Posted by Shawn Jones on March 12, 2009 at 10:18am
Last night during Letterman I had an idea and I wanted to get the input from this community. I have noticed a few postings in the forums and blogs relating to the endurance of some of our aircraft. I know that battery capacity is at a premium and that we should strive to use every bit of it efficiently. I have been thinking about an aircraft design that would tailor itself to autonomous flight and about control surface loading. Perhaps power could be saved by putting our servos into a sort of "standby."If an aircraft was in stable flight, it could be possible to disconnect power from various servos to save electricity. Perhaps even with systems such as spoilers, that would not be needed often. If your aircraft was flying level and stable perhaps we could remove power from the aileron servos and allow the rudder to make the minor adjustments that may be necessary to maintain the current flight heading. Once there was a demand for a flight control that was in "standby" there would be minimum delay in activating that servo again.It seems to me that if there is minimal loading on a flight control to maintain stable flight that the mechanics of the servo would provide enough resistance to hold the flight control in its last known position. It could be implemented in software to reactivate power to the servos at a predetermined interval as a sort of sanity check. The control signals from the hardware to the servo should not be stopped and should remain at the position that the servo was last at. If you activated the power to the servo in intervals any drift in the flight control would be corrected.I know that this may seem like a minimal power savings but I believe that it could accumulate into a substantial savings in energy over the duration. I will be trying to test various servos that I have on hand to see what there power consumption is at idle. I will also be looking into various hardware options that would allow for software control of the servo power signals. I welcome information on both subjects.I welcome and encourage any input that anyone may have. Does anyone have any information about the forces acting on flight controls when they are idle? What are the opinions on this option, could it be viable? I felt that it was proper to post this into the "software" section of the forums because this would ultimately become an algorithm that would be implemented into the flight software.Thanks for looking,Shawn Jones
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Hi loved your Flight Sim..
I really need your help here I can't get your sim setup going.. I need to test see if the AP will work on my coordinates
Here is my coordinates:
-43.561256° 172.565375° in Decimal Degrees could you please set up a few way points around it and see if it will work or not.. you may also see my post here..
Well, he savings of 1-3% of total power will not 'accumulate over time'. If you want to have longer flight duration, spend 20EUR and buy yourself a fresh lipo, you will get 10%+ more power. Second is that unpowered servos dont hold position. Third is that upon powering on some servos may glitch or lock on remote position if they see halfwave PWm of lenght say 0.5ms. Fourth you will need separate transistor to turn off specific group of servos (ESC must be always on), then there is voltage drop problem when you turn on servos simultaneously what could reset the autopilot then the fact that upon the first powerup when pwm is present some servos tend to make a small jump befor going back to continuously emmited position. Also when the servo power is off, you must to switch off the PWM output or you will power the servo via data line (it mightl pull 20mA per line overloading the uC without actuallly even trying to move). Enough to not try the idea again?
I know not much about micro controllers, but the following I read from the sparkfun tutorials amazed me:
"MSP - These are very good micros by Texas Instruments (TI), not as beefy as AVR or PICs. However they truly excel at low-power applications. More on this later, but imagine running a complete system on one AA battery for 5 years. This is in the realm of nano-amp current consumption. Crazy!"
Maybe a candidate for a project like yours?
In my opinion, the power consuption of Rx+servos+electronic is very little compared to what the brushless is burning.
And if you use two power sources (one for electronics and one for the engine), then your motor battery is going to be low long before your other power source.
Best thing to save power in my opinion:
- have a good CG setting to avoid unnecessary drag on the airframe through over trimmed control surfaces
- use a brushless motor as efficient as possible
- draw as low motor amp as possible for altitude holding
- avoid unnecessary high climb rates
- avoid windy days
- use a separate BEC on big lipos, because the ESC BEC usually are much less efficient (dissipating overpower in heat).
I think servos might not be the way for something like this, as they do not hold position unpowered. Mainly I'm afraid the control surfaces would move on their own in the air due to turbulence, gusts, etc.
Steppers on the other hand have very good hold without power if I am not mistaken, and could therefore be a better option?
Anyways most of the efficiency I believe would be attained from reducing the amount of servos and using good efficient ones.
A very drag efficient flying wing is probably the best option since it only needs 2 servos for control instead of 3-4-5 on other types of airframe.
I also think that it might make sense to use a driverboard and a normal AC motor for certain functions like lowering or raising gear, spoilers brakes etc, since this setup could be designed to have good hold by using a worm screw, and can be powered off entirely when not used.
Replies
I really need your help here I can't get your sim setup going.. I need to test see if the AP will work on my coordinates
Here is my coordinates:
-43.561256° 172.565375° in Decimal Degrees could you please set up a few way points around it and see if it will work or not.. you may also see my post here..
I have wondered if anyone has tried power and glide, like swifts and swallows do.
Good chance someone here would know.
"MSP - These are very good micros by Texas Instruments (TI), not as beefy as AVR or PICs. However they truly excel at low-power applications. More on this later, but imagine running a complete system on one AA battery for 5 years. This is in the realm of nano-amp current consumption. Crazy!"
Maybe a candidate for a project like yours?
And if you use two power sources (one for electronics and one for the engine), then your motor battery is going to be low long before your other power source.
Best thing to save power in my opinion:
- have a good CG setting to avoid unnecessary drag on the airframe through over trimmed control surfaces
- use a brushless motor as efficient as possible
- draw as low motor amp as possible for altitude holding
- avoid unnecessary high climb rates
- avoid windy days
- use a separate BEC on big lipos, because the ESC BEC usually are much less efficient (dissipating overpower in heat).
I think servos might not be the way for something like this, as they do not hold position unpowered. Mainly I'm afraid the control surfaces would move on their own in the air due to turbulence, gusts, etc.
Steppers on the other hand have very good hold without power if I am not mistaken, and could therefore be a better option?
Anyways most of the efficiency I believe would be attained from reducing the amount of servos and using good efficient ones.
A very drag efficient flying wing is probably the best option since it only needs 2 servos for control instead of 3-4-5 on other types of airframe.
I also think that it might make sense to use a driverboard and a normal AC motor for certain functions like lowering or raising gear, spoilers brakes etc, since this setup could be designed to have good hold by using a worm screw, and can be powered off entirely when not used.