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Thread: Dumb Idea: So like... what about jumpjets?

  1. #1
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    Dumb Idea: So like... what about jumpjets?

    The group in Princeton recently had a couple people join, and as usual they had a bunch of "new" ideas to solve the various design constraints of building a mech before getting a sense of why such ideas were either illegal or impractical. One stuck in my brain as being too cool and too plausible to not at least get some thoughts from you guys.

    Since multirotor parts have become increasingly cheap and reliable, it looks like it would be quite feasible to stick some EDF's on a light mech and use them to do brief hops. Naturally, this could be kind of broken and definitely would fit under the "gimmick clause" in the rules, but if thrust was specifically limited to only allow ground effect hopping and not proper flying, it could be a viable supplementary means of travel. Maybe specifically limit it to light class mechs? (I just have the light assault class jump jets from Planetside in my head.)

    I know this is pretty out there, but I can't get the image of a light mech zipping down a street, landing, getting off a few shots, then repositioning, out of my head. Let me know what you guys think.


    Quick take on game balance: It would certainly drastically change the mobility game, but slowness of matches has been a complaint in the past, and honestly the inherent instability of maneuvering this way seems like a reasonable tactical price for the mobility it provides. Allowing this without making normal walking a nonviable strategy seems quite hard though. Perhaps additional constraints concerning flight time or thrust would work, but I don't intend to be asking for serious rules additions for the sake of my dumb idea. Ah well. Please tear this to shreds below.

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    Re: Dumb Idea: So like... what about jumpjets?

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    Fundamentally I'm not opposed to the idea of jump jets. They were an integral part of the Battle Tech game that I grew up playing. If someone made a mech with "stable" jump capabilities while still able to walk on legs (no just mounting a gun on a quad rotor) I think we could allow it.


    It really comes down to the matter of practicality. Getting a walking Mech is no easy feat in itself. As one of our club members likes to say "A finished inferior mech is better than a half built great mech." So encourage them to get the walking part down first. Then it comes down to the matter of weight. Most of the "medium" Mech's weigh in at about 5 lbs. We've experimented with lighter versions that come in under 3 lbs but we have not found a reliable gun/weapon that these lighter Mechs can wield. So realistically, I think you're talking about a Mech weighing 5+ lbs. Not sure how much thrust you can get out of the EDF fans. I assume the jump jets would be power hogs.. so you would need larger batteries requiring larger fans...


    Over the years we have had suggestions of allowing Tanks or Hexapods and have had discussions of the Pros/Cons of that as well. If we remain with Maker Faire in future years, they have a more open format and would could potentially consider having an separate event allowing these vehicles, if there is a demand for it. Would like to hear opinions from others on this as well.

    Sad to hear your not able to make this year. I was kinda excited when you first posted that you thought you might make it this year. Hope to see you in 2020.
    Last edited by GhengisDhon; 04-19-2019 at 06:40 PM.

  3. #3

    Re: Dumb Idea: So like... what about jumpjets?

    Funny you should say that ... I did the math on it a couple of years back, and I could strap two EDFs with angled actuators, AND a battery big enough to run them for a total of 40-60 seconds, onto Onyx, AND get it in under the weight limit AND still have enough oomph in the servos to walk carrying that weight. My dream was to land on roof tops (and my fear was that they'd collapse under the weight.)

    For a number of reasons (most of them being "I don't have the spare time!!!!" and one of them being "oh God the kids are starting college soon!") I didn't get to the point of trying it out, but I personally don't think that should be outlawed under the "gimmick" rule. If they can make jump jets happen, more power to them!

    If you can walk for five minutes, and hit the soda cans as you do so, then any additional flying movement you can get, is fair game IMO. However, a Tachicoma-style mech that CAN walk, but only for qualification, and actually rolls when in combat, probably wouldn't be OK. This is my feeling, because jump jets are Battletech canon.

    (Btw, Onyx is no more; I've taken the MX-64 servos for other projects. I'll be bringing an AX-12 'mech (with spring assist knees) this year.)
    (Oooh! Speaking of flying, I wonder if servo overheat can be reduced with a big helium balloon? What's the max dimension of a 'mech again? :-)

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    Re: Dumb Idea: So like... what about jumpjets?

    Quote Originally Posted by GhengisDhon View Post
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    Sad to hear your not able to make this year. I was kinda excited when you first posted that you thought you might make it this year. Hope to see you in 2020.
    Yea... I'm pretty bummed, but one guy had to drop out this spring, exams are killing me right now, and then we all have issues travelling. Just wasn't going to happen this time. We'll be ready for whatever event happens next (if Tucson happens again or maybe possibly I've heard rumors of NY Maker Faire?). If there isn't anything running before May next year, at least we'll have had time to scrimmage with Columbia.

    Thanks for the feedback on the idea. I'll pass it along while nagging them again to get on the forums already. Honesty, as jwatte said, I think it's just about doable, and I might just build in space for some EDF's in the new chassis design.

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    Re: Dumb Idea: So like... what about jumpjets?

    Quote Originally Posted by jwatte View Post
    Funny you should say that ... I did the math on it a couple of years back, and I could strap two EDFs with angled actuators, AND a battery big enough to run them for a total of 40-60 seconds, onto Onyx, AND get it in under the weight limit AND still have enough oomph in the servos to walk carrying that weight. My dream was to land on roof tops (and my fear was that they'd collapse under the weight.)

    (Oooh! Speaking of flying, I wonder if servo overheat can be reduced with a big helium balloon? What's the max dimension of a 'mech again? :-)

    Glad to hear I'm not crazy, or at least no crazier than my opponents.
    Did you mention it in the forums before? I was scrolling around earlier since I could have sworn someone proposed this before.

    Also, not even kidding, someone suggested helium a couple months ago.
    Almost as good as the currently still being floated proposal to prevent overheating using ice cubes...

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    Re: Dumb Idea: So like... what about jumpjets?

    Surprised no-one has tried low volume water-cooling for their servo MOSFETs. Wouldn't take much flow/tubing diameter.

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    Re: Dumb Idea: So like... what about jumpjets?

    Dumber idea would be a true jump jet using a nitrous oxide cartridge in a throttled micro-scale monopropellant, hybrid, or liquid fuel rocket engine.
    Please pardon the pedantry... and the profanity... and the convoluted speech pattern...
    "You have failed me, Brain!"
    bleh

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    Re: Dumb Idea: So like... what about jumpjets?

    oh, dear. Someone please save me. I'm giving serious thought to building a N2O+alcohol pressure-fed liquid rocket engine using 8g N2O chargers and a few mL of denatured alcohol, and throttled by a pair of needle valves to control fuel and oxidizer flow rates.
    Please pardon the pedantry... and the profanity... and the convoluted speech pattern...
    "You have failed me, Brain!"
    bleh

  9. #9

    Re: Dumb Idea: So like... what about jumpjets?

    If you could actually bring that to the competition, all the drinks and food for you are on me for the duration.
    No matter that open fire is against the rules and nobody would actually compete against you :-)
    That's a really awesome idea, though. Maybe you could build just one nozzle and post a movie?

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    Re: Dumb Idea: So like... what about jumpjets?

    ...nope. 8g NOX is not enough to lift a mech. Isp would be roughly 260~110[s] with 8:1 NOX:diesel mass ratio with chamber pressure dropping from ~900[psi] to ~30[psi] as the NOX is depleted from the charger. More chargers would help, but be much less efficient/useful than one larger tank.

    Still might try it just for shits'n'giggles, but practical design of any sort would require several hundred grams of propellants.

    http://rocketworkbench.sourceforge.net/equil.phtml is a rather nice tool.
    Please pardon the pedantry... and the profanity... and the convoluted speech pattern...
    "You have failed me, Brain!"
    bleh

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