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About DerekF

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  • Birthday 08/12/1980

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  • Location
    San Diego, CA
  • Interests
    UFO, Dinghies, foils, wing sails, technology

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  1. Love seeing the younger generation getting flying--very inspiring. I'm going to take my 7 year old out for the first time this summer when our water gets warm here in San Diego. Good for you guys!
  2. Hey Dave, in non-foiling boats there is typically a speed limit dictated by hull drag going non-linear at a certain speed beyond which it beings to take exponentially more power to see even small increases in speed. This is really easy to see in my (non-foiling) kayak where I can paddle to 4.0 knots with a heart rate of 120 BPM but raising my heart rate (effort) to 160 BPM only raises boat speed to ~4.2 knots. Is this the case with foiling boats or are we working with different physics? If there is not really a limit, any plans for a Fulcrum foiling kayak?
  3. My GPS has recorded 18 MPH (~15.5 knots) in 15 knots of wind. Perhaps someone has done better, but that's what my garmin tells me...
  4. Good news! I just received PCBs back from the fab house and all parts fit. This simply means I know how to be very detail-oriented with a pair of calipers and my CAD software. I mentioned in a previous post that mounting all of the modules to a single PCB was easier and more electrically sound than using a "base plate and flying wire" approach. The PCBs are back and everything fits mechanically. As you can see from the photo, I have added 0805 inline footprints on every trace. The idea here is that if the trace is correct, I install a zero-ohm resistor and carry on. If a trace ends up being incorrectly connected (because of a design or fab error) there is no need to break out the razor blade and cut PCB traces, just wire up some jumpers to the 0805 pads and connect correctly. Hopefully everything goes smoothly.... Electrical checkouts have gone well and no issues with power or ground planes were found. I have started soldering parts to the PCB and am about half way done with the full assembly. The next step is to run software with all modules integrated into the PCB and running on battery power (as opposed to power supply or USB power). The integrated PCB will look like a stack up of boards, so I plan on referring to it as "the stack." I'm looking forward to seeing all these modules work and play together! First flight could happen this spring!
  5. And don't drop your mainsheet either. That's always been an immediate capsize to windward! Everytime I see the sheet slither through my hand and I lose it, it seems like slow motion trying to grab it back unsuccessfully while the sail lands on top of me!
  6. Funny you should mention wanting to adjust ride hight mid-sail without jumping in the water. I am still plugging away at a digital flight control system for the UFO--no wand or paddle and a wireless remote to adjust PID parameters, and an LCD for feedback. I have modules, servo, etc. talking to one another and am about to send a PCB out to the fab house to get built. Integration and debugging are next up, and I'm sure will be time consuming. I wasn't planning on making ride height dynamic but it wouldn't be hard to build into the firmware and make controllable from the wireless "key fob" remote. I'm hoping to get to first flight this spring. I'll keep you guys posted....
  7. A few more updates on the project with the selection of a servo and battery. Servo Sizing: I decided to actually measured the torque required to actuate the flap. I did my measurement out of the water and therefore I only measured the resistance of the linkage and the resistance of the rubber "spring" that mates the foil flap to the mainfoil. I did the measurement using a pull scale attached to the wand 6 inches from the pivot point of the wand. I found the required torque to be ~32 oz. at 6 inches -- or 192 in-oz's. Converting this to kg-cm which is how servos are spec'd, we are looking at 13.8 kg-cm for the linkage and rubber "spring" resistance. Note: I did this experiment without the paracord attached as it will not be necessary once the servo and linkage is installed. As discussed earlier, determining the amount of force imparted by water rushing past the flap is a complex fluid dynamics problem however there are several great calculators for RC aircraft servos online. I used the one at the link below: I had to make a few assumptions regarding servo deflection as I have not fully designed the linkage but all results were within a pretty tight range. If we were foiling through air we would need ~0.2 oz-in of torque to operate our flap at 18 knots airspeed. Given that water is ~825 times as dense as air, I will assume we need to multiply by 825 to get 165 oz-in of torque in addition to the 192 oz-in to overcome the rubber spring force. This gives us ~356 oz-in required or 25.6 kg-cm. Therefore, our total theoretical torque required to actuate the flap will be 25.6 kg-cm. The other feature we will need is self-locking. Looking at my GPS logs, even on high wind days, I am spending about a third of my time not on the foils. On lighter days, it can be over fifty percent. During this time, the main foil flap is at max lift when the boat is moving forward and the wand is being pushed back. This does add more drag but allows the boat to enter foil-assisted planing modes. But having to provide constant servo torque even when not foiling will likely kill the battery pretty quickly and seems wasteful. To be on the safe side, I have selected a 32 kg-cm part that has metal gears and is self locking. Some waterproofing will need to be done but there are countless tutorials on how to do this online. This part should have plenty of torque to actuate the foil flap and the self locking feature will save battery juice. Power Budget: With all parts now chosen, it's time to choose a battery that will meet our needs. As the battery is likely to be the physically largest component of the system, the battery size will drive the enclosure sizing as well. My power budget is below and the result looks ugly! Amps Volts Power (W) Arduino Mega 0.5 5 2.5 IMU 0.1 5 0.5 Sonar 0.1 5 0.5 GPS (optional) 0.5 5 2.5 Servo (Stall Current) 5 7.4 37 Total 43 Runtime 4 hours Wh required 172 2S LiPo Operating V 7.4 Ah required 23.24324324 The largest 2S RC battery I could find was 8Ah max. There are bigger batteries out there but options are few. The 800 pound gorilla in the room is the servo. While we might be able to get away with a smaller servo, having the torque headroom makes me feel much better especially on a prototype. Not to mention that worm gear, locking servos aren't too common so choices are limited. A linear actuator might also be an option but they typically respond much slower than rotary servos and are heavy and expensive--I will do some research in this area. The other design difficulty if we try to mimic the current mechanical system, is that even while not trying to foil, we will constantly be using servo torque / battery power just to fight the flap's rubber "spring" to max out flap deflection on the main foil. Soooo.....this leads me back to insisting on a self-locking servo so that we aren't using battery charge to max out flap deflection even when in irons. If a suitable self-locking servo was not able to be identified another options is to use a GPS to determine boat speed over ground and assume that it is equal to boatspeed through the water. Yes, I know that doesn't take ocean current into account, but I think it's a small price to pay right now to extend battery life. Ocean current could be taken into account at a later date with tide charts built into the firmware as well as heading data from the GPS or IMU. We could also implement a button on the tiller extension that allowed the sailor to activate the foiling system when ready to fly. My worry with a button is placement and wiring / cable harness. Any thoughts here from the peanut gallery? If we limit current draw to the servo until we are actually trying to foil, an 8Ah standard battery will give us about 90 minutes of foiling time under (close to) worst case power draw. I would still like to see more battery life, but 90 minutes of time actually on the foils is quite a bit. Hopefully, real world testing will tell us that we don't use as much power and can get closer to 2 hours of foiling time--we'll see. Sampling and Filtering of Ultrasonic Sensor: While out foiling a few days back it occured to me that simply using the sonar to look at current elevation is not really what we want. We want to know what the "average" elevation is over a ~1m stretch of water. This reduces the effect of wavelets or even small boat wake (big boat wake is a different story). The other thing we need to be cautious of is false readings. When looking at the sonar sensor output, I occasionally see 0.0cm readings. Clearly, these erroneous readings need to be filtered. As a result, I have decided to take 5 samples over a 1m distance (assuming 12 knots of boatspeed). My code then takes the median value. This mid-level vote (MLV) system comes close to the average of the readings and automatically eliminates outliers. MLV systems are often used in redundant aircraft altimeters for this very reason. The code is pretty flexible and if sample size or sample frequency needs to be updated it is not hard. Data Logging: Last thought of the post: we will probably need some data logging for the prototype phase. Specifically, it will be useful to understand the delay between commanding a deflection on the foil flap and seeing the boat actually pitch up. Understanding control loop delay will really help in tuning PID loops and eventually allow testing of algorithms to deal with more complex and challenging wave terrain. I have put zero thought energy into how to implement the data logger, but it needs to be on the tech roadmap. Thoughts?
  8. Hey guys, I was just out foiling recently and, while rigging, I noticed the screws that attach the cunningham and mainsheet blocks were starting to backout and things were loose. It was pretty straightforward to apply some Lock-Tite / Super Glue / G-Flex and retighten the screws with a phillips head. But a cunningham failure or mainsheet failure on the water could be a pretty big bummer. Just something to add to your Preflight Checklist...
  9. I had a similar (but less scary) situation when my rudder got stuck in the mainsheet bridle. The rudder was stuck sending the boat straight and I was heading quickly for a large moored catamaran. My solution was much the same as yours, Martin. I managed to stick one leg off the side of the boat to create asymmetric drag and get the boat to come to irons. It was then easy to sort out the tangle. But that experience and the fact I sail in a big bay that is typically much more of a keelboat / big boat venue led me to the question "What contingency plan do I have for various serious failures out on the water?" The 'what if I lose the rudder' scenario is one of the more troubling ones. Way to think quickly on you feet and thank you for sharing. I hope I never need to use the info, but if so, at least I know what worked for you! BTW, what caused the rudder to come free of the boat? Was there any inspection / preventative maintenance the rest of us should consider to avoid your fate?
  10. @MMbob, welcome to the club. The boat is a total blast and it has been an amazing journey for me moving from a floating Laser to a flying UFO. @burritoughs put together a roster / list of UFO owners by region. You can message him to opt in to be on the roster. I hope you can connect with some other UFO pilots!
  11. Time for another blog installment of the Digital Flight Control System for my UFO. I have been busy at work on the project and making good progress toward a first flight in early 2020! Also attached is an updated block diagram with details on various subjects below: Data Logging: In my last blog post I mentioned that we needed some sort of data logging to really get into the meat of how well our control and filter algorithms are working. Post processing data after getting off the water will also allow us to see if there is data being generated by sensors that could improve control. For example, I received a suggestion that I take vertical acceleration from the IMU into consideration and use it to derive vertical position. This vertical position would then be fed into a Kalman filter along with the ultrasonic range sensor's vertical position measurements to determine a better estimate for boat altitude. Logging and crunching data after getting off the water would allow us to take these types of ideas into consideration easily. Datalogging would also greatly improve troubleshooting of all types. To this end, I have added an 8GB micro SD card to the design as well as written some simple code to log data to a CSV file for post processing. My current code logs speed (GPS), acceleration (XYZ axes), attitude (XYZ planes), and servo control input. Any other thoughts on datalogger inputs? PID Loop Tuning: It has also occurred to me that tuning PID loops while on the water will not be possible with a laptop. As such, I have integrated a wireless, 4-button, key fob (in a waterproof bag), a wireless receiver and an LCD screen. This will allow for wireless adjustment of PID constants and LCD feedback to the user. This setup should allow for easy adjustment while out on the water between foiling runs. The enclosure chosen also has a clear plastic top to make reading the LCD screen possible. Mounting, Wiring and Power Distribution: The Arduino board I am using only has so many pin outputs for 3.3V and 5V. While my sensors easily fall within the max current output of the board, I am short on pin space. I also have a 3D model of the enclosure that requires at least one mounting plate made from plastic / metal / fiberglass / FR-4. It occurred to me that rather than mess with mounting plates and a wiring rat's nest, I should just burn a simple PCB to handle mounting and power distribution. This PCB may also contain some custom circuitry--we'll see. The PCB will minimize the wiring mess and be a mounting plate in one shot. Many PCB shops will burn custom sized, one-off boards for ~$150. It's probably a small price to pay for much better reliability and maintainability (not to mention the time saved on creating a mounting plate(s) and hand wiring all of the modules). Enclosure: Now that I have selected a battery (2S LiFePo, 8000mAh) and all other components, I created a 3D CAD model of how the boards will lay into an enclosure. It appears that a 4x6 inch case will fit everything we need to hold the system (see photo of selected case). This enclosure will mount onto a mounting plate (probably custom fiberglass or carbon fiber) that will bolt on to click bond studs bonded to the spirit. The servo and ultra sonic sensors (both waterproof) will live outside of the case and be mounted to features on the mounting plate. This section of the design is the most open at the moment and will certainly require more CAD work. That's all for now. Comments are welcome!
  12. Hey team, I finally figured out that SA will only take fairly small photos. If you are running into the -200 error when uploading photos, you'll need to downscale the images. On that note, I have a few images from a recent foiling session that my wife took with her nice DSLR camera with good zoom. There is also a photo of the racing in Cedar Point, CT at the beginning of October. Cheers...
  13. Speaking of photographing outings, does anyone have experience using a Click Bond stud on their sprit to mount camera / equipment? I have used zip ties but am looking for something more permanent and robust. My buddy who is a carbon / composite expert said it should work fine as long as I sand the bonding area before applying the Click Bond stud. Let me know if folks have any experience.
  14. With much of the code and working and sensors talking to my Arduino board, it was time for some real world testing this past weekend. I always try to find as much information online regarding sensor characteristics or what has worked for others, but at some point there is no substitute for empirical data. At the heart of the feedback loop is our ability to measure altitude. We will be measuring altitude with a waterproof sonar sensor similar to those used in automotive bumpers. There is lots of data online about sensing all sorts of items including still / non-turbulent water. There is very little data online however, about the sensor's ability to accurately measure range to turbulent water. Not wanting to take my laptop out on the UFO for a live test, I decided to use my hot tub (jets going full throttle) to simulate very turbulent, moving water like we might see on a rough day on a UFO. The results were good news / bad news. The good news was that the sensor seemed totally unbothered by the turbulent water (vs. flat water). The bad news is that the sensor's ability to give accurate readings drops off a cliff as the sensor becomes off perpendicular from the turbulent water. Some of this can be solved with filtering and throwing out values that are clearly nonsensical on the high or low side. But reality is that we will need multiple sensors mounted at different roll angles. We will then choose which one to read based on the heel angle of the boat. Luckily, we have a good IMU on board with accel's and gyro's that should help us pick. I chose three sensors based on a +/-20 degree field of regard for the sensors and a max roll angle of +/-30 degrees for the UFO based on boat dimensions and a 1m ride height. Additionally, if the altitude sensor function in the code does not return a sensical value, I will have the PID loop operate under the assumption that elevation is unchanged or perhaps just max out flap camber. Typically, when heeled to windward, you want all the lift you can get and if you are heeled far to leeward you need to bring the boat back down off the foils and start over anyway. Last thought, if the multi-sonar sensor approach seems too impractical a radar or laser/optical altimeter could also be used. These sensors are more expensive but tend to have much wider fields of regard. There are a few available with good documentation for Arduino and that operate at K or Ka band. X-band is impractical as GPS carrier signals are in the X-band and we may run into RF co-existence / self-jamming issues (should a GPS ultimately be necessary). As a bonus we could use a doppler radar / lidar to also get boat speed through water. Thanks for reading! If
  15. Hey Martin, any recommended part numbers or line diameters? Seeing your outhaul failure makes me think I should have some spare line onboard...