I have noticed in the forum a number of people advising the connection of ground (negative power) of all their ESCs to the APM. In some cases some people are also connecting multiple 5 volt lines to the APM in the hope of providing redundancy of the 5 volt line. In my opinion both these practices can lead to intermittant issues that could cause your copter to occassionly behave erratically, and at worse damage your APM (as connecting multiple ESC grounds to the APM can create ground loops). Ground loops will create a noisy and unstable ground for the APM, which is the last thing you want with sensitive gyros and accels. The random issues that ground loops/bad power can lead people to incorrectly assume that there is something buggy with the software, causing unnecessary work for the developers and testers.
Ideally a seperate, single BEC (5 volt regulator) should be used to power the APM as the 5 volt line from an ESC that is also powering a motor will get very hot, causing the 5 volt line to become noisy and possibly brown-out/shut-down in flight. The BEC should not get so hot that it is uncomfortable for you to keep your finger on it for more than a couple of minutes with APM+GPS+Xbee etc connected. If so, a BEC with a larger heatsink or a switch-mode BEC should be used. In addition using a seperate BEC also ensures that the APM does not share a noisy ground return of an ESC.
I think a lot of the intermittant and unexplainable issues people have had can be resolved by ensuring the power supply and powering wiring topology is sound to begin with.
Does anyone know who contact about having documentation updated to reflect the above?
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I'm getting a bit lost in this discussion, but I just wanted to throw a few things out there:
I think one problem with the discussion is that we are discussing electrical power wiring requirements only with a concern for the electrical noise. Unfortunately, especially with quads, we also have to worry about magnetic interference on the Magnetometer. I fear the design requirements to eliminate electrical and magnetic interference might be mutually exclusive. To eliminate mag interference, we need the power wires to always run in a twisted pair. That power distribution board might cause a big problem.
Also, Torg's image looks not to bad, but I strongly feel that the servo ground wires MUST pass through the APM. This is because the signal from the APM to the servo is based on the ground level in the APM, which may not be the same as the ground level on that ESC. This is particularly a problem if you have an Xbee. I used exactly the setup he is suggesting, and had horrible problems. Putting the servo ground through the APM ground rail made it 90% better.
I did not read this entire thread, so this might already have been covered.
Using separated ground for any R/C controlled unit like a ESC is a BIG NO-NO!
Remember that the ESC is controlled by a 0-5v digital PWM pulse coming from the APM board. If you separate the ESC ground from the APM you remove the zero (0V) signal reference for the PWM signal. It might still continue to work, but it might just as well stop working at any time.
Edit: Just to clarify. The signal cable ground and the power ground are common on most ESC units, so separating the power ground and still interconnecting the signal ground wires (trough the APM unit) has no effect other then that you now only use the thin signal wire (bad) to make a common ground.
I have my ArduQuad flying, but I am really confused about powering the APM 1.4 / 2.0, and in need of clarification for powering my custom Hexa/Ardu build. The parts I have:
1. Diydrones Hexa PDB
2. Dimension 5V / 3 amp BEC
In the PDB instructions there is a section describing the soldering of the APM power wires, and near the end of the document is says: "Finally solder in the small two-wire cable into the small holes marked “To APM” “+” and “-“, again with the red wire into “+” and the black wire into “-“.".
Should I instead solder the BEC into this location? I don't know if this +/- connection on the PDB is being being power from the big battery leads, or from one of the ESC/BEC built into via the right angle headers?
Will the RC Receiver still be powered from the APM, through this BEC?
Also, I am concerned about getting the grounds right. If I use the stand-alone BEC will I have the right ground paths for all to work?
Thanks!
Mike/Confused newbie
Just as a new point of discussion...
Yesterday I learned that bigger caps are not always better for filtering DC noise. It resulted out of a discussion on the L7805 requiring 0.33uF on the output and 0.1uF on the input, in order to stabilize the voltage and prevent it from making noise (yes, apparently even linear voltage regulators can make noise). I thought I was fine since I had a 16,500 uF cap bank on the APM.
Not necessarily. So what I learned was that caps have inductance and generally speaking, the bigger the cap, the more inductance. This prevents larger caps from being able to filter higher frequency noise. Smaller caps are better. And in particular, small ceramic caps are best. So I procurred the required small caps, and will add them to my L7805. However, there is nothing wrong with running multiple caps in parallel. So I can still use that cap bank which is intended primarily as a brown-out preventer.
The information I read is that it's quite common to use large and small caps in combination for the best effect, some circuits even have intermediate sizes.
My configuration is two different bec 6V, one linear and the other switching, both connected to APM with two diodes (the output is 5.3V).
I use this system to all my VIP model (like maxi plane and big heli), zero iusses at the moment.
For the gimbal servo power supply i've 8 bec inside the esc on my drone, and the rule is "one bec for one servo".
I measured a lot of noise at altitude sonar/baro, I disconnected the wire for measuring at apm (volt divider), thus all the noise was gone. I put on a feritt core and plugged the cable into apm again, the problem is solved.
On a large camera mount, do you think it would be better to get the power for the mount servos from a seperate BEC and just get the signal from the APM. Instead of getting power and signal from the APM???
Thanks :)
I have tried using copteret without ground(-) from esc's to the apm completely unaware of this, because I switched to separate bec right into the pdb. That led to a crash for me. The copter got a strange behavior. When it was below 5 degrees outside, I do not get the copter armed, the engines just beep rapidly.
Good discussion. I have access to modify the Wiki and I can help you get it "published" there if we can come up with a good document.
I'm fairly well off in my case as I have a trad.heli. with a single ESC, and that ESC is opto-isolated, and the motor battery is completely separate from the radio system battery. But, my radio power system is somewhat confusing... I have an L7805 5V regulator powering my receiver and APM. Then I have a 6V switching BEC powering the servo rail on the APM for my three swash servos. And then my tail servo is direct 11.1V to the 3S battery. But all of those share a common ground back to the battery. In particular, the ground for the 3S servo actually goes THROUGH the APM and the APM ground. I had to do that, because when I had the ground for that servo going directly to the battery, I had a noise problem.
It's worth discussing in this article that you want to try to keep grounds seperate, but they must be connected in some way. A signal source operating at 5V, and a signal receiver operating at 5V will not communicate if their grounds aren't connected.
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