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G-Wiz FAQ

G-Wiz, General

  1. Why doesn’t my G-Wiz have a Mach lockout?

    2. All G-Wiz Flight Computers use an acceleration sensor to determine apogee. Mach transition causes shock waves in the air, which can confuse some flight computers that rely on Barometric sensors for Apogee detection. Some of these have special code that tries to avoid confusion, and others provide a ‘mach lockout’ mechanism, usually timer based. However, while Mach transition can affect the acceleration of a rocket, this is a real effect that will also affect the altitude the rocket ultimately achieves, and the acceleration sensor will properly integrate this difference to correctly determine apogee.

    Newer units that allow for Barometric apogee as an option will automatically lockout triggering based on integrated speed.

  2. If the acceleration sensor is so great, why do some G-Wiz’s also have a barometric sensor?

    3. These sensors both have their strengths and weaknesses.  While an accelerometer is great at determining apogee, it isn’t very good at telling you how high that happens to be, and low-altitude determination for two-stage deployment is extremely difficult, if not practically impossible.  A barometric sensor, on the other hand, is great at sensing altitude, OK for apogee detection, and lousy for things like burnout detection.  Read this for more details.

  3. Why 2 batteries?

    4. Our computers are capable of channeling large currents for reletivly long periods. The capacitors that other computers use to trigger pyro events produce very short lived currents.  Also, they have a finite charge time, so 2 event close together may not work correctly. We prefer to use 2 batteries, one for the pyro circuit, one for the CPU. Newer units do allow 1 battery, when a jumper is used to restrict the current. If this jumper is not used, the ignitor may cause the computer to reset by drawing too much current. Even low current ignitors can do this. Read about it here.

G-Wiz LCX

G-Wiz LC, LC Deluxe

  1. What is the real difference between the LC and the LC Deluxe?

    2. The Deluxe adds a 3rd pyro channel, used for low-altitude main parachute deployment, and the Barometric sensor needed to determine what altitude the flight computer is, on its way down.  Acceleration sensors are great for everything up to Apogee - after that, they don’t help a whole lot.  As a bonus, the Main Altitude readout becomes more accurate, as barometric sensors do provide a more accurate altitude reading.

  2. How can I test my G-Wiz?

    3. You can test your flight computer by performing what we call a ‘swing test’. This involves holding the computer with the ‘nose’ end pointing toward your shoulder, and swinging your arm around quickly.  This test uses the angular acceleration caused by your arm’s motion to simulate liftoff. The whole procedure is outline in our Bench Test document for the LC.

  3. Why do I need 2 batteries?

    4. The ‘Switches’ (FETs) on the GWiz that turn on and off power to the ignitors can switch so much current, that with just one battery, it is possible for the ignitor to take the power the computer needs to operate. Ignitors continue to draw power even after ignition (See Rob’s study). With 2 batteries, the computer has its own power source, so this doesn’t happen.

  4. How can I setup my LC / LC Deluxe with a switch?

    5. G-Wiz LC or LC Deluxe - The use of this method does not require the use of hardwired pyro battery clip. It can be disconnected or ignored.

    1. Connect/twist the black wire (-) from each of the battery clips together
    2. Connect the red wire (+) from one of the battery clips to TB pin 7 (Battery +)
    3. Connect the red wire (+) from the other battery clips to one of the TB pyro + pins 1, 3 or 5.
    4. Connect a black wire (-) to TB pin 8 (Battery -)
    5. To power on, twist the black battery clip wires from step 1 and the black wire from step 4 together or connect to your favorite switch
       
  5. What is its maximum altitude?

    6. The Barometric sensor used in the LC Deluxe and MC can detect altitudes to approximately 38,000 feet. Local atmospheric conditions can affect this a bit.  Only barometric altitude is affected by this limit. Events, such as apogee detection will still work above this altitude.

G-Wiz MC

  1. What does MC do that LC doesn’t?

    2. Recording. With 12 bit resolution (LC samples to 8 bits). And it has a beeper. It does a bunch of other little nice things as well, but these are the big differences.

  2. FlightView will not connect with my MC.

    3. Serial port connection problems:

    1. Are you running any PDA syncronization programs (i.e. HotSync)?
    2. Do you really  have a Null-Modem cable?
    3. Is the red line on the ribbon cable lined up with the 1 on the board connector?
    4. Does the MC have power (to both inputs)?
    5. If the above don’t help, try clipping the ribbon cable wire with the red stripe.
       
  3. My MC behaves funny when I connect the serial cable to my PC or FlightView shows differences from my MC Beep pattern.

    4. This is an odd one, seen particularly with laptops.  Clip the ribbon cable wire with the red stripe, and the problem should go away.
     

  4. I like to use a power switch with my MC.

    5. Try This:

    1. FlightView Software
      1. How do I use FlightView on Linux (or other Un*x)?

        2. This is a tough one. You need to write your own startup script to start Java with the right class libraries (you can use the installed scripts for guidance).  To the Java command line, you need to add the following: “-DSERIAL_PORT_LIST=/dev/ttys0;/dev/ttys1” before specifying the classname. The driver list should be replace by the valid serial port drivers for your system.
        Also, you will need to ensure that the device permissions are set to allow a user application to open the device.

      2. I’m having trouble using the USB card on Windows XP

        3. See Issues #3

      3. I’m having trouble installing on Windows Vista

        4. See Issues #4

      Flight Computers, General

      1. I want to power up my Flight Computer from outside the Rocket. Why can’t I use a NC Phono Jack?

        2. The ‘switch’ in a NC phono jack is basically a spring that closes a circuit when the jack is removed.  While this works well to provide power in a ‘remove before flight’ pull pin, the problems happen in flight. Rocket flights are not smooth. Some motors have a rough burn profile, burnout, ejection, parachutes opening, etc all cause rough shocks.  These shocks can cause the spring switch in the phono jack to momentarily open,  causing the flight computer to reset. This can cause the computer to not perform any remaining events.  Definitely bad news!

      2. But I’ve used phono jacks before, with no problem!

        3. Good for you!  You’ve been lucky so far that none of these shocks have been on the same axis at the spring switch in the jack.  Just because is hasn’t happened yet, doesn’t mean it won’t. Find a better method.  Rob’s favorite is a locking toggle switch, and Larry’s is a small key-switch. That said, we both use our G-Wiz’s with out external power switches a lot, as a 9v battery will last over 24 hours.  Even at LDRS, we’ve never had to wait that long between prep and launch!

      3. What Batteries are best.

        4. We recommend 9v batteries with welded construction, like Duracell. We have seen problems with the Energizer 9v, and have since discovered that the inner contacts are press-fit, not welded.  These seem unable to deal with all the forces involved in a rocket flight.