I'm constantly loading and testing code and the power setup of the 2560 can be a bit of a pain. Mainly, the radio does not receive power because the Servo rails are only powered via a Lipo, which can be very dangerous. I never do anything but fly with a Lipo connected and I certainly don't connect one indoors. I'm just paranoid that way.


This hack will power the radio half of the servo rail with 5V from the APM's USB connection. The idea is to spilt the 5V rail into two halves. If you use an X-Acto knife you can easily cut the trace connecting both sides. I cut the ground rail in half as well, then used some solder to repair the bridge. Then I connected the 5v from the APM to the input side as indicated below. Now I can power the radio with the USB.


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Comment by Jeff E on September 18, 2011 at 12:34am

Interesting mod..will consider this in future. This shouldnt have issue with external BEC right just connect the BEC on the output side, right? This will make life more safe and prevent those blade strike or burnt esc.

Comment by Randy on September 18, 2011 at 2:04am

This is such a great idea.


Simple(ish) and makes it so much easier to user your radio while powering just from the usb.  Easier and safer testing while the quad/heli is on the bench.  love it!

Comment by YureZzZ on September 18, 2011 at 2:10am
Great idea! I was thinking about that a while ago. Thanx!
Comment by Mathew Wellington on September 18, 2011 at 2:59am

nice,like it :)

Comment by Helldesk on September 18, 2011 at 6:04am

I don't use a lipo indoors either, not normally anyway - I power the Rx with a 5V wall wart. This would make life that much simpler though!

Comment by Mark Colwell on September 18, 2011 at 9:54am

Thanks Jason, this is really needed for reliability and bench safety.

AP power rails should be separate so Lipos or Phoenix-10 UBEC (set to +8.2v) can power HV servos. RC receiver gets +5.0v or required voltage. Ground isolation should not be needed, Use toroids on UBEC inputs.  A super cap helps with power demand surges. For servo rail use 2 each  +5.5v, 0.1 to 0.5 Farad super caps in series,  single +5.5v, 0.1 F cap on receiver rail. Large super caps are not needed even 0.1 F work well. 1.0 F caps are huge (You can find them on power supplies and video cards) They are a bit expensive new.

I use super caps on Video Tx rails too.( 3 caps in series for +12v to 13.5v)

A two pin jumper can be used to re-connect RC and Servo rails if needed.

I have suffered a crash or two due to a power brownout re-setting AP and could not recover fast enough.

Digital servos can have a high current demand if all are working at same time or some stall out, power demand goes up fast.

I use Lion battery indoors for safety. I monitor them on OSD or use balance port to monitor each cells voltage.

I switch between a Mac for code development & loading and a PC for HK_GCS & APM_Planner all the time.

OSD stays powered on during switch over and waits for APM to start sending data. Also PC USB 2nd port is always connected between OSDs tx, rx and Gnd lines (+5v is not connected) and AMPs TM port 3. I monitor data stream to OSD with RealTerm when needed, Poor PC gets overloaded and slows down with GCG, AmCap, and RealTerm all running.

Comment by Kirill on September 18, 2011 at 12:38pm

Good hack, but it's needed to be careful to not power on too much... Maximum output amperage of USB is about 500mA.

Comment by Robert Beatty on September 18, 2011 at 9:52pm

Thanks for this info, Jason. Question: Instead of running the wire from the +5v on the APM to the "input wire as indicated," can I run the voltage wire (and a ground wire) directly to the Receiver?

Comment by Jason Short on September 18, 2011 at 10:28pm

The main idea here is the 5V rail is split into two: Input and Output. That way, the 5v power that goes into the radio doesn't loop back into the ESCs. 

Comment by steve on September 21, 2011 at 7:14pm
Would this work for the 1280 board also?


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