Power Feedback & Power Distribution

Hi there. Im currently designing Autonomous Quadrotor as my final project at school. Everything was good so far until trying to find PID parameters.
I have a question and some concerns about suppyling power from Li Po's. As you know brushless motors can supply different thrusts on different voltage levels supplied from Li Po's.
For example while using fully charged 12.6V 3S Lipo on 9000rpm with XX brand brushless, it can supply 900gr thrust. On the other hand, everything same but Lipo charged only 11.0V, it may supply like 820gr thrust. Therefore, because of different voltage conditions PID parameters will never match. It will be ok only if I have a voltage feedback from LiPo's and then change PID parameters for each voltage level. Adding voltage feedback on the control algorithm will solve the problem i guess.
The question is anybody use this approach, or power distribution board have something like that included in it or any other solution on that ? And I was wondering can i connect 2 same Li Po's as parallel to a power ring and supply all ESC's from there.

Any help will be greatly appreciated, thanks. Sorry if similar subject has already been discussed. Have a nice one...

Config is Arduino USB, Ardu IMU V2, Emax BL 2215/20, 30A ESC's, 3S 11.1V 2200mA 20C LiPo's, hand made plexi glass frame.

The mass and center of gravity of the system do not change and that is the largest factor in the PID settings. If you were burning off fuel and the fuel tank was not near the center of gravity you could change PID settings.

The PID error system doesn't care if you are changing throttle position or losing battery charge. It reacts to the change in error.

At 100% throttle the available power will drop along with the voltage. At less than 100% power the battery state cannot be detected. If you correcting for altitude there could be a higher power setting required at low battery charge but the error system only looks at the differential and corrects. At the point where you would notice a degradation in system performance you would need to land anyway.

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Dean Lamborn December 7, 2010 at 7:46am

The mass and center of gravity of the system do not change and that is the largest factor in the PID settings. If you were burning off fuel and the fuel tank was not near the center of gravity you could change PID settings.

The PID error system doesn't care if you are changing throttle position or losing battery charge. It reacts to the change in error.

At 100% throttle the available power will drop along with the voltage. At less than 100% power the battery state cannot be detected. If you correcting for altitude there could be a higher power setting required at low battery charge but the error system only looks at the differential and corrects. At the point where you would notice a degradation in system performance you would need to land anyway.
Faik Kaya December 6, 2010 at 12:57pm

Thanks 420choky. And come on guys no idea at all ? Today i had some test on my brushless motors. With 12.5V battery and 172 pwm value i have measured a thrust value of 965gr. With 11.2V battery and same 172 pwm value thrust value was 870gr. Now Im definately sure that i need to include a feedback from battery in my PID algrorithm. Anybody do that or try ? Help please...
420choky December 3, 2010 at 8:53pm

i parallel two 3s 11.1v 2200 mah
got 15 min with fpv gear on it .. under powered as well ..

now im trying something new cuz its rough to get help sometimes ..

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Power Feedback & Power Distribution

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