Double H-Bridge

Discussion in 'The Projects Forum' started by nickkelbackk, Mar 15, 2008.

  1. nickkelbackk

    Thread Starter New Member

    Mar 15, 2008
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    I am new to electronics and am building a project for my class. My idea is a turrent. It will house a motor that rotates the turrent, a motor that tilt the turrent that sits atop the other motor and also a motor to fire the turrent. It will be decently small. Anyways, I am thinking about using an H-bridge to rotate and tilt and fire. I was wondering if anybody knows of a way to do this with momentary switchs(one rotates right, one rotates left, one tilts up, and one tilts down). Also another momentary switch to spin the third motor and fire the turrent. This third motor only needs to spin one way so no h-bridge is neccesary. Another question I had is if there is any to do this with a joystick. here are the motors I was planning to use:

    http://www.hobbyplace.com/robotics/gearbox.php
    2 of the high power, high efficency motors to rotate and tilt the turrent and one of the high efficency worm gear box to fire the turrent.

    If you are wondering how I am doing to fire the turrent then you only need to look at how an airsoft gun fires. It works like this: The gear on the motor, which only has teeth on half of it meshes with a rack that has the same number of teeth as the gear. The rack is mounted on a cylinder of some sort with a spring on the inside. When the motor spins the gear spins meshing with the rack on the cylinder which makes the cylinder move back and compress the spring behind it. Then when the gear and the rack go through all the teeth the cylinder fires moves forward flinging anything that was in front of it out of the way.

    If you have any questions please post.

    Sincerely,
    Nickkelbackk
     
  2. beenthere

    Retired Moderator

    Apr 20, 2004
    15,815
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    This could be a fun project. You might want to look up material on naval gun turrets for some ideas about how it was done. For that matter, tank turrets and aircraft gun turrets.

    If you are going to use switches for controlling train (the horizontal motion), the using an H-bridge is overkill. A switch can't give any indication of how fast to slew the turret. You would need a potentiometric input to do that.

    Most turrets have a ring gear with teeth on the inside. A motor with a small spur gear drives the turret in either direction. The pointing (elevation) could be done as you describe with a 90 deg. gear, or by using a belt drive an pulleys to move the gun up and down. Once again, without some means of being able to indicate rate, an H-bridge drive is not going to work.

    Make up some good drawings for how the gun is to work and how you want the turret to be constructed. Look up how servo systems work, as something like that might be a better way to control the turret motion.
     
  3. thingmaker3

    Retired Moderator

    May 16, 2005
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    I didn't get to play with any turrets when I was in the Navy, but I did get to clean & inspect some satellite dish positioning equipment. They were similar in their movement to turrets. One feature they had was a set of gears and a pair of limit switches used to prevent the housing from turning more than 720 degrees. Without the limit, one could twist ones conductors apart.

    I've torn apart joysticks with simple switch contacts. One should work well with your project.
     
  4. HarveyH42

    Active Member

    Jul 22, 2007
    425
    5
    I've got something similar, but with an RC servo, a Attiny13 microcontroller, and a pair of PIR motion detectors. Oh, and an airsoft pistol... It was intended to deal with my neighbor's eleven cats, and their toilet usage of my backyard. Got it working on the breadboard, but never made a PCB or finished it up. I got a black lab puppy instead, almost never see a cat on my property.

    I basically concluded that the tilt would be a waste, since the guns are weak and not very accurate. The sound would scare off the cat, or maybe actually hit one in the sweep if it didn't run. Went with motion sensors, as I didn't figure on catching them consistantly to be much of a deterent.

    You don't need a microcontroller to use a servomotor, a 555 timer can provide the PPM (PWM) signal to position it. Basic standard size servos are $7-10... new, pretty much any hobby shop, and plenty strong enough to move an airsoft gun.

    Just a few things I came up with when I started my project...

    You can use gear motors, relays might be a better choice over an H-bridge. I remember so limit switches with a diode in parallel from a solar tracker, might be of some use. Most likely you will want to look into speed control, PWM...
     
  5. SgtWookie

    Expert

    Jul 17, 2007
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    If you just want something really simple, have a look at the attached.

    MotorReverse1 uses two SPDT pushbutton switches to cause a DC motor to run in forward or reverse.

    MotorReverse2 adds two SPST NC limit switches.

    You can make this as simple or as complex as you want. But for a first project I suggest you keep it simple, as that will greatly increase your chances of success.

    The third attachment is a vehicle with a turret that I'm currently restoring. It's a HMMVEE with an Avenger missile system, retired from the USMC, and was donated to our local Museum. It is NOT simple!
     
  6. nickkelbackk

    Thread Starter New Member

    Mar 15, 2008
    7
    0
    [​IMG]
    This is my design I did it in 5 seconds in microsoft paint. I am not sure why h-bridges are bad. I did not understand what you said. If you said something about them not being able to set the motor to turn for a specific time which is what I get out of it. I am just doing to press the switch or move the joystick till it rotates to where I want it.

    EDIT: Ok sgtwookie I understand you first schematic but I do not quite understand your second one. Does it mean that when you release the switch the motor will stop spinning?
     
  7. SgtWookie

    Expert

    Jul 17, 2007
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    Your photo didn't post correctly; here it is:

    [​IMG]

    The point is, that using a double H-bridge for what you're doing in this first project really is overkill.

    If you look at the attachments I made to my first reply in this thread, you'll see that what you need to do can be implemented by using just a pair of single-pole, double throw (SPDT) pushbutton switches.

    The drawback to using just switches is that it is an "all or nothing" proposition; ie: you get full speed or no speed at all.

    A simple PWM circuit could be added to give you a decent degree of speed control, without the added complexity of an H-bridge.

    When you're designing controlling circuitry for an H-bridge, one must keep in mind that you can never have both the upper and lower half conducting at the same time, or you'll wind up with "shoot-through", or a dead short across the power supply. Avoiding this condition is not as simple as you might think. Semiconductors do not turn on and off instantly; it takes time for them to make the transition. Therefore, you must ensure that the upper side has turned OFF before you can turn the lower side ON, and vice versa.

    With a SPDT switch, you don't have to worry about shoot-through - it's physically impossible for that to occur (unless something inside the switch breaks, of course).
     
  8. nickkelbackk

    Thread Starter New Member

    Mar 15, 2008
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    Ok that makes sense is there any way to make the four SPDT go to a joystick so I can use a joystick to move it around?
     
  9. SgtWookie

    Expert

    Jul 17, 2007
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    Surely ;) You might look at lever-action microswitches if you wish to use a joystick.
     
  10. nickkelbackk

    Thread Starter New Member

    Mar 15, 2008
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    How would I go about wiring the motors and such to a 4-way joystick such as this one:
    http://www.happcontrols.com/joysticks/ultimate_joy.htm
    How would the schematics look? I would greatly apprecieate it. And would I need the SPDTs or would the microswitchs replace them?
     
  11. SgtWookie

    Expert

    Jul 17, 2007
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    Hey, that 4-way joystick is perfect - it even has the SPDT microswitches already mounted!

    In the picture of the joystick on the page you linked to, you can see two of the microswitches on the bottom.

    The switch on the right side - the one with the connection blades facing the viewer?
    The rightmost blade is the COMmon connection (sticking out from the side and bent towards you)
    Then one next to it should be N.O. (normally open)
    The last one should be N.O. (normally closed)

    You will need a 4-way controller. The X-axis (right and left switches) should control the rotation of the turret left and right. The Y-axis (forward and back) should control the elevation of the "barrel".

    The schematic is "MotorReverse1.png" that I have already posted, above. It can represent both the turret rotation and barrel elevation circuits, as they can be identical.

    You could just use a solenoid as a "ball launcher", rather than trying to interface an airsoft pistol or the like. You wouldn't want it to have much range or power for a school project, and even bringing an airsoft pistol on the school grounds may cause you huge problems in this day and age. :(

    An old-fashioned "ding-dong" type doorbell solenoid could work really well for a ball launcher. But don't take the one you have off the wall - just see how it works, and try to duplicate it.

    If you can get all of these pieces working together, then this project can be taken a step further with PWM motor control.
    But this is complicated enough for now.
     
  12. nickkelbackk

    Thread Starter New Member

    Mar 15, 2008
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    I am still trying to understand your motorreverse2 picture. Do S3 and S4 make sure the motor stops instead of slowly spinning down?
     
  13. nickkelbackk

    Thread Starter New Member

    Mar 15, 2008
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    0
    [​IMG]
    I hope it works unlike last time. I was just wondering if this is how the entire schematic would work the only thing I am not sure about is how the solenoid draws power from the same battery as the motors. Sorry for double posting
     
  14. SgtWookie

    Expert

    Jul 17, 2007
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    The MotorReverse2 schematic just adds two N.C. limit switches. When I drew that one up, it was for a fellow that was doing a linear actuator project, and he needed to make sure that the motor in the linear actuator turned off before it opened or closed too far.

    There is no "brake" as such in either schematic. It simply turns the motor on or off in one direction or the other.

    I've re-drawn your schematic and added some notes. You were close, but there were a few minor glitches. See the attached.
     
  15. nickkelbackk

    Thread Starter New Member

    Mar 15, 2008
    7
    0
    Thank you for all your help. I am doing to buy a few motors from the first site I listed, a joystick, some sheetmetal, and a pushbutton also. I am doing to leave out the limiters as It will get complex and they are not needed for the project I am doing. I might also buy a doorbell to see what I can do with that. I will keep this forum updated on how my project is going and if I need any more help.

    One last thing you said something about a 4-way controller. Would that be the joystick? Or is that something else I need to buy?
     
  16. thingmaker3

    Retired Moderator

    May 16, 2005
    5,072
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    That particular joystick has four micro-swithces in the base: http://www.happcontrols.com/joysticks/507608xxx.htm

    If you connect one lead of each motor to ground, and use a dual-voltage power supply (one + and one -) you can simply connect the switches for up/down or left/right.

    turret.jpg
     
  17. SgtWookie

    Expert

    Jul 17, 2007
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    That's fine - but remember to put in some kind of mechanical stop, or if your turret gets turned around too many times, your wires will get twisted off!

    A doorbell button should work fine for the "Launch" button.

    Good luck! :)

    That is indeed the joystick. I got distracted in the middle of the post, and worded it confusingly. Sorry about that. If you look on the joystick page, you'll see that they offer 2-way, 4-way and 8-way controller joysticks. You need the 4-way controller joystick. Does that make more sense?

    Thingmaker3's suggestion is a good one, as it simplies the wiring for the moment. However, if you eventually wish to add PWM speed control for the motors, you will need to use separate PWM controls for CW/CCW and UP/DN.
     
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