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Sparkfun: Lots of electronics components
Adafruit: Similar to sparkfun. Also has great tutorials on using their products
Digikey: The McMaster of electronics components
OshPark: Sponsored us for PCB's in 2016. Quick delivery time, we can assemble the PCB components in lab.
Help! LiPo suppliers?
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Missileworks: Feature-filled rocket altimeters
PerfectFlite: Another company that makes altimeters (such as the StratoLogger) that the team has used.
Eggtimer: Solder-yourself kits for rocket electronics
Altus Metrum: High end altimeters for rockets which include telemetry and GPS.
Hobby King: Servos and lipos. Also lots of RC stuff should that be needed.
Chutes and Recovery Components
Rocketman: High quality, 4 shroud-line chutes. Different strength ratings, and descent rate table matching rocket weight to appropriate chute. Chutes also usually come with a loop sewn in the top, which proves incredibly useful for single-separation dual-deploy systems.
Fabric supplier????
Other sewing equipment suppliers??
Fruity Chutes: Chutes of many sizes.
Top Flight Recovery: Cheap, but still high quality parachutes
Tinder Rocketry: Sells Tender Descenders, which are useful for single-separation dual-deploy systems. The reliable of Tender Descenders is in question, but they have proven themselves in flight to date.