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Narrow escape for Vulture 2 spaceplane's diminutive pilot

Posted by Lester Haines on June 6, 2014 at 3:15am

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Our Vulture 2 spaceplane's miniature pilot - the plucky Playmonaut - had a narrow escape earlier this week after one of the aircraft's servos went up in smoke during testing.

As you can see in the above photo, emergency teams rushed to the scene, while we were left to ponder what caused the meltdown. The remedy might require the old Zener clamping diode ploy, and if that's so, then we're pretty well done on finally firing up the fully-assembled vehicle.

Next on the agenda is getting the Pixhawk to talk to the onboard Raspberry Pi, after which its mission parameter programming time, which promises to be a stiff-brandy-heavy task.

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Comments

  • Antonie Kruger June 7, 2014 at 4:37am

    Pic toooo funny - a futaba sevo??.what a disgrace. I'm with Gary - will have to do some deep reflection on the fortunate ....errrr character and have a drink on his good fortune.

  • Søren Kuula June 6, 2014 at 12:14pm

    Hi,

    Forgive my ignorance but where is the back EMF coming from? And on the (nominal) 5V rail?

  • Quadzimodo June 6, 2014 at 7:01am
    I shudder to think what might have happened if he wasn't wearing his suit and self contained breathing apparatus when the cabin filled with smoke.
    Just goes to show you can't be too careful when it comes to safety.
  • Developer
    Bill Bonney June 6, 2014 at 7:00am
    @gary: i agree though i am unsure the effectiveness of shaving foam as a fire suppressant. BE WARNED! ;-)
  • Moderator
    Gary Mortimer June 6, 2014 at 6:32am

    I'm going to have to open a beer shortly and reflect on just how lucky he was. Looks like the rescue team was nearby that's the value of planning, well done. 

  • Developer
    Andrew Tridgell June 6, 2014 at 5:43am

    I'm glad to hear he survived! He's a brave fella.

    The zener may be worthwhile, but I doubt the back-EMF its designed to control would cause a servo to go up in smoke. Do you have a log from the SD card at the time it went up? That would contain POWR messages which would give the servo rail voltages, and may give a clue as to what happened.

    The aim of the zener is to ensure the Pixhawk FMU keeps the servo rail as a valid backup power source in case the 3DR brick supply dies. What happens is that some servos (particularly digital servos) tend to cause voltage spikes on the servo rail when moving rapidly. On my scope I've seen over 10V on a servo rail that is nominally 5V, for brief times. The zener is meant to clip those high voltages so the rail doesn't go above 5.8V, which is the crtical voltage at which the power management on the Pixhawk will no longer consider the servo rail to be a suitable backup supply for the FMU. If it went above 5.8V on the servo rail and the 3DR brick failed then you would reset the FMU.

    Cheers, Tridge

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