The server...controls one of the canards
I can 'ardly believe it went up in smoke.
Our plucky Playmonaut has decided to take a long weekend off after a servo meltdown during a ground avionics test of our Vulture 2 spaceplane prompted a sharpish exit from the vehicle. Here's the scene immediately after the scare, as emergency crews rushed in to cordon off the area, douse the offending kit with foam and gave …
After bricking it, the Playmonaut would be off for a few beers, and then to get his legover with some young lady with nice dimples, at the bar.*
A few technicolour yawns later. Then his hangover recovery would be some nice Danish bacon.
I think I'm out of Lego puns at this point.
* Why didn't you include a reconstruction of this bit - it could have been like 'The Right Stuff'? One of my favourite films / books.
Also the heat dissipation in thinner air is lower (that's how some vacuum gauges work), so it would have got hotter faster at high altitude.
The problem with a zener is that it'll dissipate heat too in a over voltage situation, and excess heat is not something you want in Vulture 2 at altitude. The Lithium cells can deliver a lot of current in to something if it fails (as your late and lamented servo appears to have discovered).
Are you logging the current consumption from the APM?
Ref the Zener - yup, that's the catch; they clamp the voltage, but the excess energy's got to go somewhere, and that's heat. You could end up with the Zener burning out, closely followed by the motor. Might want to consider some sort of switching regulator; not as cheap as the Zener, but not wildly expensive either - and it's mission-critical after all. Not sure what oomph you need, but a TI LM2569 for example would support 3A at 5v for around a tenner with all the bits 'n bobs. wouldn't need a lot of space either.
He's also immortal, and ready to jump back into the pod even before you've finished scraping his remains out of the smouldering crater left by the last pod. I don't feel that our Playmonaut is quite so psychotically happy about a hypersonic splashdown.
Maybe we should set the Playmonaut's BadS flag to true.
Was the servo hooked up to the control board and actively being "instructed"? Perhaps the PID algorithms need some tinkering and are overstimulating the servo with very small adjustments. (I'd suggest putting in an averaging period buffer on the output). This could quickly overheat the motor since it's constantly getting instructed to move one way, then the other. This can be heard as (possibly quite soft) buzzing or rattling coming from the servo.
Replace control horns without cycling the system and zeroing out any trim with nothing attached to the servo. Failure to do so virtually guarantees a mechanical binding situation with predictable results.
Smoking a servo motor from with a random voltage spike is really, really unlikely. Overloading a servo by getting a linkage in a mechanical bind is an everyday occurance. You should be able to tell what happened by looking inside the toasted servo.
Hubris of the engineering team and ground crew has killed many test pilots. There's no need for that here :)
Zener diodes by themselves are terrible shunt regulators so you'd be wasting lots of power with very little regulation. Zener diodes have more of a precision change in resistance than the perfect shunting that people imagine. One would probably incinerate in thin air. At low voltages, forward driven power LEDs will do much better at shunting. Three pin regulator ICs are even better.
What you might actually need is good old aluminum electrolytic capacitors. Their combination of very high capacity, low resistance, and high AC losses make them perfect for smoothing out a glitchy power rail. This not only protects you from high voltage surges, but also low voltage surges that can cause damaging reverse currents from on-board capacitors. Look for the higher priced compact capacitors to keep the weight down.
Quite. Although in this case it wouldn't really need to regulate, just spring in to action when the voltage on the servo rail would be spiking, so a nominal zener voltage anything from a few 100mV to maybe one volt over the nominal servo feed voltage. But a TVS (Transient Voltage Suppressor) is actually the part you want there.
But I doubt that a brief voltage spike can kill a servo motor. You need a fair bit of excess voltage over several seconds to be problematic, and at that point a zener will have already lost its magic smoke, or its bonds with the circuit (I've had that happen: underspecced MOSFETs in a heating controller would themselves get so hot that they would melt the solder on their legs and drop out of the circuit board). I'm with Don Jefe that probably something was restricting the servo travel.
Capacitors are a better solution than that zener anyway, a couple of low-esr electrolytics (1000..2200uF) with a 100nF ceramic parallel each.