APM 2.5 and 3DR power module failure.
Recently A friend Louis and I bought a complete APM 2.5 setup for x8 flying wings
APM 2.5
3Dr radio 433 MHz
Ublox / Mediatek GPS
Airspeed sensor
And the 3DR power module , we completed our setup and started testing the configuration for elevon setup because of the x8 delta wing, then Louis started seeing a problem where after boot up he would try move the servos and APM would reboot.
After many hours of testing he asked me to test the same on my setup and since our x8 setups are identical it would be a good test. It turns out when you move servos very slowly APM would work fine but when rolling the elevons around fast on the stick my APM also restarted.
We immediately thought of power supply issue and I soldered a 5A BEC to my setup and everything was working 100% that could only mean that our setups was drawing more current then what APM power module could supply . I checked the spec sheet for the 3 DR power module and it states that the module can supply 2.25A !?
Then I checked the power consumption today on my setup and stationary I was drawing 900 mah and when motor was running and moving the servos fast it was on average 1300mah , So well under the 2.25 A max limit .
Does Anyone have any ideas ?
This problem was now confirmed on 3 different setups !
Replies to This Discussion
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Permalink Reply by Tim Green on -
Is jumper jp1 in or out? Cause if it is in, you are powering your servos from the PM. But if it is out, you should be powering your servos from the PDB, if you have one.
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Permalink Reply by Johann Van Niekerk on -
It's in
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Permalink Reply by Louis on -
Yes i was very disappointed when i had to bypass the apm and fly my X8 with rx only.
I was under the impression that 3DR power module that was included with the apm 2.5+ would make my life easer, power wise. But had to maiden my X8 with no apm. I did not have a Ubec on hand like Johan.
Very disappointed !!!
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Permalink Reply by Johann Van Niekerk on
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It's Also worth mentioning that our ESCs does not have a build in BEC and does not supply power to our setups !
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3D RoboticsPermalink Reply by Chris Anderson on -
The vast majority of our users have ESCs with BECs built in. Indeed this is the first time I've heard of a user without that. I actually wasn't even aware that it was possible to buy an ESC without an BEC. Why do people choose them?
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Permalink Reply by Johann Van Niekerk on
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Chris
See link below
http://www.hobbyking.com/hobbyking/store/uh_viewItem.asp?idProduct=... we choose them cause we figured 3DR power module would be more reliable then a china Bec. But never mind that I just have one question , if the power module is rated at 2.25 A max and my setup peaks at 1.3 A why did it reset ?
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Permalink Reply by Wanabigaplane on -
And in three pages no one answered this question.
I have been through this problem with an oscilloscope.
When the electric motor in the servo accelerates from rest to fullspeed, it draws many times its average current - often referred to as a current spike. Extra servos compound the problem. Your average current draw might be 1.3 amps, but you need way more than 2.25 amps to allow for peaks.
We tried to overcome this by adding some 100 uF capacitors, but this was not enough. We now use a good 5 amp average BEC for small aircaft. We like the Castle Creations BEC. It is switching regulator that gives 5 amps average and 10 amps peak.
For bigger aircraft we have sparate batteries for the receiver, APM and servos.
Jack.
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3D RoboticsPermalink Reply by Chris Anderson on -
Jack: Well explained. Thanks!
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Permalink Reply by Bill Bonney on -
I was looking at servo specs the other day and they say that they draw 400mA to 500mA no load. It's the no load that makes you realise that this can increase when in flight. Just with three servos you are going to draw approx 1.5A if they move togther plus the excess, ouch! So defnitly not enough power can be supplied by the APM PM for servos.
It's been said on the forum that PM is to power the APM/RX (the electronics only) but this can be made clearer in the wiki (not sure why the PM is in the optional section, but it should be moved to the setup section)
I think the problem comes in that you can power servos, maybe one, if you have a arducopter setup, but as the project moves to more plug and play, it would be good to specify the intention only and leave out the ambiguity that engineers can figure out. Too many options just confuse. Maybe there is way to sectionalize the wiki for beginners and advanced setups?
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Permalink Reply by George on -
This is the correct answer. Just to expand a bit, this is due to (I suspect) a combination of the inductive load of the motors + the fact that they just draw more current when moving quickly from one setpoint to a new one as opposed to holding a position. The large load (force) on the servos due to the big flaps on a flying wing doesn't help either. A sufficiently large capacitor will usually fix such a problem. If you put a scope on the power rail and see how long the voltage droop lasts (and/or measure the current with a scope as well, if you have the right probe), you can get an idea of how large a capacitor you need. I wouldn't expect a 100uF to be nearly large enough for current spikes on the order of an amp. At I guess I'd say you'd want closer to 10,000uF. As an aside, this is the same phenomena that causes your lights to flicker when your air conditioner turns on in the summer. The big inductive load of the motor causes a similar voltage droop until the system reaches steady state.
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DeveloperPermalink Reply by R_Lefebvre on -
Chris, most big powerful ESC's have no BEC. The reason is because they are opto isolated. There are two circuits on the board. There is the power section, that is powered by the flight battery. Then there is the Rx side. The Rx side consists of nothing but an LED, I think. The LED is the transmitter stage of the Opto-isolator.
There is no electrical connection between the power section, and the Rx section. There is an "air gap". The main reason to do this is so that there is NO WAY for electrical noise to propagate from the power section to the Rx side.
They also do it because big models using big powerful motors also have pig powerful servos, and you are expected to use a big powerful stand-alone BEC .
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