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phil alvirez's blog
Archive for May, 2012
Posted by phil alvirez | May 28, 2012 @ 07:30 AM | 5,642 Views
i have been doing ultra-micros for quite some time, and have enjoyed exchanging comments-and learning a lot-with all of you guys. i enjoy flying my um's by walking a few steps to my backyard, or to a park nearby, and so will keep doing it, but i can't find anything else to try. i have done motor/gearbox tests on all that i could find; i have designed conventional-all my Elf series in several sizes, including the slowest plane, the Snowflake. 3d-the Snowstang; canards-the Snow Fox, Snow Goose; bird-like-the Snow Owl; flying wings-Rondine, in 2 versions; and lately double deltas-the Diamante, and am having a ball flying them now and then.
but i can't bring any more contributions to the thread.
i am now doing 2 meter electric sailplanes, and again, learning a lot by designing, flying, testing, buying, and asking in the internet, and that is a new start for me. you can find me there anytime. http://www.rcgroups.com/scale-sailplanes-122/ http://www.rcgroups.com/electric-sailplanes-19/
so, thank all of you for your help and friendship. i will never forget the great times we spent talking about so many things.
Posted by phil alvirez | May 25, 2012 @ 10:54 AM | 5,582 Views
now that i have started several projects using hybrid components i have become more aware of the differences between wood and foam; their advantages and disadvantages; their limitations. i want to build some sailplanes with modern lines, hence using some fuselages already made of foam or glass, but with wing and stab of my own design, with open frame, made of balsa, and iron-on covering.

the main difference is that with foam/glass the stress is spread uniformly, whilst with wood it is concentrated on joints. there are modelers who, like me, have been building long before any other material than balsa was known, but i have been interested in the development of new ideas and materials. at the beginning there were some attempts to introduce molded plastic, but it was too heavy if was strong enough. now with the advent of eps, epp, epo (and who knows what is around the corner), things have changed. and with so many planes ready (or almost) to fly, some of wood and others from foam, it easy to see why foam wins: it is made to survive crashes way better than wood. and if you want to build something new, foam allows you to do it way faster-and requires less parts, in general less precision-and survive impacts much better. besides easier to repair. in recent times i have designed and tested so many planes that if made of balsa would take me 10 times longer.

so, there is a place for everything and every1: if you want to build that scale plane with all the details, and you no...Continue Reading
Posted by phil alvirez | May 01, 2012 @ 01:37 PM | 5,457 Views
again, i asked the master (Lucien Miller, from innov8tive designs) about the difference. he said:

Originally, servos were all analog. They used standard NPN and PNP transistors to drive the motors in the servos. When a movement was called for by the transmitter, the voltage to the servo motor would slowly ramp up and the motor would start turning. There was a certain amount of "dead-band" in this control system on small control inputs because the motor would need to get a couple volts accross it before it would start to move, and then it would move slowly without much torque. At the end of the movement, the voltage would ramp down as the servo approached the new position and would never quite get exactly to the final destination. Pilots simply learned to compensate for the short-comings in the servos and they really did not notice it.

Digital servos use FET transistors, just like speed controllers. Instead of ramping up the voltage to the motor the transistors provide full voltage in a pulse width modulated fashion, just like a speed controller does with a brushless motor. By operating this way, the motor can produce full torque right from the beginning for small control inputs, and can perfectly match the position of the stick for higher resolution and control centering. They also update the power to the servo at a much higher rate, typically 400Hz as opposed to 50Hz for analog servos. This makes the servos react quicker to control inputs and gives a more immediate feel to the control. Because of this faster update rate, the digital servos will often buzz or whine around neutral a bit.

All of this does not come without a downside though. The digital servos typically pull higher current than the comparable analog servo, so you do need to be careful that you use a large enough battery or BEC circuit to power them.

That is the basic difference between Analog and Digital servos. Hopefully that helps explain it a bit better for you.

Lucien