Need some advice please, 12v control system for wheelchair rifle rest system

Discussion in 'The Projects Forum' started by woolleyworm, Feb 3, 2010.

  1. woolleyworm

    Thread Starter New Member

    Feb 3, 2010
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    Hello to all, I have browsed many forums in the past 2 days before finding this one. I have a friend that is wheelchair bound and has a problem with his shooting aid. It is a chair mounted shooting rest with three functions; elevation, rotation and trigger control. He had someone look at it a few years ago and they "moved some wires around", there are no schematics and barely legible print on the relays. The company that made it is long out of business and a replacement is over $1800, which is far out of my friends budget. I'm hoping to get some ideas and thoughts on replacing or troubleshooting the controls for it. I have tested the motor, solenoid and linear actuator and they all function when directly powered. The trigger control is the only function that works currently; there was a broken ground wire on the power connection. I'm assuming that this was the problem all along, but then the wires got moved around and I have no idea which wires in the mess of spagetti that it was.

    I lost my first edition of this post due to pop-ups, so I'm probably leaving some things out due to my frustration level right now.... :( :D

    Here are some pics to give a little bit of a visual; the control boxes are crammed tight with the relay boards and wiring. Hoping to find a solution that would clean this up a bit. I can provide more pics and any component data as needed. Thanks for taking your time to read this.

    Semper Fi,

    Woolley
     
  2. SgtWookie

    Expert

    Jul 17, 2007
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    Hi Woolley,

    Nice of you to help your buddy with his shooting rig. :)

    Can't quite make out the specs of the Pittman motor in the 2nd pic, can you post the printed specs and part number? And what is the purpose of the Pittman motor?

    The LINAK - more specs on that too, please.
    I'm trying to figure out if the linear actuator might have an embedded potentiometer for position sensing.

    The Elevation and Rotation (Azimuth) controls are pots (potentiometers) - they seem to be missing their knobs. Did these controls effect the absolute position of the rotation and elevation, or were they to adjust the speed at which the changes occurred?

    The power switch was removed? Or is it simply out of the panel and I can't see it?

    The wires have red, yellow and blue tape on them. Please describe the function of the motors attached to these wires.

    The connectors - are they 5-pin DIN connectors?

    In the 4th image, there is an IC (integrated circuit) on the board with 8 pins under the twisted green and white wires. What are the numbers and letters on that IC?
     
  3. woolleyworm

    Thread Starter New Member

    Feb 3, 2010
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    Thanks for the reply!

    Semper Fi,

    Woolley
     
  4. woolleyworm

    Thread Starter New Member

    Feb 3, 2010
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    on the chip - MC1455P1
    KKNN
    9024


    RELAYS - M4-12H by Meisel (?) very hard to read




    I'm willing to pay for any ideas on upgrading and making the system more reliable. I have decent soldering skills and can make sense of a wiring diagram. I just can't make heads or tails of this box of spaghetti and wires in unknown places. :D:D With all the main components functional, I'm hoping that it can be updated and figure out a better mouse trap for this rig.
     
    Last edited: Feb 3, 2010
  5. SgtWookie

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    Jul 17, 2007
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    The MC1455P1 is a Motorola part number for the industry standard 555 timer IC. They're made by lots of manufacturers in huge quantities.

    The M4-12H relays are standard 12V DPDT PCB-mount relays with contacts rated for 1A. No sweat getting similar relays, either.

    How about the other items on the list of questions I already put up?

    Can you describe how it was originally meant to function?

    The "Trigger Ready" box w/button - I assume the big red button is the trigger solenoid.
    The knob to the left of that - is that a joystick? If so, is the joystick spring-loaded to automatically center?

    In the 4th image, your thumb is pointed at a 3-legged IC that has a heatsink mounted on top of it; the black metal deal with a half-dozen flaps on each side folded up. I'll bet that 3-legged IC is either a power MOSFET or a Darlington transistor.
     
    Last edited: Feb 4, 2010
  6. woolleyworm

    Thread Starter New Member

    Feb 3, 2010
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    The joystick controls the rotation and elevation motions with the pots controling travel rate. The joystick (yes, spring rtn to cntr ) makes contacts in 8 positions, so i am assuming that it can do both of these functions simultaneously. I've never seen it work before, so I'm not sure. The trigger circuit is enabled with the toggle in the up position, providing 12vdc to the Firing button, when the fire button is pushed, the solenoid pulls in against the trigger. A reset of the toggle switch is required in order to fire it again.

    If there is a replacement or smaller component available to use, I'd like to get rid of the shoddy work, it's little wonder why the company went out of business. The boards are crammed and compressed inside the panel.

    Power MOSFET that my thumb is pt'ng twoards.
     
  7. SgtWookie

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    In all fairness to the company that's no longer around - I'm fairly certain there wasn't a large demand for this type of device. Had it been made in any large quantity, the boards would have been done by a PCB manufacturer. Those look like they were hand-made in someone's garage - which is OK for small runs.

    Back to the 4th image - it looks like their might be another identical board under the one with the MC1455P1 timer and the heatsink with the 3-legged critter - is that the case?
     
  8. woolleyworm

    Thread Starter New Member

    Feb 3, 2010
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    Yes, there are two identical boards and two relay boards. One set for each function.

    I won't knock it too bad, it did work and wasn't a bad idea. My friend paid around $1300 for it in 1999. The actuator, motor and solenoid are top quality components; it's the hap hazard mashing and compression of boards that i found to be a bit distasteful, :rolleyes:. The setup was built by Blackberry Tech. I could find very little about them on the web.

    Though not high, the demand for assisted shooting devices is pretty decent. Only a few companies to choose from right now. There are grants available also, my friend is in the waiting stage to see if he can qualify. He's being patient though, most of the available grants are going to the returning veterans, as we both agree that they should.
     
  9. SgtWookie

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    Jul 17, 2007
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    OK.

    Now, the questions are - do you want to re-use as much of the original boxes and controls as possible to save money? Or do you want to start pretty much from scratch, and just save the actuators/motors?
     
  10. woolleyworm

    Thread Starter New Member

    Feb 3, 2010
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    I'd like to reuse as much as possible, but gut all the existing wiring and boards. Buying all new (less actrs/mtrs) wouldn't be too much of an issue though; I've got a decent tax return this year and I would pretty much give my left ... to help this guy out. I'm open to all suggestions and ideas; throw'em all out there.


    Really appreciate your time SgtWookie! :cool:
     
  11. SgtWookie

    Expert

    Jul 17, 2007
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    I hear ya. You're a good bro for wanting to help out your buddy.

    Let's see what we can do to retrofit the existing boxes.

    For starters, what are the internal dimensions of the box with the speed controls on it?

    I'm thinking that the joystick box could be pretty well left as-is. However, you'll need to provide documentation for all of the wiring to/from that box; such as the joystick, the "fire enable" light, the fire button.

    Usually, joysticks have switches that are controlled by the X and Y axis movements. You might have separate common terminals for the X and Y axis inputs, or their might be just one common terminal for both.
     
  12. SgtWookie

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    Here is the basic idea behind the existing elevation/rotation controls:

    [​IMG]

    M1 represents the motor, whether the linear actuator or the gear reduction rotary motor.

    RLY1 and RLY2 as shown are just SPDT relays. In your application, I'm pretty sure the other side of each DPDT relay is used to provide power to the 555 timer circuit, which provides PWM for motor speed control. I don't know if you are familiar with the abbreviation "PWM" - that means "Pulse Width Modulation". Rather than use a variable resistor or transistor to limit the current through the motor, current is applied for only a portion of the duty cycle. This means that power dissipation in the switching transistor is minimized, so you have a much more efficient use of power.

    S1 and S2 represent either the X or Y switches from the joystick.

    Not shown is the PWM circuit itself. That most likely controls the ground side of each motor.

    This is just to give you a basic idea of how the existing circuit should function.

    It should be fairly easy to make a couple of boards that incorporate the necessary controls; one for AZ (rotation) and one for EL (elevation).

    It's going to cost one heck of a lot less than $1300, I promise. But, you'll need to buy a few things - and make a couple of circuit boards.
     
    Last edited: Feb 4, 2010
  13. woolleyworm

    Thread Starter New Member

    Feb 3, 2010
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    I'll get all the internal dimensions and post some more detailed pics also. Gotta be to work in 6 hrs, so time for some shut eye. ;)
     
  14. SgtWookie

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    Jul 17, 2007
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    I think I have a solution for you.

    Board is 2" x 2" square. One relay that's between 3/4" and 13/16" tall (20mm).
    One board for EL, one board for AZ (rotation) - the boards are identical.

    Two files are attached:
    1) 12V Az-El Control Board top.pdf
    2) 12V Az-El Control Board brd.pdf

    They are both actual size. Print them out using Adobe Reader.
    12V Az-El Control Board top.pdf is the component layout on the top of the board.
    12V Az-El Control Board brd.pdf is the trace layout for the board bottom.

    Legend for connection points:
    J-COM - Joystick common connection to +V
    J-F - When the joystick supplies +V to this point, motor runs forward
    J-R - When the joystick supplies +V to this point, motor runs reverse
    12V - Battery + terminal
    GND - Battery - terminal
    MOT+ - Motor + terminal
    MOT- - Motor - terminal
    P-1 - Speed adj pot, terminal 1
    P-2 - Speed adj pot, terminal 2
    P-3 - Speed adj pot, terminal 3

    However, I still need to know about the joystick.
    [eta]
    I've since added a couple of capacitors to the 555 timer circuit for added stability; just a small change.
    [eta]
    All components now have values; the pots that are currently being used in your existing configuration are 5k Ohm; will need to be swapped out for 100k Ohm pots. This will make power consumption lower, enable the use of smaller timing capacitors (both physically as well as their uF rating) yet allow a very wide range of PWM adjustment while keeping the PWM circuit relatively simple.

    [eta]
    OK, now that I realize you actually DID answer a bunch of my questions (I thought you had just quoted what I wrote, not actually given answers), I see that some of the parts that I used are under-rated or marginally rated (diodes in several places and MOSFET) so there will need to be some parts swapped out and adjustments to the board layout. Not a problem, but it means the board will grow a bit in size.

    I'm thinking the relays the original manufacturer used were quite underrated at 1A. Would not be surprised if the contacts inside were burned up. The relay I'm considering is rated for 25A. I'm wondering what they used for a switching transistor - the 3-legged thing under the heatsink.

    Pittman GM9413-5
    Datasheet: http://lims.mech.northwestern.edu/~design/mechatronics/2006/biketrans/GM9413_5.pdf
    Resistance: 8.33 Ohms; No-load 0.1A, Peak stall 1.44A, both at 12v.

    [eta]
    OK, swapped out two of the diodes that could've caused problems. After more looking at it, the MOSFET I chose should be OK; it's rated for 2.5A and your load is going to be around 1.6A tops. I changed out the relay for a slightly smaller version that does the same thing. These relays are quite different than what Blackberry Tech used; theirs were DPDT, and these are specifically designed for controlling H-bridges. The board is still 2"x2"
     
    Last edited: Feb 5, 2010
  15. woolleyworm

    Thread Starter New Member

    Feb 3, 2010
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    Great stuff !! I have a full plate today, but as soon as I can, I will get all the info for the joystick.

    Do you have an idea of approx how much the board would cost to make? just a rough ballpark would be fine.
     
  16. SgtWookie

    Expert

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    Are you talking complete with all components?

    If you have a PCB house make the boards, they might run around $20-$35 each. However, they are pretty simple single-sided boards, and probably wouldn't be very hard to make yourself.

    The parts won't be very much. Mouser stocks the relays I'm considering for around $5/ea, but I've found another supplier where you can get them for $2/ea. Better to pick up a few spares for the same price. ;)

    The MOSFET is about $0.65, the 555 timer about $0.50 maybe; the caps maybe $0.20-$0.50 each, and the resistors and diodes are <$0.30 each. Let's just say under $20 for the rest of the parts, besides the boards themselves.

    So, the biggest expense will be making the boards, and the time involved in connecting everything.
     
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