Tilt inhibit staging configurations for EasyTimer and *Mega boards

[plugger]

Given the confusion many people run into when attempting to configure staging electronics (myself included) I thought it would make sense to start a thread where people could document their tilt inhibit staging configurations for Altus Metrum products that are configured for tilt inhibit. So if you've had a successful staging flight with one of these three boards and you'd be willing to post your configuration here I'd love to see it. Bonus points if you include the firmware version you were using in conjunction with the successful configuration.

 

[plugger]

I attempted a two stage shakedown flight maybe 6 weeks ago where I had a dummy motor installed in my sustainer to attempt to test my staging logic. Below is the configuration I flew with.

basically, I wanted height above 300 meters, tilt angle less than 20 deg, and time since launch greater than 5 seconds but less than 6 seconds. Sadly the test ematch I flew came back unlit despite having a clean and straight boost (as seen by my booster GPS below)

I'll go out tonight and see if I can fire the ematch on the bench to eliminate a bad wiring fault. If anyone has any comments on my above config to improve.correct it I'd appreciate it.
I know this is already somewhat off the thread topic as it's a possible 'not working' config but I don't think this will be a high volume thread. I'd love to be proved wrong on that though!

 

[OverTheTop]

I used a TeleMega (v2) for my two-stage O3400 to M2020 back in 2019. If the sustainer ever turns up I can share the configuration. Telemetry went dark at apogee but showed a successful flight to there. I can't find my documented config unfortunately.

I can share my method approximately. Two channels were used for sustainer ignition. One channel was set up with a delay and tilt lockout of 20deg. This is the "nominal" channel. The other channel had tilt lockout at 20deg but it had sustainer ignition at 12deg. This provided ignition if the flight was coming off vertical early and would still light the sustainer before it was going too far sideways, but earlier than optimal.

Remember to design your flight systems to be successful with off-nominal flights. Safety First!

 

[waltr]

Think this is a good thread idea.
Sharing unsuccessful and those successful failures are also important.

Sadly the test ematch I flew came back unlit despite having a clean and straight boost

Was this ematch to start the sustainer motor or recovery ejection?

Testing can be done in a Vacuum chamber. Use xmass tree lights instead of ematches then download and examine the 'flight' data.

 

[plugger]

It was a standard ematch that was wired to a Head End Ignition Forward Closure for 38mm CTI motors. I built a 'test motor' which was the HEI FC, a 29mm slice of bluetube to hold that in place, and a used CTI 38mm rear closure. I ground tested it last night on the bench with a raven to ensure the wiring was good, and the charge fired as expected.

So uh, yea. Given the EasyTimer doesn't have any logging I have no way to troubleshoot why the failure occurred. I'm swapping to my EasyMega for this moving forward as I really need data to troubleshoot ignition failures.

 

[plugger]

So circling back on this I spent a bit of time going through the latest (v1.9.11) manual on the weekend. I'm not sure when it appeared but there's an Appendix B.1 Two-Stage Flights now with some documentation regarding how to configure for staging attempts. Specifically, this.



So I've configured my EasyMega with the following config based on that advice.


I hope that will "Light sustainer motor 1.5 seconds after booster burnout IF tilt is less than 20 degrees off vertical".

Fingers crosssed.

 

[JimJarvis50]

For a variety of reasons, I like your original program much better. It is the "book" method for the Altus Metrum products in my opinion. I don't know why yours didn't light. I would ask what was your expected altitude at 5 and 6 seconds. I would probably have included 1 burnout and a firing time of 0.1 seconds.

Jim

 

[plugger]

Hi Jim. Thanks for chiming in! I checked my Raven flight data from both my booster and sustainer, relevant values below.

​	Altitude (AGL) at 5 seconds of flight​	Altitude (AGL) at 6 seconds of flight​
Booster (Raven 1, dual axis)​	1,588 ft​	1,958 ft​
Sustainer (Raven 3, dual axis)​	1,652 ft​	2,019 ft​

Given those values I'm not sure why my event didn't fire in my first shakedown 'booster only' flight. Everything seems to be good from a staging config perspective, at least from what I can tell.

I, like you, would prefer more rigour in my configurations. Do you think it would make sense to also configure an Altitude threshold on my "new" config. It's not quite as comprehensive as my previous 'only light between 5 and 6 seconds' as it wouldn't have a time out/disarm value but at least it would provide a lower bound for which the event wouldn't fire.

I'd prefer to have my config nailed down to the point where I had upper and lower bounds for both time and altitude (as well as verticality) but tbh I also want the thing to fire (safely of course).

Finally, I also tried to adjust the firing time to 0.1 and it didn't take. I'll try that again tonight. Thanks again for commenting, I really appreciate it!

drew

 

[JimJarvis50]

It does appear that it should have fired, as you exceeded your altitude threshold by quite a bit. I don't kwow what the problem was, but I don't think the program was the problem. Seems like an issue that the firing time couldn't be adjusted? Hmm.

I had a problem with a couple of EasyMega's a few years back where the termimal strip wasn't soldered properly to the board. I found it because the voltages around the main a pyro battery terminals didn't make any sense. Did the EasyMega also do deployment?

Your revised approach isn't much different than the original in that you are essentially using time (bo+1.5) in place of the 5 second value. I think this just adds uncertainty because bo is actually detected a bit before it actually occurs. I would at least add an altitude threshold and a time less than value, but then your back to the original approach, essentially,

Jim

 

[plugger]

Ok, I think I should take a step back give you a little more background. My first flight that failed to light the test sustainer ematch was with an EasyTimer. But I've pulled it due to the lack of logging and replaced it with my EasyMega. In my ShortStack rocket configuration the HEI Staging is accomplished by a stand alone flight computer (now EasyMega) but it only handles staging as apogee and main are handled by a Raven in the NC.

My 'ShortStack' two stage rocket (Chopped down Mach2 + chopped down lower half of a Firestorm54)


There might be some electronics


And now I've got the EasyMega for HEI duties instead of the EasyTimer


I've revised my staging config to be more in line with your recommendations. See below.


Fingers crossed that config works for my next staging shakedown flight on Sunday (weather permitting, it might be squirrely). Regardless, unlike the last attempt I should be able to get some data to provide some post flight analysis regardless of what happens.

 

[JimJarvis50]

I would still recommend a time less than value. There's no harm closing the window. I would also say to make the altitude criteria something on the order of 60-70% of the expected altitude at the time the igniter fires. I haven't worked through scenarios, but it seems like there might be a case where the motor fails and you're not moving very fast when things go true.

The EasyTimer seems like an interesting device. One difference with it is that the accelerometer range is only up to 16 G's. If you go above that, the calculated inertial altitude & velocity won't be correct. I was thinking about using one for a flight. It's a long story, but I was planning on using velocity = 0 as the firing criteria on the flight that would be well below the 16G's. Keith advised me not to do that and to instead go with an EasyMega. I got the feeling that there might be some other differences in how the timer works versus the easymega, even though they have the same programming screen.

Jim

 

[plugger]

Thanks Jim, I'll put an upper bound on the time less than value on the EasyMega tonight. I think you're right in that it's better to close the window so to speak.

And thanks for your comment about the EasyTimer accelerometer range. As per usual you're right, but it takes a bit of digging to confirm that as the EasyTimer does not have a "Developer View" section under "Features" on the product page. It does state the following in the device summary though.

The IMU used is the same as on TeleMega and EasyMega, allowing acceleration based launch detection, and gyro-based tilt limiting.

Heading over to the EasyMega page you see the following details in the Developer View section of that page.

• Invensense MPU-9250 Nine-Axis MEMS Motion Tracking Device
  • tri-axis angular rate sensor up to 2000 degrees/second
  • tri-axis accelerometer with +- 16g range
  • tri-axis magnetic (compass) sensor
  • three on-chip ADCs for true simultaneous sampling of all axes

Checking my Ravens it looks like I clocked in at least 14.5g on boost with a J340 so that might be at play here. And given the fact that this is my 'sport stack' and my plan is to push it on a J600 when I fly it in the two stage config I'll most likely exceed that limitation. Really happy I started this thread now, I've definitely learned a few things, most important of which is that the EasyTimer might not really be suitable for my MD staging plans. Thanks again for your advice Jim!

 

[plugger]

Hey @JimJarvis50, just wanted to circle back and say THANK YOU! I finally pressed the button on my full stack on Sunday and the flight was a 100% success! I had full recovery of the stack. Below is some data from the sustainer.

 

[Chad]

congrats on your successful flight! I have a similar setup (easyTimer for sustainer ignition). What battery did you use on for the easymega? I'm planning on using a 1s 350mah lipo with the circuit protection removed, i'm wondering if that will work. I know i can just run a quick test but was wondering what you used.

Also, have you noticed there's no giant cap on AltusMetrum stuff like there is on the Raven? I wonder what a brown out situation looks like on Altus Metrum altimeters...

 

[plugger]

congrats on your successful flight! I have a similar setup (easyTimer for sustainer ignition). What battery did you use on for the easymega? I'm planning on using a 1s 350mah lipo with the circuit protection removed, i'm wondering if that will work. I know i can just run a quick test but was wondering what you used.

Also, have you noticed there's no giant cap on AltusMetrum stuff like there is on the Raven? I wonder what a brown out situation looks like on Altus Metrum altimeters...

Thank you! As mentioned upthread, I also started with the EasyTimer but moved to my EasyMega as I wanted logging to allow me to troubleshoot if I had any issues. Plus moving forward I'd like to use the EasyMega as an 'all in one' FC for sustainers (excluding tracking) so it made sense to get comfortable with it. For the EasyMega I used a 600mAh single cell LiPo to power it as I could fit it under the Easy on the sled so it worked out well. Your 1s 350mAh LiPo should be fine for the EasyTimer.

And yes, I've noticed the lack of a cap on the Altus FCs. And I can tell you what a brown out situation looks like as I was bitten by the lipo protection circuit issue with the OG TeleMetrum v1.0 kits provided by Altus. If the FC browns out during flight it reboots and you dig a very expensive hole. Not ideal really.

 

[SDramstad]

Are the altitudes you input in meters or feet?

 

[plugger]

Meters.

 

[UhClem]

Also, have you noticed there's no giant cap on AltusMetrum stuff like there is on the Raven?

There is a comparator in the FET driver that inhibits the FET if the battery voltage drops out. The voltage dividers set a trip point of 3.5V so the LDO should still be operating.

See: https://altusmetrum.org/TeleMega/v5.0/telemega-sch.pdf