Mach Inhibit setting

Just messing around with the programming / settings on the altimeter PML provides with their CPR kits (manufactured by Missleworks) prior to my first dual deploy. Even though I'm not planning on being anywhere near mach, I thought I might just program in some inhibit time (say burnout + 3 seconds) just for grins and chucks. Plus it puts an extra note in my brain to remember that the option exists if I ever man-up to going mach+.

I can't think of any downside risk to plugging in some mach inhibit time in a non-mach flight. Am I missing something?

What rocket and what motor? If you are not going north of say 0.75 Mach I would not bother.

I have been flying Missileworks since the rrc2 hit the market in the late 1990's. They are very solid.

Which altimeter exactly are we talking about though?

JackMatt said:

I can't think of any downside risk to plugging in some mach inhibit time in a non-mach flight.

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Mach inhibit basically tells the altimeter to ignore barometric readings until after the delay, so if you get to apogee before the programmed delay for whatever reason (bad delay setting, off-nominal flight), then your apogee event will be late (assuming the altimeter detects apogee at all in this case.)

Most altimeters on the market today have some form of automatic mach detection and don't need an explicit inhibit, which is one less thing to worry about.

What rocket and what motor?

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- A modified Public Missiles Ltd. Eclipse flying on a Cesaroni J760. RockSim predicts 0.45 Mach, so not really an issue.

Which altimeter exactly are we talking about though?

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-This is one of PML's CPR series kits that comes supplied with electronics. It's branded as 'PML CoPilot V2.0' (I bought this kit a few years ago, now they have a v3.0), but it's manufactured by Missile Works and is similar to the RRC2. Very basic. No I/O interface with a computer, all settings are dialed in manually.

Most altimeters on the market today have some form of automatic mach detection and don't need an explicit inhibit, which is one less thing to worry about.

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- Thanks for that input, Mike. I am simultaneously working on a scratch build and bought a Missile Works RRC3+ for that project. Programing that unit, I never found any specific way to adjust the mach inhibit, I thought I was missing something, but maybe not.

JackMatt said:

I can't think of any downside risk to plugging in some mach inhibit time in a non-mach flight. Am I missing something?

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There are certain cases of motor malfunctions (e.g. spit nozzle) that can result in much less performance than anticipated. A mach inhibit can prevent the altimeter from saving the rocket in such a flight, but this is a rather unlikely scenario.

Reinhard

You mean the Mach inhibit switch doesn't prevent the rocket from breaking Mach?

Hah, mach inhibit.

I would not rely on any computer that needs mach inhibit settings. Maybe fly it along as an inert data recorder, or simply for kicks.

Modern computers are too good and too cheap to ignore. RRC2+ for $45 and you are done, down to $20 if you do not mind soldering a Quark. Twenty dollars!

I have a couple newer altimeters- an rrc2+ and an rrc3. I have yet to fly the rrc3. I would need to setup my rockets for it, which I plan to do with some of them.

People have been flying altimeters like this for nearly twenty years. You need to know what your rocket will do, and once you do older altimeters can work just fine.

Yes and no. The horror stories I hear about Ravens and G Wiz make me glad I skipped that whole era of rockets. I know that people get good results out of them, and certainly encourage people to fly what they know and what they enjoy, but even the Raven expert who set them up for the Carmack Prize winner tells me about his love/hate relationship with them. Meanwhile RRC2+ and SCF make it so easy that it is practically impossible to get wrong short of connecting the wrong wires. I suppose what I am getting at is that the older ones work, but the numbers favor the newer ones.

There is a current trend towards single flight computers, be it four channel or with redundant charges, that can be directly attributed to the quality of modern altimeters.

I think the Raven's are good units. That being said, at times they seem to be almost too flexible. Most of the issues I have seen with Ravens appear to be programming related.

I never flew a G-Wiz.

I know a lot of folks who still fly their old school Missileworks, Adept, and Blacksky altimeters.

I have no issue with flying a single unit. I will be really convinced though when the L3 cert process is changed to allow a single altimeter.

watermelonman said:

Yes and no. The horror stories I hear about Ravens and G Wiz make me glad I skipped that whole era of rockets. I know that people get good results out of them, and certainly encourage people to fly what they know and what they enjoy, but even the Raven expert who set them up for the Carmack Prize winner tells me about his love/hate relationship with them. Meanwhile RRC2+ and SCF make it so easy that it is practically impossible to get wrong short of connecting the wrong wires. I suppose what I am getting at is that the older ones work, but the numbers favor the newer ones.

There is a current trend towards single flight computers, be it four channel or with redundant charges, that can be directly attributed to the quality of modern altimeters.

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I agree that newer altimeters are easier and mostly more dependable to fly. You have to remember that what makes the newer ones different then the older ones is the software. The newer ones have more memory and can run larger firmware programs which allow them to do a software mach inhibit filtering instead of relying on the user to set a timer value. That doesn't make them any more reliable then the older ones, just less dependent on user input. Since eliminating human error is usually the quickest and easiest way to eliminate errors, this makes the newer altimeter seem much more reliable then the old one. What would be interesting is if we eliminated all human errors and compared just the firmware caused failures between the old altimeters and the new ones, which would prove to be more reliable. I suspect the simpler older ones would have fewer firmware errors that resulted in flight errors.

watermelonman said:

Yes and no. The horror stories I hear about Ravens and G Wiz make me glad I skipped that whole era of rockets. I know that people get good results out of them, and certainly encourage people to fly what they know and what they enjoy, but even the Raven expert who set them up for the Carmack Prize winner tells me about his love/hate relationship with them. Meanwhile RRC2+ and SCF make it so easy that it is practically impossible to get wrong short of connecting the wrong wires. I suppose what I am getting at is that the older ones work, but the numbers favor the newer ones.

There is a current trend towards single flight computers, be it four channel or with redundant charges, that can be directly attributed to the quality of modern altimeters.

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The Raven has been around since 2006, but it has always had has automatic Mach deployment inhibit based on the accelerometer-measured rocket velocity in its default settings. That way, it will work right out of the box for everything from an Estes A-powered rocket all the way up to a Mach 3, 80,000+ foot shot. You can just connect the wires and fly if you want to, like the simplest and least-expensive altimeters. Or if you want to see a lot of detailed data from your flight, or if you have a special flight with complicated airstarts, etc., you can access those features when you connect the Raven to a computer. You can also test out your settings with a simulated flight capability.

markkoelsch said:

I think the Raven's are good units. That being said, at times they seem to be almost too flexible. Most of the issues I have seen with Ravens appear to be programming related.

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Thanks, Mark. Something I was not expecting before starting this product is how additional flexibility --even if it's completely optional and ignore-able-- can create a perception of complicated operation.

I just flew my 195th successful Raven flight (7 units in total). And one of those units was sold to me because it was "bad" (said the seller). I feel like most if not all "Raven issues" are operator error.

Anyone else have any "bad" units they want to sell, send em my way.

I love the product.

Adrian A said:

The Raven has been around since 2006, but it has always had has automatic Mach deployment inhibit based on the accelerometer-measured rocket velocity in its default settings. That way, it will work right out of the box for everything from an Estes A-powered rocket all the way up to a Mach 3, 80,000+ foot shot. You can just connect the wires and fly if you want to, like the simplest and least-expensive altimeters. Or if you want to see a lot of detailed data from your flight, or if you have a special flight with complicated airstarts, etc., you can access those features when you connect the Raven to a computer. You can also test out your settings with a simulated flight capability.



Thanks, Mark. Something I was not expecting before starting this product is how additional flexibility --even if it's completely optional and ignore-able-- can create a perception of complicated operation.

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Sorry if any of my statements came out as anti Raven. A project I work on uses something like three of them in total, all to great effect. The flexibility has afforded us more possibilities than other units.

More what I was getting at, was that if one ever has reason to doubt their electronics, whether it is configuration or damage, is to simply fly with one of the new models like RRC2+ or SCF. They are too cheap and too good to skip over. I am a huge fan of throwing one in as a failsafe when using more complicated electronics, until you have proven that unit or configuration to yourself.

GRIFFIN said:

I just flew my 195th successful Raven flight (7 units in total).

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Wow, that's a lot more than I have ever flown.

watermelonman said:

A project I work on uses something like three of them in total, all to great effect. The flexibility has afforded us more possibilities than other units.

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Thanks. Glad to hear it has been useful for you.

watermelonman said:

...but even the Raven expert who set them up for the Carmack Prize winner tells me about his love/hate relationship with them. Meanwhile RRC2+ and SCF make it so easy that it is practically impossible to get wrong short of connecting the wrong wires. I suppose what I am getting at is that the older ones work, but the numbers favor the newer ones.

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Sure, there are limitations to the programming logic in Ravens as can be seen by Casey Barker's (it is Casey you're referring to, right?) analysis of the programming issues they had with the Ravens used for their 100k shot. That said IF there was a better product on the market I'm certain they would have considered using it. Both the RRC2+ and the SCF aren't even capable of staging and handling dual deploy, they're dual channel deployment only altimeters. The RRC3 does have an auxiliary channel for staging/redundant deployment but it only has one. RDAS are both expensive and very old. Ravens have 4 fully programmable pyro outputs in an incredibly small form factor. While they aren't ideal for everything they're imho the best fc for staging and airstarts on the market. I've struggled at times with wrapping my head around the programming of the 3rd and 4th outputs on a Raven in the past BUT as Adrian mentioned the flight simulation feature is quite useful as are other Raven users. Beyond the Raven the only think you can really consider is a TeleMega/EasyMega but at $300 minimum for an EasyMega you could have 2 Ravens instead. YMMV but I still believe the Raven is the most capable flight computer on the market currently.

You did forget the Marsa's nice units. They are a lot bigger than a Raven though. I think they are both great units.

markkoelsch said:

You did forget the Marsa's nice units. They are a lot bigger than a Raven though. I think they are both great units.

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Good point Mark. That said I've never played with one of those Marsa units. Any comments on the configuration capabilities (or possibly lack there of) when compared to the Raven? I guess for completeness we could/should also throw the G-Wiz HCX on the list given it also has 4 pyro outputs.

I never used the HCX, and frankly never saw one in person. I am not sure, but I am not sure G Wiz is still in business.

That said, from my reading I would say the Marsa and Raven are very comparable in feature set. The Marsa is larger, but with that comes the integrated display that allows for the programming without a computer. The Raven is really small so it fits in rockets most altimeters cannot but you need a computer to program it. It depends on what you are flying- basically design choices and trade offs.

What I acquired is an older altimeter/flight controller that I think is really the true forerunner/progenitor of these excellent new flight computers. It is called a Mission Control. Only issue is that it is not Mach immune so you need to set Mach delays. That said, the programmatic flexibility of it compared to the other units of its day put it way ahead of its contemporaries. I am likely going to build a new sled to use it in my Wildman Junior as I want to mess with it.

I will say this- we really are in what I would call the golden era of rocketry electronics. All of it is good. Whether you want something to just read peak altitude to some thing that can control staging based on multiple criteria you can get it. The basic altimeter like a PerfectFlight Stratologger or a Missileworks RRC2+ are amazing for the money. The RRC3 is an awesome value. Then you take a jump to the Raven, the Marsa, and the Altus Metrum stuff. Just awesome what can be done with this stuff.

JackMatt said:

Just messing around with the programming / settings on the altimeter PML provides with their CPR kits (manufactured by Missleworks) prior to my first dual deploy. Even though I'm not planning on being anywhere near mach, I thought I might just program in some inhibit time (say burnout + 3 seconds) just for grins and chucks. Plus it puts an extra note in my brain to remember that the option exists if I ever man-up to going mach+.

I can't think of any downside risk to plugging in some mach inhibit time in a non-mach flight. Am I missing something?

Click to expand...

Back when I flew MAWD altimeters, I would set a 4-second mach delay on all of my flights. If the altimeter was triggered prematurely, the beeping would stop, and I would have four seconds to get away from the rocket. There were very few flight profiles where the rocket would reach the arming altitude but not have time to put out a chute. I miss that feature. I don't know what the PML units do when they trigger, but if the continuity beeping stops, then a few seconds of mach delay might be a useful safety feature.

Jim

GRIFFIN said:

I just flew my 195th successful Raven flight (7 units in total). And one of those units was sold to me because it was "bad" (said the seller). I feel like most if not all "Raven issues" are operator error.

Anyone else have any "bad" units they want to sell, send em my way.

I love the product.

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I gotta "bad" unit I ain't sending anybody's way. I tried using a wood worker's spring clamp on a new Raven to aid in holding the capacitor in place while the epoxy set. The clamp slipped and "snapped" the board. Now, the slightest torsion load on the
board and it goes into reset! No I didn't test it out first before trying to epoxy the capacitor so I assume it was me (more likely) than being sent a defective unit. I checked the board under magnification and nothing was remiss but attempting to
fly this Raven could end up disasterous. A $155.00 gluing accident no less!! Kurt

Kurt, that might be the best glue thread ever. Sorry for your mishap.

markkoelsch said:

Kurt, that might be the best glue thread ever. Sorry for your mishap.

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Yeah, that was quite some time ago. I got a replacement and now do the epoxy job without clamping no matter who's device I'm using. Kurt

markkoelsch said:

I never used the HCX, and frankly never saw one in person. I am not sure, but I am not sure G Wiz is still in business.

That said, from my reading I would say the Marsa and Raven are very comparable in feature set. The Marsa is larger, but with that comes the integrated display that allows for the programming without a computer. The Raven is really small so it fits in rockets most altimeters cannot but you need a computer to program it. It depends on what you are flying- basically design choices and trade offs.

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Sorry Mark, I should have been more specific. I went back and reviewed the AeroPac 100k NARCON 2013 video on youtube as well as the compressed report as Casey Barker mentioned some caveats regarding their Raven use and programming that to my knowledge weren't known beforehand. Specifically he stated that accelerometer based apogee detection on Ravens is always substantially earlier than actual apogee. Further he states that the timer configuration isn't capable of having timers set that are over 51.5 seconds in length. Basically I was wondering if Marsa units had the same timer limitation (which I doubt) and if anyone had crunched their flight data from their Marsa to compare the differences between reported apogee from baro and apogee from accelerometer.

And yes, I don't believe G Wiz aren't in business anymore. That said I still have a HCX and I know a couple people that still fly their LCXs regularly.

plugger said:

Sorry Mark, I should have been more specific. I went back and reviewed the AeroPac 100k NARCON 2013 video on youtube as well as the compressed report as Casey Barker mentioned some caveats regarding their Raven use and programming that to my knowledge weren't known beforehand. Specifically he stated that accelerometer based apogee detection on Ravens is always substantially earlier than actual apogee. Further he states that the timer configuration isn't capable of having timers set that are over 51.5 seconds in length. Basically I was wondering if Marsa units had the same timer limitation (which I doubt) and if anyone had crunched their flight data from their Marsa to compare the differences between reported apogee from baro and apogee from accelerometer.

And yes, I don't believe G Wiz aren't in business anymore. That said I still have a HCX and I know a couple people that still fly their LCXs regularly.

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Also, I believe there is a firmware quirk in the Raven II if one is going above 60,000' that causes a deployment problem. I believe Adrian has a standing offer to flash any unit but since I'm not going to that extreme, don't feel the need to bother him.

If I'm not mistaken, even though the Raven might be in Baro/Baro mode for Apogee/Main deployment, the accelerometer is still utilized for Mach inhibit purposes?

Kurt

plugger said:

Sorry Mark, I should have been more specific. I went back and reviewed the AeroPac 100k NARCON 2013 video on youtube as well as the compressed report as Casey Barker mentioned some caveats regarding their Raven use and programming that to my knowledge weren't known beforehand. Specifically he stated that accelerometer based apogee detection on Ravens is always substantially earlier than actual apogee. Further he states that the timer configuration isn't capable of having timers set that are over 51.5 seconds in length. Basically I was wondering if Marsa units had the same timer limitation (which I doubt) and if anyone had crunched their flight data from their Marsa to compare the differences between reported apogee from baro and apogee from accelerometer.

And yes, I don't believe G Wiz aren't in business anymore. That said I still have a HCX and I know a couple people that still fly their LCXs regularly.

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The Marsa timer limitation is 25.6 seconds (8 bit timer, 0.1 sec increment). If you need longer you can install a custom version of firmware that uses 1 sec increments to give up to 256 seconds.

The accelerometer and baro altitude agreement for straight up flights is very good (within 1000 feet on several 30,000 ft flights). Exceptions are for very short burn motors where the impulse up isn't integrated as accurately as longer burn motors. There is a firmware release coming out shortly to remedy this.

plugger said:

Sorry Mark, I should have been more specific. I went back and reviewed the AeroPac 100k NARCON 2013 video on youtube as well as the compressed report as Casey Barker mentioned some caveats regarding their Raven use and programming that to my knowledge weren't known beforehand. Specifically he stated that accelerometer based apogee detection on Ravens is always substantially earlier than actual apogee. Further he states that the timer configuration isn't capable of having timers set that are over 51.5 seconds in length. Basically I was wondering if Marsa units had the same timer limitation (which I doubt) and if anyone had crunched their flight data from their Marsa to compare the differences between reported apogee from baro and apogee from accelerometer.

And yes, I don't believe G Wiz aren't in business anymore. That said I still have a HCX and I know a couple people that still fly their LCXs regularly.

Click to expand...

The Raven uses a microcontroller with an analog-to-digital converter that can have a significant non-linearity error, and this can cause inaccuracy when extrapolating from the accel calibration readings (+/- 1G to flight readings (up to 70 Gs). In other words, if the slope of the voltage vs. counts plot is different between +/- 1G than it is over the rest of the measurement range, then when you're measuring outside of +/- 1G that difference translates into acceleration errors. This effect can be as bad as 10% in some units, though other units are nearly spot-on. Accelerometer errors translate into apogee estimation errors 1-for-1, so the Raven uses the baro-based apogee detection by default, with the accel just used for detecting when the velocity is at or above 400 feet/second. If you use the accel-based apogee detection, you might see a 1 second error on a 10 second flight which is no big deal, but a flight to 30,000 feet takes around 30 seconds, and a 3 second apogee detection error could be significant.

The timer on a stock Raven can be set up to 32 seconds. On request for really high-altitude fliers (like Jim Jarvis for example) I can program a modified firmware load that allows much longer timers at the cost of worse timer resolution, and also makes the baro-based apogee detection more flitered for better performance over 80,000 feet but noticeably delayed for lower altitude flights.

ksaves2 said:

Also, I believe there is a firmware quirk in the Raven II if one is going above 60,000' that causes a deployment problem. I believe Adrian has a standing offer to flash any unit but since I'm not going to that extreme, don't feel the need to bother him.

If I'm not mistaken, even though the Raven might be in Baro/Baro mode for Apogee/Main deployment, the accelerometer is still utilized for Mach inhibit purposes?

Kurt

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Yes, this was for early Raven2 units with firmware version < 1.5. The bug was discovered and fixed in 2011.

I was aware of the firmware quirk with Raven 2 units Kurt but thanks for bringing that up as Adrian addressed it. I was fairly sure that wasn't part of the issue the AeroPac 100k team ran into, otherwise they wouldn't have reached 100k and recovered successfully!

John, thanks for the comments regarding your Marsa units. I really should check on out in the near future.

Adrian, cheers for the very detailed rundown of the accelerometer errors in some of the Raven units. I had read about this before, IIRC it was Jim Jarvis that was talking about ensuring you had a "good Raven" from an accelerometer drift perspective but I wasn't sure exactly what he was referring to. Is it a dual axis accelerometer only issue or are your single axis 250G models also susceptible to drift errors?

Adrian A said:

On request for really high-altitude fliers (like Jim Jarvis for example) I can program a modified firmware load that allows much longer timers at the cost of worse timer resolution, and also makes the baro-based apogee detection more flitered for better performance over 80,000 feet but noticeably delayed for lower altitude flights.

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That's interesting information regarding baro-based apogee detection over 80k feet Adrian. I'll have to keep that in mind when I finally get around to going near that altitude!

plugger said:

Is it a dual axis accelerometer only issue or are your single axis 250G models also susceptible to drift errors?

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Both types have the A/D converter, and the 250G units can be worse because the +/- 1G calibration covers a smaller section of the A/D converter's range.