Mail to Robert DeHate
This application uses two Roctronics units as redundant altimeters.
This required equipment will depend upon the level of redundancy used.
This determining factor is the harness board used and how it interconnects each part.
The factors that will remain the same is the protocol used between the altimeters.
One of the altimeters will be the master and the other the slave. The master will be determined by a shorted pin on the harness board so the program code will be the same. This will reduce user error.
Intercommunication
Mode 1
The master will generate a heart beat signal that the slave will
use to determin the master is alive. If the heartbeat is not received for .5 sec
then the slave takes control as the master. As master it is responsible for
firing the ejection charges.
Mode 2
The slave altimeter monitors the master and fires its output 1
second after the master. The master will fire its output when either it detects
apogee/main or when the slave tells it that it has detected apogee/main.
Mode 3
The slave monitors for the master ejection signal and also has a
ejection success shorting plug. This shorting plug is a header attached next to
the ejection charge on the bulkhead. There is a shorting jumper that shorts this
header and it is attached to the chute so when the chute deploys it pulls the
shorting jumper telling the slave that ejection was successfull.
Configurations
1) Two altimeters with optocouplers on the harness board that allow sharing of a single sensor board using seperate batteries
2) Two altimeters with independant sensor boards but attached to the same harness board using seperate batteries.
3)The manager and slave are connected and share the sensor board and power supplies but have their own ejection charges.(Mode 3)
Sandhawk implementation
I am working on a redundant pair of altimeters that will run in my Sandhawk.
It has the typical arrangement of having the charges mounted to the bulkheads on the ends of the bay so the main and drogue are on opposite ends. There are two charge wells on each bulkhead. There will also be a shorting header on each bulkhead. The header will have a jumper shorting it out. This jumper has a string that will attach to some part of the recovery system so that when it deploys it will pull the jumper. This will indicate to the slave that the ejection has occured.
I have made a harness board that will mount two roctronics controllers with thier sensor boards. From the picture you can see that there are 4 connectors. I decided to mount the controller and sensor board next to each other. This made for a lower profile that allows the threaded rod to pass by.
These will work together to deploy the chutes. The Master will be in charge of deployment. The slave will monitor the depoyment to verify it is successfull. It will deploy the chutes if the Master fails to deploy them within 1 second of Main/Apogee events. The events in the slave will either be triggered by its sensors and/or by the communication link between them.