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
Thanks Phillip,
I will raise it with 3DR, I bought it online direct from them.
Thanks for your help and advice.
Clive
It is a Pixhawh. All the periferals are the ones supplied by 3drobotics for the Pixhawk. When it all arrived about 6 weeks ago I put it all together mounted on a test frame, loaded the firmware that was relevant at that time and it all worked perfectly. The rf mavlink, the usb mavlink, the external GPS and compass (3DR). It all worked and connected to mission planner fine
I then put it away till last weekend (it was a birthday gift for me) then re connected it on Saturday, it all loaded perfectly again, but the software informed me there was a firmware update. BIG MISTAKE, I took it and ever since then it has not worked. "Unable to connect to mavlink, no heartbeat blah blah blah".
After reading a few posts that talked about a blown regulator I unplugged all the periferals and it suddenly worked. Plugged all but the compass back it still works, plug the compass in to the I2C port as correctly, and it does not work. This is using usb or battery or both to power. Not only does it not connect, but the big led status light does not come on at all. I am bot sure if it is the regulator or the compass that has failed. Without anything plugged into the I2C i measure about 3.8 volts, but don't know what it is with the compass in.
I think I will put a youtube up showing the whole scenario and hopefully someone will have a lightbulb moment for me.
For the first time I have head about a regulator issue on a Pixhawk. I hope it is not a widespread issue like APM 2.x. Pixhawk is what I plan on upgrading to in the near future...
Next, where did it come from? Was it purchased from 3DR online? Or through an agent? Either way, if you contact them, they will help you.
On the Pixhawk, there should be 5v on pin 1 of the I2C plug. But you said you have 3.8?
Please talk to the place you purchased it from, and follow up at Ardupilot.com with what happened.
If it is an APM 2.6, with a 3DR GPS compass, please let us know
Joe, I don't agree with coincidences either.
That's why I find it hard to believe that it's just a coincidence that there are 1000's and 1000's of people flying 3.1.2 on APM's without any issue at all. So if that's not a coincidence, then what is it?
You realize what you're suggesting is that there is some way that the program which did nothing other than increase the communications bus speed between two microchips, could damage a voltage regulator? Yet, this only happens on some boards, not all of them. And it seems to happen much more often on boards of *exactly the same design* that were made in China?
Don't you think that's just a little bit hard to believe?
Making it even more hard to believe, is that the the program is completely open source, and has 100's if not 1000's of people reading it. And this bit of trickery you allege just slipped by all of them?
BTW, this problem did not appear with 3.1.2. It started happening with 3.0.1 rc5 that actually dates back to ~October last year. ;)
Just to clarify (I know your making a general statement, just pointing this out), mines an original 3DR not a clone (it wasn't $60...it was $250 as a kit with 3DR GPS etc).
So even the original 3DR boards fail.
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Now once I've replaced my reg, can anyone correct my process where I might be wrong below:
1. Never connect the APM via USB unless it is already powered by external battery OR it is running COMPLETELY standalone without nothing plugged in (just the bare board).
2. Never connect or disconnect anything (except USB) with power applied (power of any sort)
3. Never connect the APM via USB if the 3DR Telemetry Radio is connected (they will conflict).
And I'm not 100% sure on the following:
1. Can the Mini-OSD be left connected as long as we are on external power? When using USB to download logs or setup?
If we ever get the ability to download the logs via radio then we should only need USB for firmware updates (unless that can also be done over radio).
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That being said, have you guys seen how long the Wiki is for the power section? No wonder people are frying things... It reads like a School House Rock cartoon from the 70's "Conjunction Junction, whats your function" lol.
http://copter.ardupilot.com/wiki/common-apm25-and-26-overview/
Cheers
Tim
But this is the problem we face Tim. Either we dumb down the system so that it is less flexible, but greatly reduced flexibility, or we attempt to educate our users.
Our Modus Operandi has always been to educate users, and provide a flexible and powerful autopilot system. The other end of the spectrum is DJI. And then you have Multiwii and sevral other options being somewhere in between. People are lucky to be spoiled for choice.
Yes, even the 3DR boards fail. Nobody has every suggested otherwise. It just seems the rate of failure appears to be much higher. If the 3DR boards failed at the rate the clones seem to, I don't think they'd be in business, since they actually offer a warranty.
If the cloners were even looking at this issue, maybe we'd have more data. But they don't have the skills to diagnose it, that's why they just copied 3DR's board design.
Hello Rob
And thankfully I fully agree with it Rob! Thanks for bringing this up. I prefer to be able to customize the death out of an APM then be trapped with a Naza and only getting the features they will let you have.
Case in point is the Eagetree OSD system. Great unit but you were crippled with the three waypoints that had to be within a certain distance of your launch point because the designer didn't want people to be able to use it for long distance FPV and feel liable. Thankfully this has changed for the new unit coming out.
I'm just still stumped how mine went when it was fine before I upgraded. Oh well, enough about that. We'll see how things go once the new reg is in and I'm vigilant about how I connect and disconnect.
Don't worry about users, I much prefer flexible and powerful. If I do something dum and have to replace a regulator, that's easy for me. Better than spending double the money and bring trapped.
Cheers!
Tim
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