Hi Craig, I've done a little bit of work like this with the EasyMega board in support of a 100k+ foot flight. The issue you'll run into is that the baro sensor is basically only good to 100k' MSL and above that the atmosphere is so thin that the baro readings are around the noise floor of the sensor. You could use Accelerometer based deployment but the *Megas don't do any integration of the data across the three axis sampling so unless you're flying perfectly straight up it's most likely not ideal. I could be making a complete hash of explaining this but in broad brush strokes those are the things you need to consider.
IMHO your best bet is to have a timer based primary and backup apogee event configured on the *Mega board you fly. So you make sure you have a reasonably accurate simulation and look into the time it takes to make it to apogee. Then add a few seconds to that to ensure you don't deploy before apogee. Ideally you'd also include some logic in the timer for added safety, for instance a config that fires after x seconds and being above 20,000 feet AGL. As Casey said at 100k a bit of a late (or early) deployment isn't much of an issue as the atmosphere is so thin there that there won't be any appreciable drag on the vehicle at that altitude to cause a zipper or something similar. It's more important to ensure your event works and separates the rocket so that once it falls back into the lower thicker atmosphere it will do so without coming in ballistically. I know both Kip and Jim have leveraged the EasyMegas in this capacity to handle their sustainer ignition (including altitude an tilt inhibits) as well as their apogee events on their two and three stage flights. Before the *Megas most people seemed to use the Ravens with the high altitude firmware or R-DAS boards for 100k+ attempts. Both were leveraged in the same way, as in, timer based apogee event configurations. Ideally you'd also configure an event for what I like to describe as an EFU (Everything's F*cked Up) event. Basically it's nice to have an event configured for if your flight is off nominal that would still fire your apogee charge if something goes wrong and you don't meet the criteria for your planned apogee event. Basically if something goes wrong you still want an apogee event to fire, and it would make sense to configure your board to do that if at all possible. > Are there any considerations for rockets exceeding Mach 3? Not from a *Mega perspective. ;) Good luck on your project! Many moons ago I was a MDRA member. Great club y'all have there. If you have any further questions please feel free to reach out. I'm sure I could pull up some pyro channel configuration screenshots and share them with you if that would help. Cheers, drew On Fri, Jun 21, 2019 at 1:08 PM Casey Barker <[email protected]> wrote: > We've had a successful flight to ~76k' with a combination of TeleMega and > EasyMega for primary and backup, respectively. I know of at least one > successful flight to well over 100k' that also used *Mega boards in some > capacity. The Kalman filter model seems to work quite well. > > If you're doing 2-stage, there are definitely some programming tips that I > think could really help, particularly around the ignition event > configuration and lock-outs. (Sadly, we've had a few flights where the > lock-out programming became all too relevant.) I can dig up my notes if > that would be of use. > > Other than that, I think it's fair to summarize the prevailing wisdom as: > - Make sure you're using the latest firmware, or at least understand the > errata for whatever version you choose to run. > - Make sure the accelerometer is reasonably calibrated. > - But as long as you're over 100k', it turns out that perfectly detecting > and ejecting at apogee probably isn't all that critical. You just need to > get the airframe in a good configuration before the atmosphere becomes > relevant. > > Casey > > On Thu, Jun 20, 2019 at 7:06 PM Craig Klimczak <[email protected]> wrote: > >> Our Maryland MDRA Team is building a high altitude project to fly at >> BALLS this year. The Avionics suite includes a TeleMega flight computer. >> The rocket is single stage dual deploy with a research motor. I'm reaching >> out to this forum for any advice on programming and using the TeleMega for >> rocket flights above the 100,000 foot mark. >> >> Are there any special considerations for setting up the TeleMega for >> flights to over 100,000 feet? >> >> Are there any considerations for rockets exceeding Mach 3? >> >> What are the highest altitudes achieved with the TeleMega to date? I've >> flown this TeleMega to 35,000 feet with no problems. Is there an altitude >> where the performance of the TeleMega may be limited? Has anyone on this >> forum flown a TeleMege to 100,000 feet before. If so, how did it perform? >> Did you have any issues with tracking? Losing GPS lock? Apogee detection? >> >> Thanks, >> Craig Klimczak >> TRA #13451 >> _______________________________________________ >> altusmetrum mailing list >> [email protected] >> http://lists.gag.com/mailman/listinfo/altusmetrum >> > _______________________________________________ > altusmetrum mailing list > [email protected] > http://lists.gag.com/mailman/listinfo/altusmetrum >
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