APM 2.x Power management and Distribution system
Hi, All
I want to test the water and learn how much support is out there for a power management and distribution system for the APM 2.x. The APM 2.x is now a well understood and reliable FC. Maybe now it is time to design a stable and reliable power system for it?
There are far too many threads and comments in the forums regarding power issues. In most situations the APM is relying upon ESC bec's that were not designed for a UAV FC and there is much trial and error patching together bits and pieces of varying quality from different sources. None of the open source UAV projects has built an intelligent power management system for our UAVs yet.
I spent the last 2 days thinking about what in my opinion our APM 2.x's need. My idea is explained below. But, I want to hear your idea's and thoughts. That's the aim of this post.
My idea is a pcb that sits underneath APM 2.x. The signal pins A0-A11, signal pins for the PWM outputs and one of the UART ports from the APM are extend down into it and attach it to the APM 2.x. Headers on the PCB to attach devices to A0-A11 and Servo/PWM outputs. The pcb has 3 switching power supplies. One for the APM, one to power the PWM outputs and one to power FPV equipment or accessories. A AT2560MEGA processor to control routing of power, and monitor voltage and current. External pcb's that attach to each battery route power to the main pcb, monitor voltage and current, and can isolate the battery.
APM 2.x Power management and Distribution system (apm pmds) pcb
- ATMEGA2560 processor
- Monitor various voltages and currents
- control routing of power between batteries and power supplies
- isolate batteries and servo/PWM outputs
- isolate batteries and power supplies
- Communicate with APM 2.x
- Develop power management strategies
3 switching power supplies
1) apm ,pmds, sensors, rc receiver & rf modem
- 2 amp
- current sensor
- voltage sensor
- able to independently switch between batteries
2) A0-A11 and servo/PWM output
- 5 amp
- current sensor
- voltage sensor
- able to independently switch between batteries
- able to adjust power output for HV servos
- Opto-Isolators on the servo/PWM signal outputs
- Isolate the power via physical switch
- support for optional external capacitor array
3) fpv transmitter and camera or accessories
- 2 amp
- current sensor
- voltage sensor
- able to independently switch between batteries
- able to shutdown fpv transmitter/camera/accessories in a low power situations
Battery controller pcb's
- Isolate battery
- current sensor
- voltage sensor
- Monitor voltage in up to 4 cells
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3D Robotics Comment by Chris Anderson on November 4, 2012 at 10:13am -
John, great post and analysis. Just wanted you to know that 3DR will be releasing an APM power supply (with integrated voltage/current sensor) in a couple weeks. It will come standard with the board, too.
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Comment by Peter Chaffe on November 4, 2012 at 11:04am -
John, I can understand that your motives are good but I can't see the APM2.5 requiring the complication of any advanced power supply unit. The specs say 5v0 -+ 0v5 ie 10% so what is special about that?
All esc becs that I've tested had tolerances better than 3%.
Even a quad will likely carry 4 becs integrated into it's ESC's, the majority of these are usually around 3a or more. The apm takes around 200mA (inc gps,Rx,3DR Radio, Sonar). The bec part will hardly get warm.
I think the reason why there has been so many questions and confusion surrounding the v2.5 power supplies is because it was so badly explained in the wiki.Peter
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Comment by Peter Meister on November 4, 2012 at 11:52am -
Chris, glad to hear of the APM power supply. This will solve a lot of problems for those just starting. Hopefully it will include dual battery supply inputs for fault tolerance :)
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3D Robotics Comment by Chris Anderson on November 4, 2012 at 12:16pm -
Peter, it's just designed for a single battery input (to keep it small and inexpensive; almost all users have a single battery). But if there's enough demand for a dual battery version, we'll add that, too.
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Moderator Comment by Zach Bayne on November 4, 2012 at 12:53pm -
I know this is off topic, but with that coming to the store soon is there any news for the apm 2.5 case?
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3D Robotics Comment by Chris Anderson on November 4, 2012 at 12:57pm -
Zach: The case will be released at the same time.
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Comment by R. D. Starwalt on November 4, 2012 at 5:27pm
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And so, perhaps, the revelation of the application for the 'mystery port'?
-=Doug
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3D Robotics Comment by Chris Anderson on November 4, 2012 at 6:02pm -
Doug. You're smart ;-)
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Comment by Matthew Crocker on November 5, 2012 at 8:04am
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I plug all 4 BECs from my 4 ESCs into my APM2.0. I haven't had an issue at all with power. Not sure why I would want to add the extra weight and complexity to my quad.
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Comment by John Rambo on November 5, 2012 at 9:45am
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some questions:
- atmega2560 costs 5x the 328P, so wouldn't it make more sense to use 328P + 4051 or 4067 MUX for voltage/current sensing? Or is it the same uC to be used, not the separate-one?
- uC controlled battery switch, where the same uC is powered from that battery sounds a bit irrational. Wouldn't analogue O-ring setup look better here?
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