Eggtimer Wi-Fi switching 2 Altimeters?

[dshmel]

Has anyone wired up an Eggtimer Wi-if switch to turn on/off 2 separate altimeters?

 

[rharshberger]

Good question. I too am waiting to hear the answer.

 

[KenECoyote]

I was wondering this myself last weekend. I used one wifi switch on a 4" Wildman Demon and want to add in a redundant system.

Initially I was thinking you can't since each has it's own wifi signal, but now I guess you can link to one, arm, then switch wifi to the other and arm (or use two cell phones!); however that's just a guess. Cris will answer on this one to be sure.

Edit: Sorry...missed that OP is noting one WiFi Switch on 2 alts. I figured redundant systems should have separate switches, so I wasn't thinking of that (especially since I had above on my mind recently).

 

[OverTheTop]

You could switch two altimeters with the one WiFi switch. As the designer/flyer it is a choice you get to make. It does mean that the configuration is partly able to experience "single string" failures that can disable both systems.

I couldn't imagine any RSO's disallowing the flight based on that configuration. I think for Tripoli L3 certification they need to be independent, but that might be dependent on who your TAPs are too.

All my HPR stuff runs some form of redundancy, although not necessarily entirely independent.

If there are other risk mitigation strategies in place then the decision is easier .

Even serious spacecraft are designed single-string in some cases, but I am sure they would run a fairly extensive FMEA (failure mode and effect analysis) to asses the risks and determine what they want to pay for (risk mitigation costs money, mass, or other things) or what they want to get away with. An article with some examples here:
https://llis.nasa.gov/lesson/1743

 

[cerving]

You could, of course... but I wouldn't recommend it from a redundancy point of view. If you're switching on two different systems (maybe an altimeter and an GPS) then that's another story. My Rocketry Warehouse G3 has a Quantum as the primary and a WiFi Switch/Quark as the backup; fully redundant, including charges. These systems are so inexpensive compared to the cost of your rocket that if you can fit two systems in, you should. (BTW, you certainly CAN have more than one Eggtimer WiFi system in the same rocket... each one has a different SSID and passkey, they play very well together. You just need to turn them on one at a time, that's all.)

 

[dshmel]

You could, of course... but I wouldn't recommend it from a redundancy point of view. If you're switching on two different systems (maybe an altimeter and an GPS) then that's another story. My Rocketry Warehouse G3 has a Quantum as the primary and a WiFi Switch/Quark as the backup; fully redundant, including charges. These systems are so inexpensive compared to the cost of your rocket that if you can fit two systems in, you should. (BTW, you certainly CAN have more than one Eggtimer WiFi system in the same rocket... each one has a different SSID and passkey, they play very well together. You just need to turn them on one at a time, that's all.)

Thanks Cris,

I lost a rocket last weekend due to faulty drogue e-match. Not sure why the main channel didn't fire at 500' (it was a Quark), but I surmise the descent was too fast to allow the system to respond. I am sure that is separate study. Anyway, I have been brainstorming ideas to create redundancy - from running parallel (or series) e-matches on a single channel output, to completely independent systems (like L3). I was looking for a solution that was a middle ground for "smaller" rockets that have limited e-bay volume > One power source (LiPo) + one switch + two flight controllers. Your Wi-Fi switch has a stated output limit of 13 amps which should power two controllers. Since the e-matches of the two flight controllers would be firing in a staggered sequence, I would think that 13 amps along with a "robust" LiPo would preclude a brown out. I will spend the build season testing various scenarios with the inventory of altimeters that I have. I was curious as to whether or not anyone has actually wired two separate altimeters in parallel to the power output channel of a singe Eggtimer Wi-Fi switch and flown it.

 

[dshmel]

...
My Rocketry Warehouse G3 has a Quantum as the primary and a WiFi Switch/Quark as the backup; fully redundant, including charges.
...

I will be purchasing a couple of Quantums during your sale. Prolly have Connor McGrath assemble them since he did a great job last year.

 

[ksaves2]

Hmmmmmm, I believe one is implying using one WiFi swtich to control two altimeters? Ahhhh, I think that would entail one large capacity battery to feed two devices. I wouldn't do it as it would lose the redundancy of an independent system. If the power connection is lost, both deployment devices shut down.
Best to have two separate deployment systems if counting on redundancy. If one doesn't have the room, perhaps have one device manually switched and one
on a Wifi switch. I've mounted a featherweight screw switch on an aft bulkhead with a form fitting hole and substituted a socket screw to turn on/off. Just takes a
ball head driver to turn off and on, lower the upper bay back down on the sustainer. Has a small foot print.
Like Cris mentions if the room is there have two complete independent systems. It's not a pretty sight to see a large project go in ballistic. Kurt

 

[cerving]

Thanks Cris,

I lost a rocket last weekend due to faulty drogue e-match. Not sure why the main channel didn't fire at 500' (it was a Quark), but I surmise the descent was too fast to allow the system to respond.

That unfortunately happens, I had a bad drogue ematch at LDRS, the main fired just high enough to keep the rocket from ending up being buried in the playa. Zippered the heck out of the FG tube, though. Did a post-mortem on the ematch, I probably couldn't have lit it with a blowtorch. Redundancy is good if you can fit it in... motor eject works for the drogue, unless the maximum delay is too short (which accounts for a lot of the stuff that I fly).

 

[OverTheTop]

I would think that 13 amps along with a "robust" LiPo would preclude a brown out.

Be careful that the LiPos you use don't have overcurrent protection electronics in them. Many have little electronic fuse boards designed to protect the battery or downstream product. These can be triggered by a temporary short circuit and trip the battery (and your recovery system ) off-line. Check your batteries are really just batteries.

Also, the larger batteries are more prone to catching fire in the presence of mechanical damage (eg crash landing). They just have more energy available than the small ones. I have heard our RSO commenting on this to someone who was flying a large battery for a telemetry system and deployment.

I use (typically) 180mAh 2S batteries for each altimeter, and 120mAh 2S batteies for each eMatch. They are quite small and don't weigh too much for my flights.

from running parallel (or series) e-matches

I would not run series eMatches myself. If one goes open then redundancy is lost. The same could be said for parallel with a short circuit . Running separate channels on the altimeter is better, but if not practical I would choose parallel myself. It comes down to the risks with the hardware you are using.

 

[dshmel]

Be careful that the LiPos you use don't have overcurrent protection electronics in them. Many have little electronic fuse boards designed to protect the battery or downstream product. These can be triggered by a temporary short circuit and trip the battery (and your recovery system ) off-line. Check your batteries are really just batteries.

Also, the larger batteries are more prone to catching fire in the presence of mechanical damage (eg crash landing). They just have more energy available than the small ones. I have heard our RSO commenting on this to someone who was flying a large battery for a telemetry system and deployment.

I use (typically) 180mAh 2S batteries for each altimeter, and 120mAh 2S batteies for each eMatch. They are quite small and don't weigh too much for my flights.


I would not run series eMatches myself. If one goes open then redundancy is lost. The same could be said for parallel with a short circuit . Running separate channels on the altimeter is better, but if not practical I would choose parallel myself. It comes down to the risks with the hardware you are using.

Good info. Thanks.

 

[bobkrech]

Read the manual. https://www.eggtimerrocketry.com/attachments/File/WiFi_Switch_Manual_Rev_A4a-2(1).pdf

1.) The maximum continuous current rating is 13 amps.

2.) The minimum recommended battery capacity is 300 mah.

So yes the switch could power 2 or more altimeters however is probably is not a good way to go....

1.) a dual altimeter system is no longer redundant since both share the same power supply and are susceptible to a single point failure.

2.) the WiFi switch is rated to deliver 13 amps so it can supply more current than many altimeter FETs can handle under shorted conditions. Many altimeters only use 5 amp rated FETs.

 

[cerving]

1.) a dual altimeter system is no longer redundant since both share the same power supply and are susceptible to a single point failure.

^^^ This ^^^

If you're using the WiFi Switch for two different devices (maybe an altimeter and a tracker) then it's OK, but it's a bad idea from a redundancy point of view to use it for both altimeters. Similarly, it would be a bad idea to use ANY switch to power both altimeters...

 

[dshmel]

Read the manual. https://www.eggtimerrocketry.com/attachments/File/WiFi_Switch_Manual_Rev_A4a-2(1).pdf

Thanks, I did some time ago when purchasing the 2 Wi-Fi switches last year.

1.) The maximum continuous current rating is 13 amps.

2.) The minimum recommended battery capacity is 300 mah.

Yes, I saw that too. I would be using a 500 mah or higher. Maybe one of my 1000's.

So yes the switch could power 2 or more altimeters however is probably is not a good way to go....

My OP was asking if anyone had actually connected two flight controllers to a single Wi-Fi switch. Redundancy is a separate question.

1.) a dual altimeter system is no longer redundant since both share the same power supply and are susceptible to a single point failure.

Using that definition, would using a single battery on altimeters that have the capability of using two (one for pyro, one for controller power) NOT be redundant?

 

[ksaves2]

Thanks, I did some time ago when purchasing the 2 Wi-Fi switches last year.



Yes, I saw that too. I would be using a 500 mah or higher. Maybe one of my 1000's.




My OP was asking if anyone had actually connected two flight controllers to a single Wi-Fi switch. Redundancy is a separate question.



Using that definition, would using a single battery on altimeters that have the capability of using two (one for pyro, one for controller power) NOT be redundant?

In that regard two flight controllers on a single switch is indeed possible but really, lose a battery connection and it's ballistic flight city. Now Cris mentions a flight controller and a tracker. Well lose that battery that has a redundant controller, it may save the flight but if it's completely sight unseen, one may lose the rocket.

As far as your comment, "Using that definition, would using a single battery on altimeters that have the capability of using two (one for pyro, one for controller power) NOT be redundant?"

The issue is onboard CPU failure with a brownout using too low a capacity battery for both the pyro side and controller side. Hence one sees people using their 9V batteries for one or two flights on single battery controllers.
Whether or not one uses two batteries in a device that allows it depends upon what one has planned for the output channels. Just blowing ematches? Probably can get by with a single battery. I look at battery weight as
useful if one needs nose weight for balance purposes. A higher capacity battery can do that (if the weight is needed) AND it allows for prolonged waits on the launchpad at a busy launch.

Again boils down to what is one going to do? I've seen people do "hot wires" for delayed deployment and the current requirements can be high for a hot wire. Best to use a deployment device that allows for two batteries in that case.
(Personally, I think that strategy is going to die out with the Jolly Logic Chute Release). Kurt

 

[bobkrech]

An example of a totally independent redundant aviation system is the dual magneto ignition system used in piston engine aircraft. 2 independent magneto systems fire 1 of the 2 spark plugs in each cylinder. Both systems are operated together, however if one fails, the RPM drops by ~50-100 rpm but the motor doesn't die so the aircraft can be flown and landed safely.

In a hobby rocket, a dual redundant deployment altimeter system consists of 2 totally independent deployment systems so that a single point failure will not inhibit the second deployment altimeter. Using a single switched power source for both deployment altimeters introduces 2 single point failure sources that disables both deployment altimeters: 1.) the battery and 2.) the WiFi switch. If you have 2 power sources, one for each altimeter, then if one battery or switch fails, the other will still function and safely deploying the recovery gear.

A few altimeters have the option of separate altimeter and pyro batteries, but most do not. This option is used for air starts that may require high current draw igniters. It is not required, or useful, for electronic activation of the ejection charges. In the deployment configuration, the use of a second battery for the pyrocircuit reduces the reliability because of the possibility of the pyro battery or switch failing.

 

[OverTheTop]

A few altimeters have the option of separate altimeter and pyro batteries, but most do not. This option is used for air starts that may require high current draw igniters. It is not required, or useful, for electronic activation of the ejection charges. In the deployment configuration, the use of a second battery for the pyrocircuit reduces the reliability because of the possibility of the pyro battery or switch failing.

I don't agree with this statement (except that airstarts require more current), particularly the last sentence. LiPo batteries can be tripped off by a high current draw if they are the type with the inbuilt fuses. This could be caused by an igniter shorting when firing. It can be a point of single-string failure.

Battery failures happen. I had a LiPo pack in my cordless drill fail yesterday. It just stopped during a small job. One cell had gone completely open with little provocation.

For HPR I fly three batteries per altimeter (two altimeters). One for the electronics, one for each pyro channel.

If you really want to get technical you would need to run an FMEA for each configuration to see where the weaknesses are and if they actually matter.

 

[cerving]

The idea of doing a FMEA is intriguing, but I'm not sure how valid it would be for hobby rockety. The reality is that batteries, electronics, and switches are all relatively low failure rate aspects of recovery. Ematches seem to be a bit higher, but the most common failure that I've seen is chutes getting stuck, the charge failing to break the shear pins, shock cord breakage at the mounting, etc.; in other words, mechanical rather than electronic. The same failure modes are common with motor eject, too.

We will now return you to your regularly scheduled post... the answer to #1 is "Yes, you can connect more than one device to a WiFi Switch". Whether you SHOULD... different story.

 

[OverTheTop]

The idea of doing a FMEA is intriguing, but I'm not sure how valid it would be for hobby rockety. The reality is that batteries, electronics, and switches are all relatively low failure rate aspects of recovery. Ematches seem to be a bit higher, but the most common failure that I've seen is chutes getting stuck, the charge failing to break the shear pins, shock cord breakage at the mounting, etc.; in other words, mechanical rather than electronic. The same failure modes are common with motor eject, too.

Correct on all statements I think

The FMEA is a tool (think of it as a blunt instrument, not a tool with finesse!) that just gets you thinking. Any of the resulting RPN scores that are high might need dealing with. Anything that has death or severe injury as an outcome must be dealt with! It is used in different ways in different applications (say automotive, or scientific instruments which have different constraints). You would tame it down a bit for model rocketry (one-off, non-commercial product etc). Just use it to help with thinking, if you are going down that track. Fairly wild guesses for occurrence probability still produce reasonable results.

 

[jderimig]

FMEA is an excellent tool, for problem prevention. For reliability modeling I would go with other approaches. I am doing a FMEA for my high alt BALL's project. It should be done before and during the design of your system, not afterwards. All failure modes should be addressed preferably with a design control (design the failure mode out if possible) and if that is not possible a detection method. The latter is very useful for creating your launch checklist.

 

[ksaves2]

I don't agree with this statement (except that airstarts require more current), particularly the last sentence. LiPo batteries can be tripped off by a high current draw if they are the type with the inbuilt fuses. This could be caused by an igniter shorting when firing. It can be a point of single-string failure.

Battery failures happen. I had a LiPo pack in my cordless drill fail yesterday. It just stopped during a small job. One cell had gone completely open with little provocation.

For HPR I fly three batteries per altimeter (two altimeters). One for the electronics, one for each pyro channel.

If you really want to get technical you would need to run an FMEA for each configuration to see where the weaknesses are and if they actually matter.

As far as over current on an ematch channel. Some controllers allow to set a time as to how long the current is applied to the ematch. Do a ground test with like 1 second and if ones matches fire consistently, then using 1 sec "on" and the device cuts
off the current thereafter could avoid vaporizing the electronics or battery if the ematch doesn't open after burning. Kurt

 

[OverTheTop]

FMEA is an excellent tool, for problem prevention. For reliability modeling I would go with other approaches. I am doing a FMEA for my high alt BALL's project. It should be done before and during the design of your system, not afterwards. All failure modes should be addressed preferably with a design control (design the failure mode out if possible) and if that is not possible a detection method. The latter is very useful for creating your launch checklist.

I am excited to hear someone is using one for HPR

It helps if you get a few people in the room with you as you do it. Plenty of more perspective on problems.