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Design => Engineering board => Topic started by: Wolfgang Nieuwkamp on September 19, 2015, 09:04:46 AM
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Last winter I built a variable pitch system using a motor that was designed for quadcopters. No shaft, so a push rod of 2 mm could be used, together with a standard servo.
The rotation speed during flight is given by the governor mode of the controller. The pitch is adjusted using acceleration sensors in the timer, trying to keep the line tension the same during all flight attitudes.
The timer has to produce two pulses, one for the controller and one for the servo. Luckily I could modify my timer to do this.
Some picture are attached. Gimmick: After the motor stops, the blades go in vane position (almost) for 10 seconds….
Any questions or comments?
Regards,
Wolfgang
(http://www.mijnalbum.nl/Foto-SJE8WGML-D.jpg)
(http://www.mijnalbum.nl/Foto-36ZHFXPM-D.jpg)
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Last winter I built a variable pitch system using a motor that was designed for quadcopters. No shaft, so a push rod of 2 mm could be used, together with a standard servo.
The rotation speed during flight is given by the governor mode of the controller. The pitch is adjusted using acceleration sensors in the timer, trying to keep the line tension the same during all flight attitudes.
The timer has to produce two pulses, one for the controller and one for the servo. Luckily I could modify my timer to do this.
Some picture are attached. Gimmick: After the motor stops, the blades go in vane position (almost) for 10 seconds….
Any questions or comments?
Regards,
Wolfgang
Wolfgang,
First, nice work and effort! H^^
Even though I have absolutely no idea what that is all about.
Comments or questions? You asked so here goes.
Variable pitch system.
Advantages instead of just having throttle? Would throttle give you what you are looking for?
What are you looking for or what is the gain?
Charles
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Wolfgang:
Cool. I'm not sure if the Igor system does more magic than just monitoring the accelerometer, but if it does you may want to figure out how to hack things to use it's signal (I could easily do this with a TUT).
In theory you should get faster response, but you probably want to juice up the frame rate and use a digital servo (the TUT sort of naturally uses a 120Hz frame rate, but that drives most analog servos wild -- digital servos and, to my knowledge, ESCs work fine with it).
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Charles,
The aim is to have fast variation of the thrust, in sharp corners. Throttle adjustments are slow, because of the inertia of the propeller.
Pitch variation is quick, because servos are fast, and the inertia is helpful to keep the revs constant (the constant sound pleases the judges…).
Tim,
How Igor uses the acceleration sensor signal I do not know. I use it simply to keep the line pull constant.
The response is much faster. As you mentioned, the frame rate should be as high as possible, I use 125 Hz. Futaba analog servos work fine at this rate. If you are interested, I could post a Castle data log.
All the best,
Wolfgang
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Wolfgang: yes, please post the log, I'm interested in seeing how the motor is loaded.
Thanks for the interesting tidbit about Futaba servos and frame rate. The old traditional servo amplifier has a thing in it called a "pulse stretcher"; if you set it up for a fast frame rate then it would be sluggish with a slow one, if you set it up for a slow frame rate then it would go nuts with a fast one (basically the incoming pulses would overrun the pulses from the stretcher, and Bad Things would ensue). I don't know if Futaba is just setting their servos up for a fast frame rate, or if they have a more intelligent sort of analog servo amplifier.
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Tim,
this data log is from the last two flights. Propeller: 12,5 x 6 Aeronaut. 2400 mAh.
(http://www.mijnalbum.nl/Foto-LSRWO63P-D.jpg)