Post by thread:[PIC]: Autopilot landing system for model aircraft

--- Tan Chun Chiek <spam_OUTcodeTakeThisOuTMXHUB.NET> wrote: > Hi, > This idea of an autopilot landing system just popped up in my > mind, and other details came almost immediately. You're aiming for the big league here! I know manufacturers are working to create safe landing capabilities for airliners, (don't know the details), but I doubt they have a system that can 100% replace the human factor in all conditions... > before? The runway is something like 10m X 50m. GPS is used for > longitudinal/latitudinal positioning and preferably velocity > measurement, I don't want to discourage you, but there are loads of problems... First of all, I am not sure GPS, (unless military weapons grade, which I doubt anyone can get their hands on) would be of any real use, other then to have navigation and get the model in the vicinity of the airport. With model aircraft, aside from scale reduction, aerodynamic rules work the same, but many parameters change dramatically due to the small size. Absolute speed measurement, the one that GPS can provide is practically irrelevant for a model, espacially at landing. It may be usefull for general navigation, remember, you need to have mapping and stuff for this. What you need is airspeed measurement, which GPS cannot provide. This is the key. Let's say your model flies well at 30kph and begins to stall below 18kph. If you come in for a landing, with 22kph, with headwind of 10 kph, GPS will say you have 12kph, and by this, will assume that you are way below stall speed and will accelerate, landing you with excess speed, and then you wander why the autopilot shoved your plane into the ground... Such a small scale air speed sensor is a challenge itself (I think). Another thing, an autopilot can be built and used ONLY, I repeat, ONLY when you know very well all the handling characteristics of the plane in all conditions. Research and flight testing of real airplanes takes years to gather most of the data for the flight manual and for the autopilot. Without this, an autopilot is next to useless. The autopilot needs to know exactly in the given conditions, and the given orders how to control the plane. Changing the propeller, adding 200grams of weight somewhere, another type of engine, etc, would throw off completely the autopilot and the planes characteristics will have to be retested and the autopilot refitted. A human pilot learns very easily and adapts very quickly to a situation, but a computer-driven pilot who has a limited knowledge of the plane and no learning capability (you're not putting an array of multiprocessor systems with complex neural nets in your model aircraft...), it won't be able to cope. Also take into account that for such a small scale, even small, apparently insignificant changes can dramatically affect the plane's handling. As a human pilot, one can adapt quickly, sometimes instinctively, maybe barely noticing it... Example: your plane, fully equiped, at 20kph stalls at 14deg. Let's say that you put a new battery pack with more capacity, but it also weighs 100 grams more. This will shift the center of gravity of the plane and now it will stall at 12 deg at 20kph. The difference may seems small, but it is actually huge! The autopilot WILL stall this plane, because it assumes that at 20kph, it is safe to fly at 13deg inclination! Unless ofcourse, you go through the whole process of getting the new flight characteristics. Don't even think of putting an autopilot in another type of plane!!! Well, it can be built, to work in a very limited range of situations and flight conditions, with less research, but will have to be at least supervised and override options should be available at all times. Actually, making such an autopilot would be much easier for model helicopter then for a plane. Due to the nature of the helicopter, and the way it flies, (excluding acrobatics, ofcourse), many things are simpler to handle. The advantage of model helicopters is the fact that they can reach a dynamic equilibrium in which they appear static and can hold this. Then it's a simple matter of slightly lowering the collective... (simplified) The plane, although by it's nature tends to fly, while the helicopter does the opposite, dynamicly balancing the parameters on a plane could be more challenging then for a helicopter. I hope this will help. P.S. keep us posted ===== ing. Andrei Boros Centrul pt. Tehnologia Informatiei Societatea Romana de Radiodifuziune __________________________________________________ Do You Yahoo!? Yahoo! - Official partner of 2002 FIFA World Cup http://fifaworldcup.yahoo.com -- http://www.piclist.com#nomail Going offline? Don't AutoReply us! email .....listservKILLspam@spam@mitvma.mit.edu with SET PICList DIGEST in the body

This guy at http://members.shaw.ca/sonde/index.htm has built a really cool computer controlled glider. Its not meant to do the final touchdown, it deploys a parachute. However the web site gives a idea of the level of detail required. Real cool, wish I knew more about flight dynamics, really fun looking! Engineering just for fun Edward Tan Chun Chiek wrote: {Quote hidden}> > Hi, > This idea of an autopilot landing system just popped up in my mind, and > other details came almost immediately. I thought why hasn't anyone done it > before? The runway is something like 10m X 50m. GPS is used for > longitudinal/latitudinal positioning and preferably velocity measurement, > the aircraft would have a GPS receiver onboard, and 2 other GPS receivers > would sit on the both long ends at center of the runway, it's something akin > to differential GPS to provide better accuracy. Height measurement is done > by a ultrasonic transceiver or maybe GPS, are they accurate enough? And > pitch and roll is sensed by a pizeo gyroscope. > > How feasible is this concept? > > Regards, > Tan CC > > -- > http://www.piclist.com hint: The PICList is archived three different > ways. See http://www.piclist.com/#archives for details. -- http://www.piclist.com#nomail Going offline? Don't AutoReply us! email listservspam_OUTmitvma.mit.edu with SET PICList DIGEST in the body

Commercial GPS updates once per second, and without real DGPS or WAAS is only accurate to about 10m horizontally and 100m vertically. Most OEM GPS receivers accept real dgps data, but a dgps sender is big bucks, and is not trivial to build. Using several of the same receivers on the same location and a computer to computer the difference would be less accurate than DGPS and perhaps WAAS - you'd still likely have a meter error. In any case you should probably throw out the vertical information from the GPS completely. Since it only updates once a second you are going to have to use accelerometers or another positioning system to fill in the gaps - think about how far an airplane goes in one second, and how far it can go in a wind gust. Straight interpolation simply won't work here (unless you can eliminate all the variables, but even large buildings big enough for your model are going to have odd air currents) I suspect you'd spend less time in development if you built your own positioning system. Radio would work, using lights on the runway and a camera in the plane would work, you could even have a transmitter on the plane, tracked on the ground using three radio receivers with all the heavy computations done by the computer on the ground. You may want to go this route first only to make it easier to program the algorithms on the computer. The hardest part, I suspect, is not the actual mechanisms for tracking and autopiloting the plane but the algorithms that control it: Example: Up until recently two legged walking robots have all been built by trial and error and/or by keeping the center of gravity above points touching the ground. The problem with doing it this way is that the algorithms are specific to the hardware/model they are using and are not generalized for other models. When they do get the algorithm working on another piece of hardware they have to change hundreds or thousands of variables and re-tweak the algorithm. Researchers have finally made a simple model, including equations to describe the model, that can walk and run in a dynamic fashion - with its center of gravity somewhere beyond its feet. This model can be described in just a few variables, and adapting it to a different piece of hardware is a matter of changing only those few varaibles, not the algorithm itself. I imagine you are going to go with the trial and error method, and being able to program a computer on the ground in the situation is going to make this a lot easier. I wouldn't try to do it with a PIC just yet. Pick some fast high level language, or even create your own program with a scripting language so you can go through the trials more easily. -Adam Tan Chun Chiek wrote: {Quote hidden}>Hi, > This idea of an autopilot landing system just popped up in my mind, and >other details came almost immediately. I thought why hasn't anyone done it >before? The runway is something like 10m X 50m. GPS is used for >longitudinal/latitudinal positioning and preferably velocity measurement, >the aircraft would have a GPS receiver onboard, and 2 other GPS receivers >would sit on the both long ends at center of the runway, it's something akin >to differential GPS to provide better accuracy. Height measurement is done >by a ultrasonic transceiver or maybe GPS, are they accurate enough? And >pitch and roll is sensed by a pizeo gyroscope. > >How feasible is this concept? > >Regards, >Tan CC > >-- >http://www.piclist.com hint: The PICList is archived three different >ways. See http://www.piclist.com/#archives for details. > > > > > > > -- http://www.piclist.com#nomail Going offline? Don't AutoReply us! email @spam@listservKILLspammitvma.mit.edu with SET PICList DIGEST in the body

----- Original Message ----- From: "Walter Banks" <KILLspamwalterKILLspamBYTECRAFT.COM> Sent: Wednesday, June 19, 2002 4:41 AM Subject: Re: [PIC]: Autopilot landing system for model aircraft > "Andrei B." wrote: > > > > Such a small scale air speed sensor is a challenge itself (I think). > > > This may be one of the easier parts to build. Airspeed measurement is > a function of ratio between ram air pressure and static pressure. > There are lots of pressure sensors these days. > > w.. I think that the subtle and challenging part of doing this (accurately) is measuring static pressure. The presence of the aircraft influences the flow field. For full size aircraft I think that they expend some effort to find a position on the aircraft that will give an accurate reading for static pressure under a representative set of operating conditions. A wind tunnel test ($$$) of an aircraft may include placing pressure taps along the model along the centerline. If you plot the pressure coefficient (comparing measured pressure to the static pressure measured well upstream or far away from the aircraft) along the axis of the aircraft, good locations for the static pressure tap would be places where this value is zero. For a flying model, to determine the static pressure, I think that they may sometimes drag an instrumented object far behind the aircraft, and compare that to the taps on the aircraft. For an R/C, you could do something similar. Another alternative would be to determine the best location computationally, a la CFD. Just my $.02. Jeremy Furtek RemoveMEjfurtekTakeThisOuTagames.com -- http://www.piclist.com#nomail Going offline? Don't AutoReply us! email spamBeGonelistservspamBeGonemitvma.mit.edu with SET PICList DIGEST in the body

Yes, positive, in relation to ambient. Since the fuselage has a shape, bernoulli's (sp?) principle still applies. Since there are curves on the fuselage, the air takes longer to travel from the nose of the aircraft to the tail around the curved surface rather than a straight line, thus, that air will be at a lower pressure, no different than the top surface of the wing. There is positive pressure inside the fuselage since air going past the fuselage is at negative pressure. In my airplane the canopy skirts bow out slightly in flight, due to the positive pressure inside the cockpit, even with the vents closed (I experimented with plugging any holes in the cockpit where air could seep through, to keep the canopy from bowing out, nothing worked; air always manages to get in). The cockpit of an aircraft is not a good place for static pressure due to the reason above, having positive pressure inside. Most IFR-certified single-engine aircraft such as the Cessna 172 etc. have an alernatic-static selector valve, that switches the static source to the cockpit if the one on the aft fuselage becomes iced-up or blocked otherwise. Not the best solution, but it is better than nothing. Or, you could break the glass of one of your pitot-static instruments, such as the vertical-speed indicator, and by breaking the glass you in effect have a static source inside the cockpit. You can compensate for static errors by experimenting with different locations along the aft fuselage, or by raising or lowering the static port from the surface, or by putting an air dam in front of the static port. Bob > {Original Message removed}

>Yes, positive, in relation to ambient. There is positive pressure inside >the fuselage since air going past the fuselage is at negative pressure. I don't think this is true. Or maybe you're just explaining it in the wrong terms. In fact, the pressure inside the fuselage is BELOW the ambient static pressure. The fuselage cannot "pressurize itself" just because there's an airflow over its surface. The reason that your canopy is bowing outward is that there is an acting pressure LOWER than ambient static on the outer surface due to the airflow, not because of a pressure HIGHER than ambient static inside the fuselage. The pressure inside the fuselage starts out AT the total, or static, pressure prior to takeoff. Once in motion, the pressure fuselage gradually starts DROPPING due to the negative pressure (from the airflow) acting outside the fuselage. Try this example of the same effect: go down the highway in your car. Open the window halfway. The pressure inside the car DROPS because the trapped static (total) pressure inside the car tries to escape to equalize the negative pressure flow going past the window. So, the actual pressure inside the car (or fuselage) will actually be LOWER than the static ambient pressure. --Andrew _________________________________________________________________ Get your FREE download of MSN Explorer at http://explorer.msn.com/intl.asp. -- http://www.piclist.com#nomail Going offline? Don't AutoReply us! email TakeThisOuTlistservEraseMEspam_OUTmitvma.mit.edu with SET PICList DIGEST in the body

> The reason that your canopy is bowing outward is that there is an acting > pressure LOWER than ambient static on the outer surface due to the airflow, > not because of a pressure HIGHER than ambient static inside the fuselage. > The pressure inside the fuselage starts out AT the total, or static, > pressure prior to takeoff. Once in motion, the pressure fuselage gradually > starts DROPPING due to the negative pressure (from the airflow) acting > outside the fuselage. > > Try this example of the same effect: go down the highway in your car. Open > the window halfway. The pressure inside the car DROPS because the trapped > static (total) pressure inside the car tries to escape to equalize the > negative pressure flow going past the window. So, the actual pressure > inside the car (or fuselage) will actually be LOWER than the static ambient > pressure. This depends on where the holes are in the fuselage are and what their orientation is. If you could open the windshield as a window, air would rush in and inside pressure would be higher than outside. A different location and orientation can just as easily create a suction causing lower than ambient cabin pressure. ***************************************************************** Embed Inc, embedded system specialists in Littleton Massachusetts (978) 742-9014, http://www.embedinc.com -- http://www.piclist.com#nomail Going offline? Don't AutoReply us! email RemoveMElistservEraseMEEraseMEmitvma.mit.edu with SET PICList DIGEST in the body

--- Walter Banks <RemoveMEwalterTakeThisOuTspamBYTECRAFT.COM> wrote: > "Andrei B." wrote: > > > > Such a small scale air speed sensor is a challenge itself (I > think). > > > This may be one of the easier parts to build. Airspeed measurement is > a function of ratio between ram air pressure and static pressure. > There are lots of pressure sensors these days. > No doubt, but there are a few tiny details: - small size, small weight - accuracy for low air speeds. (I think we're not talking about jet models with miniature turboreactor that flies at over 100kph...) - related to the above : high resolution. Am much easier and cheaper version would be a small propeller working as a windmill. Then have a PIC measure the rpm optically. This might work better for low airspeed then differential pressure sensors. It would need however accurate calibration. ===== ing. Andrei Boros Centrul pt. Tehnologia Informatiei Societatea Romana de Radiodifuziune __________________________________________________ Do You Yahoo!? Yahoo! - Official partner of 2002 FIFA World Cup http://fifaworldcup.yahoo.com -- http://www.piclist.com hint: To leave the PICList EraseMEpiclist-unsubscribe-requestspamspamBeGonemitvma.mit.edu

Here are some more thought about the landing system, and! on-topic. I don't know how today's ILS works, but I do know how the Lorentz low visibility radio guided landing helper worked during WWII. Generate 2 adiacent radio beams that overlap a little. Beams could be several km wide, but the overlap is quite narrow. The beam on the left is modulated with audio pulses with let's say 25% fill ratio and the beam on the right is modulated with audio pulses (same freq) with fill ratio 75%, in sync with the other beam. When you are in the overlap area, you hear a continuos sound. If you hear short pulses and long pauses, you are too far to the left, so go right. And the reverse. Now assume the particularities of models and an airport for them. Assume that your model has some navigation built into it and it can position itself mapwise in an pretty good corridor to come in for a landing. (assume GPS here, also see below for more). Have an ultrasonic altimeter onboard that CAN measure heights down to let's say 10cm and up to several tens of meters. Now you have a good height indication (GPS is totally useless for this due to unacceptable tolerances 10m error, 100m error, accuracy of the map you reference to). Build a Lorentz like beam system, but instead of radio waves, use ultrasound. Have the pair of transmitters at the far side of the airfield and a receiver onboard (you can definitely build it with a PIC!!!) that can control the plane's direction left/rigth, after it gets adequately aligned to the airfield by other means, so that it stays on course guided by the Lorentz beam. Navigation : Assume that you are flying at an airfield usually used by you and other model aircraft. You could build on the ground the necessary support systems for a navigation system that will work around that airport. Although I have absolutely no technical knowledge about how GPS actually works, I guess it could be an extension of the Oboe system developed and used for aircraft navigation by the british, also during WWII. This system was considered to be the most accurate radio navigation system developed during the conflict. The Oboe system : you have several stations on the ground at different location. Each transmits a pulse modulated radio wave, and all are in sync. Each station is identified uniquely. A receiver will pick up one station and use it as a reference, then it picks up another station and computes the time difference between the 2 signals. By some math (which I do not know), one can compute a hyperbola which is the geometric locus where the receiver can be, with one of the stations (i think the reference one) in it's focal point. Now pick up a third station and compute the time difference between the signals and you get a second hyperbola. Where the two hyperbolas intersect, there you are. If you are in doubt and you may have 2 intersections, measure the difference between signals 2 and 3 and get a third one. all three will have a common intersection point. (I assume GPS and similar systems use a similar method, using atomic clocks to have the signals in sync and expanding the concept to 3D, to include height and to consider the fact that you cannot simplify to 2D when your source stations are orbiting above...) According to the accuracy of the measurements and the floating point precision used, one can get a pretty accurate navigation system. Now take this concept and try to apply it to sound instead of radio. This is because sound travels much slower and on such short distances, computing picosecond differences between signals is not a practical thing to do. I leave it to you to extrapolate. One more thing: please, if anyone develops such a system, let us know about it, and hopefully, will be under GPL. P.S. And let's not forget that WE ARE TALKING ABOUTMODEL AIRCRAFT, not a military jet, not a huge airliner. I think, in general, a model aircraft is not flown in hurricane winds, and it doesn't go up in a thunderstorm so it get's lost in the clouds, etc,etc,etc. ===== ing. Andrei Boros Centrul pt. Tehnologia Informatiei Societatea Romana de Radiodifuziune __________________________________________________ Do You Yahoo!? Yahoo! - Official partner of 2002 FIFA World Cup http://fifaworldcup.yahoo.com -- http://www.piclist.com hint: To leave the PICList spamBeGonepiclist-unsubscribe-requestSTOPspamEraseMEmitvma.mit.edu

Jeremy Furtek wrote: > I think that the subtle and challenging part of doing this (accurately) is > measuring static pressure. The presence of the aircraft influences the flow > field. For full size aircraft I think that they expend some effort to find a > position on the aircraft that will give an accurate reading for static > pressure under a representative set of operating conditions. > > A wind tunnel test ($$$) of an aircraft may include placing pressure taps > along the model along the centerline. If you plot the pressure coefficient > (comparing measured pressure to the static pressure measured well upstream > or far away from the aircraft) along the axis of the aircraft, good > locations for the static pressure tap would be places where this value is > zero. > > For a flying model, to determine the static pressure, I think that they may > sometimes drag an instrumented object far behind the aircraft, and compare > that to the taps on the aircraft. > > For an R/C, you could do something similar. Another alternative would be to > determine the best location computationally, a la CFD. The easiest way to get a static port on a model airplane is to not use a port. Most model airplanes aren't anywhere close to airtight, but aren't open to the wind either. In general the air pressure inside the airframe is close enough to the ideal static pressure. Of course, this assumption breaks down if the pressure sensor is too close to a "crack" (wing attach point, gear doors, firewall...). And most importantly, you need to calibrate the sensor. Some syringes (w/o needles) and fuel tubing can be very handy for that. -- http://www.piclist.com hint: PICList Posts must start with ONE topic: [PIC]:,[SX]:,[AVR]: ->uP ONLY! [EE]:,[OT]: ->Other [BUY]:,[AD]: ->Ads

"Andrei B." wrote: > I don't want to discourage you, but there are loads of problems... Not really, any standard aircraft dynamics textbook has most everything you need to do this sort of this. Mine even has a section(s) devoted to the topic. As for GPS...autoland systems existed long before GPS. {Quote hidden}> Another thing, an autopilot can be built and used ONLY, I repeat, ONLY > when you know very well all the handling characteristics of the plane > in all conditions. Research and flight testing of real airplanes takes > years to gather most of the data for the flight manual and for the > autopilot. Without this, an autopilot is next to useless. > The autopilot needs to know exactly in the given conditions, and the > given orders how to control the plane. Changing the propeller, adding > 200grams of weight somewhere, another type of engine, etc, would throw > off completely the autopilot and the planes characteristics will have > to be retested and the autopilot refitted. > A human pilot learns very easily and adapts very quickly to a > situation, but a computer-driven pilot who has a limited knowledge of > the plane and no learning capability (you're not putting an array of > multiprocessor systems with complex neural nets in your model > aircraft...), it won't be able to cope. Human pilots learn through trial and error and so can the computer. All of the systems I've worked with for model airplanes ignore the modeling problem and just use PID or PIDD controllers. The gains for which are determined through trial and error. {Quote hidden}> Also take into account that for such a small scale, even small, > apparently insignificant changes can dramatically affect the plane's > handling. As a human pilot, one can adapt quickly, sometimes > instinctively, maybe barely noticing it... > Example: your plane, fully equiped, at 20kph stalls at 14deg. Let's > say that you put a new battery pack with more capacity, but it also > weighs 100 grams more. This will shift the center of gravity of the > plane and now it will stall at 12 deg at 20kph. The difference may > seems small, but it is actually huge! > The autopilot WILL stall this plane, because it assumes that at 20kph, > it is safe to fly at 13deg inclination! Unless ofcourse, you go through > the whole process of getting the new flight characteristics. Stall is not a function of pitch angle, its a function of angle of attack and airspeed, which are related. As long as the autopilot has a control law wrapped around the airspeed and knows not to go below the stall speed, it should be fine. Adding an angle of attack sensor will help to. {Quote hidden}> Actually, making such an autopilot would be much easier for model > helicopter then for a plane. Due to the nature of the helicopter, and > the way it flies, (excluding acrobatics, ofcourse), many things are > simpler to handle. > The advantage of model helicopters is the fact that they can reach a > dynamic equilibrium in which they appear static and can hold this. Then > it's a simple matter of slightly lowering the collective... > (simplified) > > The plane, although by it's nature tends to fly, while the helicopter > does the opposite, dynamicly balancing the parameters on a plane could > be more challenging then for a helicopter. Achieving steady state flight with a stable airplane is easier, since it will tend to stay at equilbibrium (hence "stable"). The difference is that for an airplane the equilibrium state involves forward velocity. Helicopters are inherently unstable and require constant attention to stay at the steady state point (excluding autogyro). There's a reason why papers airplanes fly better than paper helicopters. -- http://www.piclist.com hint: PICList Posts must start with ONE topic: [PIC]:,[SX]:,[AVR]: ->uP ONLY! [EE]:,[OT]: ->Other [BUY]:,[AD]: ->Ads

"M. Adam Davis" wrote: > I suspect you'd spend less time in development if you built your own > positioning system. Radio would work, using lights on the runway and a > camera in the plane would work, you could even have a transmitter on the > plane, tracked on the ground using three radio receivers with all the > heavy computations done by the computer on the ground. You may want to > go this route first only to make it easier to program the algorithms on > the computer. An inertial navigation system isn't too hard to do. > The hardest part, I suspect, is not the actual mechanisms for tracking > and autopiloting the plane but the algorithms that control it: Actually, tuning the algorithms (w/o crashing) is the hardest part. The "algorithms" can be simple uninformed control laws. {Quote hidden}> Example: > Up until recently two legged walking robots have all been built by trial > and error and/or by keeping the center of gravity above points touching > the ground. The problem with doing it this way is that the algorithms > are specific to the hardware/model they are using and are not > generalized for other models. When they do get the algorithm working on > another piece of hardware they have to change hundreds or thousands of > variables and re-tweak the algorithm. Researchers have finally made a > simple model, including equations to describe the model, that can walk > and run in a dynamic fashion - with its center of gravity somewhere > beyond its feet. This model can be described in just a few variables, > and adapting it to a different piece of hardware is a matter of changing > only those few varaibles, not the algorithm itself. Can yo provide any more info on this? I've been interested in walking stuff for a while, but haven't been able to find any good papers on it. The best thing I've seen so far is the trodon at MIT's leg lab, but they don't appear to be talking about it. > I imagine you are going to go with the trial and error method, and being > able to program a computer on the ground in the situation is going to > make this a lot easier. I wouldn't try to do it with a PIC just yet. > Pick some fast high level language, or even create your own program > with a scripting language so you can go through the trials more easily. Actually, the MP1000 used two PIC's (I forget which ones) and could keep a vehicle in the air. Although its handling qualities left much to be desired and it certainly couldn't land. -- http://www.piclist.com hint: PICList Posts must start with ONE topic: [PIC]:,[SX]:,[AVR]: ->uP ONLY! [EE]:,[OT]: ->Other [BUY]:,[AD]: ->Ads

Unfortunately no, I attended a tech luncheon at the University of Michigan. The presentation was done by a professor and graduate student who were working on exactly this with a french university. I don't even recall walking away with any documentation on it... Ah nevermind. I spent a few minutes at the engineering site and found it: http://www.eecs.umich.edu/~ewesterv/biped/ -Adam Brandon Fosdick wrote: {Quote hidden}>>Example: >>Up until recently two legged walking robots have all been built by trial >>and error and/or by keeping the center of gravity above points touching >>the ground. The problem with doing it this way is that the algorithms >>are specific to the hardware/model they are using and are not >>generalized for other models. When they do get the algorithm working on >>another piece of hardware they have to change hundreds or thousands of >>variables and re-tweak the algorithm. Researchers have finally made a >>simple model, including equations to describe the model, that can walk >>and run in a dynamic fashion - with its center of gravity somewhere >>beyond its feet. This model can be described in just a few variables, >>and adapting it to a different piece of hardware is a matter of changing >>only those few varaibles, not the algorithm itself. >> >> > >Can yo provide any more info on this? I've been interested in walking stuff for >a while, but haven't been able to find any good papers on it. The best thing >I've seen so far is the trodon at MIT's leg lab, but they don't appear to be >talking about it. > > > > -- http://www.piclist.com hint: The list server can filter out subtopics (like ads or off topics) for you. See http://www.piclist.com/#topics

On Wed, 26 Jun 2002, Brandon Fosdick wrote: {Quote hidden}>"Andrei B." wrote: >> I don't want to discourage you, but there are loads of problems... > >Not really, any standard aircraft dynamics textbook has most everything you need >to do this sort of this. Mine even has a section(s) devoted to the topic. As for >GPS...autoland systems existed long before GPS. > >> Another thing, an autopilot can be built and used ONLY, I repeat, ONLY >> when you know very well all the handling characteristics of the plane >> in all conditions. Research and flight testing of real airplanes takes >> years to gather most of the data for the flight manual and for the >> autopilot. Without this, an autopilot is next to useless. >> The autopilot needs to know exactly in the given conditions, and the >> given orders how to control the plane. Changing the propeller, adding >> 200grams of weight somewhere, another type of engine, etc, would throw >> off completely the autopilot and the planes characteristics will have >> to be retested and the autopilot refitted. >> A human pilot learns very easily and adapts very quickly to a >> situation, but a computer-driven pilot who has a limited knowledge of >> the plane and no learning capability (you're not putting an array of >> multiprocessor systems with complex neural nets in your model >> aircraft...), it won't be able to cope. > >Human pilots learn through trial and error and so can the computer. All of the >systems I've worked with for model airplanes ignore the modeling problem and >just use PID or PIDD controllers. The gains for which are determined through >trial and error. > >> Also take into account that for such a small scale, even small, >> apparently insignificant changes can dramatically affect the plane's >> handling. As a human pilot, one can adapt quickly, sometimes >> instinctively, maybe barely noticing it... >> Example: your plane, fully equiped, at 20kph stalls at 14deg. Let's >> say that you put a new battery pack with more capacity, but it also >> weighs 100 grams more. This will shift the center of gravity of the >> plane and now it will stall at 12 deg at 20kph. The difference may >> seems small, but it is actually huge! >> The autopilot WILL stall this plane, because it assumes that at 20kph, >> it is safe to fly at 13deg inclination! Unless ofcourse, you go through >> the whole process of getting the new flight characteristics. > >Stall is not a function of pitch angle, its a function of angle of attack and >airspeed, which are related. As long as the autopilot has a control law wrapped >around the airspeed and knows not to go below the stall speed, it should be >fine. Adding an angle of attack sensor will help to. Stall depends on the efficiency of the aerofoils at the given parameters, which include density (altitude), airspeed, aoa, and wing load, among other things (which include wing surface quality and any defects). I am not an expert on this but these things are *complicated*. {Quote hidden}>> Actually, making such an autopilot would be much easier for model >> helicopter then for a plane. Due to the nature of the helicopter, and >> the way it flies, (excluding acrobatics, ofcourse), many things are >> simpler to handle. >> The advantage of model helicopters is the fact that they can reach a >> dynamic equilibrium in which they appear static and can hold this. Then >> it's a simple matter of slightly lowering the collective... >> (simplified) >> >> The plane, although by it's nature tends to fly, while the helicopter >> does the opposite, dynamicly balancing the parameters on a plane could >> be more challenging then for a helicopter. > >Achieving steady state flight with a stable airplane is easier, since it will >tend to stay at equilbibrium (hence "stable"). The difference is that for an >airplane the equilibrium state involves forward velocity. Helicopters are >inherently unstable and require constant attention to stay at the steady state >point (excluding autogyro). There's a reason why papers airplanes fly better >than paper helicopters. Steady state does not exist in flight. Stable airplanes do not exist. What appears to be temporarily stable is a quirk in a balance equation that predicts a crash either by stall or by pitching into the ground sooner or later. Either that or you are spending lots of energy in wasted compensation moments that represent a significant percentage of the real forces required for 'stable' (say, efficient) flight. A (paper) helicopter with a serious coning angle and/or large mass/momentum at the rim (frisbee) is very stable for the duration of its flight, same for a model airplane or paper airplane. It follows that you can have stability two ways: 1. Waste a lot of energy (engine power) on oversized static aerodynamic moments that ensure that the plane is 'stable' (large dihedral, large arrow, large stabilizer, low cog, etc etc). This costs fuel and/or efficiency (low glide number) and/or maneuvrability. 2. Use active feedback control on an instable or critically stable airframe to keep it flying 'stable'. This costs lots of time to get the controls right and yields best results. The feedback can be a live pilot or a machine. By the time the machine does everything the pilot knows how to do, it should be about as smart as the pilot. 3. (the third way of two <g>). Use as much of <2> as you dare and keep as much as you need of <1> in the design just in case <2> is not so good. definitely not an expert, Peter -- http://www.piclist.com hint: The list server can filter out subtopics (like ads or off topics) for you. See http://www.piclist.com/#topics

Brandon Fosdick wrote: > Stall is not a function of pitch angle, its a function of angle of attack and > airspeed, which are related. As long as the autopilot has a control law wrapped > around the airspeed and knows not to go below the stall speed, it should be > fine. Adding an angle of attack sensor will help to. As I understand it, stalling on ONLY a function of angle of attack. You can stall a plane at and attitude, at high speed, and you can also fly a plane below the stall speed (however you need altitude to regain flight energy before loading the wings). To verify this, if the wing has 0g loading, how can it stall. However, if you are below the stall speed and the wing loading goes above 0g, then the lift bank balance is in arrears and it will stall. Same thing flying at the stall speed, there's nothing left in the lift bank for the wings. Lowering an aileron in this state will stall that wing immediately. Disasterous near the ground. As my areobatics instructor stresses, pull the stick back to position 'X' at any speed and the wings will stall, so you may be better monitoring the back pressure on the "stick" to detect when a stall is imminent. -- Best regards Tony mICros http://www.bubblesoftonline.com KILLspamsalesspamBeGonebubblesoftonline.com -- http://www.piclist.com hint: The list server can filter out subtopics (like ads or off topics) for you. See http://www.piclist.com/#topics

> As my areobatics instructor stresses, pull the stick back to position > 'X' at any speed and the wings will stall, so you may be better > monitoring the back pressure on the "stick" to detect when a stall is > imminent. I think that there may be two separate discussions in progress here. When you mention stalling, Tony, you are speaking specifically of a wing stall, rather than not having lift at all. They are two different things. I know of one Russian prop stunt plane that had so much prop force that it could literally hover using its prop. Not to mention that many fighter jets will not stall going straight up unless the throttle is low (for going straight up, less than 90% counts as low) but by that point, the wings are no longer causing any lift, and therefore are stalled, while the aircraft clearly continues to have lift, and is therefore not stalled. The other guy (sorry forget the name and it's waaayyyy back in my PIC box) who was talking about all the different factors was, I think, talking more about when the aircraft would cease to gain lift at all. What I'm trying to say is that a wing can stall and the aircraft can continue on un-stalled (though if the aircraft is stalled, I think you're almost guaranteed to have all wings stalled). It depends on all the factors originally mentioned. If you've built a model jet fighter, and it can climb straight up, chances are that if you punch the throttle, you'll never stall the little beggar, though the wings may only be serving as fins at that point. --Brendan -- http://www.piclist.com hint: The list server can filter out subtopics (like ads or off topics) for you. See http://www.piclist.com/#topics

>> As my areobatics instructor stresses, pull the stick back to >> position 'X' at any speed and the wings will stall, so you may >> be better monitoring the back pressure on the "stick" to detect >> when a stall is imminent. > I think that there may be two separate discussions in progress here. > When you mention stalling, Tony, you are speaking specifically of a > wing stall, rather than not having lift at all. They are two > different things. Lift has several components: 1) pressure differential lift (classic wing lift), 2) flat plate lift, and 3) vertical component of propulsive force. > What I'm trying to say is that a wing can stall and the aircraft > can continue on un-stalled As long as the total of all lift vectors exceeds the weight, the aircraft will not descend -- even if the wing is technically (in the clasic sense) stalled. > (though if the aircraft is stalled, I think you're almost > guaranteed to have all wings stalled). Not true. You can easily have one surface, the wing, stalled while another surface, the stabilizer/elevator, is not stalled. You can also have part of a single surface, the wing, stalled while another part of the same surface is not stalled -- tuned by installation of "stall strips" on the leading edge. If all surfaces stalled at the same time, the aircraft would be uncontrollable. Lee Jones -- http://www.piclist.com hint: The list server can filter out subtopics (like ads or off topics) for you. See http://www.piclist.com/#topics

On Thu, 27 Jun 2002, Brendan Moran wrote: >I think that there may be two separate discussions in progress here. When >you mention stalling, Tony, you are speaking specifically of a wing stall, >rather than not having lift at all. They are two different things. Stall is defined as the condition where the intended laminar flow around the aerofoil ceases being laminar to a great extent. It has almost nothing to do with wings or aircraft except the above mentioned aerodynamic condition just so happens to lower the wing efficiency (lift/drag ratio for that aoa) below what is acceptable for an aircraft for flying. Stall also affects other things, like turbine blades, fast-moving cutting tools in air or lubricant, fans, structures exposed to high speed air or gas or liquid flows, etc etc. As you have said, if the engines are powerfull enough you 'can't' stall. Also usually aerodynamic stall has a latching behavior, in that the transition between stalled and unstalled mode is abrupt in both directions. Peter -- http://www.piclist.com#nomail Going offline? Don't AutoReply us! email EraseMElistservEraseMEmitvma.mit.edu with SET PICList DIGEST in the body

Guys, this is *well past* the [OT]: point, please change the topic tag for any further posts. Should have sent this two days ago. Thanks. Dale -- "Curiosity is the very basis of education and if you tell me that curiosity killed the cat, I say only the cat died nobly." - Arnold Edinborough On Fri, 28 Jun 2002, Peter L. Peres wrote: {Quote hidden}> On Thu, 27 Jun 2002, Brendan Moran wrote: > > >I think that there may be two separate discussions in progress here. When > >you mention stalling, Tony, you are speaking specifically of a wing stall, > >rather than not having lift at all. They are two different things. > > Stall is defined as the condition where the intended laminar flow around > the aerofoil ceases being laminar to a great extent. It has almost nothing > to do with wings or aircraft except the above mentioned aerodynamic > condition just so happens to lower the wing efficiency (lift/drag ratio > for that aoa) below what is acceptable for an aircraft for flying. Stall > also affects other things, like turbine blades, fast-moving cutting tools > in air or lubricant, fans, structures exposed to high speed air or gas > or liquid flows, etc etc. > > As you have said, if the engines are powerfull enough you 'can't' stall. > Also usually aerodynamic stall has a latching behavior, in that the > transition between stalled and unstalled mode is abrupt in both > directions. > > Peter > > -- > http://www.piclist.com#nomail Going offline? Don't AutoReply us! > email @spam@listserv@spam@spam_OUTmitvma.mit.edu with SET PICList DIGEST in the body > > -- http://www.piclist.com#nomail Going offline? Don't AutoReply us! email spamBeGonelistservKILLspammitvma.mit.edu with SET PICList DIGEST in the body