Marc Casanova's Cluster Launch Controller

This launch controller can pump 90 to 100 amps into a cluster of motors. In its current configuration it can support up to 98 motors. It uses two batteries, one 12V tractor battery for the detection of the launch command and energizing the four internal relays, and one 850 CCA car battery dedicated to firing the igniters.

I made a special cable for connecting the igniter battery to the controller. The wire for the cable is cut from the thickest jumper cables I could find to reduce voltage drop, and I doubled up on the cable for a total of four conductors. The battery end uses brass automotive battery clamps (with two conductors going into each clamp). The controller end uses a four contact clothes dryer plug. Each contact on the dryer-plug can handle 50 amps. I double up on the contacts to get a plug that can handle 100 amps (with one conductor going into each contact).	Side view of connectors on pad unit Click for larger photo.
Inside the controller, I use #6 solid copper wire to connect the dryer-plug socket to a 100-amp bus. Again, I double up on the #6 solid copper wire, one wire per socket contact. The two dryer-plug socket negative contacts connect directly to the negative side of the bus via these #6 solid copper wires. The two positive dryer-plug contacts connect to the positive side of the bus via three high current relays wired in parallel. Each relay can switch 30 some DC amps to give me a total of about 100 amps switching capability. Everything is soldered (using a very high wattage soldering iron) for reliability and maximum current carrying capacity.	Lower subassembly Click for larger photo.
I currently have 24 phono-plug sockets on the front panel of the controller. Radio Shack sells octal phono-plug socket panels. I used three of these. Each phono-plug can handle about 5 amps (determined by gut feel), so I restrict each plug to handling between one to four igniters each depending on the igniter characteristics. Thats where I get the 98 motor limit. Each phono-plug independently connects to the 100-amp bus via #14 stranded wire. So I have 48 wires running between the 24 phono-plugs and the 100-amp bus. I have Molex connectors midway so I can remove the panel. Each contact on the Molex connector can handle 7 amps.	Top view of assembled pad unit Click for larger photo.
The two 21,500uf 35vdc capacitors supply a very fast initial current surge to the igniters when the igniters are first presented across the high current bus. The three 4,700uf 25vdc capacitors assure that the Launch Command detect relay remains energized for 1 second after the Launch Command button is released. This is to protect against accidental too-soon release of the button for whatever reason.	Top subassembly Click for larger photo.
The relays are Radio Shack part number 275-226. The contacts are rated for 30A at 12Vdc. Coil voltage is 12Vdc. These relays have a coil resistance of 66 ohms, with a pull in voltage of 6V and a drop out voltage of 3.6V. At the time the photos were taken none of the capacitors had been installed yet. Ive recently gotten a hold of the capacitors and will install them when I have time.	Back view of top subassembly Click for larger photo.

Click HERE for schematic drawing in .pdf format.

Prepping the rocket cluster

On the rocket end, I dedicated one cable to each AP motor. Each igniter had a male phono-plug soldered onto the end. A six-foot cable with a male phono-plug at one end and a female phono-plug at the other connected each igniter to a phono-plug socket on the controller.

You will find no alligator clips here.

• For the black powder motors I ohmed out the Estes igniters and threw out any that were not at about 0.7 or 0.8 ohms.
• I created sub-clusters of two or four BP motors in the rocket. Before putting in each igniter I wrapped one leg of each igniter with tape (all the way up to the head) to guarantee against short circuits.
• Then I installed igniters into each motor of a sub-cluster, dropped in a tiny bit of black powder, and put in the plastic plugs that come with the motors. Another ohmmeter check. I twisted together the leads of the igniters of each sub-cluster. Another ohmmeter check.
• Then I twisted onto those leads a two-conductor wire, at least 18 inches long, with a male phono-plug already soldered onto the other end.
• Another ohmmeter check.
• Then I soldered the twisted leads.
• Another ohmmeter check. Each BP sub-cluster was checked sequentially.
• I repeated this for every sub-cluster.

In the 36-motor cluster rocket, Darth Maul's Revenge, I had three sub-clusters of two BP motors, the rest were sub-clustered into groups of four. Each sub-cluster connected to one of the phono-plug sockets on the front panel. I had about 16 cables going between the rocket and the controller.