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Thread: My mech build have a Weapon ?

  1. #1
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    My mech build have a Weapon ?

    Concept :
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    Mechwarrior Centurion

    Travidius has had a few different configurations , Here is my current build :
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    Im looking for advice on the best way to go about firing my weapon, the gun has 2 wires all i have to do is add the juice and it fires it runs on 7.5v but is tolerant to 12v, I am running a CM-510 with zigbee , and the robotis ps3 style remote is there a way to swith the power on and off to the gun from it , or do I need to run additional board, relay ? Please excuse the noobish question Im still new to robotics and this is my first weapons setup.

  2. #2

    Re: My mech build have a Weapon ?

    Yes, the Xbee has the ability to turn digital pins on/off. A relay will draw too much power for that output, though -- better get a N-channel MOSFET with a low Vgs threshold (as the Xbee is only 3.3V.)
    So, Xbee digital out pin -> 470 ohm resistor -> Gate of a N-channel MOSFET. Then hook battery to gun to MOSFET drain, and MOSFET source to ground.
    Then re-program the Xbee to allow you to send digital pin on/off signals. (It can't do this when in "transparent serial" mode)

    I don't know if you can also do this with the CM-510. That might be simpler if it's possible, because I think that's a 5V device, and thus finding a suitable MOSFET to turn on current is easier. I know for sure that the ArbotiX can do it, and can drive a MOSFET.

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    Re: My mech build have a Weapon ?

    By "CM-510 with zigbee," I am assuming you are using the ZIG-110, not XBee, so you will not have to worry about messing with the XBee/zigbee module settings. The CM-510 has six user controlled output pins (External 5-Pin Ports) on it that could be connected to a mosfet as jwatte described, although I would add a small-ish pull-down resistor between the MOSFET's gate pin and the MOSFET's source/ground pin (just to make sure the pin does not float high and let the gun fire on its own). The pins are 5V output at 0.9A max, though I would definitely not try to directly drive anything significant with them (Robotis drives the Ollo motors, but those are quite tiny).

    See the link above for specifics, but the two pins you will need to connect are Pin 1 as the control pin and Pin 4 for ground. Individual ports are identified by the number of "|" counts on the plastic.
    Last edited by tician; 10-31-2012 at 05:32 PM.
    Please pardon the pedantry... and the profanity... and the convoluted speech pattern...
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    Re: My mech build have a Weapon ?

    Thanks guys,
    Quote Originally Posted by tician View Post
    By "CM-510 with zigbee," I am assuming you are using the ZIG-110, not XBee, .
    Yes CM-510 with zigbee.
    I did some research on MOSFET's and I actually came across this it looks like exactly what I am trying to do before i order the parts verify this is correct (substitute cm-510 for audrino in pic)
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    Does not look to bad to setup.

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    Re: My mech build have a Weapon ?

    Pretty much what we were describing, although the 470 Ohm resistor that jwatte indicated between the Gate of the MOSFET and the output of the CM-510 will help protect the CM-510 from damage (if the gate capacitance is very large, you can get really high current to the gate pin, so the resistor keeps the current reasonable without affecting the performance significantly - would only matter with high frequency switching).
    Please pardon the pedantry... and the profanity... and the convoluted speech pattern...
    "You have failed me, Brain!"
    [git][mech][hack]
    gives free advice only on public threads

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    Re: My mech build have a Weapon ?

    Now all I have to do is grab the parts and solder them up he will be shooting in no time !
    I still need to figure out the exact mosfett to get, i do not know to much about them.
    I will research that later on tonight imagine its just a matter of the correct voltage.
    Has me thinking does radio shack actually still sell any electronics ?
    Thanks again.

  7. #7

    Re: My mech build have a Weapon ?

    Radio Shack sells some resistors and capacitors, and a number of switches, breadboards, soldering irons, and cabling -- mostly for car audio type work. I doubt you'll find a suitable MOSFET there. These days, they also have a reasonable Arduino section, too, and even some Propeller stuff. You might be able to find a motor shield or motor controller that lets you do the right thing.

    If you want a reasonable power MOSFET, and the CM-510 is 5V (which I think it is, but don't know -- check the manual!) then you can use the IRLB8721PbF from International Rectifier. It is fully switchable with 4.5V, and can take up to 60 A and 30 V. Adafruit has it for $1.25 + shipping; Digi-key has it for $1.13 + shipping. When I buy components, I always buy at least 3, because the first one is probably going to be screwed up by me, and after I use the second one, it's good to have the third as a spare :-)

    The gate capacitance is kind-of high on that device, so I would recommend the resistor. For the Xbee (which you're not using) it's extra important, because it can't generate (or sink) a lot of current even instantaneously. I think the CM-510 is based on the AVR series, though (same as Arduino) which can deal with a lot more current. A 220 Ohm current limiter can't hurt, though -- the resistor is a lot cheaper than the CM-510 :-) These days, you get even high-quality 1% parts for pennies! (OK, 14 pennies each)

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    Re: My mech build have a Weapon ?

    The CM-510 has one user-controlled logic pin on each of the six external port at 5V (5V, 0.9A - switched by a BJT). The CM-530 has two user-controlled logic pins on each of the six external ports at 3.3V (3.3V, 0.3A - think it is BJT switched, but not absolutely certain).

    Radioshack will probably have a certain part in stock that should meet your needs, although jwatte's digikey recommendation works better if you are already ordering other parts (shipping can cost more than the parts) (IRLB8721PbF has an on-resistance of about 0.008 Ohm and the IRF510 has an on-resistance of about 0.540 Ohm). Their IRF510 is rated 60Vds and 3A (+/-20Vgs with +2~+4Vgs_threshold), but most of the datasheets I can find have the part rated 100Vds and 4~6A (+/-20Vgs, +2~+4Vgs_threshold, and gate-source capacitance of 110~170pF). Either way, it should be fine as long as the gun does not pull more than ~1A when firing (if you want sustained firing at anything greater than ~0.5A, then you'll probably need a heat sink).
    Please pardon the pedantry... and the profanity... and the convoluted speech pattern...
    "You have failed me, Brain!"
    [git][mech][hack]
    gives free advice only on public threads

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    Re: My mech build have a Weapon ?

    As stated in the CM-510 manual and also above by Tician The pins are 5V output at 0.9A max.
    I was able to source the Following MOSFET RFP30N06LE here is it's specs :
    30A, 60V
    DS(ON) = 0.047
    Ω
    2kV ESD Protected
    Here is it's
    Data sheet

    I can pick these up locally, Tell me if you see a problem with that, I see they are used in a lot of Arduino setups doing the same thing I want to do. I also buy 3 of everything sometimes more...

    Last edited by Ron; 11-01-2012 at 01:21 AM.

  10. #10
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    Re: My mech build have a Weapon ?

    Quote Originally Posted by tician View Post
    Radioshack will probably have a certain part in stock that should meet your needs.
    Yup my local RS has #IRF510 in stock.

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