connected when JP1 is installed.
You can connect USB with battery connected when using power module, JP1 MUST be removed
Connecting JP1 and power module will fry your board
Thats what I think i know so far, please correct me if im wrong.
Cheers
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