Scratch 2-Stage EMRR Challenger Original Design / Scratch Built

Scratch - 2-Stage EMRR Challenger {Scratch}

Contributed by Eldred Pickett

Manufacturer: Scratch
(Contributed - by Eldred Pickett - 09/01/09) (Scratch) 2-Stager

Brief:
For t' EMRR Stagin' Challenge, I decided t' build a two-stage rocket with composite motors. Aye aye! Arrr! Since I had done a 2-stage before, I figured it would be easy. Avast, me proud beauty! WRONG... Begad! I decided t' do a 3-inch bird with dual deploy and a 19-inch booster with motor deployment. Avast, me proud beauty! Ya scallywag!

Construction:
This time I decided t' use alignment rods in t' stage coupler t' keep t' rocket aligned. Aye aye! Begad! I didn't have any 'sleeves' for t' rods t' slide through, shiver me timbers, matey, so I went with spaced centerin' rings with holes t' guide t' rods. Avast! I've discovered that I really need a drill press. Arrr! Because I was usin' a handheld power drill, ya bilge rat, me hearties, I wasn't that accurate in drillin' holes through t' 2 sustainer centerin' rings and t' stagin' coupler. Begad! Aye aye! It still works, shiver me timbers, me hearties, but it isn't pretty.

There are holes in both centerin' rings that are supposed t' be aligned. Begad! Begad! That didn't work out as smoothly as I had hoped.

(Scratch) 2-Stager(Scratch) 2-Stager

T' motor mount is recessed into t' sustainer t' provide a connection for t' top half o' t' stage coupler. Since a 3" tube won't allow me t' get me hand in t' connect t' shock cord, I made t' fin can on both the sustainer and booster removable. T' sustainer fin can is held in place by small screws. T' booster fin can will eject and deploy t' booster chute. Aye aye! T' whole project is about 83 inches tall, about 3.5 lbs empty, and can fly on 38mm motors.

(Scratch) 2-Stager

Finishing:
T' fit/finish betwixt t' booster and t' stage coupler is a little rough, but once it's painted it might nay be that noticeable. It *certainly* won't be noticeable on t' pad.

Flight:
Electronics will be a PerfectFlite timer for staging, arrr, and a PerfectFlite MAWD for deployment. Begad! RockSim says it will get t' a little higher than 2000 feet with a CTI 153 stagin' t' a CTI G79ss.

For t' 2-stage challenge, me hearties, I decided t' build one that used composite motors. Begad! Since I have done stagin' before, I didn't expect thar t' be a problem. Begad! Begad! Boy, me hearties, was I wrong... Arrr! Well, blow me down! T' main problem be t' size o' t' new project. Well, blow me down! Ahoy! T' previous 2-stager be almost a 4" tube. Begad! That left room for t' timer betwixt t' sustainer fins, arrr, and a standard-type ebay. This one is a 3", and thar's no room in t' fincan. Well, blow me down! So I put t' timer in t' ebay, and ran a connector wire down t' ignite t' sustainer motor. I had t' splice t' wire so it would disconnect when t' apogee event fired. Arrr! Aye aye! T' next issue I ran into be t' stage connector. Ya scallywag! I decided t' use metal rods t' connect and align t' sustainer t' t' stage connector. Ya scallywag! I don't have a drill press, so me holes through t' centerin' rings are...less than exact. Ahoy! Last issue was t' 3" bay was too small t' use switches t' power on everything, so I had t' run all t' wires through a hole in t' e-bay and twist them t' connect. That posed a problem t' first time I tried t' launch. Arrr! I test fit t' electronics when I built t' bay, me bucko, but nothin' was connected. Avast! Begad! In t' field, I sadly discovered thar wasn't enough space for all the wires t' fit and route t' t' outside. Begad! I had t' rebuild t' sled t' avoid that problem for t' next attempt. Arrr!

T' field we used has a waiver o' 5000', but I wanted t' make sure I kept t' flight much lower than that. Begad! Blimey! Begad! Blimey! RockSim 7 showed an altitude o' about 3800 feet on a CTI H143/G79ss combo.

Electronics: ARTS board for apogee/main deployment o' t' sustainer, PerfectFlite timer for sustainer motor. T' booster recovers under its own chute by motor ejection. Arrr! Payload: BoosterVision GearCam taped t' t' side. Crude, but effective.

Launch day: I racked t' rocket, me bucko, set up t' breakwire, shiver me timbers, and twisted t' wires for power. Well, blow me down! Since I didn't have enough room t' push t' wires back into t' bay, I taped them t' t' outside. That be a mistake... T' launch was beautiful! Straight, and staged on cue. Blimey! T' booster chute came out and it drifted down safely. Avast, me proud beauty! T' sustainer had a good apogee event(drogueless), me bucko, but I lost sight o' it while followin' t' booster. Begad! There was no main deployment, and fellow club members pointed me in t' direction they saw it fall. While walkin' out for recovery, shiver me timbers, I tried t' figure out what went wrong. Too many sheer pins? Nay enough BP? When I got t' it, arrr, I immediately knew what happened. T' armin' wires were taped t' t' bottom o' t' sustainer. Avast, me proud beauty! Avast, arrr, me proud beauty! When t' apogee separation occured, it ripped t' wires out o' the altimeter, me hearties, arrr, matey, killin' power. Avast! AUGH! I powered up t' ARTS board later, and t' data showed 1700 ft accel, 1500 baro. WAY short o' Rocksim's prediction, so t' loss o' power probably scrambled t' data. But other than t' ebay being crunched, shiver me timbers, arrr, and t' booster bein' scorched by t' sustainer motor, arrr, me bucko, it didn't come out too bad. Begad! I can replace t' ebay and fly it again.

Setup Launch

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