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Thread: Starting a quad build - A couple questions

  1. #21

    Re: Starting a quad build - A couple questions

    We have a cron job that updates all exeternal dependencies and force-commits them twice a week. Yes, sometimes shit breaks, but it's usually much easier to diagnose on a monday or wednesday morning with one or two changes, than if you go a year and then have to resolve a bunch of shit at once.

    It seems like neither the open source or proprietary software is stable enough to build any sort of product on, at least not one that you can expect to operate for the next ten years.
    Static stability is an illusion; there is only dynamic stability. (Also, the race to the bottom in quality, because most people most of the time would rather have buggy new features now than well-tested old features later. Market forces do the rest.)

    Regarding direct impact, there's actually another problem, which is that you'll deform the BB and get jams in the mechanism/barrel. There's a reason AEGs have converged on air pumps...

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    Re: Starting a quad build - A couple questions

    Quote Originally Posted by sdfgeoff View Post
    It goes something like this: the world isn't perfect, and solenoids are horrible.
    The hope was to accelerate a solenoid to a low speed, and use the impact of it with the bb to accelerate it the rest of the way. Unfortunately, momentum transfer can only maximum double the velocity - even if the impactor is a hundred times heavier than the bb. So to get a bb at 50m/s, you have to get the impactor to 25m/s.
    From there you can do the required calculation for force over the distance. To get to 25m/s in 0.01m, you have to accelerate it extremely fast. Assuming a constant acceleration (and thus an average velocity of 12.5m/s, you only have some 0.00083 seconds along the 1cm stroke. To achieve 25m/s in 0.00083s, you need some serious force.
    I couldn't find my original spreadsheet, and I recall taking a different approach to solve it, so when doing the math the way mentioned above, I now get some 125kN of force:

    Very comforting to know I can't get the same answer twice with different approaches. I'm more convinced by my previous one than this quick-and-dirty approach, so let me know if there's something I'm overlooking (It's probably obvious, but I can't see it at the moment).

    Then there's the fact that a solenoid does not provide linear force, far from it. A solenoid rated at 1kg provides barely 200g of force at the far end of it's stroke. One idea we had was to use a neodymium magnet to increase the force without needing to add more electrical energy. However, I'm still not convinced you can get within an order of magnitude of enough force.

    Unfortunately this math applies to every direct acceleration method - you need a crazy amount of acceleration. Either this can be done using air to turn a very low velocity spring into a very high velocity air-stream (as in a normal AEG), or using a spinning mass with enough angular momentum to not take too much of a velocity hit when the bb gets accelerated (ie the mass of the spinning bits needs to be several times the mass of the bb).
    Part of the problem is that you are using grams in your calculations instead of kilograms. Kilogram is the standard mass in SI, and gram -despite its lack of prefix- is actually the non-standard unit. One Newton [N] is one kilogram-meter/second-second [kg-m/s-s]. One kilogram of force [kgf] is ~9.81 [N] (i.e. one kilogram at one G acceleration).





    Quote Originally Posted by sdfgeoff View Post
    Hahaha, yes, a 100kV motor may be a little hard to power on a mech of this scale. However, we were considering using electrostatics for one of our weapon ideas: charge up the bb with one polarity and have the other polarity at the end of the barrel (or somewhere else in the barrel). However, none of us have enough knowledge about electrostatics to say if this would work for certain. Either way, two spinning wheels is easy to compute and easy to build. No high-voltage sources to disrupt your onboard electronics....
    Apparently you still miss it:
    kV == kiloVolts - a unit of electrical potential; greater than 600V operating voltage is the realm of specialty motors because of the increased insulation requirements decreasing winding packing efficiency and difficulty/danger in actually getting access to the >600V power grid.
    Kv == RPM/V - one form of the motor constant - this form relating rotational speed to voltage across the winding



    Quote Originally Posted by sdfgeoff View Post
    Legacy hardware is worse than legacy code, and we've been fighting code rot at work already, despite our systems barely being more than a year old. Looking at you, docker [non enterprise version], with your 6-month support cycle, looking at you solidworks, with new files being unreadable in last years version, looking at you, ubuntu, breaking the nvidia drivers on a system with updates seemingly disabled [it did a kernel security update that borked nearly all the machines in our office for several hours at various points over a few weeks], and then there was one machine that died when daylight savings shifted time backwards for an hour....... It seems like neither the open source or proprietary software is stable enough to build any sort of product on, at least not one that you can expect to operate for the next ten years.
    Very much either "behind by six months", "legacy" or "dead"
    Still not worse than using a $500 FPGA dev board to control only two to four stepper motor drivers using acceleration profiles, because they could not get one small PIC per stepper motor driver to use acceleration profiles, because they could not figure out how to make one larger PIC control four motor drivers "simultaneously" without acceleration profiles. I'm trying to consolidate/eradicate most of the abominations with a single ATSAMD51 board and some shift registers to control all the motors, shutters, position sensors, clock lines, trigger signals, etc. they could possibly want in any of the instruments. The analog board is a bit more problematic since even a single 16-bit ADC at 1Msps dumps out more data than full-speed USB can handle. Looking at building something around a Cypress USB3 super-speed breakout board (CYUSB3KIT-003), since the existing FPGA stuff (motors and ADC) is built around a similar Cypress USB2 high-speed IC.
    Please pardon the pedantry... and the profanity... and the convoluted speech pattern...
    "You have failed me, Brain!"
    bleh

  3. #23

    Re: Starting a quad build - A couple questions

    The Cypress stuff is what Saleae uses for their logic analyzer product, so that ought to work.

    If not, make it PCI-Express and call it good :-)

    (You could perhaps squeeze it into a M.2 form factor if you don't need too many lanes.)

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    Re: Starting a quad build - A couple questions

    Quote Originally Posted by jwatte View Post
    If not, make it PCI-Express and call it good :-)

    (You could perhaps squeeze it into a M.2 form factor if you don't need too many lanes.)
    Nope. Can never be anything installed directly inside a PC and even if it could be guaranteed we were using a full PC capable of accepting any cards, PCI-Express would still be a bigger pain in the ass programming wise than plain USB or ethernet. Squeezing the buffer op-amp, ADC, microcontroller/FPGA, etc. into the M.2 form-factor would be ridiculous and pointless since it needs to accept actual wired inputs from the sensors and those slots are always inaccessible for anything except painfully tiny coaxial cables and limited durability connectors.
    Please pardon the pedantry... and the profanity... and the convoluted speech pattern...
    "You have failed me, Brain!"
    bleh

  5. #25

    Re: Starting a quad build - A couple questions

    View M.2 more as a connector (from which you run wiring) than the full card ...

    Anyway, yeah, the Saleae logic analyzers, which I love, are made from the Cypress USB 3 FPGAs, so they seem legit.

    And I still think you shouldn't mechanically impact BBS, because you will distort them and jam your gun. (To bring the thread back on topic!)

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    Re: Starting a quad build - A couple questions

    With an impact based weapon, a long tight-tolerance barrel does little other than reduce energy. It is easiest to think of it in terms of kicking an air-filled ball. Kicking a ball down a tube won't improve things any compared to just getting the position, angle, and force of impact correct. Hell, get those wrong and kicking through a tube becomes nearly impossible.
    Please pardon the pedantry... and the profanity... and the convoluted speech pattern...
    "You have failed me, Brain!"
    bleh

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    Re: Starting a quad build - A couple questions

    Only occurred a few minutes after my last post that most of the toy guns I had throughout childhood never used a barrel for anything other than appearances, and most of these things are still damn accurate 20+ years since manufacture.
    Click image for larger version. 

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    Tornado is the youngest using a spring loaded sled/holder to launch a spinning rubber ring. The pink, orange, and teal NERF thingy is the next youngest and by far my favorite with long range and high accuracy; unfortunately, the plastic lip seal inside it has shrunken with time to no longer make a great seal. The little red pop-gun and the top thing are both very, very old. The pop-gun still works quite well. The pump action thing is just two tubes: a barrel/magazine attached to the front grip that holds all the balls with one end blocked off by a disk with a hole in its center and a plastic lip to seal it inside the larger diameter pumping tube at the back. It once had a rubber lip/seal that sat on the open end that decayed long ago (increased accuracy by allowing pressure to build even with slower pumping action) and the inner plastic seal has shrunken to the point it no longer produces enough pressure to force the balls out of the barrel/magazine.
    Please pardon the pedantry... and the profanity... and the convoluted speech pattern...
    "You have failed me, Brain!"
    bleh

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