This Thanksgiving day I’m thankful for many blessings: family, friends, neighbors, shelter, food, our siberian husky who lived 16 years, and many other things. The weather was nice Thanksgiving morning so I was thankful to have an hour to run out to the field first thing to do some flying.
On Thursday, November 22 (Thanksgiving day) my Senior Telemaster past an interesting milestone: 12 cumulative hours of fully autonomous flight. This may not sound like a whole lot, but it represents 58 separate flights over the span of 3 years. In every flight it has performed beautifully and majestically and very scale like. It is not a fast aircraft, but it’s solid, forgiving, and controllable even at very slow airspeeds. It has a lot of room, a lot of carrying capacity, and it’s very tolerant of CG changes. I have flown it on calm days and I have flown it in up to 27 kt winds (31 mph) that were gusting to higher at times. With a set speed of 30 kts there have been times it has been blown backwards in flight! She has seen sun, clouds, fog, drizzle, and even rain. Winter, summer, spring, fall, hot days, cold days — she’s seen just about everything. Through all of this it has been a solid, reliable, patient, unfailing work horse — and she’s still going as strong as ever!
She has been a test bed for 4 major autopilot revisions:
An original gumstix :gumstix” processor + a Xbow MNAV sensor head.
A gumstix “verdex”+ a sparkfun 6DOFv4 IMU
A gumstix “verdex” + a VectorNav VN-100T temperature calibrated IMU
A gumstix “overo” + a 3D Robotics APM2.5 “sensor head”
I recall one close call where I made a code+hardware change and didn’t check it thoroughly enough. Transitioning to autonomous flight resulted in an immediate full throttle dive towards the earth. I switched to manual mode (almost not quickly enough) and was able to manually recover from the dive just in the nick of time. That is the only time I’ve put any serious flex on the wings!
I recall one landing when the farmer’s corn was 8′ tall and completely surrounding our little patch of flying field. I typically had to come over the edge of the corn with inches to spare in order to get it down and stopped before the end of our flying field. On this day we had crazy gusting cross winds and as I cleared the corn the wind just fell out from under the telemaster. It dropped from maybe 10′ of altitude and came to a complete stop no more than 5′ from the approach edge of the corn. That has to be my all time shorted landing with any aircraft (only counting landings on the wheels.) 🙂
So thanks to my trusty work horse for many good years of service with hopefully many more to come!
This is a little proof of concept video I just put together. The goal is to always keep my aircraft’s shadow in the field of view.
Equipment: Senior Telemaster. Fly-Cam-One-3 with built in pan/tilt. Sparkfun 6DOFv4 IMU (it was laying around so I used it.) Gumstix flight computer. Ardupilot used for controlling pan/tilt servos on the camera.
The flight is 100% manually piloted. Camera is 100% automatically pointed.
On board I am running a 15-state kalman filter for attitude estimation. The filter converges to “true” yaw angle independent of ground track, wind, and magnetometer. This is actually critical for camera pointing.
On the ground I have small app I whipped together one evening that computes the sun location for the current time in ECEF coordinates. Then converts the sun “vector” to NED coordinates based on a GPS connected to the ground station (assuming I’m not ranging very far from my start point.) The code computes a new sun angle every minute. Finally, the sun vector is inverted to get a shadow vector and that is sent up to the aircraft as it’s target point vector (once a minute.)
Notice: sun vector * [ -1 -1 -1 ] = shadow vector.
Also: sun vector * [ 1 1 -1 ] = reflection vector (where we would be looking at the suns reflection off surface water.)
Also: sun vector * [ 1 1 1 ] = rainbow vector if we would happen to fly above the clouds (this would keep us looking at the center of a rainbow circle/arc.) 🙂
In order to run myself over with the shadow from the aircraft’s perspective I need to fly the airplane through the sun from the ground pilot’s perspective.
Disclaimers: this was my first time out trying something like this so the video is rough. The pan/tilt on the flycam is very low grade, but works well enough for a demo. I’m also flying with an IMU that is about 2 orders of magnitude coarser than I’m used to flying with, so that degrades my attitude estimation more than I would have liked (but the filter still converges.) I put very little effort into aligning the IMU mount with the camera mount, so there are certainly a few degrees of bias just from mounting issues. Finally, I only eyeballed the mapping between servo commands and pan/tilt angles so I’m in the ball park, but there are certainly errors there too. It’s a hack, but made for a fun afternoon. 🙂
I am changing acronyms starting with this post. Previously I was calling this an SAS for “Stability Augmentation System” but someone pointed out that this is technically more of a CAS for “Command Augmentation System”.
SAS implies a direct connection between pilot input and control surface deflection with some additional stability augmentation mixed in. CAS implies that a flight computer is translating pilot inputs into a “request” and the flight computer then tries to satisfy that request, but there is no immediate direct mapping between stick deflection and control surface deflection.
Just to review, the ATI “CAS” system internally tracks a target bank angle and a target pitch angle. The pilot is “flying” these target bank/pitch angles and the flight computer is doing it’s best to match up with the request. The pilot changes the target bank angle by deflecting the stick; the greater the stick deflection, the faster the target bank angle changes. This is similar for the target pitch angle. When the pilot centers the stick, the target bank or pitch angle is held steady.
If the pilot banks into a 15 degree turn (target bank angle) and centers the stick, then the flight computer will hold that 15 degree bank indefinitely or until the pilot deflects the stick again. Likewise with the target pitch angle, the pilot pulls the nose up or down with the stick, but when the stick is centered, the flight computer holds that pitch angle indefinitely (as best as is possible for the available throttle and airspeed and maximum control surface deflections.)
The system can limit that maximum bank and pitch angles to stay within “nice” limits. In addition, the system can limit that maximum control surface deflections to avoid abrupt and rapid attitude changes. Currently the system is rigged so that even if the pilot commands maximum pitch up angle (+15 degrees) and pulls the throttle to idle, there is not enough allowed elevator authority to stall the aircraft. This makes the aircraft very safe to fly and very predictable.
Here is some real world flight video from the same flights shown in the first video. The CAS system is active for all but the initial take off in both of these videos. You can see in some situations the system is working quite well, in some situations the flight computer cannot completely compensate for the natural airframe dynamics and environment effects (turbulence, etc.) and in a few situations additional tuning will be required:
1. We added some additional logic to slowly roll the wings to perfect level if the pilot puts the bank angle within +/- 10 degrees of level. It’s really hard to get it exact from a ground perspective, so the idea is to let the pilot get in the ball park and the system will take over and finish the job. Auto-leveling will only kick in after the pilot centers the stick so it doesn’t fight the pilot if the pilot is intending to bank the aircraft.
2. To mimic more natural flight behavior we automatically pitch the nose up by a few degrees when the pilot adds throttle and pitch the nose down by a few degrees when the pilot pulls the throttle back. This is much more “intuitive” for a pilot and makes the system more predictable and easy to fly.
This was unfortunately another windy day, and the telemaster is a self stable, “trainer” style airframe and thus roll and yaw are very coupled and the aircraft’s natural flight dynamics react quite a bit to even small wind gusts. This means the SAS isn’t shown yet in it’s best light. I guess I’ll keep apologizing for the weather and at some point move to a more stable airframe, or try to find nicer days to fly.
I will say one thing. Even when the aircraft is bobbing around on final approach in the turbulence, it’s nice to be able to fly hands off the aileron stick and trust the SAS system to immediately return the wings to level, even when we get knocked 10, 20, or even 30 degrees off kilter. I’m still fiddling and improving and I’m not totally in love with the system yet. But it’s good enough already that I miss it when I turn it off.
ATI has been developing a number of flight control system building blocks and we have been testing them on my Senior Telemeaster airframe. This week I decided to connect them up to create a simple SAS (stability augmentation system.)
Briefly, when flying with an SAS, the pilot is still 100% in manual control over the airplane, however we have inserted a flight computer in between the pilot control inputs and the control surface actuators. Rather than the pilot’s stick commands directly moving the control surfaces, the pilot stick commands are translated to roll and pitch “rate” requests. The flight computer keeps track of the target pitch and roll angles and adjusts these according to the pilot’s stick inputs. The more the pilot deflects the control stick, the faster the aircraft rolls or pitches in that direction. When the pilot centers the stick, the flight computer holds the current bank and pitch angles, even if there are throttle or speed changes, gusts and turbulence, etc.
Here is a video of my very first SAS test flight:
The first flight test went pretty much according to script. The basic mechanics of the SAS worked as planned and produced reasonably stable and smooth flight. Transition between direct manual control and SAS flight was smooth. After the flight I adjusted two things. First, my gains were set way too low. Even at full stick deflection, the system responded much too slow to be intuitive for an average pilot. Second, I had used an exponential control mapping. This means that near the stick centers, I have to move the sticks a lot to produce just a little bit of aircraft response, but as I near the extremes of the stick deflection range, the rates ramp up quickly and the aircraft responds at maximum (programmed) rates. Below are two plots that show the difference between linear and exponential input mapping.
I had a little fun on the first landing. I included it all in the video posted above. After a couple low slow approach passes followed by a go around, I figured I had enough confidence in the system to attempt a full landing. However, the combinations of gains being set way too low along with exponential input mapping meant my flare was way way way too slow and from the video you can’t even see any pitch up at all even though my stick was pulled all the way back. I hit so hard I sent the camera tumbling … sky / ground / sky / ground 🙂 Every thing was fine … I’ve had rougher landings once in a while even under pure direct manual control.
After this flight I tripled the gains and switched to linear input mapping and the result was something that is much more intuitive to fly and allowed me to do some nice landings on subsequent flights. The system still isn’t perfect and needs some more tuning and fiddling, but for the first day out in the field after a couple days of intensive coding, I am really happy with the results!
Here is some video from my last flight of the day:
One of the most challenging aspects of autopilot setup is tuning the gains for a particular airframe. When the gains are tuned poorly, the aircraft my oscillate excessively, it may lag way behind the target pitch angle or roll angle or velocity, it may never reach the target values. Poorly tuned gains could destroy an airframe in a worst case scenario, but often people just live with non-optimal gains that aren’t great but work well enough to get the aircraft around the sky. It’s hard to know what gains to tune and why and a person could play with the numbers all day and only manage to make things worse. It’s easy to spot a problem; often the aircraft will look like it is fighting itself even though it does make it’s way to where it should be, or it just may not do what you ask it to do.
Real World Experimentation
Today I did some test flying with one goal to improve the elevator / pitch gain. Previously my gains were set too low. The result was smooth pitch control, but the actual pitch lagged far behind the goal pitch and tended to oscillate slowly above and below the desired pitch angle. To fix this, I increased the proportional gain until the pitch became unstable, then reduced the gain by 50%. This doesn’t ensure optimal results, but works pretty well in practice.
Here is a short before and after movie
The first half of the movie shows a flight where the elevator gain has been increased until we have just crossed the threshold into an fast oscillating system. You will see it stabilizes from time to time, but any little gust or even a turn can excite the system and lead to oscillations. In the second half of the video the gains have been reduced by 1/2 and you can see the pitch is much more stable. One point to note is that both flights were flown in very windy/turbulent conditions. During the second flight I was seeing sustained winds at 20 kts, gusting to 25 kts. The aircraft was set to cruise at 28 kts for a portion of the flight and on one up wind leg, it just stopped in the sky. (28 kts = 32.2 mph)
Want to learn more?
If you are interested in more information on PID controllers and gain tuning, I wrote a tutorial several years ago explaining much of the basic theory that goes into a simple PID controller. I then discuss some specifics about the autopilot implementation used in the FlightGear flight simulator. This is interesting because my UAV autopilot uses the same basic FlightGear approach. In fact, it’s possible to develop an autopilot xml configuration file in the FightGear flight simulator, and then copy the config file over to the real UAV and run it with only a few small changes.
At the end of the tutorial I include several tips and strategies for tuning PID controllers.
My standard disclaimer is that my educational background is computer science; I do not present myself as a control theory expert; instead I’d just like to share what I have learned in a way that makes sense to me.
(Sep 4, 2010 edit: I’ve moved way beyond this todo list, we are on our 2nd and 3rd gen autopilot hardware now. The software has been totally revamped. Still, kind of fun to look back to see where we were a few years ago. Never did clean the gummy residue off the load struts though …)
Setup a heading hold mode and implement waypoint following.
Setup auto-throttle control module.
Install secondary “tapped PPM signal” receiver.
Install MaxStream radio modem.
Low priority: clean gummy sticker residue off the aluminum load struts.
November 16, 2007
Today I logged about 50 minutes of fully autonomous flight. Since I fixed the MNAV firmware bug, I have not seen any servo glitching or problems. The (patched) system is starting to earn my confidence.
August 14, 2007
Today I did two test flights in some non-trivial wind.
On the first flight the gps gave me a couple sequential bogus readings so the aircraft thought it was -1000 MSL (i.e. below sea level.) This caused it to climb towards what it thought was target altitude, but in reality was way too high. So we shut down the motor and brought it back. I’ve never seen the gps glitch like this so I’m not sure what to make of it.
On the second flight we had good altitude readings, but I observed that I constructed my sequence of waypoints in a way that it was impossible to reach the 3rd waypoint from the 2nd waypoint given the existing wind conditions. I “cheated” and helped tighten that turn with the rudder and with that small amount of help, it was able to reliably negotiate the course.
July 28, 2007
Today I flew twice to collect airspeed data from the pitot tube. The data is noisier than I hoped, but seems to be pretty plausible and certainly usable if I filter/smooth it a bit.
July 27, 2007
Today I installed a pitot tube on the Telemaster and routed some flexible out the center section of the wing so I can plug it into the MNAV when I install the wing. I used a length of carbon fiber tube rather than metal. These pitot tubes take a lot of abuse, even when you know they are there and are trying to be careful. 🙂
July 13, 2007
Flight report: The goal of today’s flight was to excercise the altitude hold system after making a couple small tweaks to the gains. It was a beautiful morning, temps in the mid-60’s, not a cloud in the sky, wind out of the west at about 4-5 mph, nice smooth air.
Here is the plot of altitude vs. time. The red line is the target altitude of 426.72 meters MSL (or 1400′ MSL which is about 500′ AGL.) Altitude statistics for the flight: average altitude = 426.44m, min = 419.6m, max = 434.4m, standard deviation = 2.85m.
Here is a motor/battery plot from my eagle tree data logger:
Here is a movie of a synthetic replay of a portion of the flight:
June 23, 2007
I took the telemaster out and ran out the 8000 mAh battery over the course of two flights. I didn’t quite have a full charge on it to start with and ran it up at full throttle most of the time, so I only got about 22 minutes of motor on flight. It is a bit surreal to see such a large airplane fly so quietly, smoothly, gently, and slowly — but also very pretty to watch. The air was really smooth this evening and winds were light so the big telemaster was super stable and solid.
On the first flight the MNAV performed great. I saw one momentary servo glitch, but other than that, it tracked rock solid each time I activated the autopilot. I would fly down to one end of the field, turn around, line it up, and activate the autopilot. The autopilot would hold a pitch attitude and lock the wings level, so I could then steer with the rudder and fly a pass. At the other end of the field I’d flip back to manual control, wheel around, line her back up, and reactivate the AP again. I flew a dozen “long” passes like that and it worked well.
On the second flight, the MNAV servo output was in glitch mode the whole time. Each time I activated the AP, it drove the servos to full stop which puts the controls hard over. So I just flew it manually around the pattern, and checked periodically to see if the MNAV revived itself, which it never did. I should point out that I’m 95% sure the servo output glitch is something specific to this particular MNAV unit. It’s not a more general problem as far as I know. I should also point out that the sensors and flight computer runs fine during the time the servo output glitches out. Once I get the other MNAV back from Xbow, I will probably send this one in for service.
June 9, 2007
Today I flew two more flights with the MNAV involved. I activated the pitch angle hold and that seemed to work reasonably well to. I think the control outputs jitter more than the simulator and the plane reacts to turbulence more than the simulator, so the result is not a super smooth solid lock on the target values, but at the same time the bouncing seems really random like turbulence, not regular like an oscillating, not quite tuned, PID.
The flight control computer/mnav blipped out on me once and kept trying to put the controls hard over to full stop. I’m not sure what happened there, but it eventually recovered itself. I need to do some more ground testing to see if I can reproduce the problem.
June 8, 2007
First flight with the MNAV helping!
For the past weeks I have been battling one problem after another getting all the components together and working on this new airframe. The biggest problem has been interference and noise and a corresponding dangerous drop in range for manual control.
Ok, so tonight, I finally have everything together (I think — I hope! — it’s always those pesky oversights that can kill your airplane.) I pass my range check (not by a lot, but I pass), there is a 10 mph direct cross wind which I’m not especially fond of, but not too worried about. Skies are perfectly clear, temp is 70 degrees, I’m the only one at the field tonight, I need to be especially careful not to put my finger in the prop, I can’t dial 911 with out it! I power on the flight computer and verify it is up and running, I verify the borrowed IMU/GPS sensor is up and running, I verify I have gps lock, I double check all the controls are working and in the right direction, and finally I verify I can hand over control to the autopilot and yank it back reliably with a switch on my transmitter.
Tonight I only had the aileron channel routed through the flight computer, so when I hand off control, the AP is only going to do wing leveling, I still have manual control on all the other axes.
With everything in place, I took a deep breath and taxied out to the end of the runway and lined myself up. I took another deep breath and smoothly advanced the throttle. As the airspeed came up, the aircraft weathervaned strongly into the direct cross wind so I quickly shut down the motor and aborted the take off run. This was my first try at a cross wind take off in this aircraft so I didn’t have my thumb gains set right! 🙂 On the second try I pretty much held the runway center line, and after what seemed like an eternal take off run in the grass, the tail came up and I coaxed it off the ground. It climbed out more lethargically than I thought it should, but it was climbing … temps were warmer than when I’ve flown before and I had an extra battery pack on board … I’m not too worried just yet.
I circled the field for a couple minutes to gain some altitude and catch my breath. I was paying careful attention to whether or not I had solid manual control with no glitching. Flying this airplane manually is a no-brainer, so I’m not nervous about that. But this is the first time I’ve flown all the equipment plugged together and powered on. I’m very worried about the effect of noise and reduced range. If my receiver is overwhelmed with noise once the aircraft is at altitude, and I can’t control the airplane … it goes in hard and half my life for the past couple months goes home in a garbage bag (I did bring one just in case!) Failure at this critical point in the project could mean giving up all my UAV hopes and dreams. Success here is the gateway to all sorts of interesting future projects and fun. I’m usually not a highly dramatic type of guy, but for some reason, I felt a heavy weight that this was a very critical junction in my life. So I was *very* apprehensive about possible equipment failure or some oversight that would lead to the aircraft being destroyed.
But so far so good, I’m up and flying, control inputs feel solid, no glitches that I can see in my receiver. This was the main focus of my test flight, to validate the manual override board I have recently added to the whole system and to make sure I can fly the aircraft safely and reliably no matter what goofiness the flight computer might attempt.
So now I’m at altitude, tooling around, no more excuses … I flipped the autopilot switch to activate it and immediately my wings leveled out and stuck there. I wiggled the rudder back and forth to full stop in each direction. This aircraft has a lot of dihedral and strong roll coupling, so even though a good whack (sorry Bill) of rudder causes quite a bit of roll, and even though holding full rudder deflection puts a lot of pressure on the airframe to roll, the flight computer is able to bring the wings back to level again and hold them there.
This is the bonus part of the flight. I honestly didn’t care if the flight computer put the ailerons hard over and held them there, as long as I could recover manual control any time I wanted. But the nice bonus was that the roll angle estimation and wing leveling code worked great. The gains maybe weren’t exactly perfect, but they were ok, and did the job just fine.
I landed and then repeated everything again with a second flight. I figure anyone can hit the three point shot, but if you can do it twice in a row, maybe it wasn’t entirely dumb luck.
This UAV is running an almost exact copy of the FlightGear autopilot algorithm, it even has the same xml parser, property system, and almost the same autopilot config syntax.
The Rascal 110 dynamics model we have in flightgear is not perfect, but it’s not horrible either. I developed a bunch of flightgear autopilot modes to work with the Rascal 110 model, including a wing leveler, heading hold, pitch hold, altitude hold, speed hold, etc. etc. These autopilot configs were all developed entirely in FlightGear using a JSBSim dynamics model.
Now with this UAV I am developing, I can take the *exact* autopilot config file off the flight simulator (make a couple small syntax modifications) and the actual, real-life, real world uav autopilot can run the same algorithm on the real uav in real flight with the same gains. If the simulation model used to tune the gains is good enough, the real life UAV autopilot should work out of the box (maybe not optimally) but well enough to be stable and do the job.
In this case, the wing leveler config developed in simulation with JSBSim and FlightGear worked out of the box on the real UAV running the same algorithm. (The Rascal and the Telemaster aren’t exactly the same airframe so this isn’t a perfect conceived test case, but they are close enough …)
I hope to head out tomorrow and repeat everything with the pitch axis. So tomorrow night I could be easily be sobbing, but for tonight at least I am happy. 🙂
No pictures tonight … Ruth misplaced the digital camera …
May 28, 2007
Test flight with MNAV and GumStix collecting data
Today was really windy, but right down the pipe so I put in 3 flights on the telemaster. This weekend I mounted the Xbow MNAV connected to the GumStix flight computer. I can log about 60 hours of flight data on-board with the Gumstix’s 1Gb MMC card.
I can take that flight data and replay it in FlightGear to “visualize” the flight and also to get a sense of how well the sensors and flight computer estimate the location and attitude of the aircraft.
Here are some pictures of the initial installation of the equipment.
April 18, 2007
Temps were about 60F, clear sky, winds out of the East at 10-15 (runway is N/S.) The winds were very erratic, gusty, and changing directions. Not the nicest for flying but not insane either.
March 30, 2007
Today I tightened down the motor mounts, prop, and spinner. I plugged in the battery and fired up the motor. She seems like she generates plenty of thrust to fly. The speed controller seemed like it was getting a tiny bit warm in my short run tests, so just to be safe I moved it back out on the front of the firewall.
I installed the receiver and secured the antenna. I put a bit of effort into routing and securing all the wires so there wouldn’t be stuff flopping all over inside the cabin. With the power on, I setup all the servos to move the correct direction, and adjusted the linkages so all the surfaces start out centered. I think the current control throws look fine.
The aircraft balances pretty close, but is slightly tail heavy … I’m not sure it’s enough to worry about with this design. I think everything is just about ready for a maiden flight.
March 29, 2007
Installed the battery in the nose compartment and packed foam all around it so it can’t move or dislodge (I hope!) It’s a two pound battery. I moved the speed controller installation to just inside the front of the nose hatch.
I found a long tube to route the receiver wire through and stuck that down the tail. I’m not sure I’m happy with that, but it’s a start.
I’m to the point now where I need to finalize the receiver installation, balance, and I should be ready to fly.
March 28, 2007
Mounted the speed controller on the lower outside front of the firewall with double sided velcro tape. I found a 5/16″ washer laying around the lab for mounting the prop. Also, I ran the prop through a balancer and I think it is very close.
On the way home from work I stopped by the hobby shop and picked up a Y-harness for connecting the wing servos, a short servo extender for the throttle channel, and a packet of metal 4×40 x 1″ bolts for installing wing load struts.
March 26, 2007
Today I bent the load strut mounting tabs to the correct angles and glued the plugs into the aluminum tubes with the correct insertion distance. I “pinned” the struts for added structural security, i.e. drilled a hole through everything crossways and epoxied a wire pin in to make sure everything is solid.
I then drilled out the mounting holes and installed the blind nuts in the wings and fuselage.
Here are some various angles of everything assembled as far as I can right now:
March 23, 2007
Load struts: assembled plugs and straps that I will fit into the ends of the aluminum tubing. Sanded the wood plugs down to the inner shape of the tube for a nice snug fit … well, one is a little loose, but it will be ok.
“All” that is left is to glue the plugs into the tub ends, bend the tabs to be flush with the fuselage and wing, drill the mounting hole, feed the bolt through, and we are pretty much done.
The one small thing that I’m worried about is where I’m going to remove the wing covering in order to install the blind nut on the back side of the wood mounting block.
March 21, 2007
Today I fabricated and installed the aileron linkages. I also cut my wing load strut tubes to their proper size (aluminum tubing in a tear drop/airfoil shape.) I have brass strips to mount in each end which will bolt on to the fuselage and wing. I need to cut those and fit them into the ends of the aluminum tube.
March 19, 2007
Today I installed a light weight 1.75″ tail wheel with a collar. I also installed servo extension security clips between the aileron/elevator servos and their 24″ extension wires. This is a small added measure of security to make sure these never can pull, vibrate, or wiggle free.
This weekend I purchased short extension cables to facilitate plugging the wing servos into the receiver (so I don’t need to plug and unplug cables directly into the receiver every time I go to fly.)
Finally, I fabricated and installed a piece to re-enforce the wing leading edge mount.
Detail of tail wheel and rudder linkages …
Detail of elevator linkage …
Two shots of how the overall project is shaping up …
March 16, 2007
Progress made today:
Installed steerable tail wheel. I forgot a small step before I glued on the vertical stab. This forced me to go to the hobby shop to buy a slightly different tail wheel mount. The 2″ tail wheel is slightly too big, so I will probably need to get a 1.5″ wheel and a 3/32″ wheel collar.
Installed an elevator joiner wire. I bought something pre-bent from SIG and removed the nylon control horn. I cut a groove into both elevator halves and epoxied it in. I also notched the rudder in one spot for clearance. Note: this is another one that would have been good to do before gluing on the elevators.
Installed the elevator and rudder servos with their extension wires.
Installed the elevator and rudder control horns and linkages.
This is the elevator joiner I used …
IMG_4319 Low res cell phone shots …
March 15, 2007
Epoxied the tail surfaces onto the fuselage. Installed the main gear.
March 9, 2007
Pictures with the tail surfaces dry fitted …
After these pictures were taken, I ripped off most of the remaining yellow on the fuselage and replaced it with ferrari red.
March 6, 2007
Detail of tail servo mounting modification …
March 5, 2007
Detail of shipping damage (fixed) and re-covering plan …
While rummaging around my hard drive I stumbled on some early footage of our Senior Telemaster flying. This footage includes some of my earliest successful autonomous flight using the original MNAV sensor head (now discontinued.) There isn’t anything especially great about this footage, other than I love the way the Telemaster looks in the air, especially it’s “scale” take offs and landings. These videos date back to sometime in mid-summer 2007.
The following movie includes some take offs, landings, and some early autonomous flight. One thing that is purposely highlighted in this video is an MNAV firmware bug that would cause the servos to go hard over full stop and send the UAV spiraling out of the sky. Fortunately we could quickly flip back into manual mode and manually pilot the aircraft to safety. Eventually I personally tracked down the firmware bug and fixed it. (Now we no longer use the MNAV in our UAV work.)
Here is a second movie showing a segment of successful autonomous flight. The Telemaster is flying a bowtie — or figure 8 — pattern. This is interesting to me because it offers a visual reference for the “quality” of our early MNAV based autopilot system that we can compare our current system against.