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Permalink Reply by Nick W on May 2, 2012 at 3:06pm

Bump for any helpful comments.

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Permalink Reply by Vernon Barry on May 2, 2012 at 4:24pm

Sorry, was going to answer this earlier and got distracted.

Basically, the outputs are bussed together via fairly high current traces, so puttinng power in from a BEC on output 1, the current could be maybe an amp or two, but I wouldn't push much more stock. So in other words, the basic design centers around normal ESCs with BECs powering the output rails and then maybe one or two servos on the ouputs. If you are worried about that scenario, then take say a piece of #14 copper ground wire from some romex and solder it across the row of 5V and also the ground pins on the bottom of the board. I would not in any way, load down the telemetry rails since those are imbedded traces and are NOT high current. You are perfectly fine to power that off the output rail along with the servos since again, you normally would ONLY use a single BEC input anyway. I would not in any way try to load current accross the APM from the outputs being powered to say much more than a reciever beign powered from the inputs. I know there is at least one diode in that path. You could however, extend the #14 wire mod across to tie all the inputs and output rails 5V and ground pretty safely. This will cause problems when connected via USB since USB is specified to only be 1/2 amp MAX. Thus if you followed my mods, you would likely have brownouts with the loads you are talking, but if your high speed telemetry works and you power from battery via BEC, you won't have an issue and it's better for flying.

To recap, the outputs 1-8 are tied together and then the inputs 1-8 are tied together, but across them from inputs to outputs is a KNOWN weak point. Then further, I would not put much over maybe 1/4 amp load on the telemetry uart 0/2 port, maybe 1/2 amp is the absolute max. 

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Permalink Reply by Nick W on May 4, 2012 at 12:56pm

Thank you so much for your very thorough reply. I really do appreciate the help.

　

　

I was just wondering because I have a senior telemaster that I'll be using it in, with 4 or 5 of these servos, and just wanted to make sure that they won't overtax the board.

　

http://www.spektrumrc.com/Products/Default.aspx?ProdId=spm3702

 

Will the board power 4 or 5 of those without issue?

 

Also, I'm looking at the 9xtream modules from Digi (have a couple layin around) for extended telemetry. Those should fall under the 1/4A window, so should be good.

 

Again, I really appreciate your help.

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DeveloperPermalink Reply by R_Lefebvre on May 4, 2012 at 1:29pm

Well, I hadn't even considered the possibility that the servo output rail traces couldn't handle typical servo loads.  If that is true, then you will absolutely need to reinforce them to run those servos.

Also, I just want to say in case it wasn't clear, that the APM2 has NO power supply ability *at all*.  You MUST run an external power supply that is adequate for those servos.  Those don't look too terribly fast or strong, so I would estimate that a standard 5A rated BEC would be sufficient.  And I strongly recommend that you keep the In and Out power bus seperate (by removing that jumper as detailed in the wiki) and use a seperate power supply for the APM.

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Permalink Reply by Nick W on May 4, 2012 at 8:09pm

With the APM 1.0, I was just powering the board, along with the servos, though the inputs from the RC receiver, and that worked just fine. But, those servos were also just the little ones that were on my hawk sky. So, should I run a cable line from my rc receiver to the servo output rail on the board as well to ensure that the board is not included in the current path for the telemaster servos?

I know the receiver will power the servos themselves just fine, but I guess the apm board w/ telemetry radio does add a good bit of current draw as well. I think my best bet may just be to add another regulator...

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