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March 25, 2008
Product SEN-09570 |
about 3 months ago
Yes, it should work fine. Since you will be pointing the sensor upwards towards the sky you will want to protect it somehow from rain/dirt/etc.
You could use a germanium window, but that is a bit costly. A window made of thin plastic wrap will keep moisture and dirt from falling on the sensor while being essentially transparent to the infrared. It will not be as durable as the germanium window however.
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about 3 months ago
When you relocate the feedback pot, it is possible that the two end connections to the pot will need to be swapped. The reason for this is that depending on which side of the gear train you attach the pot from as well as the number of gears in the gear train may be different and could cause the final arrangement to differ in rotational sense than that in the original servo.
If the rotational sense is different than the original, the servo motor would turn, which would cause the final shaft to turn as well as the pot, but in a direction that will set the pot to a voltage that is further not closer to the desired voltage. It will keep on turning in this direction until it hits a mechanical stop. If you hook it up this way and the pot has internal mechanical stops, the likely result will be a damaged pot unless you remove power before it hits the mechanical stop on the pot.
Test the configuration by temporarily removing the gear which drives the pot. Then manually turning the pot in the direction the gear would be driven when the servo is commanded to change to a new position. This will determine if you need to swap the leads on the pot or not.
If the motor stops before you hit the end limit on the pot, the sense is correct. If not, and it stops if you turn the pot in the opposite direction than the output gear would have turned the pot, you need to reverse the two outside leads on the pot.
Hope this is not too confusing.
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about 5 months ago
You short changed the processor speed on the Beaglebone Black a bit, it is 1 GHz, not 800 MHz. The product page has it correct.
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about 5 months ago
The banding seen is caused by the fluorescent light illumination interacting with the sampling of the ccd sensor on the pi. The florescent light pulses on and off 120 times a second, which when sampled by a digital signal processing system can cause aliasing, which is seen as the dark bands seen in the movie.
To avoid the banding, consider using incandescent illumination during the photos since they pulse significantly less than fluorescent lights. Incandescent illumination will provide more natural looking photos as well.
To explore the effect of aliasing with digital video cameras, one could use a LED array driven by a frequency generator noting the various effects as you change the frequency the LEDs are pulsed.
Next summer, you might consider setting up a time lapse sequence of a field of sunflowers as they track the position of the Sun during the day. This is Nature’s version of people watching a tennis match.
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about 6 months ago
Is this a type of “Method 1” hacking?
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about 6 months ago
The Sparrows could grasp the coconuts by the husk.
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about 9 months ago
The crystal oscillator in the microcontroller arduino or otherwise has more than enough stability to serve as the time reference for determining rate of climb/decent, IAS (Indicated Air Speed) is not a timed parameter.
If you think about it most of our digital watches (for those of us that still wear them) are not equipped with GPS, and keep quite accurate time.
Personally, I’d look at using this design as a start:
It has a input for direct connection of a GPS sensor, has logging capability and software to display the data once it is collected. Modification of the software to give output indication for rate of climb/decent should not be too difficult. This board has a full IMU, 3 axis mag, 3 axis rate gyro, 3 axis linear accel, plus a baro sensor. Use a block of dense foam taped over the baro sensor to prevent local air flow turbulence from generating more noise than necessary. The circuit runs off 5V, is small and very light weight.
Alternatively, if a really sensitive varo is desired, then an air chamber with a “calibrated” leak can be used with a differential pressure sensor to get a higher signal to noise ratio from the pressure sensor, as the pressure in the air chamber will lag that which is sensed in the port exposed to the aircraft’s current atmospheric pressure. The calibration of the system would entail setting up a known stable decent rate holding it until the output of the differential pressure sensor stabilized, and noting the value of pressure difference that was sensed. A correction coefficient would then translate that pressure value to a feet per minute decent rate.
As a fellow pilot, here is my two cents worth.
The GPS constellation was not designed for high precision altitude determination. WAAS improved this a bit, but the results you will be able to attain will not get you to where you want to be in my opinion if you limit yourself to GPS data only.
The GPS satellites are in low earth orbits which means they move overhead and the number of satellites in view varies over time. This leads to times where the geometry of the solution for determining your altitude is particularly poor. Some of the constellation may be blocked by a mountain range you are close to as well. The result of this is that you cannot depend on GPS for altitude unless you factor this in, as IFR GPS certified GPS units do. They require several more GPS signals to be recieved to allow for multiple fixes to be calculated in a way that all agree to a certain accuracy before allowing the approach to be flown. Research RAIM for more info on this.
As a pilot, part of you wants to know your ground speed, as this tells you how long you will have to fly your given heading to get to your destination, but a bigger part of you wants to know your airspeed since this is what is making your plane stay airborne. I.E. if you were to want to fly a given airspeed you would need to know the winds aloft, your heading and apply that to the GPS derived ground speed. As the winds aloft vary with altitude and are poorly forecast this can be difficult.
Density altitude is dependent on the temperature, relative humidity, and local non-standard atmospheric pressure. Temperature and pressure being the most dominate factors. You don’t need the density altitude to seek thermals, however. What you are interested in here is am I going up or going down, which a standard baro sensor will tell you.
Density altitude is most important when determining the length of runway that will be used to take off or land. It is also useful in determining the distance to climb to altitude, and the actual airspeed that you will be flying at as opposed to what is indicated on the aircraft instruments.
So if I read you correctly, you want to add instrumentation to a certificated glider you do not own. You can do this as long as what you put into it is totally portable, I.E. you do not connect to the aircraft electrical system, or to its pitot/static system. Use suction cups to affix it to the window, or velco straps to affix it to a surface so it does not move, or to your leg like a kneeboard. Just be sure it does not affect the control stick movement, or can come loose to hit you or get stuck in the way of a control if you encounter negative g’s.
To get what you really want in my opinion you have two options.
Keep in mind that any baro sensor you place in the cockpit will have “installation” errors associated with it which will cause it to be sensitive to such things as opening or closing the cockpit vents. For vario purposes, as long as you leave the vents in the same position, it should not pose a problem. But if you open or close the vents, expect several hundred feet of difference in indicated altitude to be indicated.
What I would suggest is use a baro sensor to give you the change of altitude info you are really interested in as a glider pilot. This could even be given as a tone which varies in pitch as you find rising or descending air currents allowing you to keep your eyes outside the cockpit in the search of thermals.
Hope this helps.
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about 11 months ago
I know its early, way early, but please let us know when next year’s event is planned along with any rule changes planned as early as possible.
I would really like to attend next year’s event with a vehicle to compete!
Thanks for holding this great event!
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The linear accelerometer does not output a signal that tells you how fast you are traveling in three directions, it would be great if it did. I am sure you know this, and since you covered so much in the video I understand the oversimplification. People who are new to accelerometers might not know this, however. Three axis linear accelerometers tell you how much you are accelerating in three axes. If you were in a spaceship in microgravity with your rocket motor off, you would expect a zero signal on each axis. If the rocket thrust is aligned with the x axis, turning the rocket on will make the x axis signal change to some value which is proportional to the thrust of the rocket. As long as the rocket puts out a constant thrust, this new value will be maintained, but your speed (velocity) is not maintained, it is ever increasing. If you now shut off the rocket motor, the x axis signal will return to zero, but your speed (velocity) will be equal to the speed when you shut the rocket motor off. On earth, you also must account for the direction and magnitude of the force of gravity, since at rest we are experiencing 1g of acceleration due to the force of gravity. So, to determine your vehicle velocity, you have to “add up” or integrate the instantaneous accelerations along all three axes and also keep track of any rotations of these axes due to the vehicle turning. This is where the fun starts. There are also bias errors, noise, and gain errors which can change over temperature. The point is that determining vehicle velocity in three axes is a challenge, which can be done, but not with only a three axis linear accelerometer for most situations.
No public wish lists :(