We are now recording the foil actuator positions during tests. Looking at tow and kiting test data from last Thursday, we’ve plotted the relationship between the T-foil setting and the boat speed. The T-foil is controlled by the helmsman and is used in conjunction with the J-foils to control the pitch and ride height of the kiteboat. A relatively simple relationship between the two (as we see here) suggests that we may be able to automate the boat’s pitch stabilization, which would free the crew to concentrate on other tasks.
We’ve been curious about the distribution of rear line loads, and have recently been collecting load data from both lines. The result is a bit of a surprise. As expected, the “top” rear line has a higher load, but the difference between the top and bottom lines is smaller than anticipated: typically only a few kgf, out of a total rear line load of up to 120 kgf.
The top attached histogram shows the distribution of the total rear line loads. The second histogram shows the difference between the right and left lines when on a starboard tack, and the third histogram shows the same for port tack. This data comprises the entire test on March 5 during which the […more]
We have dramatically improved our true wind estimates by using better sensors that we have on hand. To decide which sensors to use in the future, we have graphed the effect of each type of sensor error on the true wind estimate. Using these values, we can predict the level of true wind accuracy that we can expect from candidate sensors. One thing that these plots make obvious is that small errors in apparent wind speed (lower-right plot) lead to very large errors in estimated true wind angle. Thus, it makes sense to keep our current GPS compass (with approximately 1 degree error), but to choose a new wind sensor with a very high windspeed accuracy.
The group of four […more]
Kite Inflator Specification
[This document is a work in progress.]
The kite inflator is a device that monitors and sets the inflation pressure of the kite. It will also serve as a general purpose data logger and transmitter for sensors such as an altimeter, temperature sensor, and GPS.
Physical, Environmental, Performance
1. max size: ?
2. max weight: ?
3. kite attachment method: ?
4. splashproof, but not submersible
5. external power switch and on/off display
6. normal use constitutes the motor valve operating for 25% of the time
7. must run for 12 hours of normal use on a full charge
8. reliable radio range of 100m on the water
We tested the inflator on a kite in the shop on Friday. The overall performance of the pump, pressure release valve, and radio link exceed our requirements. The firmware crashed after several hours of operation, however, so we will need to fix this bug and ensure that any future errors do not result in a deflated or exploded kite. The test showed that the inflation rate is 1.4 psi/hour and deflation rate is 5.6 psi/hour with a 40 sqm kite in the pressure range of interest. This is fast enough to handle small leaks, temperature-related pressure changes, and minor inflation adjustments for performance optimization.
Jamie has made several changes to the KAICam Android application, in support of the cruise with MBARI this week. To make the screen space on larger tablets more usable, the layout is now dynamically adjusted to maximize the preview image size.
To help in situations in which the network topology changes frequently, the app now automatically find other instances of itself that inhabit the same network. This way, the remote viewing client can connect to a camera server without being specially configured with the camera’s IP address in advance.
Other improvements include better networking efficiency and stability, and the continuous logging of GPS and air pressure (for altitude) where available.
The two images are screenshots of the app running on […more]
A few weeks ago we did some testing of the kite inflation system with a new motor, electronics, and firmware. Everything has been looking good and we are looking forward to testing it on a boat or lifting kite soon.
In the attached plot, the green line indicates the target pressure, which is changed remotely using the web interface to cause the system to inflate and deflate the kite. The red line shows the measured air pressure. The measurement is somewhat noisier than the actual air pressure because the sensor is attached to the same tube as the in intake and outlet. The improved firmware filters this noise enough to keep the actual pressure within the kite quite stable.