[NRVR-Members] More Technical Details About Jolly Logic Chute Release
Thomas Tweeks Weeks
tom at theweeks.org
Sat Sep 8 16:12:31 CDT 2018
So I've been talking with the engineer/owner of Jolly Logic again.
Older vs Newer Style Servo Clips:
It seems there is indeed a slight difference in the early revision (hardware) servo clips and the newer clips. There's not super obvious way to visually tell the difference, except that the old one looks shiny and a little more rounded on the tip. See here (old clip design, left):
As soon as John upgraded my case and servo to the new design, the old clip no longer engaged and he had to send me a couple new clips (right) to match the new case & servo anchor. So just FYI, if you ever buy new clips.. look at your clips closely (compare to my photo) and get the right version (old/shiny vs new/matte). If you need new clips.. look at yours closely before ordering. John at Jolly Logic knows the difference, but other third party vendors may not have both versions or know about this difference.
Problems With Oversized Chutes or Smaller BTs (causing crashes):
I've been seeing problems with my Jolly Logic over the last couple of years and have slowly been digging in to the issue. I had John upgrade my firmware from v1.1 to v1.3 (current latest) but that didn't change the behave differently. The failing combination seems to be smaller BT (body tubes) & larger chutes (or any size BT with an overstuffed chute). This has happened on my old LOC 2.6" Hi Tech (with a larger, tight fitting chute + kevlar wrap), once on my 2.6" HoJo (with larger chute), and even once on my Pershing (4" BT, but with an oversized chute + kevlar protector wrap) and this latest time on my beautiful Bomarc (also 2.6" + wrap). In each case it was a larger than normal chute and/or smaller BT.. the laundry always came out at apogee (usually free fall).. and the CR always failed to open at the programmed altitude when a config like this was used. Smaller chutes + wrap (that don't make as tight of a seal) never seem to be a problem.
I've been flying Jolly Logic since it came out a few years ago.. and one consistent observation I've had is that I tend to like to pop big (oversized) chutes down low (4-500ft)... AND that all of my BT vent holes are always down lower between my chute and my fins (to prevent air pressure diffs from pushing the laundry and popping off the nosecone on the way up). I discussed this with John from JL, and discussed the theory that the JLCR might be "insulated" from real time (correct) barro readings through the small, aft-chute vent hole, and that the CR may not be getting these barro changes fast enough to register the "in air" activation-trigger of "being 100ft off the ground for > 3 seconds" and thus may not have enough time to arm before apogee. He says the LJ should be able to compensate for this after apogee and go into "Flying/Falling" mode, but said that he's not sure, and said that compensating for this "delayed barro pressure" couldn't hurt (to try).
So that's what I've done in my last couple of flights by drilling additional vent holes higher up near the nosecone (just aft of the nosecone shoulder) so that the CR can get better/faster barro readings as goes up. I can't be 100% this has been the cause of my problems, but this seems to have worked fine the last couple of flights (with oversized chutes+wraps), and I'll continue to test this out and will keep you all (and John) posted.
In the mean time, if you have a rocket you plan on using the JLCR on, and you like to pop big-fat chutes under 500ft (as I like to do).. then you might want to consider having (or adding) a vent hole both below and above your chute space to get better barro data to the CR. I still recommend a small vent hole below your laundry to keep it from pushing your laundry out prematurely and under powered flight ("really cool" failure mode).. but if you're using a JLCR, you might want to go with a second vent hole, up front just aft of your nosecone.
Also.. please send me any JLCR crash/no-crash flight descriptions too so that I can gather more data. If this does end up being determined to be a related cause.. maybe John can amend his setup instructions (and warnings) and our club can share these observations with the rest of the community.
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