3DR APM 2.5+ max current through power module???

[Bartman]

Hi everyone,

I've got a coaxial quad build in the works and I'm looking at my as-yet-unused APM 2.5+ as the FC for it but I don't know what the power module can handle in the way of max current.

Looking at it it looks like it goes inline between the batteries and the ESC's. It only has 13 awg wire though and I'm thinking I wouldn't want to put power for eight motors through that.

Thanks,
Bart

 

[Bartman]

After some continued hunting around the interweb I found this

Specifications:
Max input voltage: 18V
Max current sensing: 90A
Voltage and current measurement configured for 5V ADC
Switching regulator outputs 5.3V and 2.25A max
6-pos DF13 cable plugs directly to ArduPilot Mega 2.5's 'PM' connector


Note: The Power Module is only designed to power APM, a RC receiver and APM accessories (GPS, Telemetry radio). It is not designed to power servos., use a uBec or the aircraft's own ESC/BEC for this application.

so it looks like the max current that should be passed through the PM is 90A. With an Oktokopter that means you're designing to be at 11.25 amps per motor maximum or you can't use the power module and you lose the ability to monitor volts/amps or trigger the auto-RTL feature.

Bart

 

[J.T.]

Bart,

I've been looking for the same info and came across this page. looking forward to trying the new 3.1 firmware on the APM.

http://copter.ardupilot.com/wiki/common-measuring-battery-voltage-and-current-consumption-with-apm/

 

[dazzab]

If you are going to going higher than 90Amps you can use an AttoPilot sensor instead which is compatible with the APM. See http://copter.ardupilot.com/wiki/common-using-a-current-sensor/ for instructions. If you just want to past the 4S limit of the 3DR power module there are knockoffs that go much higher such as: http://www.goodluckbuy.com/index.php?target=products&product_id=101526

I'm using the AttoPilot 180Amp on a SkyJib Octo with using 2 x 6S 8Amp batteries and it works fine. I also use their 90Amp sensor on my quad and hexa. But I've ordered the knockoff power module above to try on them as they can power the APM directly eliminating the need for a separate BEC to power the APM.

 

[Bartman]

an important detail to consider if trying the Attopilot module to replace the 3DR power module;

In a practical sense, this board was made for bursts of current over 100 Amps that might be experienced in a large electric powered UAV on takeoff acceleration, but otherwise would pull continuous amperage under 100, AND have constant flow of cooling air forced through the UAV body by the airstream to carry heat away from vicinity of this sensor and its leads.

i'm still trying to quantify what my current levels will be in different phases of flight but I think these limits might be too low.

gotta check out the goodluckbuy option although it's unsettling to have to settle on an option from them

 

[Bartman]

the goodluckbuy unit has higher a higher voltage rating but the same 90A current limit so it's no better than the 3DR PM for what I'm trying to do with my 4S system.

Might have to try to work within the limits of the AttoPilot option for now.

 

[Bartman]

video demo showing set-up of the 180A AttoPilot option

 

[dazzab]

The 180Amp AttoPilot will work fine. Remember, typically you place it between one of the batteries and the power distribution board so only half of your current will be going through it (assuming you are using two batteries in parallel). Then you scale the current reading via configuration parameters in the APM. Works just fine. Here's a pic of one on a SkyJib

View attachment 15339

 

[Bartman]

thanks dazzab, i've got one on order as of about ten minutes ago. i'm going to keep going ith things and see how it works. which version of the APM are you using?

 

[dazzab]

which version of the APM are you using?

I'm using 2.6 so I can use the external compass/GPS to get the compass away from the electronics. I have one 2.5 but I converted it to 2.6 which is fairly easy. It just requires cutting a small trace on the board which disables the internal compass. I also have a Pixhawk on order which I probably will put on the SkyJib but I'm not sure. The 2.6 is working just fine and once things are working I don't like to change them.

 

[dazzab]

looking forward to trying the new 3.1 firmware on the APM.

I ran every RC version of 3.1 before the final and let me tell you, it's amazing! Arducopter software has advanced so quickly in the last six months. It has some really great features now such as GPS glitch protection, Drift mode and just about anything else you think of. But just yesterday I tried a new feature on my Droidworx CX-600 quad that just blew me away. I finally got around to trying the Autotune function. I've been using the default parameters for some time as tuning the PIDs wasn't really giving me the results I wanted and the defaults were quite good. Well, let me tell you, after running the Autotune function my copter is rock solid! And I mean rock solid! It flies like it's on wires and so incredibly smooth that I just couldn't believe it. It's like a totally different copter and a joy to fly. I can do precision flying just inches above the ground or circle at height in full speed with no problem at all. I can't wait to put the camera back on it and do some videos. This copter has a flight time of over 15mins so it's a blast to fly.

I'm working on an Aquacopter and a Droidworx XM-6 right now. I can't wait to use the Autotune on them as well. The guys who are writing this code are just amazing. I'm lucky enough to know one of the developers personally and I read all the notes from their meetings etc so I'm fairly familiar with their work. Although most of it goes right over my head.

 

[Bartman]

is the autotune a standard feature now?

i read about the 2.6 upgrade and posted it to the 3DR sub-forum, i should probably buy the parts for that upgrade ad just get it all done before I fly it.

Bart

 

[ovdt]

I ran every RC version of 3.1 before the final and let me tell you, it's amazing! Arducopter software has advanced so quickly in the last six months. It has some really great features now such as GPS glitch protection, Drift mode and just about anything else you think of. But just yesterday I tried a new feature on my Droidworx CX-600 quad that just blew me away. I finally got around to trying the Autotune function. I've been using the default parameters for some time as tuning the PIDs wasn't really giving me the results I wanted and the defaults were quite good. Well, let me tell you, after running the Autotune function my copter is rock solid! And I mean rock solid! It flies like it's on wires and so incredibly smooth that I just couldn't believe it. It's like a totally different copter and a joy to fly. I can do precision flying just inches above the ground or circle at height in full speed with no problem at all. I can't wait to put the camera back on it and do some videos. This copter has a flight time of over 15mins so it's a blast to fly.

I'm working on an Aquacopter and a Droidworx XM-6 right now. I can't wait to use the Autotune on them as well. The guys who are writing this code are just amazing. I'm lucky enough to know one of the developers personally and I read all the notes from their meetings etc so I'm fairly familiar with their work. Although most of it goes right over my head.

That's exciting! Now, I want to convert my APM 2.5 to 2.6 and try it on my Droidworx CX4 asap.

 

[dazzab]

is the autotune a standard feature now?
Bart

Yes it is. Very simple to use. Have a look at the list of videos for the release of 3.1. One shows a copter being tuned in flight.

 

[R_Lefebvre]

Hey Bart, sorry I haven't been around here lately.

I actually don't use the current sensor on any large machines. I use it on my 450 quad, and I'd use it on my 450 heli, maybe my 500 heli, but that's about it. I never used it on an Octo or my large Heli. The reason being... well, if you look at it, it's actually a fuse. I don't think it would be smart to use it on anything over 50A total hovering current. Even that...

I don't know where the limit is, I haven't really tested it. But that shunt resistor can get very hot. I've already heard of one guy with a clone PM who melted the solder, the resistor came off, and he crashed. So... be careful.

I've actually picked up a sensor from www.amploc.com, it's a ring that slides over an existing wire. I just haven't got around to trying it out yet. But it should be much more failure proof.

Just another warning for you guys, because we don't have a lot of users using these things on big machines yet. So I don't want somebody to have an incident. I mean, we do have some users flying what I'd call Mid-Lift Octos with them. But some of you guys have REALLY big machines.

 

[mackar]

Hey Bart, sorry I haven't been around here lately.

I actually don't use the current sensor on any large machines. I use it on my 450 quad, and I'd use it on my 450 heli, maybe my 500 heli, but that's about it. I never used it on an Octo or my large Heli. The reason being... well, if you look at it, it's actually a fuse. I don't think it would be smart to use it on anything over 50A total hovering current. Even that...

I don't know where the limit is, I haven't really tested it. But that shunt resistor can get very hot. I've already heard of one guy with a clone PM who melted the solder, the resistor came off, and he crashed. So... be careful.

I've actually picked up a sensor from www.amploc.com, it's a ring that slides over an existing wire. I just haven't got around to trying it out yet. But it should be much more failure proof.

Just another warning for you guys, because we don't have a lot of users using these things on big machines yet. So I don't want somebody to have an incident. I mean, we do have some users flying what I'd call Mid-Lift Octos with them. But some of you guys have REALLY big machines.

Just found this thread... Do you know what clone PM the guy was using?
I bought a 10S 90a power module from hobbyking to use while testing the pixhawk and was thinking about using it when flying since the PM from 3dr that was supposed to be released in Q1 isn't here yet.
After reading this I don't think I'll be using the HK power modul or at least not the current sensing from it. Im thinking about soldering the cables that are going to my power distribution board on the input side of the HK power module, I guess I should still be able to monitor voltage via the module and get 5v to pixhawh via it without risking heat problems and melt any solders. I'll have a redundant power to Pixhawk from a stepdown module that is delivering 5v.

Do you see any problems with such solution?

 

[R_Lefebvre]

I think what you are describing should work and not pose any risk other then generally questionable reliability of anything coming from Hobby King. Some of it is good, some is bad. Sometimes BEC's fail wide open, which would send 42V through the PM port, and will blow it all up. You have that risk with anything you're using, but the risk is maybe greater with HK.

So you will be providing backup power via a BEC, and input to the servo rail? If so, that's a good plan.