Alt & tracker on same battery?

[ksaves2]

Another perspective...tying the grounds of two different electronic systems creates a path for electrical noise to move from one to another. Putting a transmitter and a computer on the same ground, unless designed to be done that way, can create issues. Test well...

I never do it.

Good rule of thumb except for when the products are known to play well together as mentioned in message #29. I've witnessed three anomalies related to Rf/deployment device adverse interactions. Suffice it to say the newer products out there are more resistant. If one doesn't know, put bare confined ematches in the rocket, turn everything on and stand it up on the rail at home or lean it up against the wall. If the matches don't pop or the altimeter(s) don't recycle or shutdown
after 45 minutes to an hour, you can be pretty certain you won't have an issue. Kurt

 

[cerving]

Cris, what about a Quantum & Eggfinder Mini?

If you have a big enough battery, they should be fine. That 600 mAH would probably be OK. My question on that would be why you are doing that in the first place... that's a pretty fair amount of AV bay real estate, so if your rocket is 3" dia or larger then you're going to have enough room in the NC to mount the tracker there anyway. Smaller than that and unless you've extended the AB bay somehow it probably won't fit.

 

[dr wogz]

Ok, based off all that's been written ( what's applicable!) I've got two sleds under way.. all will have 2 batteries; 2S 450mAh & 600mAh...

First up is a very tight fitting set up for my Darkstar Jr. I'll be adding some stop blocks to help hold the batteries in place.. sadly, the NC is all glued n painted, and all sealed up.

Next is the sledge for my 4" patriot. More room!

Also, while trying to figure out stand-offs, I came across these beads at the local hobby shop. Plastic, about 3/16" tall, and a perfect fit for a 4-40 screw! $4 for a bag of about 200!

 

[ksaves2]

Hot diggity on those beads Paul. Neat find. Do a range check if you can of your setup with the ebay buttoned up. If you can hoist it up in the air, on a tree or a pole all the better and see what kind of reception you get.
Make sure you walk away and see when you lose the signal. If it's just a 1/2 block over open terrain, you may have a problem.

The carbon black used as a colorant in black tubing can modestly shield Rf and I hope the tubing isn't real carbon fiber or you could be in big trouble with that setup. True CF is an Rf shield.
The paralleling all-thread might distort or retard the radiation pattern of the EggFinder mini. With 100mW on 33cm/900Mhz you want the best propagation you can get if you are going to really punch it up there.
Eggfinders can sometimes be squirrely on descent with the tumbling of the rocket under drogue so don't expect every position to be received. The EF mini might have more of an issue though I haven't tried mine yet.
The EF's really shine when the rocket settles down under main deployment. That's the most importanst thing to get a successful recovery. I've had close to 20 EF flights and never lost one rocket. Even the one
with two positions right over the fincan on a ballistic recovery. Walked up to the last position and there it was butt end out of the ground. I don't get every transmitted position from my EF's to plot on a live map but it's enough to find the
derned things. I do have to say though, I use a 1/2 wave antenna such as this: https://linxtechnologies.com/wp/wp-content/uploads/ant-916-cw-hw.pdf or this https://linxtechnologies.com/wp/wp-content/uploads/ant-916-cw-hwr.pdf
(I picked up a bunch on ebay a few years ago)

You don't want to get the rocket out of sight and at altitude with no positions received. I had that happen 11 years ago and it's a sick feeling. It was metallic paint that shielded the Rf from getting out the rocket.
I failed to do an adequate range test and was burned. Lucky the one rocket was seen and recovered so I could remedy the setup. I had a second one with the same paint that went in due to apogee deployment failure.
Was found in a week and I got the remains back a year later. No positions received. I really learned a lesson that launch.

Another thing, don't punch it the first flight. Minimize the out of sight time so if the tracking setup is a failure you can visually recover in a normal fashion and at least get your hardware back for another project or
try a remedy. I do this every time with a first time project now as force of habit.

Again, do a good ground test. I can't stress this enough. How far is "good enough"? I put my ebays or NC trackers on my single story roof (actually a table top chimney) and walk away. There is a 3 story brick house directly
to the east from me which is a line of sight obstruction so I walk north or south on a line east of me. I keep a line on my house and with obstructions I get 1/2 mile easily with the EggFinders. With the 70cm 16mW Beeline
GPS tracker I can hear it in the Walmart parking lot one mile away. Kurt

 

[mpitfield]

Below are the results of my testing. As I originally commented I initially performed bench tests, but not to the point of failure. The following tests are on the extreme side in an effort to understand, as well as, prove the limits of my specific configuration.

Day 1:
I started what was going to be a full-up run-time until failure test. However after 6 hours and 15min I stopped the test. This was using my 610 mAh fully charged (8.4v) 2S LiPo. The devices consuming power were all the previous mentioned devices. The Quark with no continuity on the apogee and a resistor across the main. I am only using the altimeter for apogee as I use a JLCR for main on this rocket. Also included were the EggFinder Mini and the Featherweight Magnetic switch. I also left the EggFinder LCD running with it's own battery, just to know it's limits. My EggFinder LCD has both the BT and GPS module so it is a worst case scenario, unless you turned the LCD back-lighting on.

Post test the sled battery was 3.69v and 3.68v (7.37v combined), The Eggfinder LCD with BT and GPS module was 3.72 and 3.73 (7.45v combined), as stated both batteries are the same and started at 8.4v.

Day 2:
I picked up from where I left off to run the battery down to failure, but I decided to see how well the altimeter performed. That is if the altimeter could still fire the channels with the batteries starting off somewhere around 30-40% of capacity. In total, I performed 3 e–match tests. I connected the full length of e–match wire (as a worst case for resistance) to apogee only. I performed this test twice back to back by using a vacuum to trigger the altimeter. Then I immediately removed power, swapped the e-match, powered everything up and performed the test over again, once the altimeter was ready. This is the setup I would normally fly with, that is a resistor on the main channel so apogee only. The 3rd test was using both channels, which this rocket will never do, so both apogee and main. Again I used the full length e-matches on both channels (a worst case for resistance) and both channels fired nominally.

Post test the voltage of the sled was unchanged from the start of the test, which was the same as the day before, 3.69v and 3.68v (7.37v combined)

I then decided to leave the rig running until it died. This took another 40 min and the final voltage was 4.3v total. I could not measure the cells individually as the voltage was too low for my charger to measure or even charge. I had to use the NiMH charging method to recover the battery. For those who know LiPos you will know what I am referring to.

Conclusions, I will let you come to your own conclusion after carefully reading and weighing each post. My opinion is that this is a topic of nuance and that it can be an acceptable safe configuration, but its fair to criticize it as not an ideal configuration. To provide an example, when I was considering which tests to perform I realized that the GPS can take a bit of time to fully settle, that is between the tracker and receiver with the GPS module in it. So having the ability to independently power up the tracker well ahead of time is a plus. However with the total run-time I realized I am very confident in this configuration, even with an extreme delay.

 

[dshmel]

I then decided to leave the rig running until it died. This took another 40 min and the final voltage was 4.3v total. I could not measure the cells individually as the voltage was too low for my charger to measure or even charge. I had to use the NiMH charging method to recover the battery. For those who know LiPos you will know what I am referring to.

You may have damaged the cells taking them down that low. I would test the capacity of the battery before flying it.

 

[mpitfield]

You may have damaged the cells taking them down that low. I would test the capacity of the battery before flying it.

I was comfortably aware of what might happen before I began the test. Post test I completed several internal resistance tests and compared it to 3 other same LiPos, and they were all within a similar range. I then fully charged it up to 8.4v, took it down to storage 7.65v (3.825 per cell), then back up to 8.4v and it was nominal on internal temperature, 26°-27° C, charging at .3A. Post reconditioning I powered the tracker for a few hours then took it back down to 7.65v for storage. Having said that I did mark the battery to identify it from the others, so when I use it next and charge it up, I will be paying attention.

I use the SkyRC iMAX B6AV v2 charger which has some good tools for diagnosing, charging and reconditioning batteries.

I don't profess to be an expert on LiPos or even know a lot on the subject. However I have been using them for years and out of curiosity I have done a fair amount of research over many sources. I have also participated and read several threads on TRF discussing the pros and cons of LiPo battery chemistry, specific to our applications.

 

[manixFan]

Great write-up mpitfield on testing and results. Says a lot about the capacity of LiPo batteries for our usage. And according to the designer of the units there is no issue having a common ground.

Some folks will still be uncomfortable with the idea but as I stated earlier I would not have a problem with it and your testing backs that up. Thanks for letting us know your results.


Tony

 

[dshmel]

Agree. Great information about real world testing of non-traditional set ups. Much effort and emphasis is placed on miniaturization of flight computers, when you can conserve weight and volume with a single battery set up. My 38mm MD will have two altimeters powered by a single LiPo via a FW magnetic switch. I will have a separate tracker in the nose cone. As far as deep discharging LiPos, my experience has been mixed. I have discharged a few cells below 3.0V and have been able to rehab them. I have also let a couple discharge overnight to complete depletion. For those, I didn't risk the recharge "work around" process. Sounds like you did not get into the deep discharge "red zone."

 

[dr wogz]

OK, thanks all, there' a lot here to digest. I've read it about 3 times now, and will be making a plan-of-action..

 

[dr wogz]

An update:

The boss was away for a few days. so, I took advantage of our 'down time'.. I designed up a modular system to put in my 8" x 2" AV bay. the standard 2x 1/4-20 threaded rod holes at each side, the battery 'cup' and a recess for the tie wraps. The top-side features the hole patterns for either the Eggfinder Quantum or the Eggfinder Mini.. Intended for 3D printing (hence the flat top)..

This was my first draft, and was printed as such. I'd like to revise it sometime soon, as I found the symmetry didn't really lend itself well, and (being a mechanical guy) kinda forgot about the wiring! I'd also like to incorporate a better switch than trying to fish wire up & thru a vent hole (a la "twisted wires" switch).. And, I feel I can also remove a bit more material where it's not needed. (And this is why we prototype stuff!!) But still, and good stab at it, and it only took about 3hrs design time (4 to print!)

I can make this file available is there is interest..

 

[smugglervt]

Paul,
Can you incorporate a switch mount for either a rotary switch or PCB screw switch in the front like Missileworks does with their sleds? Another nice feature would be some type of modular shelf to go under the switch so it can be used with various diameter tube sizes. (another words, a way to keep the switch close to the wall of the tube so you can use the same sled on 2", 3", 4" diameter tubes and still be able to easily access the switch with a short screw driver.

 

[dr wogz]

Jim, one step ahead of you! the intent is to add a switch. still deciding on what & what type.. Remember, there are two things that need to be switched. so it either a 2 pole, single throw type toggle / slide, or 2x single pole, single throw.. or two of the rotary type..

This one is dedicated to my Darkstar Jr. Because it's a tight fit, trying to mash everything in there! I figure the DS is a good test bed as it's pretty firggin' tough!

You'll see soon enough! [wink]

 

[dr wogz]

Some shots of the finished and mounted sleds. The GPS to needed to be skewed as the antenna is just a tad too long.. another reason for a version 2. I have a 600mAh and a 450mAh battery in there..

And the token cat shot. She lives on my bench!

 

[smugglervt]

Would the lab rat double pull pin switch fit? Right around 2" wide.

 

[dr wogz]

Would the lab rat double pull pin switch fit? Right around 2" wide.

thinking about it, or something similar..