The Blair Chronicles

Tripping Your Trigger

Wiring and schematic [10.19.05]

The art of tripping the trigger on the RBS is not as easy as a guy thinks it might be. This is the final rough draft of the wiring schematic. There are dozens of sheets of paper donated to the trash with tons of chicken scratches on them that led up to this final work of art. It took several months to get the basic idea to work, that is, reverse the trigger motor after firing and having a light indicate both the actual shot and the ready state. The net is replete with resources on "H-Bridges", the typical way a DC motor is driven in both forward and reverse in a "electronic" circuit. The circuit allows for voltage feedback and other protections for the motor and more delicate semiconductors. The trouble I had, because of my total ignerts, was finding something simple. Not understanding what I needed, the H-Bridge circuit seemed to be the answer so I studied it long enough to educate myself to understand it was way to complex and would only be used in an analog or digital circuit. Needing something less than that I got stuck on what I should do. Finally, I went to Radio shack and got a switch. My thinking was that all I needed to do was reverse the motor because I could do that with a couple of test leads hooked to a small battery pack. Hook the battery pack one way to the motor and it spins forward, reverse the wires and the motor reverses direction, very simple. The switch I bought was a double pole, double throw (DPDT) toggle. I inspected it at the store and concluded it was worth a shot to play with it because it had six terminals coming out the back and the toggle acted like I wanted it to. Clicked forward the toggle would stay engaged, clicked backward it would stay. Let go and the toggle would return to center position. When I got home I hooked up test leads and checked for continuity between the six terminals and liked what I found. Between the six terminals when the switch was thrown one way or the other it disconnected two of the opposing terminals. This meant that I could supply power to both sides of the switch at separate times but not at the same time. Exactly what I needed because all I had to do then is hook up a positive and negative to one side to supply the motor power and reverse it on the other side to reverse it. And I could never short out the motor because the switch would not allow me to do both at the same time since it worked only in one direction at a time, not both. Cool, huh?

This may all seem trivial in the long run and I only mention it because it was a huge amount of work to achieve the end result. And the end result is never final. I'm sure there will be changes but, the changes will be much easier to deal with because they mainly will consist of how wires are routed in the physical space I'm working with. The "pretty wiring schematic" is a formality in the overall scheme of things, if someone else wants to build this thing then drawings beyond hand sketches are a must. Clarifying ideas in your head and transferring them to paper is not easy in itself, let alone trying to have it make sense to anyone else. As ideas progress and firm up, it's much easy for others to understand conventional symbols, that is, what's tried and true and most representative of common components in the art. You know, a red wire is usually considered "hot" or "positive" whereas black is considered "ground" or negative. Remember, ignerts is bliss and the last statement may be ripped to shreds at the level of electrical engineering. For our sake though, it works for the purpose of this discussion.

You can see how the circuit works with the mechanics of the trigger action by watching the video. In essence, when the RBS is ready to fire no lights are on. If you try to move the switch to the "ready" position, the green light comes on and nothing else happens. This tells your mind and eye that the RBS is waiting for you to move the switch in the other direction to fire a shot. What takes place in the circuit? When the RBS is in the ready state, reed switch 1 has disabled/disconnected the reverse movement of the motor used to re-cock and enabled/connected the "shot fired" or forward movement of the motor and the green light. When the toggle is moved toward the "shot fired" position the motor is powered forward until the trigger is depressed far enough and the shot is fired while simultaneously hitting reed switch 2 which disconnects/disables any more forward movement and turns on the red light which tells your mind and eye that the shot has been fired. If you try to move the toggle forward to shoot again, all you get is a red light. Finally, the "ready" part of the circuit is now re-connected/enabled. Your only alternative is to move the toggle back to reverse the motor and re-cock the RBS. Sounds confusing and even looks worse in the picture that I took while testing out the circuit, I know, but it's an idea that is much easier to watch and understand.

You know what? Any ignert can make a mess but a truly "good" ignert can de-tangle mere rocket science. Given enough time. Well..., money too. Takes lots of luck also. Did I mention help from others?

The mechanics [10.19.05]

The mechanism that pulls the trigger is another fine mess to work out. After weeks of brain drain you can tell by the pics, progress is slow...

Of course with time, things do progress...

	61 some odd parts depending how you count. Nicely painted in my favorite paint scheme. I like it cause it's fun and easy to do.
It's not all that complicated. Mostly constructed from off the shelf parts found in the robotics and small parts industry. A little nylon string-line and a couple of pulleys sandwiched between some aluminum and you have magic.
	Notice the coil spring here. It acts as a counter spring to help return the trigger to the cocked position. It rests against a small strip of copper which is used to trip the leaf limit switches (not shown) used to stop the movement of the trigger motor in both directions. This will make more sense later when I show you how the circuit works.
This picture gives you an idea of the placement of individual parts hiding from the outside view, note the spacers. You can also see where the nylon line runs around the pulleys and is wrapped around the motor shaft.
	The entire mechanism is attached to the gun using a modified set of scope mounts. There are two thumbscrews used to mount the gun and it takes less than a minute to get the job done. In the area of the trigger, you will see a round piece with a slot with another part inserted in it, the part is the opposite end of where the nylon line hooks to a cotter pin and is also the piece that is wrapped by the coil spring.
Again, you can see more of the trigger pieces. Also note the bearing the with the stub shaft, that's actually the end of the motor shaft and a bearing is used because there's quite a bit of force placed on the shaft. See the long part on top fastened by the two bright looking screws? That's the part that holds one of the two limit switches. Look close on the right side and you can see two small mounting holes. As you are looking at it now, if the limit switch were in place, the copper piece that holds the coiled spring would be hitting the leaf limit switch to tell the circuit to stop the motor.