Hi everybody!Can anybody suggest that whether we can rely on the altitude from GPS alone for altitude hold function. The GPS module l am using is ETek EB-85A. My airframe is a motorized glider.
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so we're lik in the same boat...im also using an EM406 gps for altitiude hold..though i was gonna use a good PID controller reather than only P cuz i wouldnt want my plane to pitch up n dwn all the time..i need it to be stable cuz i also have to yaw it for taking turns and manoeuvres, so preferably 0 pitch and 0 roll...so wht kind of autopilot are u planning to use? and wht stabilisers are u gonna employ?(sensors).....ol the best pal...
Hello everybody! Chris,Alec thanks for your suggestions. I think working within a range of 10-15m will be ok for me. I will be flying at more than 500ft in autonomous mode, so being 10-15m up or down is in safe limits. Although the control algorithm being a proportional one(control action proportional to error), I will be setting the maximum control action to such a limit so that the aircraft does not stalls or dives badly. So a sudden large error won't cause any adverse effects on the aircraft.
GPS altitude is only accurate +-10m... on a good day. If that's all you want then go for it. But if you want precision altitude, you're looking at high quality pressure sensors. I'm playing around with the cheep freescale MEMS sensors, and get roughly +-5m, but then again I'm in one of those countries that don't have reliable GPS, and yes they do exist.
Our experience is that a standard SIRFIII GPS is pretty noisy (random jumps of tens of meters), but if you keep a running average and throw out deltas of more than 10% or so, you can maintain altitude within a range of about 10-15m. Switching to a high-end GPS like the Ublox5 will give you altitude data nearly as good a barometric sensor, however.
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