Chute release alternative

Discussion in 'Rocketry Electronics and Software' started by jdbwizzard, Dec 16, 2016.

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  1. Dec 22, 2016 #31

    georgegassaway

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    Yeah, here's a couple of pics of her first version, which was a bit heavier and longer than the C.R. but fit inside a BT-55. A later version fit inside a BT-50 and IIRC weighed about 10 grams.

    Early mock-up of the first one with J.L. Chute Release above

    [​IMG]

    First one packed for flight.

    [​IMG]


    For anyone who does do an R/C Chute release, make sure the receiver is capable of "Fail Safe", so that if it loses signal, it will hold itself to a pre-set position rather than randomly move/jitter the servo. Most would probably want to set the failsafe to NOT release the chute, so if the model flew really high and lost signal then it could fall back down into range of the transmitter to activate it (If the rocket is not going to come down close enough to resume signal, something is wrong as the whole idea is to quickly come down close to the launch area then deploy the chute). Although some super-careful fliers might prefer the opposite, to default to release the chute early in case of signal loss. BTW - pretty much any receiver worth using will re-acquire the signal and respond properly, if it did lose signal on boost.

    That said, I am super-impressed with the JL Chute Release. That is a revolutionary device for the hobby, which anyone can learn to use easily, that ranks up there with the Cineroc, and altimeters.
     
    Last edited: Dec 22, 2016
  2. Dec 26, 2016 #32

    Winston

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    For the loss of signal servo jitter problem, orient the 'chute reefing latch mechanism (servo arm) so that it is latched in the neutral position. Jitter won't make any difference then with respect to early release. For durability use metal gear servos. Chinese ones are cheap.

    From investigation, here's the problem I've discovered for anyone who doesn't already own a R/C TX who might want to buy a cheap TX/RX combo to use this R/C reefing method - there is a nice selection of long range mini/micro receivers for the more expensive R/C TXs (Spectrum, FrSky, JR, Futaba, etc.), but not so for low cost TXs (FlySky, Turnigy, etc.) at least from what I've been able to locate. Range is definitely not a problem for the cheap TX/RX combos as shown in the video below, but the RX size will relegate this technique to maybe 2.5" and above body tube diameters:

    $50 FlySky FS-i6 2.3km range test - no mods! (Jun 3, 2016)

     
  3. Dec 26, 2016 #33

    tab28682

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    Don't forget that Spektrum has an entry level full range Transmitter, the DXE, that retails for under 60 bucks. This allows the use of the inexpensive tiny full range AR400 RX. It is nominally a 6 ch TX, but can be configured for more channels, up to 9.

    The DXE is programmable via your phone, with an app, or via your computer with some free downloadable software.
     
  4. Dec 26, 2016 #34

    ttabbal

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    One thing to be aware of with some systems is that they lack failsafe. So the servo positions when signal is lost is not defined. Most will hold the last sent position, which will work in this case. But it's something to be aware of if you are buying something. FrSky is the cheapest setup I know of with failsafe and good small receivers. If you get a transmitter that can take a module, the FrSky module is about $30.
     
  5. Dec 26, 2016 #35

    Winston

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    But definitely will not work with aircraft if you weren't flying straight and level at loss of signal which is the reason for failsafes.
     
    Last edited: Dec 26, 2016
  6. Dec 26, 2016 #36

    tab28682

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    Failsafe on all channels is a complete crap shoot for model aircraft, unless you are flying straight and level. Most people spend little time straight and level and if failsafe activates while doing aerobatics, it can put you in the ground as likely as saving you. I saw a fully setup failsafe on all channels plane go straight in, at low throttle, after activating while pointed nose down.
     
  7. Dec 26, 2016 #37

    tab28682

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    I have my servos rigged for minimal force applied to the servo arm while in locked mode before release. I have tested both loss of TX signal and loss of RX power and the servo does not move, even with a non failsafe channel (5) being used for the release.

    My unit designed for 2.6-3" dia airframes uses a non metal gear servo (the reliable, common and very inexpensive HXT900) and has always worked perfectly, on 7 mid power flights and one high power flight (4"x78" rocket on an I140).

    I have a slight larger unit designed for 4" and larger rockets that does have a 9 gram metal gear servo. Has not flown yet.
     
    Last edited: Dec 26, 2016
  8. Dec 26, 2016 #38

    Winston

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    I didn't know about that cheap Spektrum TX and I really like that RX. They even state in a roundabout way that it has an LNA ahead of its RX chip whereas the front end of RX chips alone typically have better than -100dBm noise figures all by themselves (@ low data rates) and usually don't need to use an LNA for anything other than long range use. The RX's allowable voltage range (3.5V - 9.6V) also makes possible its use with a fully charged (4.1V) single cell lipo and a mini/micro servo using the same voltage range (3.7V typically for them), which would further reduce overall dimensions and mass of the system. The AR400 RX dimensions - 17 x 31 x 11mm, I assume width, length, height.
     
  9. Dec 26, 2016 #39

    tab28682

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    Here is a shot of my yet unflown unit for BT50-55 models. The sub micro servo is on a ply tab by itself and the caseless AR400 RX (pins cut down and servo lead and power lead soldered directly to the board) and 1s lips battery is in the segment of BT20 tube shown. For models with no payload bay, I will tie the BT20 electronics bay to the screw eye on the nose cone. If the model had a payload bay, can insert the electronics bay into the payload bay.

    IMG_2033.JPG
     
  10. Dec 26, 2016 #40

    Winston

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    Yep, mostly useful for far less common aircraft with on-board flight controllers with programmable failsafe positions.
     
  11. Dec 26, 2016 #41

    Winston

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    Cool. Great to hear about the larger version working so well, too. I have a number of HXT900s and a few same-size metal gear servos (can't recall the number) from HK on hand. On the HXT900 version, you're still using a 1S lipo?
     
    Last edited: Dec 26, 2016
  12. Dec 26, 2016 #42

    tab28682

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    Actually, many of the modern micro RX units do fine on 1s lipo. I have about 10 RC RG models, all using the Lemon DSM2 compatible micro 6 channel RX on 1s lipos, plus another Lemon RX in the 2.6-3" RC Chute Sled. All my Chute Sled flights have been done using 1s lipo power with one of the small 150-160mAh packs as used in the 1s uM and uMX RC models from Horizon. I fly a lot of those models and have a lots of those batteries.

    The Lemon line of DSM2 and DSMX compatible RX units are excellent, despite the brand name implication...;)
     
  13. Dec 26, 2016 #43

    Winston

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    Thanks for that info. I've never tried operating RXs below their specified operating voltages. The only R/C stuff I've ever flown on 1S are small quads.

    The 4V (too high for the use of a slightly discharged lipo cell) minimum operating voltage I often see in inexpensive RX specs is, I think, related to the required input voltage headroom to maintain voltage regulation for RXs that don't use low dropout linear regulators. I think they're simply going by the voltage at which the regulator will lose it ability to regulate. From that point on the voltage on the RX board will simply follow the lipo cell voltage minus the regulator's voltage drop. However, since everything on a modern RX's board will almost certainly be made to operate at 3.3V and the minimum operating voltage on the RX chips I've read the datasheets for is 2V, the dropping voltage doesn't matter much although I could see a lower voltage perhaps increasing front end noise.
     
  14. Dec 26, 2016 #44

    tab28682

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    Quite a few of the modern RX manuals state the minimum of around 3.5v. The Lemon RX manual states 3.45 volts minimum. Like I said, a lot of the modern micro RX units are good with a 1s lipo. Worth checking the manual, which I do. All Spektrum RX units work down to 3.5 volts per this:

    http://www.spektrumrc.com/Articles/Article.aspx?ArticleID=1683

    Having said all that, I almost never operate more than two micro servos on a 1s setup, (except for the uM and uMX factory model setups on 1s) as the servo loads can drop the voltage close to minimum.

    I have zero worries about a Lemon or Spektrum micro RX with one servo on 1s for a Chute Sled. If using one larger servo, I would upsize to a larger 1s pack of 200-600 mAh capacity, as the larger capacity reduces voltage drop under load.
     
  15. Dec 27, 2016 #45

    Winston

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    The 4V figure I was going by was gleaned from my recent investigation of cheap FlySky/Turnigy compatible RXs from places like Banggood. Many give a range bottoming out at 4V while others simply specify 5V instead of giving a range.

    I plan to do bench RX minimum voltage tests for the FlySky FS-iA6B, the $9.99 diversity RX supplied with the FS-i6 TX and the one used in the 2.3Km range video I linked to above and the $7.99 non-diversity FS-R6B.

    Yeah, I trust Chinese lipo C ratings as much as I do their other specs, which isn't much, and if already operating at 4.1V fully charged, you don't have much room to drop. I plan to use 240mAh packs for my RC triggered and Arduino Trinket triggered reefing sleds and only plan to use one HTX900 servo in each, maybe trying a TGY-90B metal gear servo which I have on hand just because I have it, but I'll of course check the lipo voltage drop with the servo activated in both cases.
     
  16. Jan 9, 2017 #46

    sl98

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    I had some time today to run a test today using a Quark and some safety igniters that were sent to me by mistake. I used some elastic thread and powered my Quark with a 1s LiPo. In test mode, the Quark fires for 1 second. I took a video of the test but can't upload. Instead I grabbed a few stills from the video. The safety igniter popped the thread off instantaneously and because it was elastic if flew clear of the couper I was using for the test. In the 4th picture you can see the orange glow of the wire inside the clip.

    ImageUploadedByRocketry Forum1483925722.321418.jpg ImageUploadedByRocketry Forum1483925741.538229.jpg ImageUploadedByRocketry Forum1483925761.824265.jpg ImageUploadedByRocketry Forum1483925773.820445.jpg ImageUploadedByRocketry Forum1483925787.501459.jpg ImageUploadedByRocketry Forum1483925803.929167.jpg ImageUploadedByRocketry Forum1483925815.545362.jpg
     
  17. Jan 9, 2017 #47

    GrouchoDuke

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    That looks awesome. Go fly it!
     

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