Completing the safety circuit as a means of firing the stampede is going to be unreliable. If the power to the motor is cut before the firing cycle is complete, you could have a dart in the breech, and one at the top of the magazine, which the breech attempts to chamber when you resume firing.
I did this once when installing a stampede in briefcase, and if you didnt fire the entire magazine, you had serious problems with jamming due to the firing cycle being partially completed.
The best way remotely(via arduino) actuate a stampede is to use the circuit that hasbro designed that mechanically ensures that the firing cycle is complete. Inside the stampede, there is a SPDT(single Pull Double Throw) switch that is pressed down by a lever and then held in that position by a part of the breech until the breech returns to the full rear position.
The two throws of this switch go to the motor and the firing circuit, while the center connects to the other lead of the motor. WHen this switch is in the 'off' position, it will form a closed loop with both leads of the motor, devoid of power, effectively providing a brake to the motor.
In the other position, this switch will complete a circuit with the motor and power source, making the motor spin and firing the stampede.
When I used a relay to drive a stampede, I kept this switch in the control circuit, upstream(logically) of the relay itself. THe relay directly powered the motor, and this switch actuated the relay. However, in order to know when the firing cycle was actually started, I had to wire a pin of the arduino to a part of this circuit downstream of this switch. The arduino then turn on power to the switch, which would in turn power the motor, wait a little bit(10ms or so) then turn off power and see if the switch was being held on. This would indicate that the breech had moved forward enough to engage the switch mechanically, and that kept the relay powered until the firing cycle was completed.
This ensured that the stampede fired a round precisely and reliably.
I'll post code once i go get some pictures of how i did this.
Edit:
Pictures of the switch im talking about above.
![Posted Image](http://wordpress.digitalcrowbar.net/wp-content/uploads/2013/08/IMG_0444-e1376302089342.jpg)
![Posted Image](http://wordpress.digitalcrowbar.net/wp-content/uploads/2013/08/IMG_0443-e1376302007288.jpg)
I was unsatisfied with the final product when i finished this project in march, and it has since been scrapped for parts(the arduino, LCD display, AR15 Grip), or I would provide a firing video.
It was a while ago that i designed this, but if memory serves, I wired the top (right as pictured) pole of that switch to the arduino, the middle goes to the relay control pin, and the lower pole to ground. My relay board was low active, so during the firing cycle, when the breech forces the middle and lower pins to connect(second picture), the relay is held active, regardless of the arduino's input. The line going to the relay also goes to another pin on the arduino, as the sensor for when the firing cycle is complete, but this is not strictly neccessary for your application.
Edited by Oryhara, 11 August 2013 - 05:23 PM.