# TeleMega: Is it Reliable?

### Help Support The Rocketry Forum:

#### jdeveau

##### Member
Two years ago at BALLS 24, our team from Tripoli San Diego made a 100K' attempt using a two stage rocket derived from the AeroPac 100K' rocket design (98mm booster, 75mm sustainer). In the sustainer, we used a TeleMega for drogue deployment, staging with tilt sensor, and GPS tracking (our backup was a Raven). We liked the features in a small form factor for a reasonable price. Our launch, however, was plagued by a booste motor nozzle failure, followed by an unrelated and explicable loss of telemetry downlink. Those failures, along with a failure of proper chute deployment resulted in a core sample of the whole stack, followed by hours of digging of playa to recover the remnants.
Anyway, we are a planning another attempt and are evaluating electronics, but are understandably wary of the TeleMega, even though we still have the receiver USB module and haven't found a better value of price vs features and form-factor. There have been some firmware upgrades since our ill-fated attempt that, among other things, fixed a bug that may or may not have been at the root of our telemetry failure (it is not clear that this failure was just telemetry or the whole unit). Does anyone have experience with this device and can lend some advice?

Thanks!

#### Q-Aero

##### Well-Known Member
Balls 24 was in 2015 I think, they release a version of AltOS after ( I think it's 1.6.8 ) that fix this kind of problem with Telemetry and Data recording [h=3][/h]

#### OverTheTop

##### Well-Known Member
TRF Supporter
I have a couple. Never been a problem. Many flights to 10-12k', one flight to 21500', Mach 1.8, 52Gs during boost.

I Love them

Haven't been to 100k' yet...

#### blackjack2564

##### Crazy Jim's Gone Banana's
TRF Supporter
I have 2 and great success using them.
I would hope you flew yours several times in lesser projects to get a good feel for how it work s & tracks.
Please tell me you did not just buy it & fly it in the big project from the get go?

#### plugger

##### Well-Known Member
In the sustainer, we used a TeleMega for drogue deployment, staging with tilt sensor, and GPS tracking (our backup was a Raven). Our launch, however, was plagued by a booste motor nozzle failure, followed by an unrelated and explicable loss of telemetry downlink. Those failures, along with a failure of proper chute deployment resulted in a core sample of the whole stack, followed by hours of digging of playa to recover the remnants.
I find this a bit confusing. If you had a Raven as backup and yet you lost the entire stack it seems like you've got bigger problems than telemetry with the TeleMega. Seems like a deployment or chute issue to me.

I'll be the first to admit that initially AltusMetrum products had some issues. I core sampled a TeleMetrum v1.0 due to the lipo protection board issue they had. I had flown the unit twice before but never tested the unit with an eMatch in a non-critical deployment scenario. CJ's right; Test, Test, Test. All that said the product line is quite mature now imo, I fly my TeleGPS nearly every launch and I've got an EasyMega coming across the pond now.

If I were you I'd pick up another TeleMega if you want GPS tracking, tilt detection, and telemetry. It's the only unit on the market that's proven and provides all those capabilities. Protip: grab yourself a USB OTG cable for your Android phone or tablet (yes, I'm aware I'm making an assumption). Last week I tested out connecting my TeleGPS to my phone via my Teledongle + USB OTG cable + my Nexus 5X. It worked flawlessly and is much more comfortable than lugging your laptop + Teledongle for a recovery. This feature has been available since June 2015 but I only learned about it last week when reading through the mailing list archives.

#### ChrisAttebery

##### Well-Known Member
Pro tip: If you buy the TeleBT you don't need a cable at all. You can connect your tablet via Bluetooth.

#### ksaves2

Two years ago at BALLS 24, our team from Tripoli San Diego made a 100K' attempt using a two stage rocket derived from the AeroPac 100K' rocket design (98mm booster, 75mm sustainer). In the sustainer, we used a TeleMega for drogue deployment, staging with tilt sensor, and GPS tracking (our backup was a Raven). We liked the features in a small form factor for a reasonable price. Our launch, however, was plagued by a booste motor nozzle failure, followed by an unrelated and explicable loss of telemetry downlink. Those failures, along with a failure of proper chute deployment resulted in a core sample of the whole stack, followed by hours of digging of playa to recover the remnants.
Anyway, we are a planning another attempt and are evaluating electronics, but are understandably wary of the TeleMega, even though we still have the receiver USB module and haven't found a better value of price vs features and form-factor. There have been some firmware upgrades since our ill-fated attempt that, among other things, fixed a bug that may or may not have been at the root of our telemetry failure (it is not clear that this failure was just telemetry or the whole unit). Does anyone have experience with this device and can lend some advice?

Thanks!
Remember the Raven II has a firmware glitch when going above 60k that could lead to early deployments. If using that unit, they need to be sent back to be flashed with new firmware. If one is staying below 60k there is no issue. Kurt

#### mikec

##### Well-Known Member
Remember the Raven II has a firmware glitch when going above 60k that could lead to early deployments.
Yes, we knew that and so we were using a Raven 3, which performed as expected. We could go into more detail about the configuration and what happened on the flight, but Jim (optimistically, IMHO) was only asking for real-world experience about the Telemega. And yes, we did test flights prior to the 100k attempt.

#### Random Flying Object

##### Well-Known Member
I have had good luck with the TeleMega. I have put it through its paces with very high G's, but only to ~25kft. Make sure to understand and pay attention to antenna type and placement.

If you plan to use your TeleMega near strong RF fields for video, etc. pay attention to power distribution, filtering, etc.

#### ksaves2

Yes, we knew that and so we were using a Raven 3, which performed as expected. We could go into more detail about the configuration and what happened on the flight, but Jim (optimistically, IMHO) was only asking for real-world experience about the Telemega. And yes, we did test flights prior to the 100k attempt.
Right, but posted for those who might be new and unfamiliar with that characteristic. I have read a few reports on TRF where some high fliers had issue with the Tele-Mega at extreme altitudes. Wished I saved the link but since I'm never going to go there
didn't. Perhaps someone will post of a less than stellar experience. Bottom line I read discussed was that apogee deployment might be better based on "simmed like crazy" flight times and using time for apogee deployment or GPS altitude.
I've seen posted if a windup clock was "good enough" for an Arcas rocket it should be good enough here too.

The other thing is with a deployment in the really rarefied altitude I'd suspect there would be a little more leeway as there shouldn't be as much stress on the harness in a near vacuum. Sure, a rocket under thrust in a vacuum that comes apart is
likely going to turn into a mess but I think there would be a little more leeway with an early or late deployment as opposed to early/late in the lower denser air.

From following high altitude balloon videos in the past, I was initially surprised on the payloads with an upward facing camera that showed the limp chute and covered the balloon bursting, the chute appeared to "fill" pretty quickly.
What I lost track of was even with little air, the payload pack was likely plummeting at a very high speed and collected enough of the few gas molecules up there to fill the canopy. As it reached the lower atmosphere with denser air, the payload pack would begin to slow in descent velocity.

Again, I didn't mean to sound condescending. Kurt

#### mikec

##### Well-Known Member
If I were you I'd pick up another TeleMega if you want GPS tracking, tilt detection, and telemetry. It's the only unit on the market that's proven and provides all those capabilities.
Define "proven". I've heard some people expressing concerns about the tilt detection accuracy (one guy we talked to at BALLS said he added 10 degrees to the tilt limits because he'd found it was off that much.) I'm curious to know just how and how thoroughly the tilt calculations have been validated with in-flight data. As to tracking, we were trying to use our Telemega at the lowest data rate for improved range but had a lot of difficulty with it failing to connect initially. We also had some trouble with APRS not decoding correctly. But that was with older firmware so maybe those issues have been resolved.

Not bagging on Altus Metrum specifically, just looking for real-world experience.

#### ksaves2

Define "proven". I've heard some people expressing concerns about the tilt detection accuracy (one guy we talked to at BALLS said he added 10 degrees to the tilt limits because he'd found it was off that much.) I'm curious to know just how and how thoroughly the tilt calculations have been validated with in-flight data. As to tracking, we were trying to use our Telemega at the lowest data rate for improved range but had a lot of difficulty with it failing to connect initially. We also had some trouble with APRS not decoding correctly. But that was with older firmware so maybe those issues have been resolved.

Not bagging on Altus Metrum specifically, just looking for real-world experience.
Exactly. I've heard the Easy Mega is pretty reliable. Kurt

#### plugger

##### Well-Known Member
Pro tip: If you buy the TeleBT you don't need a cable at all. You can connect your tablet via Bluetooth.

Jim

#### JimJarvis50

##### Well-Known Member
I'm planning to use two EasyMega's in my upcoming three-stage flight. As suggested by plugger, there really isn't much choice, but I really like the features built into them.

I have two higher altitude flights to look at the tilt result (comparing the tilt reading with the video horizon). One was very good nearly 30 seconds into the flight, but the other was not very good at all. It is my belief that if the rocket spins, the accuracy of the tilt estimate can degrade rather quickly. I haven't yet verified this for the EasyMega, but tests with the same gyro chip clearly show that trend. My strategy is to minimize or eliminate spin, such that the tilt reading can actually be used as intended.

Others can elaborate if they choose, but I would recommend that anyone using a Telemetrum product should check the integrity of the solders between the terminal strip and the board. Just verify the battery voltage across the outputs and that there is continuity when a charge is connected. Other than that caution, I am very happy that they are available and I'm happy with the customer service provided by all involved. I tested my second unit a few weeks back and it worked flawlessly. I'll have a Raven on board too, but at this point in time, the *mega is the best option for staging imo.

Jim

#### jdeveau

##### Member
Yup, we tested on one flight before that, although it was not a multistage flight. This time around, we have several test flights planned before going for 100K'

#### jdeveau

##### Member
Wow, great response from all of you! Great to also hear from folks that have already successfully made it to 100K.

Thanks!

Jim

#### jdeveau

##### Member
I only mentioned the Raven so that someone wouldn't assume that we were using the TeleMega as our only altimeter. But yes, we had multiple problems and the chute was one of them. From aerial photos, we believe the chute got stuck in the airframe (OK, quick laughing). So, we believe the Raven did get the nosecone off of the sustainer but we didn't get a chute, and core sampled.

#### JimJarvis50

##### Well-Known Member
Wow, great response from all of you! Great to also hear from folks that have already successfully made it to 100K.

Thanks!

Jim
Didn't mention it, but I had one flight to 130K where the EasyMega did everything on the sustainer. There were two timers for apogee, but the EasyMega did the separation charge, motor ignition, contingency deployment (baro if below 90K), and two main chute events.

Jim

#### mikec

##### Well-Known Member
But yes, we had multiple problems and the chute was one of them.
A little more detail (and Jim, I don't think the chute was stuck in the airframe): when the first-stage motor CATOed it apparently took out the redundant first-stage electronics and that's about when the Telemega telemetry went dead also. The backup Raven in the second stage fired both the apogee and main charges as it was supposed to, but we were using Archetype cable cutters for the main chute and the bundle was hopelessly tangled from the fact that the stages stayed attached; had they come apart, there's a chance that the second stage at least would have recovered intact. We clearly had some problems with our harness and packing procedure.

Obviously some lessons learned for the next try. Thanks for all the feedback on the Telemega.

BTW, this is the rocket in the hole on the cover of the latest TRA report

#### plugger

##### Well-Known Member
A little more detail (and Jim, I don't think the chute was stuck in the airframe): when the first-stage motor CATOed it apparently took out the redundant first-stage electronics and that's about when the Telemega telemetry went dead also. The backup Raven in the second stage fired both the apogee and main charges as it was supposed to, but we were using Archetype cable cutters for the main chute and the bundle was hopelessly tangled from the fact that the stages stayed attached; had they come apart, there's a chance that the second stage at least would have recovered intact. We clearly had some problems with our harness and packing procedure.

Obviously some lessons learned for the next try. Thanks for all the feedback on the Telemega.

BTW, this is the rocket in the hole on the cover of the latest TRA report
OOH, that's rough. Reminds me of my mate's flight at Balls 22. IIRC he was flying an N5800 to a Gorilla M staging stack. Things went south, the sustainer came in ballistic, and below are the results.

Oh, and funnily enough he was able to find it because he was flying a TeleMetrum in it and I was able to replay the flight and get us some usable GPS data to narrow down the hole search. The sustainer motor detonated on impact. Even though that hole doesn't look like much it was quite a cavernous hole below ground from the detonation.

#### reddrock

##### New Member
Does anyone have information on how the TeleMega deals with rocket spin or what amount of spin it can sustain and still have good tilt measurement? For example, the RockeTiltometer manual says it can handle 520 degrees per second of spin (~93 RPM) and not affect the tilt calculations. Is there any similar information on the TeleMega?

#### mikec

##### Well-Known Member
Is there any similar information on the TeleMega?
In theory the MPU-6000 the Telemega uses can handle up to 2000 deg/sec. In practice people (see Jim Jarvis's posts upthread) have said that after a few spins the tilt angle is no longer usably accurate, but I don't think anyone understands exactly what would cause this.

#### JimJarvis50

##### Well-Known Member
Does anyone have information on how the TeleMega deals with rocket spin or what amount of spin it can sustain and still have good tilt measurement? For example, the RockeTiltometer manual says it can handle 520 degrees per second of spin (~93 RPM) and not affect the tilt calculations. Is there any similar information on the TeleMega?
This topic is of interest to me as well for high altitude staged rockets. I can share a few observations, but there are folks here that know much more about this than I do. The problem is that there is "cross talk" between the axes of the MEMS gyros. Basically, rotation on one axis causes rotation to be measured on the other axes. The specification for the MPU-6000 is +/- 2%. So, you can imagine that a 1000 degrees of spin rotation would result in enough rotation on the other axes to make a tilt measurement less accurate. In many uses of this chip, the gyro errors don't matter that much because the accelerometers work continuously to correct those errors. For rockets, however, the accelerometers can't be used in flight, so this and other errors accumulate.

My solution to the tilt problem for high altitude flights is to try for active vertical stabilization. The board I'm using isn't the TeleMega, but it has the same MPU-6000 gyros (but not the magnetic sensor). The brains behind my effort are the guys that developed the tiltometer, and we have collectively come to realize that for the purpose of vertical stabilization, rotation has to be essentially stopped. So, the vertical stabilization approach also employs roll control to help maintain the accuracy of the vertical stabilization, and also to give the best chance for the EasyMega's I use to correctly inhibit staging if need be.

Jim

#### Tinker

##### Well-Known Member
I don't know what the possibilities are, but can you use a Arduino and the 3 axis gyroscope and accelerometer with some voting circuitry (Multiple OR gates) and use that and the Telemega?

Tinker

Edit -- Hmmmm its the MPU 6050 Gyro, I don't know if it is susceptible to the same errors.