A collection of note-to-self's
The graphs of the ESC logging data I made earlier aren’t as pretty as HTML5 allows… So I retried it using HighCharts and a bit of JavaScript. The result is a standalone LogViewer page which interprets and graphs the log data entirely client-side. The page itself is fairly boring until you feed in a log file.
Clearly I’m not a layout specialist, but the functionality is there.
Place: Home
Batteries flown: 0.2
Time flown: 0h07 (cumulative model timer: 4h40)
Flight battery recharged with: (2) <not recharged>
Tx battery recharged with: <not recharged>
Comments:
Got my miniTitan repaired; at around €20 it was fairly cheap. But the governor-config still needed to be done. So I gave the collective a punch while in a hoover and noticed a drop in RPM, as it was last time. I changed the settings to have a governor gain at “Medium (25)” instead of “Low (15)”.
Place: Home
Batteries flown: 0.2
Time flown: 0h03 (cumulative model timer: 4h33)
Flight battery recharged with: (2) 2398 mAh (after full discharge)
Tx battery recharged with: <not recharged>
Comments:
My miniTitan was repaired and had a new ESC. Time for the first test flight. After a minute of hoovering, I shortly pushed full collective to check the governor. The headspeed dropped, not surprisingly since the governor is set to it’s lowest setting. So I pushed full collective again, to see if the governor is able to compensate.
Again the rotor headspeed dropped. The governor did compensate, but only the motor rpm increased, not the rotor’s… And then the ground intervened. I squeezed the remaining rpm’s out of the rotor to soften the crash, but it did hit fairly hard.
As mentioned, my new ESC also has data-logging capabilities. The provided software actually has a fairly descend viewer, but it lacks some features.
A friend of mine has the exact same behaviour on his miniTitan. Although my crash may have caused some damage, his heli started this behaviour after a regular flight. I guess this is an additional indication against the ESC. So I bought a new ESC.
Some people seem to be obsessed by long keys for cryptographic purposes. While it does increase the strength of the key, it also decreases the performance. Beyond a certain point, adding extra bits just isn’t worth it. Bruce Schneier did the calculations in his book Applied Cryptography, I added the conversion to SI units: (I’m quoting without permission, under the “review/criticism” and “research/study” exceptions. If the copyright owner does not agree, please contact me.)
One of the consequences of the second law of thermodynamics is that a certain amount of energy is necessary to represent information. To record a single bit by changing the state of a system requires an amount of energy no less than kT, where T is the absolute temperature of the system and k is the Boltzman constant. (Stick with me; the physics lesson is almost over.)
Given that k = 1.38×10-16 erg/°Kelvin [1.38 × 10−23 J/K], and that the ambient temperature of the universe is 3.2°Kelvin, an ideal computer running at 3.2°K would consume 4.4×10-16 ergs [4.41 × 10−23 J] every time it set or cleared a bit. To run a computer any colder than the cosmic background radiation would require extra energy to run a heat pump.
Now, the annual energy output of our sun is about 1.21×1041 ergs [1.21 × 1034 J]. This is enough to power about 2.7×1056 single bit changes on our ideal computer; enough state changes to put a 187-bit counter through all its values. If we built a Dyson sphere around the sun and captured all its energy for 32 years, without any loss, we could power a computer to count up to 2192. Of course, it wouldn’t have the energy left over to perform any useful calculations with this counter.
But that’s just one star, and a measly one at that. A typical supernova releases something like 1051 ergs [1044 J]. (About a hundred times as much energy would be released in the form of neutrinos, but let them go for now.) If all of this energy could be channeled into a single orgy of computation, a 219-bit counter could be cycled through all of its states.
These numbers have nothing to do with the technology of the devices; they are the maximums that thermodynamics will allow. And they strongly imply that brute-force attacks against 256-bit keys will be infeasible until computers are built from something other than matter and occupy something other than space.
The calculations are slightly off; however, it does give a very good indication how far bruteforcing can go, ever.
When you cycle through all possibilities by incrementing the counter, the number of bit changes is higher. To count up to N, you need N flips of bit 0 (the least significant bit); N/2 flips of bit 1; N/4 flips of bit 2; … Some clever mathematicians proved that 1+1/2+1/4+1/8+… = 2, so you need 2N bitflips in total. A 187bit counter hence requires 2 * (2^187-1) bitflips, roughly 3.9E56.
By iterating in a smart way, you can reduce the number of flips to half of that. Calculating this smart way may however require more energy than you’re saving…
I never had a course in aerodynamics. If I had, I might have programmed a power-calculator myself, but I doubt that it would have been as complete and easy-to-use as this calculator.
Sometimes, you want to manually alter the caching behaviour of linux. Making sure all data is committed to disk can be done by the sync command. If you want to flush the caches for reads as well, you need to go deeper into the system.
echo 3 > /proc/sys/vm/drop_caches
Writing 1 only clears the pagecache; 2 clears the dentries and inodes; 3 clears all.
I recently bought the Phoenix R/C simulator. It comes with its own USB-cable to plug into your remote controller’s trainer cable. A friend of mine has a Spektrum remote, and the stereo 3.5mm jack plugs right is.
I have a Futaba FF9 remote, so they wanted me to buy the “adapter cable to FF9″ for €16. Since I already had the pinout of the FF9-connector figured out, I figured I could make this cable myself.
Place: Roeselare
Tanks flown: 0.1
Time flown: 0h15 (cumulative model timer: 32h22)
Rx battery recharged with: 885 mAh
Tx battery recharged with: 273 mAh
Glow heater battery recharged with: 825 mAh
Starter battery recharged with: 132 mAh
Comments:
Looking for, buying and rennovating a house appears to have a remarkable ability to consume every bit of spare time I had. I finally found some time to wake my bird from hibernation.
I topped the batteries to compensate their self-discharge during the last 10 months. I wasn’t expecting my nitro-engine to start smoothly, but it worked perfectly.
I only hoovered a bit around to regain my muscle memory.
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